Early Embryonic Patterning Flashcards
Nodal
Stimulates Pitx2 expression –> L/R asymmetry
Signaling molecule NOT transcription factor itself
Transient
Starts symmetric then specifically on L side (L lateral mesoderm)
Pitx2
Transcription factor stim by nodal
Expressed asymmetrically for an extended time –> L/R asymmetry (PERSISTS)
BMPs
Released from epiblast –> start cascade that eventually leads to transcription
Promote epidermal fate AND suppress neural fate
Noggin and Chordin
BMP antagonists
Released from node and notochord
Promote neural fate by blocking BMPs and inducing neural tissue
Experiments showed inc in Noggin led to more neural tissue
FGFs Wnt and RA
FGF and Wnt are proteins
RA (retinoic acid) is lipophilic molecule that binds in nucleus
**From Vit A in diet and in Accutane (do not use in first weeks of pregnancy)
All released by posterior/caudal regions and promote CAUDAL identity
Dickkopf
Wnt inhibitor
Prod by anterior visceral endoderm (AVE - anterior to primitive streak)
Promotes CRANIAL/anterior identity (along w/ noggin and chordin)
HOX
Transcription factors that encode regional identity in mult places…
- on anterior-posterior (cranial-caudal) axis
- expressed on mesodermal tissue for lumbar vertebra identity
- reproductive tract
Expressed in restricted patterns
On 4 chromosomes - genes in specific order that corresponds to anterior-posterior axis
(5’ end is caudal/posterior higher # and 3’ end is anterior/cranial lower #)
Program identity of cranial nerves
What happens if there is an excessive amount of RA in a cell?
Identity of nerves are converted to that of more posterior nerves (ex- trigeminal converted to facial nerve)
What affect does cilia have on embryo patterns?
Both motile and non-motile cilia are thought to trigger L sided Nodal expression
Laterality defects linked to mutations that affect both kinds of cilia
1- situs inversus totalis - totally flipped - little effect
2- heterotaxy - situs ambiguus - partial reversal - effects
2 Types of Cilia
Motile - on groove of nodes
Non-motile (primary) - on edge of nodes - sensory
In what way does RA work with Hox?
-RA exposure in hindbrain –> sets Hox patterns and inc POSTERIOR (caudal) identity in hindbrain
Morphogen
- Molecule that emerges from 1 cell then diffuses away to form GRADIENT (cells differentiate depending on conc level they are exposed to)
- Ex) how RA works- amount of RA gradient a cell is exposed to determines which Hox is expressed
