Quarterly Journal of Microscopical Science, Vol s3-103, 25-35, Copyright © 1962 by Company of Biologists

Cytological and Biochemical Studies of Anucleolate Xenopus Larvae

¹ The Embryological Laboratory, Department of Zoology, University Museum, Oxford; present address, Department of Zoology, the Queen's University of Belfast, Northern Ireland

A larval lethal mutant of Xenopus laevis lacks true nucleoli but possesses analogous intranuclear organelles, here termed blobs, which are smaller and more numerous than nucleoli. Cytochemical tests reveal that blobs (like nucleoli) contain ribonucleic acid (RNA), arginine, and alkaline phosphatase, but probably no Feulgen-positive material. Anucleolate larvae are deficient in cytoplasmic RNA. By biochemical methods the nucleic acid content of anucleolate embryos is found to be normal at the tail-bud stage, but does not increase after this. By the time they hatch, anucleolate larvae are deficient in both RNA and deoxyribonucleic acid (DNA). The implications of this and related mutations on the formation and function of the nucleolus are considered. The term ‘blob’ is justified in that it would be misleading to regard such organelles as nucleoli produced by normally latent organizers.