Differential accumulation of mRNA and interspersed RNA during Xenopus oogenesis and embryogenesis.

Xenopus oocyte cytoplasmic poly(A)+ RNA has been shown to include two major complex classes: mRNA and interspersed RNA. The former is defined by its translatability, while the latter consists of non-translatable repeat-containing transcripts with unknown functions. In this study we compared the accumulation patterns of total mRNA and a subfamily of interspersed RNA, the XR family (McGrew & Richter, 1989, Dev. Biol. 134, 267-70). The results showed that the XR interspersed RNA level continued to increase throughout oogenesis, while the total mRNA level reached a peak at late stage II and then decreased as much as 40% between stage II and stage VI of oogenesis. In addition we have found that, like mRNA, only about half of the non-translatable XR interspersed RNA underwent deadenylation at oocyte maturation. This result suggested that about half of the interspersed RNA, like certain mRNAs, also contains the U-rich element to protect it from the automatic deadenylation, implying the poly(A) tail of interspersed RNA may play a role during early development.