1 - Insights into the amphibian egg to understand the mammalian oocyte

Summary

Abstract

Amphibian eggs and oocytes have been widely used as a model system for understanding animal development. They have led to numerous major discoveries in cellular and developmental biology. These findings have greatly helped us to understand the physiology of mammalian oocytes. Amphibian eggs have also played an important role not only in revealing genomic conservation and plasticity historically, but also in gaining a mechanistic insight into nuclear reprogramming. This chapter summarizes major findings using amphibian eggs and oocytes, focusing on reprogramming aspects. We also discuss how Xenopus eggs can be used to study mammalian oocytes.

Introduction

For over 100 years, amphibian embryos have been the favored choice of material for research into mechanisms of early vertebrate animal development. This is because amphibian embryos are unusually large, being about 1 mm in diameter. The whole amphibian egg divides into an embryo whereas, in birds, for example, only a very small amount of material in the huge egg actually forms an embryo. All mammalian eggs are relatively inaccessible and are very small, usually 70–120 μm in diameter. European amphibia include the Urodeles (salamanders, newts, Triturus, etc.) as well as Anura (frogs, toads, Rana, Bufo). Members of these groups usually lay abundant eggs in natural pond water in the northern-hemisphere spring. The eggs are easy to culture. Their large size and consistency make them exceptionally favorable for microdissection and other manipulative experiments. This was the material used by Spemann, Hamburger, and Holtfreter and others.