PCNA MESSENGER-RNA HAS A 3'-UTR ANTISENSE TO YELLOW CRESCENT RNA AND IS LOCALIZED IN ASCIDIAN EGGS AND EMBRYOS

The myoplasm is a localized cytoplasmic region that is involved in axi s determination, gastrulation, muscle cell specification, and the patt ern of cell divisions during ascidian development. The noncoding yello w crescent (YC) RNA is localized in the myoplasm, but the function of this transcript is unknown. Probes containing the 3' region of YC RNA hybridize to other RNAs in ascidian eggs. A cDNA library from the asci dian Styela clava was screened with a YC probe to identify maternal YC -related RNAs. This screen resulted in isolation of ScYC26b, a cDNA cl one encoding the ascidian proliferating cell nuclear antigen (PCNA). T he PCNA mRNA has a long 3' untranslated region containing a 521-nucleo tide sequence with antisense complementarity to part of the 3' region of YC RNA. The PCNA and YC genes appear to be single copy and may over lap in their 3' regions on opposite DNA strands. The ascidian PCNA pro tein has 61, 69, and 71% amino acid identity to the Drosophila, Xenopu s, and human PCNAs, respectively. S. clava embryos contain maternal an d zygotic PCNA mRNAs. Maternal PCNA mRNA is localized in the ectoplasm , a cytoplasmic region that is segregated to cell lineages that prolif erate extensively during embryogenesis, and is depleted in the myoplas m, which is segregated to cell lineages that undergo fewer divisions. Zygotic PCNA mRNA is confined to the developing nervous system and is still abundant after the neural cells have ceased to proliferate. PCNA protein, detected with PC10 monoclonal antibody, is also excluded fro m the myoplasm. These results show that the 3' UTR of PCNA mRNA is ant isense and complementary to YC RNA and suggest that differential cell proliferation in the embryo may be limited by localization of maternal PCNA mRNA and protein. furthermore, zygotic PCNA may have a novel rol e in neural development in the tadpole larva. (C) 1996 Academic Press, Inc.