Embryology Test 1 Flashcards
What is the study of embryo?
Embryology
What includes all developmental processes from conception to death?
Ontogeny
What is the part from conception to birth or hatching?
Embryogeny
What is the process by which a cell or part of an embryo become restricted to a given developmental pathway, the point at which a cell becomes committed to specific cell line?
Determination
What is a complex change involved in progressive specialization of structure and function, often resulting in the formation of luxury moleucles
Differentiation
Increase in cell numbers
Hyperplasia
Increase in cell size
Hypertrophy
What are the six component processes?
Determination Differentiation Growth Morphogenesis Induction Integration
Generation of form or assumption of new shape
Morphogenesis
What happens in Anaphase I?
Homologous chromosomes move to opposite poles
Each homologue consists of two chromatids
Chromatids are not genetically identical because of crossing-over
Daughter cells will be haploid
An effect one embryonic tissue (inductor) has upon another (responder) such that the development course of the responding tissue is qualitatively changed from what it would have been in the absence of the inductor
Induction
When do the primordial germ cells first appear? Where do they appear?
24 days after fertilization
Found in the endodermal layer of yolk sac
Migration route of primordial germ cells?
Yolk sac –> hindgut epithelium
Through dorsal mesentery
Into developing gonads
Teratomas
Growths from misdirected migrating primordial germ cells, contains mixtures of highly differentiated tissues
Process by which different tissues are brought together and combined to form organs and tissues
Integration
What are the 5 phases of prophase I
Leptotene Zygotene Pachytene Diplotene Diakinesis
Growth
Permanent increase in mass
Hyperplasia
Increase in cell numbers
What happens in Leptotene?
Chromosomes are threadlike
Each chromosome consists of two chromatids
Chromosomes begin to coil
What happens in Zygotene?
Homologous chromosomes pair (synapsis)
Synaptonemal complex forms
Determination
Process by which a cell or part of an embryo becomes restricted to a given developmental pathway
What happens in Pachytene?
Maximum coiling
Tetrads
Crossing-over begins
What happens in Diplotene?
Crossing-over continues
Chiasmata are well-defined
Differentiation
Complex changes involved in progressive specialization of structure and function, often resulting in the formation of luxury molecules
Hypertrophy
Increase in cell size
Integration
Process by which different tissues are brought together and combined to form organs and tissues
What happens in Diakinesis
Crossing over is complete
Terminalization
Spindle apparatus is in place
Nuclear membrane is disrupted
At what stage is terminalization?
Diakinesis of Prophase I
When do chromosomes begin to coil?
Leptotene of Prophase I
Induction
An effect one embryonic tissue (inductor) has on another (responder) such that the development course of the responding tissue is qualitatively changed from what it would have been in the absence of the inductor
Morphogenesis
Generation of form or assumption of new shape
At what stage does the synaptonemal complex form?
Zygotene
During what stages does crossing-over happen?
Pachytene & Diplotene
At what stage in Prophase I is the nuclear membrane disrupted?
Diakinesis
At what stage does maximum coiling occur?
Pachytene of Prophase I
What happens in Metaphase I?
Tetrads line up along equatorial plate
Centromeres do not divide
At what stage is the Chiasmata well defined?
Dipletene
At what stage do homologous chromosomes move to opposite poles?
Anaphase I
At what stage do homologous chromosomes pair (synapsis)?
Zygotene of Prophase I
At what stage is crossing-over complete?
Diakinesis of Prophase I
What happens in Teleophase I?
Cytokinesis occurs (usually)
Nuclear membrane reform (maybe)
Spindle apparatus disassembles
Chromosomes may uncoil to varying degrees
What happens in Prophase II?
Chromosomes again condense
Nuclear membranes disappear
Spindle apparatus reforms in each cell
Each chromosome consists of two chromatids
Each daughter cell has one complete set of chromosomes (haploid)
What happens in Metaphase II?
Chromosomes line up on equatorial plate?
What happens in Anaphase II?
Centromeres divide
Chromosomes move to opposite poles
Each chromosome consists of a single chromatid
At what stage are there tetrads?
Pachytene of Prophase I
At what stage is the spindle apparatus in place?
Diakinesis of Prophase I
Daughter cells in Anaphase I are diploid or haploid?
Haploid
At what stage does the nuclear membrane reform?
Teleophase I
Telophase II
At what stage does crossing-over begin?
Pachytene of Prophase I
At what stage do tetrads line up along equatorial plate?
Metaphase I
At what stage do chromosomes condense again?
Prophase II
At what stage does the nuclear membrane disappear?
Prophase I and Prophase II
At what stage does cytokinesis occur
Telephase I
Telophase II
At what stage does chromosomes line up on equatorial plate?
Metaphase II
At what stage does the spindle apparatus reform in the cell?
Prophase II
In prophase II are the daughter cells haploid or diploid?
Haploid
What happens in Telephase II?
Chromosomes uncoil
Cytokinesis is complete
Nuclear membrane reform
End result is four genetically unique haploid daughter cells
At what stage do each chromosome consist of a single chromatid?
Anaphase II
Telophase II
At what stage do the chromosomes move to opposite poles?
Anaphase II
At what stage does the spindle apparatus disassemble?
Telophase I
At what stage do centromeres divide
Anaphase II
Aneuploidy
Abnormal number of chromosomes
Nondisjunction
Monosomy
Trisomy
Euploidy
Change in number of complete sets of chromosomes
Monoploidy
Diploidy
Polyploidy
There are how many germ cells at embryonic midterm?
7 million
Fetal period characteristics
No follicle
Diploid oogonium not surrounded by follicle cells
1 chromatid/ chromosome
Later Fetal period through birth
Diploid primary oocyte
Primordial follicle with a few flattened follicle cells
2 chromatid/ chromosome
How many primary oocytes are ovulated?
400
Birth to puberty
Diploid primary oocyte
Primary follicle w/ single layer of cuboidal follicle cell
Oocyte & follicle cells are connected via microvilli and gap junctions
Zona pellucida separates primary oocyte from follicular cells
2 chromatids/ chromosome
After puberty
Diploid primary oocyte
Secondary follicle w/ multiple layers of follicle cells & beginning of antrum formation
Membrane granulose surrounds outside of follicle cells
2 chromatids/chromosome
Haploid secondary oocyte + haploid polar body
Tertiary follicle w/ multiple layers of follicle cells, corona radiate and large antrum
Mural granulose cells
Cumulus cells
2 chromatids/ chromosome
There are how many primary oocytes shortly after birth?
At what stage of meiosis are they arrested in?
400,000
Diplotene stage of Prophase I
Mural granulose cells are found
cells between membrane granulose and antrum
Cumulus cells are found
Cells between zona pellucida and antrum
How many germ cells are present at birth?
2 million
Oocyte and follicle cells are connected by what 2 things?
Microvilli and gap junctions
What separates the primary oocyte from the follicular cells?
Zona pellucida
How many primary oocytes survive to puberty?
40,000
2 factors that lead to meiotic arrest in diplotene?
1) High concentration of cAMP from oocyte and follicular cells
- Inactivates MPF
- Leads to meiotic arrest
2) cGMP from follicular cells that inactivates phosphodiesterase 3A in oocyte
- prevents conversion from cAMP to 5’AMP
- maintains high concentration of cAMP
Ovulation
Haploid secondary oocyte with corona radiata and theca cells + haploid polar body
-Granulosa cells develop FSH receptors and LH receptors
-Circulating FSH stimulates granulosa cells to produce estrogen
2 chromatids/chromosome
About 10-12 hrs before ovulation meiosis resumes
1) resumes due to response to LH surge by cumulus cells
2) Cumulus cells shut down gap junctions, cAMP and cGMP can’t get to oocyte
3) no cGMP, activates PDE3a, converts cAMP to 5’AMP
4) Decrease cAMP activates MPF and resumes meiosis
What develops FSH receptors and LH receptors?
Granulosa cells
Circuating FSH stimulates granulosa cells to produce what?
Estrogen
Tertiary follicle consists of what four things?
Antrum
Cumulus cells
Zona pellucida
Oocyte
Mural granulosa cells
Develop FSH receptors
Synthesize aromatase in response to FSH
What does aromatase do with concern to ovulation?
Aromatase is secreted by mural granulosa cells in response to stimulation by FSH
The aromatase converts testosterone into 17beta-estradiol (estrogens)
Estradiol stimulates the formation of LH receptors on granulosa cells
Theca internal cells produce what?
Androgens (testosterone)
Role of LH
LH surge shuts down gap junctions between granulosa cells and oocyte
-causes activation of MPF and resumes meiosis
LH surge, LH binds to receptors on follicular cells Activation of adenyl cyclase Progesterone secretion by follicle cells Activation of collagenase enzyme Release of oocyte
Stages of Spermatogenesis
Primordial germ cell (2N) Spermatogonia (2N) -Type A (stem cells) -Type B (leave mitotic cell to enter meiotic cycle under influence of retinoic acid) Primary spermatocyte (2N) -First maturation division (meiosis I) Secondary spermatocyte (N x 2 cells) -Second maturation division (meiosis II) Spermatids (N x 2 cells)
Influence of what causes type B spermatogonia cells to leave the mitotic cell and enter meiotic cycle?
Retinoic acid
Testosterone is produced by what?
Theca internal cells
Sertoli cells are located where?
Seminiferous tubules within the testis
Cells of Leydig
Location?
Function?
Interstitial cells in testis
Produce testosterone
Functions of sertoli cells (6)
- Physical support & maintenance
- Maintain and coordinate spermatogenesis
- Secrete estrogen, inhibin, androgen binding protein & anti-mullerian factor
- Maintain blood-testis barrier
- Secrete tubular fluid
- Phagocytize residual bodies of sperm cells
Sperm histones
proamines
What sertoli cells also called?
Sustentacular cells
Blood Testis Barrier with Sertoli cells
Sertoli cells form an immunological barrier between the forming sperm cells and the rest of the body and spermatogonia
1) surface adhesion complexes bind to sertoli
2) SAC brake down & release spermatids in lumen
3) Laminin frag from SAC plus cytokines and proteninases break down tight junctional proteins
- Developing spermatocytes move closer to lumen
4) Testosterone stimulates formation of new barrier
What breaks down the blood testis barrier?
Laminin fragments from surface adhesion complex plus cytokines and proteinases
What stimulates formation of a new blood-testis barrier closer to basal lamina?
Testosterone
Testosterone effect on Sertoli cells & secondary sex characteristics
Testosterone is carried by blood to sertoli and secondary sex tissues
FSH binds to receptors on Sertoli cells
-Sertoli converts testosterone to estrogen and synthesizes leydig cells stimulatory factor
-Produce androgen binding factor
-Binds to testosterone and carries it to seminferious vesicles
Ovulation occurs when?
Roles of FSH & LH on ovulation?
Ovulation occurs on day 14 of the ovarian cycle
The stimulus for ovulation is a rise in levels of FSH and a sharp peak in LH
(ant. pit)
What components of the graafian follicle form the corpus luteum?
The residual theca and granulosa cells proliferate and form a large glandular structure called the corpus luteum
Outer part of graafian follicle that remains is made of what and secretes what?
Thecal cells
Secrete progesterone
Fate of corpus luteum without fertilization
Corpus luteum regresses and levels of progesterone and estradiol decrease resulting in beginning of next menstral cycle
Inhibin is released by?
What does it do?
Released by granulose cells
Inhibits secretion of gonadotropins, esp. FSH, resulting in regression of corpus luteum
What is the role of corpus luteum in endometrial cycle?
In pregnancy, the corpus luteum continues to produce progesterone which maintains that early embryo until the placenta begins to produce sufficient hormones to maintain pregnancy
Proliferative phase
- Endometrial growth increases the endometrial thickness from 1-2 mm to 8-10 mm by day 14
- Blood vessels & glands grow
- Cells that initiate growth come from bases of the glands that formed previous endometrium that were deep enough to survive the loss
- Proliferation phase is due to increase in levels of estradiol secreted by the grandulose cells of the developing ovarian follicle
- Near the end of this phase is sharp rise in estradiol levels
Vasoconstriction by what?
Prostaglandins
Secretory phase
- During the phase levels of estrogen decrease & the endometrial growth stops
- Mucous glands develop more fully and begin secretion
- The spiral arterioles in this area expand & heavily vascularize the area
- The secretory phase is controlled by rising levels of progesterone, secreted by both the granulose & theca cells of the ovarian follicle
Graffian follicle prior to ovulation
Mature Graafian follicle
- expansion of follicle (FSH & LH)
- Thickening of outer layers of follicle
- Rupture of follicle wall (24 hr after surge)
Fertilization age
Date age of embryo at time of fertilization
Menstrual age
Date age is from start of last menstrual period, 2 weeks greater
Rapid egg transport is through where and what hormone is required?
Isthmus
Progesterone
What contributes to semen and with what?
Seminal vesicles: fructose and prostaglandins
-Fructose provides energy
Prostate: citric acid, Zn, Mg, Phosphate
pH of upper vagina
4.3
Adjusts to 7.2 for sperm
What is the optimal pH for sperm motility and is where?
6.0-6.5 in the cervix
Fertilization in the oviduct occurs where?
Ampulla
What is the purpose of capacitation? What occurs
Required for sperm to undergo acrosomal reaction
-Occurs inside uterine in isthmus
-Requires binding of sperm to tubule epithelium
-Involves:
1. Removal of cholesterol from sperm surface
(acts to inhibit premature capacitation)
2. Removal glycoproteins (epididymus)
Where does capacitation occur in the female tract?
Inside the uterine tube in Isthmus
Major enzyme of acromsome?
Hyaluronidase
Penetration of Corona Radiata (4)
- Fusion of the outer acrosomal membrane with the sperm plasma membrane creates portals through which the contents of the acrosome can be released
- Fragmentation of fused acrosomal membrane and plasmalemma of the sperm results in the release of acrosomal enzymes
- Hyaluronidase is one the major enzymes in the acrosome
- Swimming movements of spermatozoa help in the penetration through the corona radiata
Function of ZP3
Zp3 is one of four glycoproteins that make up the ZP
Attachment of sperm to the ZP is mediated by ZP3 protein
ZP3 protein stimulates acrosomal reaction in mammals
1. Acts through a G protein in the sperm plasma membrane
(Leads to influx of calcium through sperm plasma membrane, exchange of sodium and hydrogen increase pH, then penetration)
What is the most important enzyme involved in the penetration of the zone pellucida
Acrosin (serine proteinase)
aka zona lysin
Remains attached to the portion of the acrosomal membrane that fuses to the remaining sperm plasmalemma and overlies nucleus
Digest small hole through ZP
Fast block
Consists of a rapid depolarization of egg plasmalemma
-70 to +10 mV within 2-3 sec (to min)
Fast block temporarily prevents polyspermy and allows time for the egg to establish slow block
Slow block
Most characterized by release of polysaccharides from the cortical granules located just under the plasmalemma of the egg
- Polysaccharides enter perivitelline space (between plasmalemma and the zona pellucida) and become hydrated
- Hydration produces a swelling that increases the width of the perivitelline space
Role of phospholipase C zeta in metabolic activation of the egg following fertilization?
Metabolic activation of egg is initiated by release of calcium within egg cytoplasm in response to introduction of phospholipase C zeta by sperm
Pronucleus
Is the nuclear material of the head of the spermatozoan (male pronucleus) or of the oocyte (female pronucleus) after the oocyte has been penetrated by spermatozoan
- Each pronucleus carries a haploid set of chromosomes
- The male pronuclei consists of decondensed nuclear material
- A pronuclear membrane, derived from endoplasmic reticulum of the egg, typically forms around the female chromosomal material
What introduces phospholipase C zeta to the cytoplasm?
Sperm
Zygote
Is the term used to denote the single-cells stage of which the male and female pronuclei have fused together and share a common membrane, establishing the diploid chromosome number
Inside-Out Hypothesis
Fate of balstomere is determined by its position within the embryo, not from intrinsic properties
Cell polarity Model
Fate of blastomere depends on plane of cell division during cleavage Parallel -outer: trophoblast (polar) -inner: inner cell mass (apolar) Perpendicular -Both daughter cells trophoblast
Trophoblast cells are what layer
Forms what?
Outer layer cells
Forms extra embryonic structures including placenta
Inner Cell Mass are what layer
Forms what?
Inner mass of cells
Forms embryo proper plus some extra embryonic structures
What makes the blastocyst polarized?
The eccentric placement of blastocoel and inner cell mass
- Embryonic pole marks the pole of the blastocyst where the inner cell mass is located
- Abembryonic pole marks the opposite side
Invertebrates and non-mammalina genetic control of cleavage
Early control of cleavage is through gene products transcribed from the material genome and embryonic gene products often do not appear until after blastulation
Mammalian embryo genetic control of cleavage
Maternal gene products are produced but generally degraded by the 2 cell stage
By the four cell stage, most transcription is via the embryonic genome
Cdx-2
- Essential for trophoblast cell differentiation
2. Antagonistic toward Oct-4
Oct-4
- Expressed in developing oocytes and zygote
- Required to permit cleavage to proceed to 2-cell stage
- Expressed in all morula cells
- May play a role in the maintenance of the undifferentiated state
Nanog
- Produced by inner cells in the late morula stage
- Maintains integrity of inner cell mass along with Oct4
- Without nanog, inner cell differentiate into endoderm
- Without Oct4, inner cell differentiate into trophoblast
Sox2
- First expressed in 8 cell stage
2. Along with Oct-4 it helps to control regulation of genes involved in differentiation
Genomic imprinting
Is differential gene expression depending on whether a chromosome is inherited from the male or female parent
- It refers to observations that expression of certain genes derived from the egg differs from the expression of the same genes derived from the sperm
- Due to DNA methylastion differences in sperm and eggs
Methylation of DNA
- In mammals methylation is erased in the germ cells of each generation and then re-established in the course of gamete formation
- Sperm and eggs undergo different levels of methylation resulting in the differential expression of male and female alleles in the offspring
Prader Willi
mental retardation
Obese
Mutation from father
Chrom 15
Angelmann syndome
Uncontrolled muscle movement
Large mouth
Seizures
Mother mutation
Barr bodies
What do they tell us about a person’s genome?
Barr bodies are inactivated X chromosome
Show genome is female
Regulation
- Refers to ability of embryo to compensate for removal of structures or for addition of structures
- At the cellular level, this means that the fates of cells in a regulative system are not irretrievably fixed, and the cells can still respond to environmental cues
Identical twins
Product of single fertilized egg
More commonly arise by subdivision of the inner cell mass in a blastocyst or splitting of the epithelial epiblast
Dizygotic twins
Product of fertilization of 2 ovulated eggs, mechanism for formation involves endocrine control of ovulation
Common attachment site for parasitic twins
Oral region
Mediatinum
Pelvis
Bateson’s rule?
When duplicated structures are joined during critical development stages, one structure is the mirror image of the other
Functions of Zona pellucida
- It promotes maturation of the oocyte and follicle
- Serves as a barrier that normally allows only sperm of same species to access the egg
- It initiates the acrosomal reaction
- After fertilization, the modified zona pellucida prevents any additional spermatozoa from reaching the zygote
- During the early stages of cleavage, it acts as a porous filter through which certain substances secreted by the uterine tube can reach the embryo
- Because it lacks histocompatibility (leukocyte) antigens, the zona pellucida serves an as immunological barrier between the mother and antigenitically different embryo
- It prevents blastomeres of the early cleavage embryo from dissociating
- It facilitate the differentiation of trophoblastic cells
- It normally prevents premature implantation of the cleaving embryo into the wall of the uterine tube
Ectopic pregnancy
Common occur?
Implantation other than uterine wall
Most common is a tubal pregnancy
-Ampulla
-Next isthmus
Homeobox
The highly conserved sequence of 180 nucleotides in the gene that encode the homeodomain
Homeodomain
Highly conserved domain of 60 amino acids
A homeodomain is a type of helix loop helix region
X inactivation is brought about by the action of what?
Xist
What prevents the mother’s immune system from recognize the embryo as a foreign body?
Interleukin-2
Homeobox-containing genes
Are activated in a 3 to 5 direction (opposite of transcription)
Helix-loop-Helix genes
Codes for basic helix loop helix transcription factors
Basic regions of proteins bind to DNA
Involved in homodimerization and heterodimerization
Important in myogenesis
Zinc finger transcription factors
These proteins have zinc ions bound to polypeptides chain that cause the chain to form finger-like projections that can be inserted into the DNA helix
Gene families: Sox and WT1
Sox Genes
Sox transcription factors have a high-mobility group domain that binds to minor groove on DNA helix rather than major groove
Sox gene family includes SRY gene
WT1
Is important for the development of the embryonic kidney and the adult kidney
It takes name from child kidney tumor
Egg polarity Genes
Egg polarity genes are important in the establishment of the dorsal-ventral and anterior posterior axis in the fruit fly
Genes that establish the dorsal ventral axis
Dorsal, Cactus, Toll
Genes that establish the anterior posterior axis
Bicoid, Nanos, Hunchback
Morphogen
A protein that varies in concentration and causes different developmental responses as a result of the concentration differences
Dorsal protein
Expressed in ovary
Cactus protein
Expressed in the ovary and binds to the dorsal protein and traps it in the cytoplasm
Toll
Expressed in ovary and leads to the degradation of the cactus protein, allowing the dorsal protein to move into the nuclei of the ventral cells
Bicoid protein
Expressed in the ovary, regulates expression of genes responsible for anterior structures and stimulates hunch back (forms a gradient with high concentration at anterior end)
Nanos
Expressed in the ovary and regulated the expression of genes responsible for posterior structures. Inhibits translation of hunchback mRNA
Hunchback
Forms a gradient with high concentration at anterior end
Segmental genes
- These are 25 segmentation genes that are transcribed after fertilization; so they do not exhibit a genetic maternal effect
- Expression of the segmentation genes is regulated by the Bicoid and Nanos protein gradients
- Three classes of segmentation gene include:
a. Gap genes
b. pair rule genes
c. segment-polarity genes
Gap genes
Delete adjacent segemnts
Pair rule genes
Delete same part of pattern in every other segment
Segment-polarity genes
Affect polarity of segment
Homeotic genes
- Determine the identity of individual segments
- Products of homeotic genes activate other genes that encode these segment-specific characteristics
- Expressed after fertilization
- Activated by concentration of products of gap, pair-rule, and segment polarity gens
- Contain homeobox
- Two major groups of homeotic genes
- Antennapedia complex (Hox genes)
- Bithorax complex (Hox genes)
Antennapedia complex
Affects development of head and thorax
Bithorax complex
Affects development of posterior thorax and abdominal segments
Signaling Factor families
Transforming Growth Factor Beta superfamily
Fibroblast Growth Factor Family
Hedgehog family
Wnt family
Transforming Growth Factor Beta Superfamily
TGF-beta Activin Inhibin Mullerian inhibiting substance Decapentaplegic Vg1 BMP Nodal Glial cell line neurotrophic factor Lefty
Hedgehog Family
Desert
Indian
Sonic hedgehog
Process of lateral inhibition
1) Type of signaling between a dominant cell and neighboring cells
2) Dominant cell refers to a cell in a population that begins to differentiate along a particular path
3) Dominant cell expresses Delta signaling molecules on its cell membrane
4) Delta then binds to Notch receptors on neighboring cells and via the Delta-Notch pathway represses genes in the neighboring cells
In the absence of Wnt, what is bound to an intracellular destruction complex within the target cell (wnt pathway)
beta-catenins
Role of nanog in the establishment of the epiblast and hypoblast
Cells entering inner cell mass earliest express nanog and are destined to become epiblast cells
Role of Gata6 in the establishment of the epiblast and hypoblast
Cells entering inner cell mass later express gata6 and are destined to become hypoblast cells
Roles of Wnt and TGF-beta on formation of primitive streak?
Begin the process of induction of primitive streak
What are the three classical molecular markers expressed by nodal cells
Chordin
Goosecoid
Hepatic nuclear factor-3 beta (Foxa-2)
Chordin
- Signaling molecules associated with the node
- Involved in neural induction and expression of nodal of the left side of the embryo, key element in setting of left-right asymmetry
Goosecoid
Homeodomain transcription factor
Activates chord in, noggin, and other genes
If ectopically expressed, stimulates formation of secondary body axis
Hepatic nuclear factor-3 beta (Foxa-2)
Transcription factor
Establishment of midline structures cranial to node
In absence, notochord and the floor plate fail to form
Bottle cells
What role do they play
- Epithelial cells head towards primitive groove and change shape to bottle shape, thrust themselves through primitive groove
- Breaks down cell adhesion molecules becomes free and irregular shaped
- Transforming cells are freed from the basal lamina and lose E-cadherins
- Epitehlial mesenchymal cell transformation is correlated with expression of transcription factors snail
- changes in the shape of a cell as it migrates along the epiblast through the primitive streak (bottle cell) and away from the groove as a mesenchymal cell that will become part of the mesodermal germ layer.
(same cell can later assume epithelial configuration as part of somite)
Role of E-caherin and N-cadherin in epithelial mesenchymal transition
1) Prior to induction ectoderm expresses both E-cadherin and N-CAM
2a) After neural tube induction, overlying ectoderm only expresses E-cadherin
2b) After neural tube induction, neural tube ectoderm expresses N-CAM and N-cadherin
What transcription factor is correlated with epithelial mesenchymal cell transformation
Snail
Source and role of Cerebrus-like signaling molecule in development of anterior posterior axis
- From the anterior visceral endoderm
2. inhibits development of posterior structures
DSource and role of Dkk-1 signaling molecule in development of anterior posterior axis
- From Anterior visceral endoderm
- Blocks Wnt
- Inhibits development of posterior structures
Effects of Foxa-2 on early primitive streak stage
Multiple targets
Establishment of primitive node
Initiates notochord functions
Establishes midline structures cranial to node
In the late primitive streak stage, what signaling molecule is necessary for normal head function?
Cerebrus- related 1
Origin: prechordal plate
In the late primitive streak stage, what signaling molecule is released from the primitive streak activate Hox gene?
Retinoid acid, Wnt, and FGF
Targets Cdx to activate Hox
Experiments for neural induction
- The dorsal lip of the blastopore was grafted beneath the belly ectoderm of another host
- Result: secondary nervous system and body axis formed in the area of the graft
- Hensen’s node from one avian embryo to another induces the formation of secondary neural tube
- The dorsal lip is the organizer because of its ability to stimulate the formation of a secondary body axis
- In higher vertebrate, the primitive node and the notochordal process at as the neural inductor and the overlying ectoderm is the responding tissue
What is the first sign of asymmetry in early developemnt
Involves the beating of cilia around the primitive node
Role of Nodal
Symmetry breaking molecules in the left side of the embryo
Swept to left side of primitive node by ciliary current
Stimulates mulitple gene expression pathways via: Pitx-2
Lefty1
Left side of the primitive streak
Expresed on left side of the embryo
Blocks diffusion of molecules to the right side
