Differentiation of Drosophila cells lacking ribosomal DNA, in vitro

Functional assay of a putative Drosophila sodium channel gene in homozygous deficiency neurons

Using voltage-clamp techniques, we have examined embryonic sodium currents in neurons deficient for a gene located at 60E5/6 that shares extensive amino acid similarity with vertebrate sodium channel genes. These neurons expressed sodium currents similar to wildtype, supporting the hypothesis that para, and not the gene at 60E5/6, is the primary sodium channel gene expressed in embryonic neurons. A simple marking procedure allowing positive identification of the genotypes of cultured Drosophila embryos obtained from heterozygous parents was used to recognize cultures homozygous for deficiencies. The morphological development of both neurons and myotubes in these cultures was similar to wildtype, making it feasible to compare the properties of normal diploid cells and cells completely lacking a putative sodium channel gene.

Actinomycin D-sensitive periods in the differentiation of Drosophila neurons and muscle cells in vitro

Observations were made of neuroblasts differentiating into neurons, and myoblasts differentiating into myocytes in cultures of embryonic Drosophila cells. Axons greater than 50 mum long appeared in vitro between 7.5 and 16.5 h, and pulsating myocytes appeared between 12.5 and 23.5 h. Actinomycin D treatment prevented neuroblasts and myoblasts from proceeding in differentiation. Neurons became resistant to actinomycin D when they reached the stage of axon initiation, and axon elongation was not actinomycin D-sensitive. Myocytes were sensitive to actinomycin D until they attained the ability to pulsate, and ongoing pulsations were not halted by the drug. Autoradiographs and controls indicated that actinomycin D prevented uridine incorporation by about 90% but prevented leucine and thymidine incorporation by 6% or less in these cells. The result favour the interpretation that transcription is necessary in neuron differentation up to the point of axon initiation and in myocytes up to the point where pulsations can begin. Since ribosomal RNA synthesis is unnecessary for these differentiations, necessary RNA synthesis would be messenger or transfer RNA, or RNA of unknown identity.