POU domain transcription factors in embryonic development

Molecular Biology Reports -     

Dissecting Drosophila embryonic brain development using photoactivated gene expression

The Drosophila brain is generated by a complex series of morphogenetic movements. To better understand brain development and to provide a guide for experimental manipulation of brain progenitors, we created a fate map using photoactivated gene expression to mark cells originating within specific mitotic domains and time-lapse microscopy to dynamically monitor their progeny. We show that mitotic domains 1, 5, and 9 give rise to discrete cell populations within specific regions of the brain. Two novel observations were that the antennal sensory system, composed of four disparate cell clusters, arose from mitotic domain 5 and that mitotic domain B produced glial cells, while neurons were produced from mitotic domains 1, 5, and 9. Time-lapse analysis of marked cells showed complex mitotic and migratory patterns for cells derived from these mitotic domains. Photoactivated gene expression was also used either to kill, to induce ectopic divisions, or to alter cell fate. This revealed that deficits were not repopulated, while ectopic cells were removed and extra glia were tolerated.     

The embryonic development of larval muscles in Drosophila

Each of the abdominal hemisegments A2-A7 in the Drosophila larva has a stereotyped pattern of 30 muscles. The pattern is complete by 13 h after egg laying, but the development of individual muscles has begun with the definition of precursors at least by the onset of germ band shortening, some 5.5 h earlier. The earliest signs of muscle differentiation are cell fusions, which occur in the ventralmost mesoderm overlying the CNS and at stereotyped positions in the rest of the mesoderm as the germ band shortens. At the end of shortening, the pattern of muscle precursors produced by these fusions is complete. Precursors filled with dye reveal extensive fine processes probably involved initially in cell fusion and, subsequently, in navigation over the epidermis to form attachment points. The muscle pattern is formed before innervation and without cell death. Thus, neither of these processes is involved in determining the distribution of precursors. Evidence is presented for the view that the development of the larval muscle pattern in Drosophila depends on a prior segregation of founder cells at appropriate locations in the mesoderm with which other cells fuse to form the precursors.     

Dynamic expression of the cell adhesion molecule fasciclin I during embryonic development in Drosophila.

A number of different cell surface glycoproteins expressed in the central nervous system (CNS) have been identified in insects and shown to mediate cell adhesion in tissue culture systems. The fasciclin I protein is expressed on a subset of CNS axon pathways in both grasshopper and Drosophila. It consists of four homologous 150-amino acid domains which are unrelated to other sequences in the current databases, and is tethered to the cell surface by a glycosyl-phosphatidylinositol linkage. In this paper we examine in detail the expression of fasciclin I mRNA and protein during Drosophila embryonic development. We find that fasciclin I is expressed in several distinct patterns at different stages of development. In blastoderm embryos it is briefly localized in a graded pattern. During the germ band extended period its expression evolves through two distinct phases. Fasciclin I mRNA and protein are initially localized in a 14-stripe pattern which corresponds to segmentally repeated patches of neuroepithelial cells and neuroblasts. Expression then becomes confined to CNS and peripheral sensory (PNS) neurons. Fasciclin I is expressed on all PNS neurons, and this expression is stably maintained for several hours. In the CNS, fasciclin I is initially expressed on all commissural axons, but then becomes restricted to specific axon bundles. The early commissural expression pattern is not observed in grasshopper embryos, but the later bundle-specific pattern is very similar to that seen in grasshopper. The existence of an initial phase of expression on all commissural bundles helps to explain the loss-of-commissures phenotype of embryos lacking expression of both fasciclin I and of the D-abl tyrosine kinase. Fasciclin I is also expressed in several nonneural tissues in the embryo.     

Neural expression of hikaru genki protein during embryonic and larval development of Drosophila melanogaster

 Hikaru genki (HIG) is a putative secreted protein of Drosophila that belongs to immunoglobulin and complement-binding protein superfamilies. Previous studies reported that, during pupal and adult stages, HIG protein is synthesized in subsets of neurons and appears to be secreted to the synaptic clefts of neuron-neuron synapses in the central nervous system (CNS). Here we report the analyses of distribution patterns of HIG protein at embryonic and larval stages. In embryos, HIG was mainly observed in subsets of neurons of the CNS that include pCC interneurons and RP5 motorneurons. At third instar larval stage, this protein was detected in a limited number of cells in the brain and ventral nerve cord. Among them are the motorneurons that extend their axons to make neuromuscular junctions on body wall muscle 8. Immunoelectron microscopy showed that these axonal processes as well as the neuromuscular terminals contain numerous vesicles with HIG staining, suggesting that HIG is in a pathway of secretion at this stage. Some neurosecretory cells were also found to express this protein. These data suggest that HIG functions in the nervous system through most developmental stages and may serve as a secreted signalling molecule to modulate the property of synapses or the physiology of the postsynaptic cells. Received: 28 May 1998 / Accepted: 4 August 1998