SpBra

Function

SpBra is a transcription factor, ortologue of the vertebrate Brachyury gene.
This gene appears to be an excellent marker for the progeny of the set-aside cells of the sea urchin embryo.
SpBra is a single-copy gene (Peterson et al., 1999).

Protein

Subcellular location

Expression Pattern

RNA gel blot hybridization showed that the SpBRA signal is easily observed by hatching blastula stage and the gene is then odwnregulated following gastrulation.
In mesenchyme-blastula stage embryo (24 hr) SpBra expression is localized to the vegetal plate. At 36 hr of development (midgastrula stage) SpBra transcripts are detected by WMISH in the delaminating secondary mesenchyme cell population, consistent with the report for the H. pulcherrimus Brachyury (HpTa) gene (Harada et al., 1995).
The early spatial pattern suggests that the SpBra gene could be involved in some initial function of the vegetal plate and that its later expression is downstream of the process by which endodermal precursors are segregated from secondary mesenchyme precursors, to which the expression of this gene in the embryo is ultimately confined.
At the 2-week larva SpBra is abundantly but specifically expressed in both the vestibule and left hydrocoel. Expression begins with the initial invagination of the vestibule and continues through contact and flattening of both structures. SpBra is also expressed in the right axohydrocoel.
The expression is not seen in the somatocoels nor in any larva-specific structures outside the rudimant from which the adult body plan forms. SpBra is again undetectable by WMISH by 3 weeks of development (Peterson et al., 1999).

mRNA spatial localization
Method: Whole mount in situ hybridization
Reference: Peterson et al., 1999

Stage	24 hr mesenchyme blastula	36 hr midgastrula	2-week larva
Tissue	Vegetal plate	Delaminating secondary mesenchyme cells	Vestibule, left hydrocoel and right axohydrocoel