Cell affinities in antennal homoeotic mutants of Drosophila melanogaster.

Abstract

DISSOCIATED embryonic cells show, in culture, cell affinities and morphogenetic movements which are tissue characteristic. While cells which derive from the same organ and tissue are able to reconstitute the original cell arrangements in mosaic fashion, cells from different organs sort out and regroup separately. This situation holds for vertebrate cells as well as for cells of many other lower organisms (see TRINKAUS 1966 for discussion). In Drosophila the adult cuticle consists of several cell structures specifically arranged into segment characteristic patterns. The adult cuticular structures are formed from cells of the imaginal discs of the larvae which undergo differentiation during metamorphosis. A variety of mutants in Drosophila meLanogaster change the color or form of single cuticular structures (cell mutants). With the aid of cell marker mutants HAWRN, ANDERS and URSPRUNG (1959) have shown that dissociated cells of the same imaginal disc are able to reaggregate and reconstruct the adult patterns of this disc integrated in mosaic fashion. However, dissociated cells deriving from different imaginal discs (NOTHIGER 1964; GARCIA-BELLIDO 1’36613) or from different regions of the same disc (GARCIABELLIW 1966a) sort out or segregate in aggregates. Furthermore, cells from homologous imaginal discs (different leg discs) reconstruct the common patterns in a typical mosaic integration; whereas they segregate when they correspond to different patterns (GARCIA-BELLIDO 1966a). These results are indicative of a highly specific cell determination correlated with highly selective cell affinities in the dissociated cells of the imaginal discs. When cultured in u h o , aggregated cells may change their prospective differentiation into that typical for other imaginal discs. The underlying phenomenon is called transdetermination and is assumed to be based upon a non-mutational change in the activity of sets of genes (HADORN 1966). When studied in cell aggregates, the transdetermined cells show new cell affinities which correspond to their new cell determination ( GARCIA-BELLIDO 1966b). The hypothesis was advanced then that the same specific genes are responsible for both the selective affinity and the correlative differentiation of the imaginal disc cells. There are mutants in Drosophila which specifically change the arrangement of the differentiated structures in the adult cuticle. Such mutants can be con-