Distinct Effects of Abelson Kinase Mutations on Myocytes and Neurons in Dissociated <i>Drosophila</i> Embryonic Cultures: Mimicking of High Temperature
<div><p>Abelson tyrosine kinase (Abl) is known to regulate axon guidance, muscle development, and cell-cell interaction <i>in vivo.</i> The <i>Drosophila</i> primary culture system offers advantages in exploring the cellular mechanisms mediated by Abl with utilizing various experimental manipulations. Here we demonstrate that single-embryo cultures exhibit stage-dependent characteristics of cellular differentiation and developmental progression in neurons and myocytes, as well as nerve-muscle contacts. In particular, muscle development critically depends on the stage of dissociated embryos. In wild-type (WT) cultures derived from embryos before stage 12, muscle cells remained within cell clusters and were rarely detected. Interestingly, abundant myocytes were spotted in <i>Abl</i> mutant cultures, exhibiting enhanced myocyte movement and fusion, as well as neuron-muscle contacts even in cultures dissociated from younger, stage 10 embryos. Notably, <i>Abl</i> myocytes frequently displayed well-expanded lamellipodia. Conversely, <i>Abl</i> neurons were characterized with fewer large veil-like lamellipodia, but instead had increased numbers of filopodia and darker nodes along neurites. These distinct phenotypes were equally evident in both homo- and hetero-zygous cultures (<i>Abl/Abl</i> vs. <i>Abl</i>/+) of different alleles (<i>Abl<sup>1</sup> and Abl<sup>4</sup></i>) indicating dominant mutational effects. Strikingly, in WT cultures derived from stage 10 embryos, high temperature (HT) incubation promoted muscle migration and fusion, partially mimicking the advanced muscle development typical of <i>Abl</i> cultures. However, HT enhanced neuronal growth with increased numbers of enlarged lamellipodia, distinct from the characteristic <i>Abl</i> neuronal morphology. Intriguingly, HT incubation also promoted <i>Abl</i> lamellipodia expansion, with a much greater effect on nerve cells than muscle. Our results suggest that Abl is an essential regulator for myocyte and neuron development and that high-temperature incubation partially mimics the faster muscle development typical of <i>Abl</i> cultures. Despite the extensive alterations by <i>Abl</i> mutations, we observed myocyte fusion events and nerve-muscle contact formation between WT and <i>Abl</i> cells in mixed WT and <i>Abl</i> cultures derived from labeled embryos.</p></div
