title: Argos and Spitz group genes function to regulate midline glial cell number in Drosophila embryos.
abstract: The midline glia of the Drosophila embryonic nerve cord undergo a reduction in cell number after facilitating commissural tract morphogenesis. The numbers of midline glia entering apoptosis at this stage can be increased by a loss or reduction of function in genes of the spitz group or Drosophila EGF receptor (DER) pathway. Argos, a secreted molecule with an atypical EGF motif, is postulated to function as a DER antagonist. In this work, we assess the role of argos in the determination of midline glia cell number. Although all midline glia express DER, argos expression is restricted to the midline glia which do not enter apoptosis. Fewer midline glia enter apoptosis in embryos lacking argos function. Ectopic expression of argos is sufficient to remove all DER-expressing midline glia from the nerve cord, even those that already express argos. DER expression is not terminated in the midline glia after spitz group signaling triggers changes in gene expression. It is therefore likely that an attenuation of DER signaling by Argos is integrated with the augmentation of DER signaling by Spitz throughout the period of reduction of midline glia number. We suggest that signaling by Spitz but not Argos is restricted to adhesive junctions. In this manner, midline glia not forming signaling junctions remain sensitive to juxtacrine Argos signaling, while an autocrine Argos signal is excluded by the adhesive junction.
authors.affiliation: Department of Biology, McMaster University, Hamilton ON, Canada.
authors.forename: C
authors.initials: C
authors.lastname: Stemerdink
authors.forename: J R
authors.initials: JR
authors.lastname: Jacobs
mesh_terms: D000818:Animals; D001369:Axons / Q000502:physiology / Q000648:ultrastructure; D019521:Body Patterning; D029721:Drosophila Proteins; D004331:Drosophila melanogaster / Q000196:embryology* / Q000235:genetics*; D004625:Embryo, Nonmammalian / Q000166:cytology / Q000502:physiology*; D004815:Epidermal Growth Factor / Q000096:biosynthesis; D066246:ErbB Receptors / Q000096:biosynthesis / Q000502:physiology; D005136:Eye Proteins / Q000096:biosynthesis / Q000502:physiology*; D018507:Gene Expression Regulation, Developmental; D017344:Genes, Insect; D006358:Hot Temperature; D008565:Membrane Proteins / Q000096:biosynthesis / Q000502:physiology*; D008954:Models, Biological; D009419:Nerve Tissue Proteins / Q000096:biosynthesis / Q000502:physiology*; D009420:Nervous System / Q000196:embryology; D009457:Neuroglia / Q000166:cytology / Q000502:physiology; D011494:Protein Kinases; D012333:RNA, Messenger / Q000096:biosynthesis; D018010:Receptors, Invertebrate Peptide / Q000096:biosynthesis / Q000502:physiology; D015398:Signal Transduction; D014158:Transcription, Genetic
chemical_list: D029721:Drosophila Proteins; D005136:Eye Proteins; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; D012333:RNA, Messenger; D018010:Receptors, Invertebrate Peptide; C075638:aos protein, Drosophila; C076026:spi protein, Drosophila; D004815:Epidermal Growth Factor; D011494:Protein Kinases; C066532:Egfr protein, Drosophila; D066246:ErbB Receptors