The orthodenticle (ota~ locus of Drosophila is required for embryonic development, and null mutations of otd cause defects in head development and segmental patterning. We show here that otd is necessary for the formation of the embryonic central nervous system (CNS). otd mutations result in the formation of an abnormal neuropil and in the disappearance of identified neurons associated with the midline of the CNS. In addition, otd is allelic to ocelliless (oc), a mutation that causes the deletion of the ocelli of the adult fly. We have identified a transcription unit corresponding to the otd locus and find that it is expressed early in a stripe near the anterior pole of the cellular blastoderm and later in the region of the CNS from which these neurons normally arise. The predicted otd protein contains a well-conserved homeo domain and is therefore likely to be a transcriptional regulator involved in specifying cell fate both in the embryonic CNS and in the ocelli.
Apidaecins are the most prominent components of the honeybee humoral defense against microbial invasion. Our analysis of cDNA clones indicated that up to 12 of these short peptides (2 kDa) can be generated by processing of single precursor proteins; different isoforms are hereby linked in one promolecule. Assembly of the multipeptide precursors and the putative three‐step maturation are strongly reminiscent of yeast alpha‐mating factor. Bioactive apidaecins are flanked by the two ‘processing’ sequences, EAEPEAEP (or variants) and RR; joined together, they form a single unit that is repeated numerous times. The number of such repeats is variable and was reflected in the observed diversity of transcript lengths. Each such transcript is likely to be encoded by a different gene, forming a tight gene cluster. While transcriptional activation upon bacterial challenge is not exceptionally fast, the multigene and multipeptide precursor nature of the apidaecin genetic information allows for amplification of the response, resulting in a real overproduction of peptide antibiotic. Enhanced efficiency of the ‘immune’ response to bacterial infection through such a mechanism is, to our knowledge, unique among insects.
The metameric pattern of the Drosophila embryo is regulated by a combination of maternal and zygotic genes. The segment-polarity class of genes are required for the correct patterning within each segmental unit. Mutations in any one of these genes results in deletions and duplications of parts of each segment. The segment-polarity genes act coordinately by means of local cellular interactions to assign and maintain an identity for each cell in the segment, and to establish segment boundaries. Here we describe the molecular characterization of a novel segment-polarity gene, zeste-white3 (zw3). Embryos derived from germ lines that are homozygous for zw3 mutations (zw3 embryos) have phenotypes similar to embryos that are mutant for the segment-polarity gene naked (nkd). These embryos lack most of the ventral denticles, which are differentiated structures derived from the most anterior region of each segment. We have isolated the zw3 gene and compared the structure of one maternal and one zygotic transcript encoded by the gene. The zw3 gene is unique among the segment-polarity genes so far characterized, in that it encodes proteins that have homology to serine-threonine protein kinases. This indicates that zw3 may play a part in a signal transduction pathway involved in the establishment of cell identity within each embryonic segment.
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