In chaetognaths, a marine phylum of approximately 120 species, paralogous ribosomal protein genes and two classes of both 18S and 28S rRNA gene sequences have been evidenced. Moreover, differential and specific expression of the rRNA genes has been demonstrated suggesting implications of regulatory mechanisms in the synthesis of the ribosome constituents. Results of in situ hybridization of ribin-like mRNAs in Spadella cephaloptera were compared with immunofluorescence localization of the corresponding protein. Previous studies showed that in rat Ribin protein is encoded on the antisense strand of the 28S rRNA gene and known as rRNA promoteur binding protein. In chaetognaths, expression of ribin-like gene(s) is restricted to oocytes similarly to both18S and 28S class II genes and to gut, whereas Ribin-like proteins have been identified in the nervous system, oocytes and gut. Chaetognath nuclear regions, homologous to ratribin mRNA have been sequenced; however, no complete open reading frame can be reached. Analysis of DNA databases reveals that deduced sequences of several animal nuclear sequences exhibit a region having a great level of conserved amino-acids with the COOH-part of the rat Ribin, suggesting a high selection pressure in this region. Moreover, analysis of EST libraries shows that Ribin-like genes are expressed in both animals and plants. In addition, in invertebrates, these transcripts are principally found during the first stages of development or in nervous tissues or in infected/stressed organisms. The selective expression and translation of Ribin-like genes added to their large evolutionary distribution suggest important physiological roles of the corresponding proteins.
Key words: Ribin, chaetognath, nervous system, oocytes, gut.
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