Stem cells and transgenic mice in the study of development.

In recent years, totipotent stem cells and transgenic mice have been widely used to understand the complex changes that occur during development, and these approaches underlie much of the dynamic growth in this field. The work of Barry Pierce in defining the multipotential characteristics of teratocarcinoma or embryonal carcinoma stem cells in the 1960s was an important milestone for the field and was instrumental in our choice of these cells for transfer into blastocysts in the first experiments designed to colonize a mouse with foreign totipotent cells. Following the development of transgenic techniques, the stem cell approach has become even more powerful, and during the past five years the combination of the two techniques has made possible the experimental creation of virtually any genetic change in mice, and ultimately in other species. In this review, the work in our laboratory over the past 30 years is summarized, and it reflects only a small part of the exciting array of experiments that have contributed to the explosive evolution of developmental biology during this period.