Transgenic Xenopus: Microinjection Methods and Developmental Neurobiology

Transgenic Xenopus: Microinjection Methods and Developmental Neurobiology. SHLOMO SEIDMAN AND HERMONA SOREQ. Humana Press, 1997. 216 cloth, $79.50 (ISBN 0-89603-457-7).

When this book arrived I was very surprised by its title, as the first method for production of transgenic Xenopus was only published in late 1996. But in fact the authors are not dealing with what we would normally regard as transgenesis, the introduction of new genes into the germ line. They are instead dealing with transient overexpression methods based on the injection of synthetic messenger RNA or of plasmid DNA. The ease with which transient overexpression can be carried out has explained a large part of the rapid progress that has been made in the last 15 years in understanding developmental mechanisms in Xenopus, and can also be used for studying a variety of other processes using oocytes or embryos of Xenopus as test systems.

Xenopus is the African clawed frog and has been a common inhabitant of biological laboratories since its use for pregnancy testing in the 1950s. The Xenopus oocyte has been an invaluable tool in cell biology for much of this time. In particular neuroscientists have found it useful for the expression of receptors, channels and ion pumps as they often display their normal pharmacological and electrophysiological characteristics, and it is possible to study assembly and membrane insertion as well as function. But just as important there are a number of embryobased methods that are also described in this book. The most commonly used has been the injection of a synthetic mRNA for the gene under study. When made off suitable plasmids, mRNA can remain stable for long periods of time after injection. A remarkable variety of experiments has been possible using this technique, as it is possible to inject individual cells, or graft between an injected and an uninjected embryo, or inject several mRNAs whose protein products interact in some way. Overexpression from injected DNA has proved less satisfactory because it inevitably leads to expression only in a minority of cells of the embryo ("mosaic expression"). The reasons for this are not clear and it has limited the use of injected DNA to those cases where mosaic expression does not matter, for example the analysis of promoters to find the regions responsible for temporal or cell type specificity. Xenopus does not lend itself to genetic studies and so it is not possible to mutate genes to inactivity. But there are several methods for inhibiting the activity of specific genes. These include the use of antisense RNA, antisense oligonucleotides, antibodies and, perhaps most importantly, the use of dominant negative versions of normal gene products.

The book is intended to introduce readers to this world and to include practical protocols for the various procedures. It has four chapters. The first contains a brief description of normal development with current thinking about the molecules involved, together with a description of the methods used for overexpression and tables of references for studies on particular gene products. This is competent but the diagrams are rather small and might not convey a lot to readers unfamiliar with the subject. The second chapter contains practical protocols for the various manipulations. A warning is required here because the methods described for isolation of oocytes would be unacceptable in the UK, and probably in the USA, for animal welfare reasons. The UK Home Office would certainly not license workers to anaesthetise frogs on ice, nor to suture muscle and skin layers together, nor to reuse animals at 3 month intervals. The third and fourth chapters are entirely given over to a long accounts of the authors own experiments on the overexpression of acetyl cholinesterase in oocytes and embryos.

The main problem with the book is that the authors have allowed their own interest in acetyl cholinesterases and the neuromuscular junction to overwhelm every other topic. For a book nominally about developmental neurobiology we can read 27 pages about the neuromuscular junction in chapter 1 but there is almost nothing about early development of the nervous system, and nothing at all about neurogenesis or about the formation of specific nerve connections. Chapters 3 and 4 are entirely devoted to the authors' own experiments. Because of this extreme lack of balance the book is less satisfactory than its main competitor (Kay, B. K. and H. J. Peng. 1991. Methods in cell biology 36. Academic Press, San Diego) as a practical handbook on the use of Xenopus oocytes and embryos. It does contain some useful tables of references to particular overexpression studies, but anyone who buys this book will be disappointed unless they are seriously interested in acetylcholinesterase.

J. M. W. SLACK Developmental Biology Programme School of Biology and Biochemistry University of Bath Bath BA2 7AY, U.K

Copyright Society for Integrative and Comparative Biology Sep 1997
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