Isolation and expression study of a maternally expressed novel xenopus gene Xem1 encoding a putative evolutionarily conserved membrane protein

A novel Xenopus maternally expressed gene, Xem1, was isolated by differential display PCR and 5'-RACE. Xem1 coded for a putative transmembrane protein of 172 amino acids. Sequence analysis, including the clustering and reconstruction of ESTs (Expressed Sequence Tags), revealed that homologs of Xem1 are widely distributed in eukaryotic phyla, suggesting that Xem1 is a member of evolutionarily conserved proteins. Expression of Xem1 mRNA occurred from the previtellogenic stage and its level increased during oogenesis, maintained throughout oocyte maturation to blastula stage and then decreased in post gastrula stages. In cleavage stage, Xem1 RNA was distributed uniformly, and in adult, occurred predominantly in ovary and testis. We assume that Xenopus Xem1 may have its function in gametogenesis and in early phase of embryogenesis, whose function may be related to transport mechanism of small molecular weight substances like metal ions, from analogy to the function of its homologs in other organisms.