2 Transforming Sperm Nuclei into Male Pronuclei in Vivo and in Vitro

Abstract

This chapter discusses transformation at several levels. The morphological outlines of male pronuclear development have been known from light microscopy analyses for over a century. Much further work and the addition of ultrastructure analysis have enriched views of the process. This chapter discusses the four organisms, in which the cell-free systems prepared from egg lysates, have been devised to analyze male pronuclear formation: amphibians (particularly Xenopus laevis and Bufo japonica ), fruit flies ( Drosophila melanogaster ), surf clams ( Spisula solidissirnu ), and sea urchins (mostly Lytechinus pictus ). This group represents four different fertilization strategies and encompasses vertebrates and invertebrates. Researchers examine where the data from these four systems are in accord and where they are not. This chapter explains the recent in vitro results, compare them, where possible, with the corresponding observations in vivo and speculate some unresolved issues. Experimental approaches, in which pronuclear development is perturbed, by chemical and other inhibitors, the extension of the techniques for microinjection of sperm nuclei and their subsequent analysis, the use of polyspermic eggs for isolation of male pronuclei or augmentation of transcription signals, sensitive reagents and techniques particularly fluorescent antibodies and autoradiography, and most recently the development of the cell-free systems have added more molecular information and insight into the regulation of pronuclear transitions. Relatively little attention has yet been paid to the genetic analysis of pronuclear development.