ABSTRACT
In Xenopus embryos, the major mechanisms driving both initial cell lineage formation (including the germ cell lineage) and axial patterning are dependent on the spatial distribution of maternal gene products in the oocyte. Uncovering these mechanisms has revealed the molecular nature of classical embryological phenomena and has helped establish the deep conservation of vertebrate embryology. This chapter covers (1) the history of amphibians and of Xenopus in particular in the conceptualization of enduring models for the formation of bilateral symmetry, germ layers, and germ cells; (2) the contributions of maternal gene products in these processes, including the identification and characterization of localized mRNAs in the oocyte; (3) the development of methodology for studying these maternal RNAs using oocyte transfer; and (4) a summary of the main studies centered on the roles of maternal Vegt and β-Catenin in germ layer and axis formation, and on the specification of the germline by germ plasm. Emphasis is on critical analyses of the key experiments from the last few decades, recent studies extending those results, and future prospects for exploring the connections of subcellular molecular behaviors with multicellular morphogenesis at the level of gene regulatory networks in Xenopus.
