Abstract
In the Drosophila brain, neural lineages project bundled axon tracts into a central neuropile. Each lineage exhibits a stereotypical branching pattern and trajectory, which distinguish it from other lineages. In this study, we used a multilineage approach to explore the neural function of the Par-complex member Par3/Bazooka in vivo. Drosophila bazooka is expressed in post-mitotic neurons of the larval brain and localizes within neurons in a lineage-dependent manner. The fact that multiple GAL4 drivers have been mapped to several lineages of the Drosophila brain enables investigation of the role of Bazooka from larval to adult stages Bazooka loss-of-function (LOF) clones had abnormal morphologies, including aberrant pathway choice of ventral projection neurons in the BAla1 lineage, ectopic branching in the DALv2 and BAmv1 lineages, and excess BLD5 lineage axon projections in the optic medulla. Exogenous expression of Bazooka protein in BAla1 neurons rescued defective guidance, supporting an intrinsic requirement for Bazooka in the post-mitotic neuron. Elimination of the Par-complex member Par6 recapitulated Bazooka phenotypes in some but not all lineages, suggesting that the Par complex functions in a lineage-dependent manner, and that Bazooka may act independently in some lineages. Importantly, this study highlights the potential of using a multilineage approach when studying gene function during neural development in Drosophila.
Highlights
Neurons of the Drosophila brain are grouped into individual units, termed lineages
Bazooka is expressed in neuroblasts, ganglion mother cell (GMC) and postmitotic neurons in third instar larvae To establish a global view of endogenous Bazooka localization throughout larval secondary lineages, we double-labeled third instar brains with monoclonal antibodies against Bazooka and Neurotactin, a surface glycoprotein that marks all secondary axon tract (SAT) [24]
Bazooka elimination disrupts SAT morphology Using the developmental profiles of the BAla1, BAmv1, DALv2 and BLD5 lineages, we investigated the in vivo function of Bazooka protein in neurons
Summary
Neurons of the Drosophila brain are grouped into individual units, termed lineages. Neurons born in the embryo and larva compose the primary and secondary lineages, respectively. Each group of secondary neurons emits a secondary axon tract (SAT) into the central neuropile along the existing primary axon tracts (PATs). As early as embryonic development, lineages begin to acquire a unique morphology that is retained into the larval stages [1,2,3]. Approximately 40% of embryonic-born primary neurons are lost, and the secondary neurons begin to generate an intricate network of arbors in the pupal neuropile compartments [3]. SATs are the primary scaffolding and functional units of the adult brain, in the context of using Drosophila as a model to understand circuit formation, it is important to elucidate the mechanisms that underlie stereotypical lineage morphologies
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