Lecture 10: Objective 1

Question 1

Step 1 in notochord formation: role of primitive node

Answer 1

primitive node provides cells that will form notochord

Question 2

Step 2 in notochord formation: migration

Answer 2

cellular precursors migrate anteriorly

left behind as rodlike aggregation structure when primitive groove recedes

Question 3

Step 3 in notochord: fusion

Answer 3

notochord cells fuse with flanking endodermal cells forming temporary neurenteric canal

neurenteric canal is just a small area connecting aminotic sac with yolk sac,

Question 4

Step 4 in notochord: Separation

Answer 4

notochordal cells separate from endoderm to form definite notochord

Question 5

Oropharyngeal membrane

Answer 5

superior to notochord, area is missing mesoderm and only consists of “abutting” ectoderm and endoderm

Question 6

Prechordal plate

Answer 6

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

Question 7

Inductive functions of notochord

Answer 7

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

Question 8

Foxa-2+Goosecoid

Answer 8

transcription factors which cause notochord cells to produce noggin and chordin

Question 9

noggin and chordin

Answer 9

potent neural inducers