Autonomous specification Flashcards
What is autonomous specification?
Specification as a result of cell-intrinsic properties due to asymmetric cytoplasmic determinants (proteins, reg RNA, mRNA)
When does initial activation of endomesoderm GRN occur?
At the 16 cell stage
Why does the initial activation of endomesoderm GRN occur?
B-catenin, the mediator of the canonical Wnt signalling pathway, is prevent from degradation by vegetal Dsh allowing translocation to the nuclei of micromeres.
What happens if there is no B-catenin in the nuclei?
Embryos that lack nuclear β-catenin function develop as primarily ciliated ectoderm without any endomesodermal tissue
What does B-Catenin do in the nuclei of blastomeres?
Workes with TCF/Lef transcription factor complex to uprgulate target genes.
What are the target genes?
β-catenin–dependent determinant Pmar1 is transiently expressed in micromere progeny during the initial stages of specification of this cell lineage
What does pmar1 do?
pmar1 represses hesC transcription. hesC encodes another repressive TF. This creates a double negative gate.
What is a double negative gate?
A double negative gate operates by relieving an otherwise global inhibitor through localized transcriptional repression of the inhibitor in a specified domain. It is used to install a specific regulatory state in a specific region of the developing embryo
What is the result of hesC repression?
The normally hesC repressed genes can now be activated.
What are the hesC genes that can now be activated and what do they encode?
Include alx1, ets1, tbr, tel and soxc. These synthesis transcription factors that activate another set of genes which activate skeletal determinants. They also activate each other’s genes once activated to maintain activity.
How is this proved to be autonomous specification?
If micromeres are isolated from the rest of the embryo, the double negative gate still occurs and become specified as expected. Therefore they don’t rely on other signals so this is autonomous specification.
