Module 3 - Development Flashcards
Eggs and cleavage
Cleavage - splitting
Size and distribution of yolk
Polarity in some
Animal pole - embro
Vegetal pole - yolk
Holoblastic cleavage
complete, all embryo
isolechital eggs
sparse, evenly distributed yolk
- therian mammals, amphixous
Mesolechital eggs
moderate vegetal yolk disposition
- amphibians
meroblastic
incomplete cleavage
telolecithal (megalecithal)
dense yolk
discoidal cleavage
only small part becomes embryo
- most fish, reptiles, birds, monotremes
Early stages
- morula - solid ball of cells
- Blastula - becomes hollow
- Hollow - Blastocoel
- inner cell mass = embryo
- Also source of embryonic stem cells.
Label:
Blastopore
Gastrocoel
Endoderm
Ectoderm
yellow; ectoderm
blue; endoderm
red; gastrocoel
dark blue; blastopore
gastrula
invagination
opening
blastopore
deuterostome
“second mouth”
- becomes anus in craniates
tube
gastocoel or archenteron
diploblastic - two layers
Endoderm - inside
Ectoderm - outside
Mesoderm
- part of the endoderm differentiates
- takes part of the gastrocoel with it
- enterocoely
- primitive streak in amniotes - occurs at the same time
- sets up axes of the body
- different in protostomes
- triploblastic
Differentation
Quickly the tissue layers begin to differentaite
- notochord already visible early
- Neural plate will form neural tube
Neuralation
- neural plate folds
- neural crest begins formation
- mesoderm differentates
- coelom forms
Mesoderm splits
Dermatome - dermis
myotome
muscle
sclerotime
vertebrae, vertebral rib
nephrotome
kidney
somatic hypomere
limbs, peritoneum, gonads
splachnic hypomere
heart, blood vessels, mesenteries that cover organs (dorsal and ventral mesenteries)
ectoderm
epidermis, nerves and brain, some other contributions thrugh neural crest
Neural crest formation
- Synapomorphy for craniates
- form from tissue near neural tube
- break off
- migrate along sepcific pathway
- pluripotent cell - can form many cell types
- types produced defined by surroinding tissues
zebrafish embryo
36 hours post fertilization
Neural crest
- ganglia of spinal and cranial nerves
- most pigement cells except those of eye and spinal cord
- most cartilage of lower jaw
- through evolution, more and more of the skull is of neural crest origin
- differentiates very early
- not tied to mesoderm or neural tissue
- green cells are neural crest
- disurptions in development can cause cleft palate, heart valve malformations and tumors.
Neuroblastoma - cancer of NC-derived sympathic nerve cells
- most common solid tumor in children
- 15% of childhood cancer deaths
- 1,000 new cases/year in US
- usually near adrenals, but can be anywhere along spine
- symptoms are vague and non specific
Are vertebrates segmented?
yes
which is the sclerotome?
D
Haeckel, biogenetic law
Ontogoney - Development
Recapitulates - Reviews/Replays
Phylogeny - Evolutionary History
Biogenetic tendency - not law
- Recapitulation ..What’s wrong?
- We aren’t fish, we look like fish embryos
- Evo-Devo
Von Baer’s Law
Development proceeds from general to specific
- an embryo that can be anything
- preserve early stages
- modify them later in development
Epigenetics
- Proteins affected by manu things through interaction
- almost all development above the gene
- due to interaction of proteins
- no eye gene or hand gene
Homeobox genes
- short (180bp)
- 60AA homeodomain
- Highly conserved
- Approx 235 in humans
- homeotic genes - HOX genes
HOX genes
Proteins with homeodomains acts as TF
Homeodomain attaches to regulatory regions of target genes
these are found in order on chromosomes
Are human eyes and fly eyes homologous?
Yes, in that they both use PAX6, but not structurally
Human aniridia
no iris
The eye case study
- Complex eyes evolved 50-100 times
- Pax6 gene controls it (homeobox gene)
- Conserved - mouse works on fruit fly
- Eyes not even homologous
- Controls expression of rhodopsin pigments
- genes that have been around since bacteria
Heterozygous mutation to pax 6 = Human aniridia
Homozygous = lethal
induction
- stimulatory effect between developing tissues
- neural tube induces sclerotomes to form vertebrae
- insures fit
- remove neural tube, not vertebrae grow in that section
- opposite not true
- usually mesoderm induces ecto-or endoderm
Reciprocal induction
- Two or more developing tissues effect one another’s development
- tissues link better
- Apical Ectodermal ridge - length og limb
- mesodermal core - front or back limb
- switch mesodermal cores
- limbs reversed
- no AER, no limbs
- AER effected by hox genes
snake limbs
- pythons have hind limbs, not forelimbs
- loss caused by interaction of Hoxc6 and Hoxc8
Limb bud
- time spent in PZ derermines that forms along length
- Patterning uses Sonic Hedgehog gene
- Which orders the digits and sets number
- Active in ZPA
Removal of AER (Apical Ectodermal Ridge) at different stages results in terminal truncation
a humerus may have the proximal end normal but the distal portion cut off
What is expressed in this diagram?
Mirror image dupilication
Forming hands
- Apply retinoic acid to developing skate fin
- causes fin to not have single axis
- like tetrapod limbs
B
Heterochrony
- changes in timing of development
- Peramorphosis
- Elder form - exaggeration of adult morphologies
- Paedomorphosis
- Child form - retention of juvenile morhpology
Heterochrony –> Paedomorphosis
Progenesis - early offset
Neoteny - Slow raye
Ppstdisplacement - late onset
Heterochrony –> peramorphosis
Hypermorphosis - late offset
acceleration - fast rate
predisplacement - early onset
hypermorphosis
mature past adulthood and demonstrate hitherto unseen traits
acceleration (peramorphosis)
part grows faster than in ancestors
predisplacement (peramorphosis)
onset of growth earlier
Hypermorphosis (peramorphosis)
Peramorphosis
Predisplacement
Peramorphosis
Acceleration
allometry
differential growth of structures
- ex: beak on some birds
- grows more rapidly than heads
isometry
parts grow at the same rate
hypermorphosis?
acromegaly
Ex: of acceleration
Part grows faster than in ancestors
- tentacles in bristlenose plecos
- narwhal tusk
what do these fish show an example of?
Acceleration
What is this an exmaple of?
Predisplacement - onset of growth earlier
- bird Meckel’s Cartilage forms earlier than in ancestors
Progenesis in Paedomorphosis
Neoteny in Paedomorphosis
Postdisplacement in paedomorphosis
Progenesis ex
Early offset, growth halts early (Paedo)
- some fishes
- tree salamanders
- juvenlie hands, unfused skull bones
Neoteny ex in paedo
part grows slower than in ancestors
- mudpuppies and axotyls
- humans - decreased skull allometry
Postdisplacement ex in paedo
Onset of growth later than in ancestor
- Mammal Meckels cartilage
- Tympanic
- Malleus
- Articular
- Angular
Are chimps neotenic?
no
Cartilage and bone characters
- unique craniate characteristics
- provide muscle attachment sites
- protect nerves, brain, blood vessels
- protects body (armor)
- bone produces blood
- calcium storage for body
Elastic cartilage
Cartilage
- firm, flexible material
- chondroitin sulfate and collagen
- cells = chondrocytes
- cells in lacunae (spaces)
Hyaline (Type of cartilage)
- glassy appearance
- long bones
- mostly replaced by bone in adult
- synovial capsules
Hyaline Cartilage
Fibrocartilage
Fibrocartilage
- Reinforced liberally with collagen
- invertebral disks, pubic symphysis
- Relaxin loosense pelvic symphysis before birth
in what place do we have elastic cartilage?
epiglottis, ear
Cartilage structure
Pericondrium - outer connective tissue
- with blood vessels
Inner matrix - food diffuses in and waste out.
slow to heal
Bone composition
Calcium, phosphate and other minerals salts in regular order in matrix.
Osteon (Haversion System)
- Canal - haversion canal, blood vessels, lymph and nerves.
- Calcium phosphate in concentric rings, lamellae (layers near surface)
- Volkmann’s canals - diagonally between haversion canals, connects blood vessels.
osteoblasts
produce new bone (osteogenesis), mononulceate
osteocyte
osteoblast encased in bone
osteoclasts
remove existing bone, multinucleate
osteoclast
Osteoblasts
Osteocyte in Lacuna
Cancellous (spongy) bone
Looks spongy
In long bone
- increase strength(lie along stress lines)
- Ability to change (alter depending on load)
- many bones start as spongy and become compact
compact bone
- thicker, most bones (outside)
- many bones start out as spongy and become compact
Cortical vs. Medullary
Cortical - outside (hard bone)
Medullary - inside
Endochondral vs. Intramembranous
Endochondral - cartilage model
Intramembranous - no cartilaginous precursor
Endochondral bone
- long bones, vertebrae, some skull bones
- diaphysis - shaft
- epiphysis - tips
- metaphysis - sometimes recognized as area between the two
Perichondrial cells adjacent to hypertrophic chondrocytes become osteoblasts, forming bone collar (bc).
Mesenchymal cells
condense
Cells of
condensations
become chondrocytes
Chondrocytes at the center of condensation stop proliferating and become hypertrophic (h, become larger).
Osteoblasts of primary
spongiosa accompany
vascular invasion, forming
the primary spongiosa
(ps).
Chondrocytes continue
to proliferate, lengthening
the bone.
Osteoblasts of primary
spongiosa are precursors
of eventual trabecular
bone; osteoblasts of bone
collar become cortical
bone.
Epiphysial plate
1. Zone of hyalin cartilage
2. Zone of proliferation
3. Zone of hypertrophy
4. Zone of Ossification
Zone of resting
hyaline
zone of proliferation
cartilage cells being produced
zone of hypertrophy
cartilage elongating
zone of ossification
new bone forming
Endochondral bone development
- When epiphyseal plate reaches epiphysis, growth stops
- Mammals with secondary center of ossification at epiphysis
- Birds and mammals with deteminate growth
- Other craniates with indeterminate
Growth of which tissue made you taller?
Cartilage, and then this is replaced by one.
Intramembranous Bone Development
Mesenchyme Compacted into sheets (memnranes)
1. Mesenchyme cells condense, supplied with blood vessels, gel-like ground substance formed.
2. Bone matrix deposited form (deeper red)
3. Bars take up whole of bone
4. Growth by adding layers
Intramembranous bone types
- Dermal
- Sesamois
- Perichondral and periosteal
Dermal intramembranous bone type
formed in dermis (most of skull, clavicle)
sesamoid - intramembranous bone type
because of mechanical stress in tendon (patella, pisiform)
perichondral and periosteal intramembranous bone type
formed from connective tissue around cartilage and bone (adds thickness to structures).
Joints
Synovial (diarthrosis) - where bones move
synovial capsule
fluid filled, connective tissue cap at the end of bone
Amphiarthrosis
slightly movable, pubic symphysis
synarthrosis
no movement
Cartilaginous joints
- symphasis (at midline) - armphiarthrosis
- Synchondrosis - synarthrosis (epiphyseal plate)
Fibrous joint
- Suture - synarthrosis
- syndesmosis - amphiarthrosis (radioulnar joint)
- Gomphosis - teeth in socket, synarthrosis
synostosis
fused bones (ankylosed), synarthrosis
Jaw joint is a
synovial - monoaxial
Joint between two dentaries
Synarthrosis/symphysis
Thalidomide
- Used for morning sickness
- fetal development
- strange syndrome where the distal features of the limbs developed but limb developed but limb lengthening did not occur.
phacomelia and thalidomide
- Decreased limb bud mesenchyme
- Normally the apical ectodermal ridge (AER) grows and only the distal part is exposed to fibroblast growth factor
- FGF re-specifies cells to a distal fate (form hand bones)
- lots of other problem throughout embryo.
- all of AER is exposed to FGF
- Therefore all cells re-specified for distal fate
- Tested on rodents bu tnot for teratogenic effects
- The reason why the US congress and president Kennedy signed a law requireing testing of drugs before used on pregnant women.
US FDA
- Dr. Frances Kelsey
- Believed the drug lacked proof of safety and prevented its sale in the US
- she was under strong pressure from the pharmaceutical industry to approve it - rejected 6X.
Structure: Bony fusion
Type: Synostosis
Functional Category: Synarthrosis
Structure: Fibrous joint
Type:
- Suture (Synarthrosis)
- Gomphosis (Synarthrosis)
- Syndesmois (Amphiarthrosis)
Structure: Cartilaginous joint
Type:
- Synchondrosis - Synarthrosisi
- Symphysis - Amphisarthrosis
Structure: Synovial Joint
Monoxial - Diarthrosis
Biaxial
Triaxial
