Preferential adhesion maintains separation of ommatidia in the Drosophila eye

In the Drosophila eye, neighboring ommatidia are separated by inter-ommatidial cells (IOCs). How this ommatidial spacing emerges during eye development is not clear. Here we demonstrate that four adhesion molecules of the Irre cell recognition module (IRM) family play a redundant role in maintaining separation of ommatidia. The four IRM proteins are divided into two groups: Kirre and Rst are expressed in IOCs, and Hbs and Sns in primary pigment cells (1°s). Kirre binds Hbs and Sns in vivo and in vitro. Reducing activity of either Rst or Kirre alone had minimal effects on ommatidial spacing, but reducing both together led to direct ommatidium:ommatidium contact. A similar phenotype was also observed when reducing both Hbs and Sns. Consistent with the role of these factors in sorting ommatidia, mis-expression of Hbs plus Sns within a single IOC led to complete separation of the cell from neighboring ommatidia. Our results indicate mutual preferential adhesion between ommatidia and IOCs mediated by four IRM proteins is both necessary and sufficient to maintain separation of ommatidia

Activity-Independent Prespecification of Synaptic Partners in the Visual Map of Drosophila

SummarySpecifying synaptic partners and regulating synaptic numbers are at least partly activity-dependent processes during visual map formation in all systems investigated to date [1–5]. In Drosophila, six photoreceptors that view the same point in visual space have to be sorted into synaptic modules called cartridges in order to form a visuotopically correct map [6, 7]. Synapse numbers per photoreceptor terminal and cartridge are both precisely regulated [8–10]. However, it is unknown whether an activity-dependent mechanism or a genetically encoded developmental program regulates synapse numbers. We performed a large-scale quantitative ultrastructural analysis of photoreceptor synapses in mutants affecting the generation of electrical potentials (norpA, trp;trpl), neurotransmitter release (hdc, syt), vesicle endocytosis (synj), the trafficking of specific guidance molecules during photoreceptor targeting (sec15), a specific guidance receptor required for visual map formation (Dlar), and 57 other novel synaptic mutants affecting 43 genes. Remarkably, in all these mutants, individual photoreceptors form the correct number of synapses per presynaptic terminal independently of cartridge composition. Hence, our data show that each photoreceptor forms a precise and constant number of afferent synapses independently of neuronal activity and partner accuracy. Our data suggest cell-autonomous control of synapse numbers as part of a developmental program of activity-independent steps that lead to a “hard-wired” visual map in the fly brain

Weg- und Zielfindung wachsender Nervenfasern im Sehsystem von Fliegen und Fischen

Der Vergleich der Weg- und Zielfindung von Sehfasern bei Fliegen und Fischen ist attraktiv, da die wachsenden Nervenfasern trotz der verschiedenen Augenformen möglicherweise vergleichbare Strategien verwenden. Es ist sogar möglich, daß die grundlegenden Mechanismen der Zellerkennung bereits so früh in der Evolution erworben wurden, daß homologe molekulare Komponenten bei Vertebraten und Invertebraten hieran beteiligt sind

The Cell Adhesion Molecules Roughest, Hibris, Kin of Irre and Sticks and Stones Are Required for Long Range Spacing of the Drosophila Wing Disc Sensory Sensilla

Most animal tissues and organ systems are comprised of highly ordered arrays of varying cell types. The development of external sensory organs requires complex cell-cell communication in order to give each cell a specific identity and to ensure a regular distributed pattern of the sensory bristles. This involves both long and short range signaling mediated by either diffusible or cell anchored factors. In a variety of processes the heterophilic Irre Cell Recognition Module, consisting of the Neph-like proteins: Roughest, Kin of irre and of the Nephrin-like proteins: Sticks and Stones, Hibris, plays key roles in the recognition events of different cell types throughout development. In the present study these proteins are apically expressed in the adhesive belt of epithelial cells participating in sense organ development in a partially exclusive and asymmetric manner. Using mutant analysis the GAL4/UAS system, RNAi and gain of function we found an involvement of all four Irre Cell Recognition Module-proteins in the development of a highly structured array of sensory organs in the wing disc. The proteins secure the regular spacing of sensory organs showing partial redundancy and may function in early lateral inhibition events as well as in cell sorting processes. Comparisons with other systems suggest that the Irre Cell Recognition module is a key organizer of highly repetitive structures.status: publishe

Glia in the chiasms and medulla of the Drosophila melanogaster optic lobes

Different classes of glia cells in the optic lobes of Drosophila melanogaster were defined by the enhancer trap technique, using expression of the lacZ reporter gene. At both the outer and inner optic chiasms, there are stacks of glia, arrayed from dorsal to ventral, interpersed between the crossings of axonal fiber bundles. The giant glial cells of both the outer and inner chiasms are similar with respect to their nuclear shapes and positions, indicating similar functions of these cell types. Another class of glia is found in the medulla neuropil. Their cell bodies anchor in the most distal region of the neuropil, and their processes extend into the deeper neuropil layers. Birth dating using BrdU shows that both groups of chiasm glia are born early in larval life; they may participate in the development of the optic lobe. The medulla glia are born later and may be involved primarily in adult functions. In the wild type, and in mutants with structurally altered optic lobes, the numbers of tract-associated glial cells in the outer and inner optic chiasms seem to vary with the number of visual columns, whereas the complement of medulla neuropil glia correlates with the volume of the optic lobe

Glia in the chiasms and medulla of the Drosophila melanogaster optic lobes

Different classes of glia cells in the optic lobes of Drosophila melanogaster were defined by the enhancer trap technique, using expression of the lacZ reporter gene. At both the outer and inner optic chiasms, there are stacks of glia, arrayed from dorsal to ventral, interpersed between the crossings of axonal fiber bundles. The giant glial cells of both the outer and inner chiasms are similar with respect to their nuclear shapes and positions, indicating similar functions of these cell types. Another class of glia is found in the medulla neuropil. Their cell bodies anchor in the most distal region of the neuropil, and their processes extend into the deeper neuropil layers. Birth dating using BrdU shows that both groups of chiasm glia are born early in larval life; they may participate in the development of the optic lobe. The medulla glia are born later and may be involved primarily in adult functions. In the wild type, and in mutants with structurally altered optic lobes, the numbers of tract-associated glial cells in the outer and inner optic chiasms seem to vary with the number of visual columns, whereas the complement of medulla neuropil glia correlates with the volume of the optic lobe

Loss- and gain-of-function analysis of the lipid raft proteins Reggie/Flotillin in Drosophila : they are posttranslationally regulated, and misexpression interferes with wing and eye development

Reggie/Flotillin proteins are upregulated after optic nerve dissection and evolutionary highly conserved components of lipid rafts. Whereas many biochemical and cell culture studies suggest an involvement in the assembly of multiprotein complexes at cell contact sites, not much is known about their biological in vivo functions. We therefore set out to study the expression pattern and the effects of loss- and gain-of-function in the Drosophila melanogaster model system. We found that in flies these proteins are mainly expressed in axons at the root of fiber tracts, in places where strong fasciculation is required, e.g. at the neck of the peduncle of the mushroom bodies and in the optic chiasms. Despite their evolutionary conservation which implies fundamental and important functions, a P-element-induced null mutant (KG00210) of reggie1/flotillin2 (reggie1/flo2) in D. melanogaster shows no apparent phenotypic defects. This was even more surprising as we show that in this reggie1/flo2 null mutant the paralogous Reggie2/Flo1 protein is unstable and degraded, while the transcript is still present. The requirement of Reggie1/Flo2 for Reggie2/Flo1 stabilization is confirmed by misexpression experiments. Reggie2/Flo1 can only be misexpressed when Reggie1/Flo2 is provided as well. Conversely, Reggie1/Flo2 immunoreactivity can be detected, when its transgene is misexpressed alone. Using appropriate Gal4 driver lines, misexpression of Reggie1/Flo2 alone or together with Reggie2/Flo1 in the eye imaginal disc results in a specific and severe mislocalization of cell adhesion molecules of the immunoglobulin superfamily (IgCAMs) (while DE-Cadherin is unaffected) and in differentiation defects pointing to impaired signaling. In the wing imaginal disc, global overexpression of Reggie/Flotillin proteins leads to a significant extension of the Wingless signal and severely disrupts normal wing development. Our data support the notion that Reggie/Flotillin proteins are implicated in signaling processes at cellular contact sites

The Cell Adhesion Molecules <i>Roughest</i>, <i>Hibris</i>, <i>Kin of Irre</i> and <i>Sticks and Stones</i> Are Required for Long Range Spacing of the <i>Drosophila</i> Wing Disc Sensory Sensilla

<div><p>Most animal tissues and organ systems are comprised of highly ordered arrays of varying cell types. The development of external sensory organs requires complex cell-cell communication in order to give each cell a specific identity and to ensure a regular distributed pattern of the sensory bristles. This involves both long and short range signaling mediated by either diffusible or cell anchored factors. In a variety of processes the heterophilic <u>I</u>rre Cell <u>R</u>ecognition <u>M</u>odule, consisting of the Neph-like proteins: Roughest, Kin of irre and of the Nephrin-like proteins: Sticks and Stones, Hibris, plays key roles in the recognition events of different cell types throughout development. In the present study these proteins are apically expressed in the adhesive belt of epithelial cells participating in sense organ development in a partially exclusive and asymmetric manner. Using mutant analysis the <i>GAL4/UAS</i> system, RNAi and gain of function we found an involvement of all four Irre Cell Recognition Module-proteins in the development of a highly structured array of sensory organs in the wing disc. The proteins secure the regular spacing of sensory organs showing partial redundancy and may function in early lateral inhibition events as well as in cell sorting processes. Comparisons with other systems suggest that the Irre Cell Recognition module is a key organizer of highly repetitive structures.</p></div

Irregular chiasm-C-roughest, a member of the immunoglobulin superfamily, affects sense organ spacing on the Drosophila antenna by influencing the positioning of founder cells on the disc ectoderm

We describe a role for Irregular chiasmC-roughest (IrreC-rst), an immunoglobulin (Ig) superfamily member, in patterning sense organs on the Drosophila antenna. IrreC-rst protein is initially expressed homogeneously on apical profiles of ectodermal cells in regions of the antennal disc. During specification of founder cells (FCs), the intracellular protein distribution changes and becomes concentrated in regions where specific intercellular contacts presumably occur. Loss of function mutations as well as misexpression of irreC-rst results in an altered arrangement of FCs within the disc compared to wildtype. Sense organ development occurs normally, although spacing is affected. Unlike its role in interommatidial spacing, irreC-rst does not affect apoptosis during antennal development. We propose that IrreC-rst affects the spatial relationship between sensory and ectodermal cells during FC delamination