The Stability of the Determined State in Cultures of Imaginal Disks in Drosophila

Abstract

The development of different cell types in higher organisms, arising from one cell type (the zygote), is designated as cell differentiation. Differentiation is initiated by the process of determination which programs the cells for their future developmental pathway. There is accumulating evidence that the developmental programs reside in the genome and represent sets of genes acting in a coordinate fashion. The fundamental problem of how different genes are coordinately controlled remains to be elucidated. Two major categories of determinative processes are known: one is embryonic induction which involves cell or tissue interactions by means of diffusible inducing substances, and another is cytoplasmic segregation which is based upon factors intrinsic to the differentiating cells. In the latter case differentiation may be achieved by unequal distribution during cell division of cell components acting as determinative factors. Since determination creates the first essential differences among cells, an understanding of this process might be a key to the problem of differentiation in general. One approach to elucidate determination is to isolate the inducing substances produced by the inducer tissue and to study their action on the reacting tissue. Another approach, which will be considered in this chapter, is to study determination in “mosaic systems” in which intrinsic factors are responsible for setting up the developmental program.

I am grateful to Professors E. Hadorn and A. Garen for their critical reading of the manuscript.