Characterization of a cDNA clone coding for a sea urchin histone H2A variant related to the H2A.F/Z histone protein in vertebrates.

A cDNA clone coding for a sea urchin histone H2A variant has been isolated. The coding region of the clone has been sequenced and the sequence found to be closely related to the H2A.F sequence in chickens. The nucleotide sequence of the sea urchin H2A.F/Z is 74% conserved when compared to chicken H2A.F and 51% conserved compared to sea urchin H2A early and 60% compared to sea urchin H2A late. The nucleotide-derived amino acid comparisons show that H2A.F/Z is 97% homologous with H2A.F in chickens and 57% and 56% homologous when compared to sea urchin H2A early and late respectively. There are between 3-6 copies of the H2A.F/Z sequence in the S. purpuratus genome. The H2A.F/Z gene sequence codes for the previously identified H2A.Z protein. All embryonic stages and adult tissues tested contain mRNA for H2A.F/Z. The mRNA appears in the poly A+ RNA fraction after chromatography over oligo dT cellulose

Very early and transient vegetal-plate expression of SpKrox1, a Krüppel/Krox gene from Strongylocentrotus purpuratus

All endodermal and mesenchymal cells of the sea urchin embryo descend from the vegetal plate, a thickened epithelium of approximately 50 cells arising at the early blastula stage. Cell types that derive from the vegetal plate are specified conditionally by inductive interactions with underlying micromeres, but the molecular details of vegetal-plate specification remain unresolved. In a search for regulatory proteins that have roles in vegetal-plate specification, a screen was performed to clone Krüppel/Krox-related genes from a Strongylocentrotus purpuratus embryo cDNA library. One newly identified clone, named SpKrox1, contained four zinc fingers and a leucine zipper domain. SpKrox1 expression was low in unfertilized eggs, increased severalfold to the early blastula stage and decreased between the early gastrula and pluteus stages. SpKrox1 mRNA was first seen in macromeres of 16-cell stage embryos and was restricted to cells of the developing vegetal plate thereafter. Vegetal-plate expression corresponded to a ring of cells around the blastopore and overlapped the expression patterns of other genes with potential roles in vegetal plate-specification. As the vegetal-plate cells invaginated into the blastopore, SpKrox1 expression was lost, suggesting that its role was not in endoderm differentiation per se but rather in the initial establishment of the vegetal plate