Gene Networks Database

Hemicentrotus pulcherrimus Genes in Development: Brachyury (T) homologue



HpTa is the sea urchin Brachyury (T) gene homologue, member of the T-box family of genes.
In vertebrates Brachyury (T) gene is essential for notochord formation.
During sea urchin development, the T gene is utilized to specify the developmental fate of embryonic cells to the secondary mesenchyme.
Southern blot analysis indicated that that HpTa is present as a single copy gene, and that the sea urchin genome contains T domain genes other than HpTa (Harada et al., 1995).



Subcellular location

Expression Pattern

HpTa mRNA is 3.7 kb in length.
Northern blotting of the HpTa gene during embryogenesis of H. pulcherrimus revealed that the HpTa transcripts are transient. Hybridization signals were undetectable in unfertilized eggs and early embryos at the cleavage and early blastula stages. This result was confirmed by longer exposure. A weak but distinct hybridization signal was first detected in hatching blastulae. A distinct band was found at the mesenchymal blastula and gastrula stages, at which time the intensity of the band was maximal. The intensity of the band decreased after the gastrula stage. Although a band was detected in prism larvae, it was barely detectable at the pluteus larva stage. This pattern of transient HpTa expression coincides with that of the chordate T genes.
The first stage at which a clear result was obtained by in situ hybridization was the mesenchyme blastula, when the distribution of hybridization signals was not even but restricted to cells of the vegetal plate. At the early gastrula stage, the signals were found in cells of the invaginating tip of the vegetal plate or newly formed archenteron. Neither aboral and oral ectoderm nor primary mesenchyme cells that have delaminated from the vegetal wall into the blastocoel showed signals above the background.
At the mid-gastrula stage, the archenteron has extended to nearly a half of the blastocoel and two islands of skeletogenic sites are formed by the primary mesenchyme cells. Hybridization signals were found in cells of extending tip of the archenteron and secondary mesenchyme cells migrating from there. In contrast, signals were not so evident in cells of the middle and posterior parts of the archenteron.
At the late gastrula stage, the archenteron has almost reached the wall of the most anterior part of the oral ectoderm and some secondary mesenchyme cells have separated from the archenteron wall into blastocoel. Intense hybridization signals were detected in the secondary mesenchyme cells and cells of the archenteron tip, whereas the other cells of the archenteron showed barely detectable signals.
At the prism larval stage, the secondary mesenchyme cells are scattered over the inner wall of blastocoel. At this stage, hybridization signals were not detected above the background level. The distinct signal above the background level could not be detected at the late prism and the pluteus larval stages.
Thus, HpTa is expressed in the secondary mesenchyme cells, but not in the endoderm cells (Harada et al., 1995)

mRNA level

Temporal accumulation

Method: RNase protection assay
Reference: Harada et al., 1995

Unfertilized egg
16 cells
Early blastula
Hatching blastula
Prism larvae
Pluteus larvae
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Spatial localization

Method: Whole mount in situ hybridization
Reference: Harada et al., 1995

Mesenchyme blastula
Early gastrula
Late gasrula
Prism larvae
Pluteus larvae
Cells of the vegetal plate
Intense signals in cells at the tip of the invaginating archenteron
Secondary mesenchyme precursor cells around the tip of the archenteron, and secondary mesenchyme cells migrating from there
Secondary mesenchyme precursor cells, cells of the tip of archenteron



Regulatory Regions

Regulatory Connections

Upstream Genes


Downstream Genes

Evolutionary Homologues



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Comments are welcome to Sveta Surkova
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