dev bio lab conceptual-practical I

deuterostomes

blastopore becomes the anus, second opening becomes the mouth

chordates

notochord, dorsal nerve cord/tube (neural, becomes CNS), gill slits that connect the pharynx to the exterior (anterior most part of gut tube

notochord

long rod of connective tissue that runs the midline of the organism. provides rigidity and structure.

vertebrates are chordates that have:

a backbone composed of bone or cartilage that partially encloses the central nervous system

distinct head with a tubular, differentiated brain with elaborate skull

bilaterally paired masses of skeletal muscles

non amniotes

fish and amphibians, lay eggs in water

amniotes

reptiles, birds, and mammals lay their eggs on land or allow them to develop internally, so they create a fluid filled sac called an amnion in which their embryos develop

extraembryonic membranes- yolk sac, chorion, allantois, amnion

triploblastic

inner most

endoderm (yellow)- lining of respiratory and digestive tract

mesoderm (red)- muscle, blood, heart

ectoderm (blue)- skin, neural tissue

outer most

gastrulation

process whereby the germ layers separate from each other

body axes- waist to head

anterior, rostral, cephalic

body axes- waist to tail

posterior, caudal

body axes- back

dorsal

body axes- stomach

ventral

how to read a transverse section slide

most rostral is in top left corner, most caudal is in bottom right corner

avian gastrulation

mesoderm and endoderm precursors enter the blastocoel via ingression of epiblast cells through the primitive streak

endoderm precursors migrate to midline of epiblast, undergo ingression where they lose their attachments to their neighbors, migrate into hollow space called blastocoel

mesoderm then does the same

endoderm goes all the way to bottom to replace hypoblast, mesoderm precursors fill in middle, ectoderm precursors don’t undergo ingression. they stay within the epiblast and give rise to ectoderm

hensen’s node

the primitive ridge stops 2/3 the way to rostral end. last cells undergo ingression, pile up inside blastocoel right under primitive streak. make big bump called hensen’s node

hensen’s node regression

holds precursors to notochord, regresses to the posterior end

when it regresses, leaves notochord precursors in its wake

notochord and neurulation

notochord first forms anteriorly and then later more posteriorly

neurulation is anterior to posterior, epidermal ectoderm and neural ectoderm physically separate

neurulation process

separation of neural and non-neural ectoderm and gastrulation

neural plate→neural groove→neural fold→neural tube

neural tube becomes spinal cord in caudal, expands to form brain in rostral part

embryonic ectoderm is subdivided into 4 domains

non-neural: skin and its derivatives

neural plate: CNS

neural border: neural crest AND pre-placodal region (cranial placodes)

neural crest cells

as neurulation is occurring, a subset of cells exits from the tissue that was adjacent between the edges of the neural fold and the non neural ectoderm migrates away from embryo and these are what are called the neural crest cells

neural crest migration

migrate extensively throughout the embryo and what they give rise to depends on what level of the embryo they form at

neural crest cells arise at the border between neural and non neural ectoderm

neural crest cells that arise from the anterior part of the cervical region contribute to the outflow tract of the heart

primary brain vesicles- 24 & 33 hours

forebrain: prosencephalon

midbrain: mesencephalon

hindbrain: rhombencephalon

secondary brain vesicles- 48 & 72 hours

forebrain: telencephalon, diencephalon

midbrain: mesencephalon

hindbrain: metencephalon, myelencephalon

adult derivatives of telencephalon

olfactory lobes

hippocampus

cerebrum

adult derivatives of diencephalon

optic vesicle, epithalamus, thalamus, hypothalamus

adult derivatives of mesencephalon

midbrain

adult derivatives of metencephalon

cerebellum and pons

adult derivatives of myelencephalon

medulla

markers for 33 hour prosencephalon and 48+ hour diencephalon

eye structures

markers for 33 hour rhombencephalon and 48 hour myelencephalon

ear structures

cranial placodes

thickening of ectoderms, arise in early development, most give rise to neural derivatives

cranial placodes we focus on in lab

olfactory- gives rise to olfactory epithelium

lens- derivative of surface ectoderm arises from a placode that forms early in development

otic- give rise to acoustic ganglia of inner ear

what do the trigeminal, geniculate, and epibranchial cranial placodes give rise to?

cranioganglia in face and head that are important for lower jaw, teeth, tongue

optic vesicles

derived from neural tube, induce overlying ectoderm to become lens

otic placode

thickening that will keep invaginating to make otic vesicle

seen at 33 hour cross section of rhombencephalon

48 hour optic structures

optic cup derived from optic vesicle

lens placode invaginates to become lens vesicle

olfactory pit

derivative of olfactory placode which is almost impossible to see at 48 hours

on a good slide, the olfactory pit is bilateral

apical ectodermal ridge (AER)

a distal thickened ridge of ectoderm on the anterior/posterior surface of the limb buds that is a key signaling center for limb development

aka on tip of limb buds and plays a role in proximal to distal outgrowth