Conditional specification Flashcards
What is conditional specification?
A cell-extrinsic process that relies on cues and interactions between cells or from concentration-gradients of morphogens
How is conditional specification related to endomesoderm specification?
The micromeres function as crucial signalling centre, inducing differentiation of mesoderm and endoderm.
What is the first signal?
The first signal is factor Wnt8.
How is Wnt8 activated?
Maternal B-catenin and Otx activate Blimp1 genes, whose product (along with more B-cat) activates the gene encoding Wnt8.
What does Wnt8 do?
Wnt8 acts on micromeres to activate B-catenin. This sets up positive feedbck loop between Blimp1 and Wnt8 that establishes a stable source of B-catenin for the nuclei of micromeres.
What is the second inducing signal?
The yet unidentified ‘early signal’. The early signal gene is under the control of the double negative gate of pmar1 and hesC.
What does the early signal do?
Signals to adjacent cells (above micromeres) instructing them to have endomesodermal fate, and may create competence in veg2 cells to respond to the third signal, the delta signal.
What is the third signal?
Juxtacrine protein delta - also controlled by double negative gate
What does delta do?
Activates Notch protein in adjacent cells which induces components of non-skeletogenic mesoderm.
What is the final signal?
Wnt8 appears again, a product of micromeres and endoderm cells.
What does Wnt8 do this time?
Acts in autocrine manner to boost specification of veg2 cells to faciliate their separation into two distinct lineages.
