The locus elav of Drosophila melanogaster is expressed in neurons at all developmental stages

The locus elav (ella-vee) of Drosophila melanogaster, which is necessary for the proper development of the embryonic and adult nervous systems, has been characterized both genetically and molecularly. This locus has been shown to be transcribed exclusively within, and ubiquitously throughout, the developing nervous system during Hours 6 to 12 of embryogenesis. We present in situ RNA localization data which demonstrate that elav is expressed in the central nervous system as well as the peripheral nervous system of embryos, larvae, pupae, and adults. We also demonstrate that elav is not transcribed in embryonic or larval neuroblasts (the neuronal progenitor cells), or in at least one type of glial cell. These data provide evidence that the requirement for elav function is not limited to the 6- to 12-hr embryonic nervous system and the adult eye and developing optic lobe, but that its function is required for the development and continued maintenance of all neurons of the organism.     

Organizational analysis of elav gene and functional analysis of ELAV protein of Drosophila melanogaster and Drosophila virilis.

Drosophila virilis genomic DNA corresponding to the D. melanogaster embryonic lethal abnormal visual system (elav) locus was cloned. DNA sequence analysis of a 3.8-kb genomic piece allowed identification of (i) an open reading frame (ORF) with striking homology to the previously identified D. melanogaster ORF and (ii) conserved sequence elements of possible regulatory relevance within and flanking the second intron. Conceptual translation of the D. virilis ORF predicts a 519-amino-acid-long ribonucleoprotein consensus sequence-type protein. Similar to D. melanogaster ELAV protein, it contains three tandem RNA-binding domains and an alanine/glutamine-rich amino-terminal region. The sequence throughout the RNA-binding domains, comprising the carboxy-terminal 346 amino acids, shows an extraordinary 100% identity at the amino acid level, indicating a strong structural constraint for this functional domain. The amino-terminal region is 36 amino acids longer in D. virilis, and the conservation is 66%. In in vivo functional tests, the D. virilis ORF was indistinguishable from the D. melanogaster ORF. Furthermore, a D. melanogaster ORF encoding an ELAV protein with a 40-amino-acid deletion within the alanine/glutamine-rich region was also able to supply elav function in vivo. Thus, the divergence of the amino-terminal region of the ELAV protein reflects lowered functional constraint rather than species-specific functional specification.     

Molecular organization of the cut locus of Drosophila melanogaster

Mutations of the cut locus (ct) of Drosophila can be divided into four groups based on their phenotypes and complementation patterns. Each group alters the phenotype of a different set of tissues. Two hundred kilobases of ct DNA, located in 7B1-2, have been cloned by chromosomal walking, and the cloned sequences have been used to analyze more than 40 mutants. Based on the location of transposable element mutations and the extent of deficiencies and an inversion, four cut locus regions can be defined. Mutations in each region affect the phenotype of a different set of tissues. The most centromere proximal region contains mutations that are null for cut locus function. Within individual regions, a higher level of organization can be detected.     

Molecular analysis of a cellular decision during embryonic development of Drosophila melanogaster: epidermogenesis or neurogenesis

In Drosophila melanogaster, the neuroblasts (neural progenitor cells) develop from a special region of the ectoderm, called the neuroectoderm. During early embryonic development, the neuroblasts separate from the remaining cells of the neuroectoderm, which develop as epidermoblasts (epidermal progenitor cells). The separation of these two cell types is the result of cellular interactions. The available data indicate that a signal chain formed by the products of several identified genes regulates the cell's decision to enter either neurogenesis or epidermogenesis. Various kinds of data, in particular from cell transplantation studies and from genetic and molecular analyses, suggest that the proteins encoded by the genes Notch and Delta interact at the membrane of the neuroectodermal cells to provide a regulatory signal. This signal is thought to lead, on the one hand, to epidermal development through the action of the genes of the Enhancer of split complex, a gene complex that encodes several functions related to the transduction and further processing of the signal, including the genetic regulation in the receiving cell; on the other hand, the signal is thought to lead to neural development through the participation of the genes of the achaete-scute complex and daughterless, which are members of a family of DNA-binding regulatory proteins and of the gene vnd whose molecular nature is still unknown.     

Molecular analysis of large transposable elements carrying the white locus of Drosophila melanogaster

A large transposable element (TE) comprising the white-apricot and roughest genes has been found to transpose to well over a hundred sites scattered over the Drosophila genome. We report the cloning of the essential parts of several TEs. TE98 and TE28 sequences were cloned by `walking' along the chromosome from the previously cloned heatshock genes. The ends of the TEs are characterized by dispersed repetitive elements belonging to the foldback (FB) family. FB elements are also associated with two independently isolated transposable elements originating from the white locus, Tp w^c-1 and Tp w^+IV. The strong correlation between FB elements and large composite transposons suggests that a pair of these elements can mobilize large intermediary DNA segments. One particular FB family member, FB-NOF, is associated with TE28, the white-crimson (w^c) mutant, the w^c-derived Tp w^c-1 and probably also with Tp w^+IV. A unique sequence located close to the white end of TE28 was used to clone the borders of TE77 and the surrounding sequences in the bithorax region, indicating that the TE can be used as a probe for gene isolation. Some evolutionary implications of the large composite transposons are discussed.     

Molecular analysis of chemically-induced mutations at the RpII215 locus of Drosophila melanogaster

A substantial fraction, perhaps 50% or more, of spontaneous mutations in Drosophila melanogaster have been shown by molecular analyses to be associated with the presence of a transposable element (TE) inserted into the affected gene. We are interested in the molecular structure of induced mutations in Drosophila, in particular whether TEs are also responsible for a significant proportion of chemically-induced mutations. We report here the molecular analysis of 58 mutations at the RpII215 locus induced with EMS or ENU. While we find evidence for moderately sized deletions at this locus (in 3/58, or 5% of the examined mutants), we failed to detect any mutations which were associated with an insertion event. It may be the case that induced mutations are qualitatively different from spontaneous mutations.