MtC Block 3 Flashcards
Progeria
Premature aging, associated with shortened telomeres
Maternal non-disjunction causes _________.
Down-Syndrome - Trisomy 21
Mosaic down syndrome can be caused by
Mitotic non-disjunction - affections phenotype
Trisomy 13 - Patau syndrome
Heart defects, midline defects, malfomred forbrain - cyclops - longterm survival rare
Trisomy 18 - Edwards syndrome
Severe heart defects, profound developmental delay, overlapping digits - differnet CNS wiring - most lost before term
Telomerase is active in
Germ and cancer cells
Nearly all microscopically visible autosomal aneuploidy is _________
Deliterious
Turners Syndrome (XO)
Short, streak ovaries, heart defects, normal intellect, infertile, 99% lost before term
Turner’s syndrome is often due to
Loss of male Y
Klinefelter’s XXY
Feminized, low androgen, small testes, normal IQ, - difficulty w/ relationships, infertile - sperm don’t mature
XIST
All females have one fuctioning X - dosage comp - a few escape
47XYY
Tall, fertile, sub-average IQ, impulsive, low confidence/anxiety - CNS hardwiring change
Male determining locus - SRY
One gene on Y that determines maleness - causes problems with two - 47XYY
3 types of prenatal genetic testing
Amniocentesis > 16 weeks
Chorionic villus > 9 weeks - more invasive
Non-invasive prenatal testing - 5-15% fetal DNA recoverd from blood sample from mother
Most structural rearrangements occur from
Double-standed breaks
Results of deleterious mutations of autosomal chromosomes (2)
- Haplo-insufficiency
- Expression of recessive gene
Ex. cri-du-chat
Repairs of DS breaks can result in (3)
- Ring
- Inversion
- Translocation between non-homologous chromosomes
Pedigree analysis applies most to
Monogenic disorders
Characteristics of monogenic (Mendelian) disorders (3)
- Determined by a single mutant gene - very speicific point mutation in coding region usually
- Rare
- Show specific patterns of inheritance
Characteristics of complex disorders (4)
- Polygeneic inheritance - more than one gene locus
- Multifactorial inheritance - combo of genetic and environmental factors
- Major group of human disease
- No specific patterns of inhericance - familial clustering
Principle of Segregation
Alleles segregate so that each gamete is equally likely to contain either member of the pair
Principle of Independent Assortment
During gamete formation, segregating pairs of alleles assort independently of eachother
Pedigree
Graphic representation of family’s interrelationhsips and health problems - focused
Three other important things to gather for a pedigree
- Ethnicity
- Religious heritage
- Country of origin
Two reasons to use a pedigree
- Quantify risk of developing disease for family members - family planning
- Analysis to obtain mode of inheritance
In a pedigree a male is represented by a _______ and a female by a __________
- Square
2. Circle
An autosomal dominant disase will have what distinguishing characteristics on a pedigree (4)
- Each affected individual has an affected parent - does not skip
- Normal offspring will have normal offspring
- Males and females affected equally
- Each generation tends to have an affected individual
An autosomal recessive disease will have what distinguishing characteristics on a pedigree (4)
- Can skip generations - carriers
- Males and females affected equally
- Normal parents can only have an affected offspring if both are carriers
- The less frequent the allele in the population - the more likely the individuals are a product of a cosanguineous marriage
An X-linked dominant disease will have what distinguishing characteristics on a pedigree (3)
- Trait is never passed from father to son
- All daughers of an affected male and normal female are affected
- Females are more likely to be affected than males
An X-liniked recessive disease will have what distinguishing characteristics on a pedigree (3)
- Never passed from father to son
- Passed from affected grandfather to carrier daughter to all of her sons??
- Males more likely to be affected than females
Ex. Colorblindness
A Y-linked disease will have what distinguishing characteristics on a pedigree (2)
- Always in males
2. Passed from father to son
A mitochondrial disorder will have what distinguishing characteristics on a pedigree
- If the male is affected none of the children get it
2. If the female is affected they all do
What two things must you know to use a Punnett square
- Mode of inheritance
2. Parental phenotypes
What are two problems with obtaining an accurate pedigree analysis
- Variable expressivity - varying severity - trouble assigning disease to family members
- Incomplete penetrance - person with genotype does not express diesase
Genetic anticipation
Members exhibit progressivley earlier age of onset and increased severity w/ each generation
-Seen in disorders involving multiple repeats
Mosaicism
Mutation originated as a somatic mutation during embryogenesis of one of the parents
Considerations for mosaicism in a pedigree
- Risk to future offspring could be the same as from an affected parent
- Shows features of both recessive and dominant
- Consider a parent mosaic for a dominant allele before deciding its recessive
De novo mutation
Spontaneously originated in parental gamete - presents as recessive - may show dominnat inheritance in next generation
Genetic (locus) heterogeneity
Existance of multiple genes when mutated cause same phenotype
Lethality (2)
- Recessive lethal - embryonic lethal
2. X-linked dominant disorders - male lethality
Linkage analysis
Statistical method used to ID position of human disease genes relative to known genetic markers
Syntenic genes
Two genes on the same chromosome - close enough that they don’t segregate independently
Lod Score Method
- Log (Probablity assuming linked)/(Probability assuming not linked) >3 indicates linkage > -2 indicates not linked
________________ works better in conjucntion with linkage analysis.
Whole genome appraoch. Better if you have genomes from multiple family members
Personalized medicine can (3)
- Help with genetic predisposition, early diagnosis
- Pharmacogenetics - drug dosages
- Predict outcomes
On average human DNA differs between individuals by ____?
.1% - majority are single base changes
SNP
Single nucleotide polymorphsim
_____ is the most common variation in human genome
SNP
- inversino/deletion
- block
- copy number - identical sequences repeated on some chromosomes, not others
Genetic markers
Identified physical location on a chromosome whose inhericance can be monitored
A genetic marker can distinguish between ____________ and determine which ____________.
2 copies of alleles; allele is inherited from parent to child
A __________ can ID regions that harbor disease causing mutations
genetic marker
Restriction Fragment Length Polymorphism
Cut the DNA with a restriction enzyme - Southern Blot - look at size of chunks
Short sequence length polymorphism
Short repeats of 2, 3, or 4 nucleotides - randomly disbursed thorughout genome - PCR - Southern Blot - See size variations
SNPs occur on average _______ and are _________.
1/1000bp; bialleleic
Most ____ are distribued across entire gneome and have no discernable function
SNPs
Types of SNPs (4)
- Coding -synonymous - no change in aa sequence
- Coding - non-synonymous - change aa sequence
- Promoter - alter gene expression
- Splice site SNP - alter RNA processing
Copy number variants
Relatively large duplications/deletions of specific regions 50-1Mbp
On average there are ____ CNV/individual
12
High throughput platforms allow you to…
…analyze large numbers of SNPs (300k - 1M)
Reverse genetics
ID a gene by positional cloning based on its molecular properties (Phenotype - gene)
Positional cloning
Finding a gnene of unkown function by mapping them relative to a gene/marker you can clone and walking down chromosome
Single gene disorder
Mutation of single gene is necessary and sufficient to cause the diseae - severity due to modifier gene
Triplet expansion disease
Threshold of repeats before disease occurs
HD, Fragile X syndrome, Kennedy syndrome, Myotonic dystrophy
Cystic fibrosis
Deterioration of lungs, Autosomal recessive, IDed gene thru linkage analysis - RFLP to ch7
Cystic fibrosis transmembrane conductance regulator
Codes chloride channel responsible for salt balance - salty cellular secretions promotes bacteria build up
Symptoms of Huntington’s Disease
Degenerative disorder of the brain with progressive dementia and uncontrolled movement
-no symptoms til puberty or middle age
Pedigree of Huntintons disease
Autosomal dominant w/ modifier genes,
genomic imprinting & anticipation
-when inherited from the father earlier onset and greater repeat expansion
Hungtintin gene
180 kb, 67 exons, protein s 3150aa
Repeats of CAG in coding region (microsatellite in coding region)
9-36 normal and 37-100 in diseased - higher repeats, the earlier age of onset
Epigenetics
Heritable changes affecting gene expression that do no result from alterations in DNA sequence
Genomic Imprinting
Epigenetic phenomenon in which the sex of the transmitting apretn determines whether particular genes are expressed in offspring or not
Beckwith-Wiedemann Syndrome
Methylation of imprinting control region of both gametes - turns off H19/turns on IGF2 - fetal overgrowth
Silver-Russell Syndrome
No methylation of ICR in either gamete - turns on H19/turns off IGF2 - fetal growth retardation
Prader-Willi Syndrome
Missing genes from dad - low muscle tone, short stature, cognitive disabilities - uniparental disomy (2 copies from mom) - epigenetically silenced gene from father - deletion of 15q11
Angelman Syndrome
Missing genes from mom - Neuro-genetic disorder w/ severe intellectual/developmental disability, sleep disturbance, seizure, usually happy demeanor - Uniparental disomy from dad - deletion of 15q11
What is the difference between a mutation and a SNP?
A mutation occurs in 1%
Transition
One purine or pyrimidine swapped for another
Transversion
Purine for pyrimidine - higher chance for damage
Each gamete has ______ de novo mutation
~75
Why do most mutations disappear?
Most are not in the germline and aren’t passed down to offspring
Genetic drift
Random process by which some mutations rise in the population and others disappears - how most mutations become SNPs
Selection
Occurs if a mutations affects the reproductive fitness of an individual - positive helps - negative hurts reproductive success
Migration
Mating between two sub-populations - depends size of population over successive generations
_________ has lead to unique polymorphisms to different ethnic/regional gropus
Human migration
Hardy-Weinberg Equilibrium
Describes and predicts genotype and allele frequencies in a non-evolving population - if no evolution is occuring allele freq will remain in equilibruim
Assumptions of Hardy-Weinburg (5)
- No mutation must occur - no new alleles
- No gene flow can occur - no migration
- Random mating
- Population must be large - no genetic drift influencing fruqency
- No selection can occur
Why did Sickle Cell Anemia depart from Hardy-Weinburg?
It conveyed some defense against malaria - postive selection
Linkage disequilibrium
Non-random assortment due to proximity of two SNPs
Haplotype
Patterns of SNP alleles on a single chromosome (haploid)
Does a high LD correlate to a high or low number of haplotypes?
Low - more linkage - fewer combinations
LD Blocks
LD does not continuously decline with distance - ∃ blocks that inform eachother - highly conserved
Tag SNPs
Minimum SNP set to ID a haplotype - Need ~500K tag SNPs for entire genome
Expect ___ haplotypes when genotyping 1000 individuals from MIlwaukee for X SNPs if in linkage equilibrium
2^x haplotypes
What did the HapMap project do?
Looked at 6 million SNPs and identified tag SNPs in each population - Only need to look at ~ 500k SNPs
Polygeneic disorders
Multiple genes with multiple phenotypes and multiple environmental factors
What are two characteristics of polygeneic disorders?
- Have a genetic disposition - not Mendelian Inheritance
2. Variable due to environmental stresses
Association Studies
Test for assocaition of marker allele with the disease - look at presence of genotype w/ pheontype
Association studies are used to look at what type of diseases
Complex inheritance, common diseases, polygenic - Look at presence of genotype w/ phenotype - ID of associated alleles
Linkage studies are used to lok at what types of diseases?
Mendelian genes with high penetrance - correlate inheritance of genotype with phenotype - ID of linked region
Indirect association
Indirect association of each marker with a quantitative trait - frequency of allele T signficantly correlated w/ higher level of the trait
Common variant-Common disease model
Susceptibility to common disease is conferred by alleles that are commin the population and have modest phenotypic effect - affected indiviudals have an excess
What is the benefit of a genome wide association study?
Allows for search of common variants without any assumptions about their nature
Case control
GWAS selecting individuals from both categoreies and ID frequncy differneces between groups - Analysis by chi-square test
Population based study
Select indiviudals randomly from population and ID phenotypic differnces between genotype group - anlysis by t-test
Problems with candidate gene studies (3)
- Replication
- Selection of candidate genes
- Selection of SNPs - comprehensive analysis better than analysis of individual SNPs
Significance in GWAS
(.05/# of SNPs) P-values must be < .5 X 10^-8
PPAR-γ
Nuclear hormone receptor on chr. 3 - over-expression in mice inhibits insulin release - associated with diabetes
Genotype quality control measures (3)
- Testing sample duplicates - same platform/different platform
- Blank tests - establish specificity distinguishing blanks from non-blanks
- Comparison between observed frequency w/ HW
Heat Shock Serine Protease HTRA 1
Associated with wet from of age-related macular degeneration
Problems in complex disease genetics (4)
- GWAS are difficult and elaborate
- Phenotype/diseases are often heterogeneous - same clinical manifestation - differnt cause
- Differing severity
- Tag SNPs make ID of “true” causal mutations difficult
eQTL Analysis
Have there been changes in DNA that affect expression levels
Inbred strain
Individuals of a particular species which are nearly identical to each other in genotype due to long inbreeding
Quantitive Trait Loci Analysis
Cross inbred diabetes rat w/ normal rat
- F1 is normal
- F2 is combination generation - look at large panel of F2 and level of diabetes - LOD scores
Three structures of sperm
- Flagellum
- Acrosome
- Nucleus
Layers around ovulated oocyte (outside to in)
Zona pellucida, PM, cortex, and cortical granules
Ovulations occurs from the _______. The oocyte is surrounded by __________ and __________.
- Stigma
- Follicular fluid
- Cumulus cells - critical for oocyte pick up
Genetic abnormalities in gametes usually occur during _______________.
Gametogenesis
Ideally, fertilization occurs in the _________.
Ampulla - early part of fallopian tube.
Journey of sperm thru male reproductive tract
Testes, epididymis, vas deferens, urethra
Barriers to sperm in the female (4)
- Low pH
- Sperm antibodies
- Cervical mucosa
- Travel up wrong fallopian tube
Journey of ovulated oocyte
- Oviduct moves up around ovary to capture cumulus mass
2. Oviduct has cilia to move oocyte and peristaltic contraction when it’s in the ampulla
Capaciation
Sperm membrane changes, increased metabolism, hypermotility - sense temp gradient
Acrosome Rx
1st thing that happens right before sperm encounters cumulus mass - fusion btw cell membrane and outer acrosome - vesicles are shed - exposes enzymes
What receptor do sperm bind to?
ZP2 - sperm membrane protein is SED
Sperm-oocyte fusion occurs at the ________ region of sperm.
Equatorial
What proteins does a sperm need to fuse with an oocyte?
Feritlin B, IZUMO
What proteins does an oocyte need to fuse with a sperm?
Integrin, CD9
Polyspermy preventing reactions (3)
- Ca++ Oscillation
- Activates cortical granules - release into perivertellen space
- Cross link zona pellucida proteins
What happens immediately after a sperm enters an oocyte (3)
- Polyspermy preventing reactions
- Resume meiosis of oocyte (MII metaphase)
- M and F pronuceli form metaphase plate - zygote!!
What stage of IVF has the highest risk of failure?
Embryo transfer
At what stage are the embryos transferred to uterus?
The 4-8 cell stage
Preimplantation genetic diagnosis
Taking away one cell does not inhibit development or damage embryo
What main things happen during the embryonic period? (4)
- Form body plan - 3 layers & 3 axes
- 3 layers create 4 tissues - organs and organ systems
- Segmentation, head, limb and trunk formation
- Embryo folding
What two main things happen during the fetal period?
- Growth and maturation
2. Continued development of some systems
What weeks make up the embryonic period?
Week 1-8
What weeks make up the fetal period?
Week 9-38
What is the difference between the fertilization age and the gestation age?
The fertilization age is the age of the embryo where gestational age starts from the last menstruation
What main events occur during Week 1? (3)
- Fertilization
- Cleavage - Blastocyst formation
- Implantation initiated
Cleavage and formation of the blastocyst is controlled by what?
Maternal RNAs
The nucleus from an early cleavage state _________ is capable of generating a whole embryo.
Blastomere
The morula is formed at the 8-cell stage via __________ and the blastocyst is formed via ___________.
- Compaction
2. Cavity formation
Cavity formation in a blastocyst forms the ____________ and the _________________.
Inner cell mass and outer cell mass
What is the result if nondisjunction occurs during an early cleavage?
Mosaic embryo
The outer cell mass forms the _____________.
Trophoblast
Trophoblast formation is an example of _____________.
Genomic imprinting - requires expression of unknown parental derived alleles
The ICM remodels to form the ____________.
Bilaminar disc (epiblast and hypoblast)
What will the hypoblast make?
Will make extraembryonic membrane - primitive endoderm
What will the epiblast make?
Will make the embryo - primitive ectoderm
What is the function of the ZP?
- Keeps blastomeres together
- Immunological barrier
- Prevents premature implantation
How does the embryo shed the ZP?
Trophoblasts produce an enzyme to help it hatch out
Cleavage stage embryos have the potential for regulation. Define regulation.
The ability of an embryo to produce a normal embryo when parts have been removed or added.
What mediates the cell diversity in the blastomere? (4)
Cell position, number of divisions, cytoplasmic determinants, and cell-cell interactions
What is the difference between terminal differentiation and post-mitotic cells?
Terminally differentiated cells can not become anything else, some are post-mitotic - neurons & some are not - cells lining GI
Stem cells
Differentiated cell that retains some pluripotent capabilities
Gene expression is patterned, it occurs at different levels, along specific axes, is the result of ___________ mediated by ______________.
Gene expression, transcription factors
HOX genes
Differential expression of HOX is how patterning during development is developed
How are dizygotic (paternal) twins formed?
Two ovulation and two fertilizations
How are monozygotic twins formed?
Early or late cleavage - 65% at blastocyst stage
35% at two cell stage (between blastocyst and morula) - two embryos and two implantations
How are conjoined twins formed?
Monozygotic twins divide after formation of embryonic disc
What three main things have occurred at the end of week 2?
- Complete implantation
- Formation of bilaminar disc - amnion and umbilical vesicle
- Formation of additional extraembryonic mesoderm
Implantation occurs between days _______
5-12
The decidual reaction of the attachment phase of implantation involves
- Trophoblast binds to endometrium - forms of compact layer of endometrium - makes mass of cells for implantation of embryo
The 2 phases of implantation are
- Attachment - receptor mediated
2. Penetration and embedment into compact layer
Phase 2 - Penetration and embedment - of implantation is characterized by what?
The formation of the syncytiotrophoblast
What are four characteristics of the syncytiotrophoblast?
- No cell boundaries - lots of nuclei
- Mediates invasion of endometrium - more is formed as embryo embeds further
- Microvilli on surface help it incorporate nutrients
- Lacunae (spaces) are formed for blood and glandular secretions
At 12-14 days the embryo is ________ ________.
Completely embedded
What is the most common cause of spontaneous abortions in the first three weeks?
Chromosomal abnormalities
Placenta previa
Implantation occurs too close to the cervix
What is the most common site of extrauterine pregnancy?
Outer 1/2 of oviduct
Amnion
Extraembryonic membrane formed from epiblast - Surrounds embryo by Week 8
What is the function of the amnion?
- Creates a space for amniotic fluid
- Protects embryo and allows for symmetrical growth
- Allows for proper growth of lung
- Allows for movement
- Assists in fluid homeostasis
Umbilical Vesicle (Yolk sac)
Exocoelomic membrane formed by hypoblast - bounded by extraembryonic membrane
What is the function of the umbilical vesicle?
- Metabolism and transfer of nutrients from trophoblast to embryo
- Site of initial blood and vascular formation
- Primordial germ cells and hematopoiesis appear in wall
- Portions may become primitive gut
- Positions site of gastrulation - primitive streak
- Controls epiblast cell migration
Extraembryonic mesoderm
Coats the inside of the trophoblast and outside of amnion and UV.
Mesenchyme
Free cells, non-polar, motile
Where does the extraembryonic mesoderm originate?
From exocoelomic membrane by delamination of cells - epithelial-mesenchymal transformation
Chorion
Extraembryonic mesoderm and trophoblast
Connecting Stalk
Bridge of extraembryonic mesoderm between chorion and embryo
What are 4 main things that happen in week 3?
- Establish 3 primary germ layers
- Beginnings of organogenesis
- Embryo begins to fold - neural tube growing so fast it can’t remain a disk
- Establishment of asymmetry
Conceptus
Embryonic disc and chorionic sac
The trilamiar disc is formed via __________.
Gastrulation
Primitive Streak
Transient thickening of epiblast with a midline groove - converging epiblast cells
The first cells that pass the the PN form ______________, other cells pass thru and move to the opposite end of the disc to form ______________, the 2nd cells to pass thru the PS form _________________.
- Definitive endoderm - replaced hypoblast
- Prechordal plate (endoderm)
- Intraembryonic mesoderm - between endoderm and epiblast
Epithelial-mesenchymal cell transformation occurs at ________________.
The primitive streak.
What is the ectoderm formed from?
Cell leftover from gastrulation
Primitive Node
An expansion at the cranial end of the primitive streak - also a side of E-M transformation
What axis does the primitive node establish?
Cranial and caudal
How is the notocord formed?
Cells from prechordal plate invaginate thru PN - migrate cranially, they join up with the endoderm temporarily - help form the neural tube
The primitive streak regresses, is restricted to the _____ and forms the ____________.
Tailbud, caudal eminence
At what two points of the embryo is there no mesoderm?
- Oropharyngeal membrane cranially
2. Cloacal membrane caudally
Allantois
Diverticulum of umbilical vesicle - signaling center, becomes part of median umbilcal ligament
Teratoma
Neoplasm of multiple cell types - usually sacrococcygeal - most common tumor of newborns
What causes a teratoma?
Part of the primitive streak that didn’t disappear
Caudal dysgenesis
Abnormalities of lumbosacral spine, lower limbs and urogenital system
What genes establish the cranial-caudal axis?
Otx2, Lim1, Hesx1
What genes establish the dorsal ventral axis?
Chordin, noggin, follistatin
What establishes bilateral symmetry?
The notochord
What establishes asymmetry L/R axis?
PN gene expression - Lefty 1, Lefty 2
Situs inversus
Lefty 2 misexpression on the right
Gastrulation
Three primary germ layers formed
Neurulation
- Formation of neural plate - day 17
- Neural plate cells get taller
- Neural folds elevate - neural groove formed
- Neural folds fuse
Neural crest
Mesenchyme derived - separate from tube jsut be fore fusion - Precursor for 1˚sensory neurons, PNS sheathing cells, neurons of autonomic ganglia, adrenal medulla, and pigment cells
Ectoderm will become
epidermis, CNS, parts of eye, ear, and sense of smell
Mesoderm will become
Organs, sk. muscle etc
Endoderm will become
Internal tube of GI, Resp, part of UG
Paraxial mesoderm will become
Sk. muscle and vertebral column
Intermediate mesoderm will become
Kidneys, gonads, and UG
Lateral mesoderm will become
Split
Paraxial mesoderm is segmented in the trunk and forms _______.
Somites
How are somites formed?
Mesenchyme aggregation and separation of somite pairs is mediated by segmentation clock and wave model
What patterns the somites along the cranial-caudal axis?
Homeobox Genes
Intracellular Ceolom
Splits lateral mesoderm - Somatic and Splanchnic Mesoderm
Somatic Mesoderm
Associates with ectoderm - body wall, limbs, epithelium and connective tissue of parietal layer lining body cavity
Splanchnic Mesoderm
Associates with endoderm - GI organs, reproductive
What does folding in the transverse plane yield?
Tubular embryo - outer tuber - ectoderm ; inner tube - endoderm - Also the body plan
What does folding in the sagittal plane yield?
C-shaped embryo - embryo lifted into amniotic cavity
Result of folding (3)
- Establishment of body form
- Structures relocated from dorsal wall to ventral wall
- Closure of ventral body wall
- Embryo elevated into amniotic cavity
Characteristics of embryo at week 4
- Heart is beating
- Embryonic circulation is established and connected to the yolk sac and placenta
- Neural tube is most closed
- Folding has begun
- Somites continue to form
- Embryo is 2mm long
- Chorionic sac is 2mm in diameter
Gastroschisis
Intestinal tract is out to side of umbilical cord - 10% are stilborn
Emphalaceal
Intestinal tract comes out thru umbilical cord covered by a membrane - harder to fix
Throachoabdomanoschisis
Ventrothorasic and ventroabdominal wall didn’t close - organs outside body
Failure of ventral body wall to close can result in which three anterior body wall defects?
- Gastroschisis
- Emphalaceal
- Throachoabdomanoschisis
What are the pleuropericardial folds formed by and what do they contain?
Growth of septum from body wall
Contains a few veins and the phrenic nerve
Pericardio-peritoneal canals
Connect pleural cavity and peritoneal cavity
What is the diaphragm composed of? (3)
- Pleuroperitoneal folds - diaphragm
- Septum transversum - liver
- Dorsal mesentery of esophagus - crura
What is the primitive node?
Signaling center at the cranial end of the primitive streak. Forms at day 16.
What is the prechordal plate?
An area of mesoderm caudal to oropharyngeal membrane and cranial to the notochord - important organizing and signaling center for head development
Mesenchymal-Epithelial Transformation
Cells lose cell processes, become polarized, and develop cell junctions that enable them to form a layer or sheet.
Anterior Ventral Endoderm
An area of endoderm located at the cranial most margin of bilaminar disc - prior to gastrulation - determines head
Describe the clock and wave model of signaling
- Segmentation clock - negative feedback of notch signaling
- Wave - gradient of Fgf8 expression that regulates the competence of paraxial mesoderm cells to respond
Intraembryonic coelom
Space within lateral mesoderm
What do hemeangioblasts form?
Lining of the vascular system and blood cells
What happens in Week 4? (3)
- Embryo folding
- Appearance of limbs and pharyngeal arches
- Beating heart
What is the Critical Period and when is it?
The time when the embryo is most sensitve to external insult is between the 3rd and 8th week
Besides HOX, what are two other families of genes that mediate patterning in the embryo?
- Paired Box (Pax)
2. POU genes
What happens in Week 4? (3)
- Embryo folding
- Appearance of limbs and pharyngeal arches
- Beating heart
What is the Critical Period and when is it?
The time when the embryo is most sensitve to external insult is between the 3rd and 8th week
Besdies HOX, what are two other families of genes that mediate patterning in the embryo?
- Paired Box (Pax)
2. POU genes
What are four things associated with increased incidences of birth defects?
- Increasing parental age
- Season of the year when the child is conceived
- Country of residence
- Familial tendencies
What percentage of babies will be born with a clinically significant (major) birth defect?
2-3%
What causes birth defects (4)
- Genetic - 13-15%
- Environmental 7-10%
- Multifactorial 20-25%
- The rest are unknown 50-60%
What are four things associated with increased incidences of birth defects?
- Increasing parental age
- Season of the year when the child is conceived
- Country of residence
- Familial tendencies
What is a defect or malformation and give an example
A morphological abnormality from abnormal developmental mechanisms - cause is intrinsic to development can be inherited i.e. dysplasia
What is a disruption?
A morphological abnormality resulting for a breakdown or interference with an originally normal development process - chemicals/drugs/infections - extrinsic factors
What is a deformation?
The abnormal form, shape, or position of a normally formed body part - caused by mechanical forces - can sometimes be reversed
Polytopic field defect
Pattern of anomalies derived from a disturbance o f a single developmental field
Normal variation
Morphological variation of a structure is a predictable variance - i.e. branching pattern, extra muscle belly
A syndrome
Patterns of multiple anomalies that are seen together and are thought to have a common cause - differs from a polytopic field
An association
A statistically significant, non-random occurrence of two or more individuals of multiple anomalies
Normal variation
Morphological variation of a structure is a predictable variance - i.e. branching pattern, extra muscle belly
Polyploidy
3n, 4n, etc
Teratogen
Any agent that can produce a congenital anomaly or raise the incidence of an anomaly
What are the five major classes of teratogens?
- Infections - Rubella
- Ionizing radiation and other physical agents
- Drugs and chemicals - thalidomide, alcohol
- Imbalance of essential metabolites and hormones - Congenital adrenal hyperplasia
- Maternal factors - illness, T2D, smoking
Teratology/Dysmorphology
Branch of science that studies the causes, mechanisms, and patterns of abnormal development
What are the major principles that describe how teratogens affect development? (5)
- Susceptibility is dependent on age of embryonic development
- Activity is most sensitive during periods of organ/structure development
- Genotype of embryo and mother can modify susceptibility
- Degree depends on dose and duration
- Effects are due to specific mechanisms
What is on the A-list of drugs that cause birth defects?
Antibiotics, Anti-nauscants, anticoagulants, alcohol, anti-anxiety agents, antiHTN, antipsychotic, androgenic steriods
What is the defining characteristic of pluripotent stem cells?
Ability to generate all cell types of the body or form an entire organism
Where do embryonic stem cells come from?
Derived from inner cell mass of blastocyst - preimplantation stage embryo
What 2 methods can be used to produce pluripotent stem cells from differentiated cells?
- Somatic cell nuclear transfer
2. Direct reprogramming
How would you describe the potential of a mesenchymal stem cell?
Multipotent - osteoblasts, chondroblasts, and adipocytes
What is the main role of resident stem cells?
Primarily involved in tissue homeostasis and repair
What stage is the embryo in during the initial stage of implantation?
Bilaminar disk - epiblast and hypoblast
Trophoblast - mitotically active when it attaches - syncytiotrophoblast
Functional Zone
Outer 2/3 of the thickness of the endometrium - participates in cyclic changes of menstrual cycle - Implantation occurs here
Basal Zone
Inner 1/3 of endometrium adjacent to myometrium - generate new functional zone each menstrual cycle
What stage is the embryo in during the initial stage of implantation?
Bilaminar disk - epiblast and hypoblast
Trophoblast - mitotically active when it attaches - syncytiotrophoblast
Where is hCG secreted and what is its role?
By the syncytiotrophoblast - rescues corpus luteum until the placenta can take over production of estrogen and progesterone
Decidual reaction
- Stromal cells become enlarged - Compact layer
- Enlargement of glands and the decidual cell thickens endometrium
- Blood flow is increased
Which zone of the endometrium participates in the decidual reaction?
The Functional zone?
What are the layers of the decidua from the embryo out
Decidua basalis - adjacent to embryo
Decidua capsularis - surrounds chorionic sac
Decidua parietalis - remainder of uterine endometrium
Primary chorionic villi
Little fingers of cytotrophoblast that extended into the syncytiotrophoblast toward the endometrium
Secondary chorionic villi
Occurs when extraembryonic mesoderm forms a central core - days 12-20
Tertiary/Mature chorionic villi
- Vascular precursor ells of extraembryonic mesoderm form a primitive vascular network within mesodermal core of villi
- Connect with the vascular network in chorion
What components of mature chorionic villi are formed in the placenta
- Stem villi - central core/tree trunk
- Intermediate (floating) villi - branches
- Terminal Villi - leaves - contain sinusoids - exchange happens here
Chorionic plate
Chorion that forms the wall of the chorionic sac - stem villi are rooted here
Cytotrophoblastic Shett
Extension of cytotrophobast from stem villus that join together - anchors the chorionic sac to the endometrium
Chorion Laeve
The chorionic villi formed in the disidua capsularis disappear as the chorion gets thinner w/ growht of fetus - smooth leftover layer
Chorion Frondosum
Chorion adjacent to the decidua basilis
Umbilical vessels
Connects vasculatures of the embryo to the chorion
Vascular formation in Week 4
- Vascular system of embryo is connected to the vasculature of chorion as well as the yolk sac
- When blood vessels appear in embryo circulation becomes intraembryonic
Viteline vessels
Vessels connecting the vasculatures of the embryo to the yolk sac
Umbilical vessels
Connects vasculatures of the embryo to the chorion
In the placenta the chorionic villus trees are surround by intervillous spaces containing ____________. The _______________ deliver ________________.
- maternal blood
- endometrial arteries
- blood to the intervillous space
What constitutes the placental barrier in the 1st trimester? (6)
- Syncytiotrophoblast
- Cytotrophoblast
- Basement membrane
- CT of villi
- BM
- Sinusoid endothelmium
What constitutes the placental barrier in the 3rd trimester? (4)
- Think layer of syncytiotrophoblast
- CT
- BM
- Sinusoid endothelium
After 4 months of development what changed occur in the placenta?
The syncytiotrophoblast thins and the cytotrophoblast begins to disappear
What is the difference between the fetal face and the maternal face of the placenta?
- The fetal side is the shiny side - chorioamniotic membrane - placental blood vessels converging into umbilical vessels
- Maternal side is the muddy side - cotyledons are visible
Cotyledon
Mature 3˚chorionic villus separated by placental septa
Placental septa
Partition of placental tissue separating adjacent intervillous spaces
What substance can cross the placenta?
Gasses, ions,glucose, proteins, hormones, some drugs, infectious agents, EtOH
How do proteins and larger molecules cross the barrier?
Via endocytosis or pinocytosis
What does the placenta produce?
- Steroid, peptide, glycopeptide hormones
- Placental proteins
- Can make glycogen, cholesterol, and FA
What factors prevent the mother from rejecting the fetus?
- Absence of paternal-derived histocompatibility antigens on the surface of the syncytiotrophoblast
- Selective suppression of maternal immune system
- Creation of immunologically privileged site by decidual reaction
Basal plate
Formed by the deciuda basalis (functional zone) and chorionic tissue
Placental base
Basal zone next to placenta - remains to form new functional zone
Placental abruption
Unexpected hemorrhage can mediate premature separation of the placenta - blood acts like a wedge that separates the placenta from the uterus
What can cause placental abruption?
- Smoking
- Maternal malnutrition
- Hypertension
- Trauma
- Drug abuse
Molar pregnancy
Only paternally-derived DNA is present in trophoblastic tissue (genomic imprinting)
What is an indicator of a molar pregnancy
Abnormally high hCG
Placental accreta
Implantation extends into basal zone - separation is impossible - otherwise it becomes cancerous
Velamentous cord insertion
Umbilical vessels extend into chorioamniotic membrane
Field defect
Pattern of anomalies derived from a disturbance of a single embryonic field - midline, tailbud region - rare
Syndrome
Pattern of multiple primary anomalies which are seen together and causally related - fetal alcohol syndrome
Sequence (defect)
Pattern of anomalies which results from a single primary anomaly - insufficient amniotic fluid - compressed facial features
Chronic granulomatous disease
Inherited NADPH oxidase deficiency - infections
Reperfusion injury
Ischemia - resumption of blood flow causes damage - inc. hypoxanthine and inc. xanthine oxidase - increased formation of oxygen-derived radicals
How do you treat a reperfusion injury?
Allopurinol, antioxidant enzymes, iron chelators
How do you form singlet oxygen?
Photosensitive dye - oxygen with empty orbital - very short lived oxidizes target very quickly
Photodynamic therapy
Using singlet oxygen to selectively bind dye to tumor - localized light delivery
Cutaneous porphyria
Defective heme synthesis - accumulates in skin - sun causes skin blistering/swelling due to formation of singlet oxygen
Peroxynitrite
Potent oxidant - reacts with lipid, protein, and DNA - also removes NO required for vasodilation
NO synthase
L-arginine, NADPH, O2, (cofactors: calmodulin, Ca, and BH4)
LNAME and LNMMA
Inhibit NO
LNAME - nonspecific
Inhibitors of BH4 synthesis will _______ nitric oxide biosynthesis
Inhibit
NADPH oxidases
Generate superoxide and hydrogen peroxide - only known function
NOX1 etc.
(NADPH Oxidase) Multi-enzyme complex - different types
Inhibition and interception of ROS and RNS (3)
Small molecular weight antioxidants (vitamin E, C glutathione)
- Antioxidant gene expression (heme, glutathione syn)
- SOD - not completely detox - reduces superoxide
Catalase
Reacts with hydrogen peroxide - use in conjunction with SOD
Glutathione peroxidases
Removes hydrogen peroxide - uses up one NADPH - pentose phosphate pathway
Small Molecule Antioxidants (4)
- Vitamin C
- Vitamin E
- Glutathione (GSH)
- Beta-carotene
Cross talk between lipophilic and hydrophilic antioxidants
Vitamin E is lipophilic - Vitamin C is hydrophilic
Vitamin E radical is recycled back to Vita E by reacting w/ ascorbate at the surface
Oxidative stress
Imbalance between prooxidant and antioxidant levels - favoring prooxidants
Oxidative damage
Modification of lipids, proteins, DNA
When will antioxidant therapy work?
Kwashiorkor (low levels of glutathione) - chronic inflammatory conditions - iron overload - vitamin deficiency
Lipid peroxidation
Associated with atherosclerosis - cycle can go on and on - need terminating reaction i.e. Vitamin E
Keap1-Nrf2-ARE pathway
ROS activate this pathway to transcribe more antioxidant genes (SOD, Heme oxygenase)
Nrf2 = TF
Curcumin
Activates Keap1-Nrf2 pathway
Mitohormesis
Links physical exercise and formation of ROS to insulin sensitivity and antioxidant defense
Adverse side effects of chemotherapy (doxorubicin)
From ROS/RNS - cardiomyopathy years later
What is the cause of cardiotoxicity with doxorubicin use?
Mitochondrial DNA damage, protein oxidation, lipid peroxidation (From Fe + H2O2)
What is given to avoid doxorubicin toxicity?
Iron chelators and vitamin E
Cisplatin
Chemotherapy - nephrotoxicity - DNA damage, inhibits DNA repair - increases NOX, iNOS
Cisplatin
Chemotherapy - nephrotoxicity - DNA damage, inhibits DNA repair - increases NOX, iNOS