Proteins Associated with Lampbrush Chromosomes

Abstract

Amphibian oocytes offer many advantages for studying nucleo-cytoplasmic interaction, the nature and properties of the nuclear membrane, the protein constituents of cell nuclei, the proteins involved in RNA transcription, and those that accompany RNA to the cytoplasm, some of which are concerned with RNA stockpiling and perhaps with the masking of mRNAs that are not translated until oocyte maturation has occurred. How these virtues have been exploited has recently been reviewed by Scheer and Dabauvalle (1985). For studying nuclear proteins there are two particular advantages. Potential cytoplasmic contaminants can be eliminated by manual isolation in saline, and rapidly; for “easy” species this operation takes about 30 s. Some loss of soluble protein occurs even in so short a time (Paine et al. 1983) but substantial loss is avoided (Macgregor 1962). Amphibian oocyte nuclei are exceptionally large. According to Paine et al. (1983) a single Xenopus nucleus from an oocyte approaching maturity, with a water content of about 90%, contains about 5 μg of protein. According to Maundrell (1975) a half-grown 0.8 mm diam oocyte of Triturus c. carnifex, at a stage when the lampbrush chromosomes have reached their maximum bulk, contains about 1.2 μg of nuclear protein, of which more than 1 μg represents the contribution from nuclear sap, 100 ng is nucleolar, and 30 ng is chromosomal. However despite the exceptionally large amount of protein associated with lampbrush chromosomes, analysis of the constituent polypeptides by direct means has so far merely established their complexity. This is in marked contrast to the wealth of information that has come from experimental studies where various materials have been injected into oocytes, notably those of Xenopus,the host oocytes cultured in vitro, and thereafter subjected to analysis by various sophisticated techniques. The virtues of the oocyte as an experimental system were first spectacularly exploited by J. B. Gurdon and his many colleagues, and more recently other groups of cell and developmental biologists have done likewise. The field has been extensively and repeatedly reviewed, and for the most part lies beyond the scope of this monograph. Nevertheless some general conclusions arising from this work are directly relevant, and these will be briefly discussed before turning to the main topic of this chapter.KeywordsXenopus OocyteGerminal VesicleLabel Amino AcidLampbrush ChromosomeLateral LoopThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.