Genetic control of reproductive cell differentiation in Volvox

Abstract

It is 100 years since August Weismann (1889) first suggested that Volvox might be the ideal organism in which to study the differentiation of germ and soma. But it was not until Richard Starr described the life history of V. carteri forma nagariensis (Fig. 1) exactly 80 years later (Starr, 1969) that material suitable for genetic analysis of germ-soma differentiation in Volvox became available to biologists¹. Within a year of his description of normal development in this organism, Starr demonstrated its developmental-genetic potential by describing a number of Mendelian mutations that caused modified patterns of reproductive and/or somatic cell development (Starr, 1970). Huskey and his associates made substantial advances in the isolation and study of such mutants (e.g., Sessoms and Huskey, 1973; Huskey and Griffin, 1979, Callahan and Huskey, 1980), and succeeded in placing them on a preliminary map of the Volvox genome (Huskey et al, 1979). Currently, we are attempting to extend the pioneering studies of Starr and Huskey by saturating the genome with mutations that cause a breakdown of the germ-soma dichotomy, in hopes of eventually defining all of the major loci whose actions are required to establish the complete division of labor between somatic and reproductive cells that characterizes this species.