Xenopus Module

The first thing that springs into mind when thinking about amphibian studies is likely the induction of twinned axes by Spemann-Mangold organizer graft.  However, this is but only one example of a long list of important contributions of amphibian research to embryological concepts. Pioneering experiments from Holtfreter brought focus on cell adhesion and movements as well as the concept of developmental potentials, and Nieuwkoop’s tissue separation, recombination and transplantation studies broadened the views of embryonic induction and patterning.

These classical experimental embryology studies rely on a salient feature of amphibian embryos that parts of the embryos (explants) can be isolated and cultured in simple salt solutions for developmental programs to continue.  The “cut-and-culture” and “cut-and-paste” experiments are carried over to the modern days of amphibian research and remain a crucial tool in embryo manipulations nowadays.  The toolset is further enriched by incorporation of advanced molecular and cellular technologies, such as using fluorescence microscopy to investigate cell morphology, cytoskeleton dynamics, cell and tissue movements, and signaling mechanisms.

The ease to introduce exogenous molecules into early embryos allows gain- and loss-of-function studies. The application of CRISPR/Cas9-mediated genome editing technology complements the antisense morpholino-based approaches for analysis of endogenous gene activities. The abundance of embryos (thousands of eggs from a single adult female in a day) also makes –omics research readily available, including RNA-seq, ChIP-seq, ATAC-seq, proteomics, and metabolomics studies. Today, the favored amphibian species has shifted from a range of frogs, salamanders, and newts to the African clawed frogs Xenopus laevis and Xenopus tropicalis, and the Mexican axolotl Ambystoma mexicanum, but the topics of research have diversified.

Some of the examples include studies of molecular nature of and signal tuning and crosstalks at the Spemann organizer, embryonic patterning along different axes, mechanical and signaling control of tissue morphogenesis both at early developmental stages (gastrulation and neurulation) and during organogenesis (e.g. heart formation, gut looping, ciliated skin cell development), wound healing, tissue regeneration, and epigenetic control of embryogenesis (including the Nobel prize winning experiments by John Gurdon that demonstrated nuclear equivalence and cellular reprogramming). In addition, the Xenopus model is increasingly used for studies of genetic variants that are associated rare human diseases.  All these demonstrate that Xenopus continues to be a powerful system ripe for in depth investigations that lead to vital discoveries. 

In the Xenopus module, students will be introduced to the more than 100 years of history of experimental embryology in amphibians and be given the opportunity to apply modern molecular and imaging technologies to the Xenopus embryos.  Students will learn how embryos are generated via in vitro fertilizations, how to prepare and inject embryos, how to make fine surgical dissections to obtain various explants and perform tissue transplant experiments, and how to mount fixed or live samples for imaging.  They will be provided with reagents to inactivate or alter gene expression and instructed to design and analyze their experiments.  They will also be provided with embryos from another amphibian species, the Mexican axolotl, for comparative and cross-species experiments.  This module will give students the necessary skills to use the frog to determine the function of a novel gene along with the ability to apply modern methods to uncover molecular and physical mechanisms that underlie the classic observations made by the famous embryologists of the past century.