Spineless provides a little backbone for dendritic morphogenesis.
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Animals↗
Biomedical subjects
Stephen T Crews
Publications and source records attributed to Stephen T Crews.
Single-cell mapping of neural and glial gene expression in the developing Drosophila CNS midline cells.
Understanding the generation of neuronal and glial diversity is one of the major goals of developmental neuroscience. The Drosophila CNS midline cells constitute a simple neurogenomic system to study neurogenesis, cell fate acquisition, and neuronal function. Previously, we identified and determined the developmental expression profiles of 224 midline-expressed genes. Here, the expression of 59 transcription factors, signaling proteins, and neural function genes was analyzed using multi-label confocal imaging, and their expression patterns mapped at the single-cell level at multiple stages of CNS development. These maps uniquely identify individual cells and predict potential regulatory events and combinatorial protein interactions that may occur in each midline cell type during their development. Analysis of neural function genes, including those encoding peptide neurotransmitters, neurotransmitter biosynthetic enzymes, transporters, and neurotransmitter receptors, allows functional characterization of each neuronal cell type. This work is essential for a comprehensive genetic analysis of midline cell development that will likely have widespread significance given the high degree of evolutionary conservation of the genes analyzed.
Animals↗
Dysfusion transcriptional control of Drosophila tracheal migration, adhesion, and fusion.
The Drosophila dysfusion basic-helix-loop-helix-PAS transcription factor gene is expressed in specialized fusion cells that reside at the tips of migrating tracheal branches. dysfusion mutants were isolated, and genetic analysis of live embryos revealed that mutant tracheal branches migrate to close proximity but fail to recognize and adhere to each other. Misexpression of dysfusion throughout the trachea further indicated that dysfusion has the ability to both inhibit cell migration and promote ectopic tracheal fusion. Nineteen genes whose expression either increases or decreases in fusion cells during development were analyzed in dysfusion mutant embryos. dysfusion upregulates the levels of four genes, including the shotgun cell adhesion protein gene and the zona pellucida family transmembrane protein gene, CG13196. Misexpression experiments with CG13196 result in ectopic tracheal fusion events, suggesting that it also encodes a cell adhesion protein. Another target gene of dysfusion is members only, which inhibits protein nuclear export and influences tracheal fusion. dysfusion also indirectly downregulates protein levels of Trachealess, an important regulator of tracheal development. These results indicate that fusion cells undergo dynamic changes in gene expression as they switch from migratory to fusion modes and that dysfusion regulates a discrete, but important, set of these genes.
Alleles↗
Gene expression profiling of the developing Drosophila CNS midline cells.
The Drosophila CNS midline cells constitute a specialized set of interneurons, motorneurons, and glia. The utility of the CNS midline cells as a neurogenomic system to study CNS development derives from the ability to easily identify CNS midline-expressed genes. For this study, we used a variety of sources to identify 281 putative midline-expressed genes, including enhancer trap lines, microarray data, published accounts, and the Berkeley Drosophila Genome Project (BDGP) gene expression data. For each gene, we analyzed expression at all stages of embryonic CNS development and categorized expression patterns with regard to specific midline cell types. Of the 281 candidates, we identified 224 midline-expressed genes, which include transcription factors, signaling proteins, and transposable elements. We find that 58 genes are expressed in mesectodermal precursor cells, 138 in midline primordium cells, and 143 in mature midline cells--50 in midline glia, 106 in midline neurons. Additionally, we identified 27 genes expressed in glial and mesodermal cells associated with the midline cells. This work provides the basis for future research that will generate a complete cellular and molecular map of CNS midline development, thus allowing for detailed genetic and molecular studies of neuronal and glial development and function.
Animals↗
The Drosophila dysfusion basic helix-loop-helix (bHLH)-PAS gene controls tracheal fusion and levels of the trachealess bHLH-PAS protein.
The development of the mature insect trachea requires a complex series of cellular events, including tracheal cell specification, cell migration, tubule branching, and tubule fusion. Here we describe the identification of the Drosophila melanogaster dysfusion gene, which encodes a novel basic helix-loop-helix (bHLH)-PAS protein conserved between Caenorhabditis elegans, insects, and humans, and controls tracheal fusion events. The Dysfusion protein functions as a heterodimer with the Tango bHLH-PAS protein in vivo to form a putative DNA-binding complex. The dysfusion gene is expressed in a variety of embryonic cell types, including tracheal-fusion, leading-edge, foregut atrium cells, nervous system, hindgut, and anal pad cells. RNAi experiments indicate that dysfusion is required for dorsal branch, lateral trunk, and ganglionic branch fusion but not for fusion of the dorsal trunk. The escargot gene, which is also expressed in fusion cells and is required for tracheal fusion, precedes dysfusion expression. Analysis of escargot mutants indicates a complex pattern of dysfusion regulation, such that dysfusion expression is dependent on escargot in the dorsal and ganglionic branches but not the dorsal trunk. Early in tracheal development, the Trachealess bHLH-PAS protein is present at uniformly high levels in all tracheal cells, but since the levels of Dysfusion rise in wild-type fusion cells, the levels of Trachealess in fusion cells decline. The downregulation of Trachealess is dependent on dysfusion function. These results suggest the possibility that competitive interactions between basic helix-loop-helix-PAS proteins (Dysfusion, Trachealess, and possibly Similar) may be important for the proper development of the trachea.
Amino Acid Sequence↗
Novel behavioral and developmental defects associated with Drosophila single-minded.
In Drosophila, the development of the midline cells of the embryonic ventral nerve cord depends on the function of the bHLH-PAS transcription factor Single-minded (Sim). The expression domain of sim, however, is also found anterior and posterior to the developing ventral cord throughout the germ band. Indeed, mutations in sim were identified based on their characteristic cuticle phenotype. Eight abdominal segments (A1-A8) can be easily seen in the larval cuticle, while three more can be identified during embryogenesis. Cells located in A8-A10 give rise to the formation of the genital imaginal discs, and a highly modified A11 segment gives rise to the anal pads that flank the anus. sim is expressed in all these segments and is required for the formation of both the anal pads and the genital imaginal discs. A new temperature-sensitive sim allele allowed an assessment of possible postembryonic function(s) of sim. Reduction of sim function below a 50% threshold leads to sterile flies with marked behavioral deficits. Most mutant sim flies were only able to walk in circles. Further analyses indicated that this phenotype is likely due to defects in the brain central complex. This brain region, which has previously been implicated in the control of walking behavior, expresses high levels of nuclear Sim protein in three clusters of neurons in each central brain hemisphere. Additional Sim localization in the medullary and laminar neurons of the optic lobes may correlate with the presence of ectopic axon bundles observed in the optic lobes of sim mutant flies.
Amino Acid Sequence↗
Expression of the Artemia trachealess gene in the salt gland and epipod.
The Drosophila trachealess gene encodes a basic-helix-loop-helix-PAS transcription factor that controls the formation of the trachea and salivary duct. An ortholog of trachealess was identified in the brine shrimp, Artemia franciscana, and was shown to be highly conserved by sequence identity. Expression of Artemia trachealess was observed at two sites during development: the naupliar salt gland and the juvenile thoracic epipod. These two organs function at their respective times of development in osmoregulation, an important aspect of brine shrimp physiology. This extends the range of putative functions of trachealess to include formation of osmoregulatory, respiratory, and ductile organs.
Amino Acid Sequence↗