EXPRESSION OF HOMEOBOX-CONTAINING GENES IN THE SEA-URCHIN (PARANCENTROTUS-LIVIDUS) EMBRYO

Two homeobox-containing genes that belong to different homeodomain cla sses have been isolated from a sea urchin genomic library. One, P1Hbox 11, is the sea urchin homologue of the human and mouse Hox B3 gene, th e other, P1Hbox12, shows about 55% identity with paired class genes. E xpression profile analysis of the two sea urchin Hbox genes suggests t hat they play different roles during embryogenesis. In fact, P1Hbox11 transcripts are rare and are detected only in the pluteus larva and in the Aristotle's lantern and intestine of the adult. The P1Hbox12 gene is, on the contrary, transiently expressed in the very early embryo a lready at the four cell stage; it accumulates at the 64 cell stage and disappears at later stages of development. In situ hybridization expe riments to 16 and 32 cell stage whole mount embryos showed localizatio n of the P1Hbox12 mRNA to part of the mesomere-macromere region of the early cleavage embryo. These observations suggest a possible role of this gene in early events of cell specification.