Replication in Drosophila chromosomes. Part V. Polytene chromosome replication after in vitro culture of larval salivary glands

Abstract

Salivary glands from mid and late 3rd instar larvae of D. nasuta have been cultured in vitro in a modified Poels' medium [Peels, C.L.M., Cell Differentiation, 1 (1972), 63] and the progression of polytene replication under different in vitro culture conditions have been analysed autoradiographically. Results show that mass culture (30 glands/300 μl medium) of salivary glands from mid 3rd instar larvae in presence of larval fat bodies provides optimal conditions. Under these conditions, even 48 hr after in vitro culture, a large number of polytene nuclei continue to replicate and in many nuclei, new cycles of polytene replication are initiated during this period. The patterns of ³H-thymidine incorporation in different regions of polytene nuclei under these in vitro conditions are closely comparahle to those seen in freshly excised glands from late 3rd instar larvae of D. uasuta, The feasibility of maintaining and Initiating new cycles of polytene replication under the in vitro condition opens scope for a detailed analysis of the factors regulating polytene replication.