Formation of Axon to Myocyte Contacts in Drosophila Cell Cultures

Cultures of Drosophila embryonic cells offer new opportunitiesfor studying myoneural junctions. In culture, neuroblasts andmyoblasts differentiate and yield neurons and myocytes. Someaxons grow across the surface of the culture vessel and attachto myocytes, forming functional myoneural junctions. Therefore,all stages in junction formation may be examined in vitro underconditions where pharmacological, electrophysiological, andother commonplace approaches are facilitated. This method offersan additional, most powerful approach for studying the junctions,that of genetic analysis. Drosophila mutations may be soughtwhich affect junction formation and function. Altered cellsand junctions from mutants may then be compared to those fromwild-type animals in order to dissect the gene-directed stepsunderlying junction phenomena.     

A 5-Bromodeoxyuridine-sensitive Interval during Drosophila Myogenesis

Drosophila myogenesis was monitored in vitro and the cells were treated with 5-bromodeoxyuridine (BrdU) or with thymidine at certain intervals. Muscle cells were scored for survival, contractility, and the uptake of thymidine and BrdU. Results indicated that the final S period for myoblasts takes place in vitro between 1.3 and 3.3 h following the initiation of gastrulation in the donor embryos. Treatment with 10^-4 M BrdU during this interval inhibited myogenesis, but later treatment did not. Thymidine reversed or prevented the BrdU effect if given before the final myoblast division, but not if given afterwards. All results support the hypothesis that BrdU inhibits Drosophila myogenesis through its incorporation into DNA.     

A Genetic Approach to the Study of Neurogenesis and Myogenesis

Extensive sequences of morphological differentiation have beendescribed for Drosophila melanogaster neurogenesis and myogenesis.Neuroblasts and myoblasts become determined in the blastodermor shortly thereafter. Each blast cell will then morphologicallydifferentiate in vitro in sequences that closely resemble theevents in vivo. Functional neurons, muscle cells and neuromuscularjunctions form and these have normal biochemical and ultrastructuralcharacteristics. A mutant hunt was conducted which was designedto generate mutations specific to neurogenesis or myogenesis.One mutation was recovered that apparently interfered only withmyogenesis. The frequency of recovered mutations that affectedcell differentiation was low and led to estimates that relativelyfew genes are required to preserve the structural integrityof cells during neurogenesis and myogenesis.