A clonal analysis reveals early developmental restrictions in the Drosophila head

Abstract

Head development of Drosophila melanogaster was studied by forming, in a background of Minute ( M) cells, clones whose cell division rate was higher ( M +). By studying such clones true developmental restrictions on clonal growth may be revealed, and not restrictions on clones which are just the result of interactions between neighboring cells. Pigment, bristle, and trichome markers allowed clone detection in both the compound eye and in much of the head cuticle. Clones were formed by X-ray-induced mitotic recombination at three stages in the first and second instar. Initial experiments determined some parameters of cell division in the compound eye and verified the differential division rate of M + cells growing in an M background, and vice versa. The earliest and most striking developmental restriction on clonal growth divides the head into a dorsal and a ventral compartment. No evidence for anterior-posterior compartmentalization was found. By 75 hr of development in Minute flies, several lines of developmental restriction are formed which subdivide these two compartments. Evidence is presented which supports these conclusions: One subdivision may contain cells of different clonal origin, cells derived from the same progenitor blastoderm cell may be in different subdivisions, and each subdivision is formed from a group of contiguous cells.