Gene Networks Database

Strongylocentrotus purpuratus Genes in Development: Homeobox Genes



SpHmx encodes a transcription factor of H6 subfamily of homeobox proteins.
SpHmx functions as a cell-type-specific regulator of pigment cells differentiation.
This gene is present in a single copy per haploid genome (Martinez et al., 1997).


SpHmx is a homeodomain protein. Adjacent to homeodomain in the SpHmx amino acid sequence is a putative bipartite nuclear localization site.
SpHmx homeodomain belongs to H6 subfamily of homeodomains (Martinez, 1997).
GenBank: 1332413

Subcellular location

Cytoplasm and perinuclear regions of pigment cells (Martinez, 1997).

Expression Pattern

SpHmx is transcribed during oogenesis and is represented as a maternal transcript, the prevalence of which is about 4,000 copies per egg. The level of transcript then declines abruptly, and it is undetectable from 4 hr postfertilization until 12 hr.
During the next 12 hr there is a steady accumulation of SpHmx transcripts. At 24 hr (blastula) the number of transcripts per embryo is approximately 12,000. After 24 hr the levels decrease slowly until 72 hr, the last point analysed, when 4000 transcripts per embryo were detected (Martinez et al., 1997).
At the 36-hr midgastrula stage transcripts are detected by whole mount in situ hybridization throughout the archenteron, including the blastopore rim. No staining is observed in sceletogenic mesenchyme, or in ectoderm, though some staining is detected in the mesenchymal cells just beneath the apical region of the oral ectoderm. The highest level of mRNA at this stage is in the delaminating secondary mesenchyme. However close inspection reveals that only some, and not all secondary mesenchyme cells contain SpHmx transcripts.
In 48-late gastrula-stage embryos transcripts are confined strictly to pigment cells. This pattern is stable and persists at least into the pluteus stage.
In 48 hr embryo there are about 360 SpHmx transcripts per average pigment cell. This value falls to about 140 transcripts per average pigment cell by the end of embryogenesis.
SpHmx continues to be transcribed in the pluteus-stage embryo and shows clearly a pigment cell-specific pattern of expression (Martinez et al., 1997).

mRNA level

Temporal accumulation (transcript prevalence)

Method: single-stranded probe excess titration procedure (as described by Lee and Costlow, 1987)
Reference: Martinez et al. 1997
4-12 hr
24 hr
72 hr
Level (transcripts/embryo)
400 copies
12000 copies
4000 copies

Spatial localization

Method: whole mount in situ hybridization
Reference: Martinez et al., 1997

36 hr blastula
48 hr gastrula
72 hr pluteus
archenteron, mesenchymal cells beneath the apical region of OE, some cells of secondary mesenchyme
pigment cells
pigment cells


Regulatory Regions

Regulatory Connections

Upstream Genes


Downstream Genes

Evolutionary homologues



[Previous] UrchiNet[Up] Search the GeNet
Comments are welcome to Sveta Surkova
Copyright © 1997 GeNet Team