Lecture 10: Objective 1 Flashcards
Step 1 in notochord formation: role of primitive node
primitive node provides cells that will form notochord
Step 2 in notochord formation: migration
cellular precursors migrate anteriorly
left behind as rodlike aggregation structure when primitive groove recedes
Step 3 in notochord: fusion
notochord cells fuse with flanking endodermal cells forming temporary neurenteric canal
neurenteric canal is just a small area connecting aminotic sac with yolk sac,
Step 4 in notochord: Separation
notochordal cells separate from endoderm to form definite notochord
Oropharyngeal membrane
superior to notochord, area is missing mesoderm and only consists of “abutting” ectoderm and endoderm
Prechordal plate
Referred to as head organizer
releases sonic hedgehog (involved in ventral patterning of forebrain)
source of “survival signals” for neural crest cell migration into early forebrain
first cells to pass through primitive node, superior to notochord, small clench of mesoderm unattached to notochord
Inductive functions of notochord
important in formation of axial structures: uses Shh (sonic hedgehog) (signaling molecules)
induces overlying embryonic ectoderm to form neural ectoderm
foxa-s and goosecoid (transcription factors) induce noggin and chordin, neural inducers
specifies identity of certain cells within early nervous system
transforms certain mesodermal cells of the somites into vertebral bodies
stimulates earliest steps in the development of the pancreas
Foxa-2+Goosecoid
transcription factors which cause notochord cells to produce noggin and chordin
noggin and chordin
potent neural inducers