[Differentiation, pattern formation and mechanisms of transdetermination in heteroplastic and homoplastic transplants of proboscis primordia in Drosophila].

Proboscis primordia (labial discs) from fourDrosophila species were cultivated in the abdomens of adult females and then transplanted into larvae. After metamorphosis, the imaginal structures of the implants were studied both in homoplastic and heteroplastic transplantations. - After at least two days of culturing in an adult host of the same species one labial disc furnishes the same structures as one pair of discsin situ. - For the formation of such a symmetrical duplicate structure proliferation is required. When the blastema has reached a certain size, it becomes arranged into two adjacent areas i.e. - two connected proboscis halves of approximately normal size (homonomous arealisation). - By cell multiplication, the state of determination of the single cell is passed onto the daughter cells (cell heredity). These organize themselves along an axis of symmetry. - After the transitory culturing labial discs transdeterminate to such allotypic structures as palpus, leg or antenna. - Transdetermination occurs only in proliferating cells and, in symmetrical preparations, only in the newly developed half. - The frequency and the pattern of allotypic structures varies greatly in the four species under investigation. The differences are specific for the species and are not due to different proliferation activity. - There is a positive correlation between the growth of the blastema, the duration of culture, and the frequency of transdetermination. This finding indicates that cell reproduction is relevant to transdetermination. - Heteroplastic transplants of labial discs betweenD. melanogaster andD. simulans develop autonomously with regard to proliferation and transdetermination in both combinations. - Proboscis primordia fromD. hydei change their properties of transdetermination inD. melanogaster andD. virilis. In the first case, development of leg and antenna is inhibited. In the second case, the frequency of transdetermination diminishes. These differences are not due to reduced proliferation in a different species of host. They are based on some other effect of the culture medium.