SpHbox7, a new Abd-B class homeobox gene from the sea urchinStrongylocentrotus purpuratus: Insights into the evolution of hox gene expression and function

Expression of the Hox gene complex in the indirect development of a sea urchin

“…Fig. 3 shows that only SpHox7 and SpHox11͞13b, as previously shown (23,24), are expressed significantly in the embryo.…”

“…23) and a paralogue of Hox11͞13 (SpHox11͞13b, originally ''Hbox7,'' ref. 24). The S. purpuratus cluster contains 10 genes but differs slightly from the vertebrate consensus in that it has only one gene of the Hox4 and 5 type (SpHox4͞5).…”

“…Of the three posterior genes, SpHox9͞10 is more closely related to Hox9 and Hox10 than to Hox11-13, whereas the others, SpHox11͞13a and SpHox11͞13b, are more similar to the latter (P.M., J. P. Rast, C.A.-M., and E.H.D., unpublished data). The SpHox7 and SpHox11͞13b genes had been found to be activated before gastrulation, and by late embryogenesis their products are confined, respectively, to the vertex region of the aboral ectoderm (23) and to subregions of the oral ectoderm, the larval arms, and the foregut (24). There was little significant evidence regarding utilization of the other Hox genes in development.…”

“…During postembryonic life, skeletal elements later incorporated into the rudiment begin to form within this region, and perhaps SpHox7 expression carries out a function related to that process. SpHox11͞13b expression is also activated at the blastula stage but is unlikely to play a role in regional specification because its transcripts are then distributed ubiquitously, as is also the protein (24). The RNA and protein are later found in multiple regions of the embryo, which are related neither in morphogenetic function nor by lineage, including the ciliated band, the tip of the archenteron, the oral ectoderm, and some regions of the forming larval arms (24).…”

“…SpHox11͞13b expression is also activated at the blastula stage but is unlikely to play a role in regional specification because its transcripts are then distributed ubiquitously, as is also the protein (24). The RNA and protein are later found in multiple regions of the embryo, which are related neither in morphogenetic function nor by lineage, including the ciliated band, the tip of the archenteron, the oral ectoderm, and some regions of the forming larval arms (24). These areas are all sites where cell division continues or resumes late in embryonic development, and SpHox11͞13b could be engaged in cell division control.…”