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Hox genes are known to control the identity of serially repeated structures in arthropods and vertebrates. We analyzed the expression pattern of the Hox genes Deformed (Dfd), Sex combs reduced (Scr), Antennapedia (Antp), and Ultrabithorax/abdominal-A (Ubx/abd-A) from the honey bee Apis mellifera. We also cloned a cDNA with the complete coding region of the Antennapedia gene from Apis. Comparison with Antp proteins from other insect species revealed several regions of homology. The expression patterns of the isolated Hox genes from Apis showed that the original expression patterns of Dfd, Scr, and Antp appear between late blastoderm and early germ band stage in a temporal and spatial sequence. Each of them shows up as a belt, spanning approximately two segment anlagen, Dfd in the anterior gnathal region, Scr in the posterior gnathal and anterior thoracic region, and Antp in the thoracic region. Following expansion of the Antp domain in the abdomen as a gradient towards the posterior, Ubx/abd-A expression appears laterally in the abdomen. During gastrulation and in the germ band stage the domains of strong expression do not overlap any more, but touch each other. After gastrulation the borders of the expression domains partly correlate with parasegment and partly with segment boundaries. Laterally, gaps between the domain of each gene may show no expression of any of the genes examined.

During early brain development in Drosophila a highly stereotyped pattern of axonal scaffolds evolves by precise pioneering and selective fasciculation of neural fibers in the newly formed brain neuromeres. Using an axonal marker, Fasciclin II, we show that the activities of the extradenticle (exd) and homothorax (hth) genes are essential to this axonal patterning in the embryonic brain. Both genes are expressed in the developing brain neurons, including many of the tract founder cluster cells. Consistent with their expression profiles, mutations of exd and hth strongly perturb the primary axonal scaffolds. Furthermore, we show that mutations of exd and hth result in profound patterning defects of the developing brain at the molecular level including stimulation of the orthodenticle gene and suppression of the empty spiracles and cervical homeotic genes. In addition, expression of a Drosophila Pax6 gene, eyeless, is significantly suppressed in the mutants except for the most anterior region. These results reveal that, in addition to their homeotic regulatory functions in trunk development, exd and hth have important roles in patterning the developing brain through coordinately regulating various nuclear regulatory genes, and imply molecular commonalities between the developmental mechanisms of the brain and trunk segments, which were conventionally considered to be largely independent.

We have previously isolated a 500 bp-long cDNA clone, NO9-15, which is derived from a nuclear transcript originating from the heat shock locus 2-48B of Drosophila hydei (Peters et al. 1982). Sequence analysis shows that this clone carries 4 complete copies and 1 partial copy of a 115 bp repeat unit. The repeats are closely homologous with a maximal sequence divergence of about 10%. The sequence does not contain an open reading frame. The genomic organization of heat shock locus 2-48B, as probed with the cloned cDNA sequence NO9-15, is highly polymorphic. Four different allelic arrangements have been found in different inbred strains. A number of genomic clones isolated from region 2-48B, both in phage lambda and in cosmid vectors, all differ in length, mainly due to varying numbers of the NO9-15 repeat unit. These differences are found primarily in the proximal region of the locus. The transcribed region of these clones includes the distal sequence flanking the NO9-15 repeat as well as the NO9-15 repeat itself. An oligo A stretch was found between the distal flanking sequence and the NO9-15 repeat region.

The heat-shock locus 93D from Drosophila melanogaster has recently become available for a molecular analysis. We established a restriction site map of a recombinant DNA clone covering the major part of heat-shock locus 93D. This clone includes part of a repetitive Taq I region and neighbouring unique sequences. The portion of the Taq I repeat analysed consists of tandemly arranged sequence blocks of about 280 base pairs (bp) in length. Using genomic and cDNA as hybridization probes we examined the transcription of 93D in 2- to 4-day-old flies. We identified two major RNA classes enhanced after heat shock, namely nonpolyadenylated transcripts of heterogeneous length derived from the repetitive region and one discrete polyadenylated transcript in spliced and unspliced form from the neighbouring unique region. The occurrence of a highly heterogeneous poly(A)- transcript and high levels of an unspliced discrete poly(A)+ species suggests unusual mechanisms of transcription regulation in the 93D region.