The 10 sea urchin receptor for egg jelly proteins (SpREJ) are members of the polycystic kidney disease-1 (PKD1) family

The 10 full-length SpREJ cDNA sequences were determined. The secondary structures of their deduced proteins were predicted and compared to the five human hPKD1 proteins. The genomic structures of the 10 SpREJs show low similarity to each other. All 10 SpREJs are transcribed in either embryos or adult tissues. SpREJs show distinct patterns of expression during embryogenesis. Adult tissues show tissue-specific patterns of SpREJ expression.Possession of a REJ domain of about 600 residues defines this family. Except for SpREJ1 and 3, that are thought to be associated with the sperm acrosome reaction, the functions of the other SpREJ proteins remain unknown. The sea urchin genome is one-fourth the size of the human genome, but sea urchins have 10 SpREJ proteins, whereas humans have five. Determination of the tissue specific function of each of these proteins will be of interest to those studying echinoderm development. Sea urchins are basal deuterostomes, the line of evolution leading to the vertebrates. The study of individual PKD1 proteins will increase our knowledge of the importance of this gene family.The sea urchin is a model animal for cell and developmental biology and genomics. As a basal deuterostome, it provides an out-group for the chordates, and thus insights into vertebrate genome evolution. The genome of the purple sea urchin, Strongylocentrotus purpuratus (Sp), is one-quarter the size of the human genome and encodes ~23,300 genes [1], the majority having vertebrate orthologs. Sea urchin genes are closer to human and mouse than to other invertebrate models such as Drosophila and C. elegans. For example, the number of reciprocal pairs of genes between sea urchin and mouse is about 50% greater than between sea urchin and Drosophila [1]. The sea urchin lacks four of the human kinase subfamilies, while Drosophila lacks 20 and nematodes 30 [1,2]. Regarding gene conservation, 11 of the 13 known animal Wnt genes are present in the sea urchin [3]. The sea urchin h