The frequency distributions of polyadenylylated RNAs from the polysomes of sea urchin blastulae and gastrulae were estimated from their kinetics of hybridization with complementary DNA. Developmental decreases in complexity were observed among abundant, intermediate, and rare frequency classes. The class of highest abundance in the blastula polysomes had a complexity of 5.6 X 104 nucleotides and contained about 30 mRNA species, which divided into subsets according to developmental fate. Studies with purified DNA complementary to this abundant class revealed that five of these mRNA species remained abundant in the gastrula, wherein each comprised 2% of the polyadenylylated RNA in the polysomes.Approximately 5 species decreased to a nearly rare frequency and2o were absent or at the limits of detection in polyadenylylated RNA of gastrula polysomes. These distinctly different developmental fates suggest distinct modes of regulation of mRNA concentration for different subsets. Focusing on the small number of abundant blastula mRNAs, we ascertained that those which were absent from gastrula polysomes were nevertheless represented in the gastrula nuclear RNA. Therefore, the appearance of abundant mRNA species in polysomes can be regulated by posttranscriptional processes.Cell types are distinguishable by characteristic differences in their prevalent species of mRNA (1, 2), and the processes of cellular differentiation (3, 4), embryogenesis (5), and oncogenesis (6) may all involve shifts in both complexity and frequency distribution of mRNAs. The mode of regulation of mRNA complexity and abundance, however, is not clear. The decrease in the number of different mRNA species during sea urchin development (5) appears to be attributable to posttranscriptional processes rather than to a block on transcription. This conclusion follows from the essentially constant complexity and sequence representation of nuclear RNA (7) and the persistence of complex-class mRNA sequences in nuclear RNA long after they have ceased to be present in the polysomes (8). However, prevalent mRNA sequences have not been shown conclusively to be present in nuclear RNA. of cells that do not express these genes. For example, the induction of ovalbumin synthesis involves turning on ovalbumin gene transcription (9, 10), whereas globin mRNA sequences have been reported variously absent from (11) and present in (12) nuclear RNA of cells not engaged in globin synthesis. Hence, an unequivocal demonstration of the persistence in nuclear RNA of mRNA sequences that shift between abundance and absence is still needed as evidence for a possible posttranscriptional regulation of abundant mRNA species.In the present study we observed changes in the frequency distribution of mRNA species during development from blastula to gastrula. Prominent among these changes was the drastic loss of blastula abundant mRNA species; some 20 out of 30 were no longer detectable in gastrula polysomes. This observation affords us the opportunity to test whether or not the prev...
Frog embryo nuclear and cytoplasmic RNA populations, labeled in vivo and in vitro, were hybridized to, filterbound homologous and heterologous DNA. The transcription of homologous (frog) repetitive DNA into nuclear RNA decreases qualitatively during development while the transcription of heterologous (minnow, human) repetitive DNA into nuclear RNA remains relatively constant qualitatively. The diversity of homologous repetitive mRNA increases during development, but there is only a slight change in the diversity of heterologous repetitive mRNA transcripts. There is a marked restriction of transport of the heterologous RNA sequences to the cytoplasm at a later stage of development.
A patient presented with a painless palpable mass located just below the right ear. This mass was examined with sonography, and the appearance suggested the presence of a pleomorphic adenoma. Pleomorphic adenomas are common benign neoplasms of the major salivary glands. Fine-needle aspiration of the tumor was performed with sonographic guidance, and cytology confirmed its identification as a pleomorphic adenoma.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.