Characterization of the Hox cluster from the mosquito Anopheles gambiae (Diptera: culicidae)

Abstract

The Hox genes have been found to encode transcription factors, which specify the morphological identity of structures along the anteroposterior axis of animals ranging from worms to mice. The canonical set of nine genes is organized in a cluster in the genome of several protostomes and deuterostomes. However, within insects, whereas the Hox genes are organized in a single cluster in the beetle Tribolium castaneum, they are split into two separate groups in the flies Drosophila melanogaster and Drosophila virilis. The significance of a split Hox cluster is unknown and has been observed in only one organism outside the Drosophila lineage: the nematode Caenorhabditis elegans. We have cloned a majority of the Hox genes from the mosquito Anopheles gambiae (Diptera: Culicidae) and compared their genomic organization with that of Tribolium and Drosophila to determine if a split Hox cluster is found in dipterans aside from the Drosophilidae. We find that the Hox genes in Anopheles, as in Tribolium, are organized in a single cluster that spans a genomic region of at least 700 kb. This finding suggests that, within the insect genome, the partition of the Hox cluster may have evolved exclusively within the Drosophila lineage. The genomic structures of the resident genes, however, appear to be largely conserved between A. gambiae and D. melanogaster.

Conservation of regulatory sequences and gene expression patterns in the disintegrating Drosophila Hox gene complex

“…A plausible reconstruction of HOM-C evolution in the Drosophila subgenus that accounts for the current organization of Hox genes in D. buzzatii is shown in Figure 5. In lower Dipterans, such as Anopheles gambiae, the eight Hox genes, plus Hox3 and ftz, are arranged as a single cluster (Powers et al 2000). Before the radiation of the Drosophila genus, two transpositions occurred as follows: the Ccp gene cluster between lab and pb, and the gene CG31217 between Antp and Ubx (Lewis et al 2003).…”

Organization of Hox genes in ascidians: Present, past, and future

“…Nonchordate Hox clusters have been reported with Drosophila (Lewis, 1978;Von Allmen et al, 1996), mosquito (Devenport et al, 2000;Powers et al, 2000), red flour beetle (Brown et al, 2002), silk moth (Ueno et al, 1992), a grasshopper (Ferrier and Akam, 1996), nematode, Caenorhabditis elegans (Wang et al, 1993;Van Auken et al, 2000), ribbon worm (Kmita-Cunisse et al, 1998), and sea urchin (Popodi et al, 1996;Martinez et al, 1999). Of these bilaterians, vertebrates have multiple Hox clusters, whereas all invertebrate species that have been examined contain a single Hox gene cluster.…”

Hox cluster duplications and the opportunity for evolutionary novelties

“…Another trend in the structural evolution of Hox clusters after duplication is the total size of the cluster. Invertebrate Hox clusters are huge, Ͼ1,000 kb (22). The closest relative of vertebrates, Amphioxus also has a comparatively large Hox cluster (Ϸ450 kb; C.A., unpublished work).…”

“…In addition, inverted Hox gene orientation has been documented for dipterans. For instance, the Deformed gene (Hox4) is the same as the other Hox genes in vertebrates, the mosquito (22,40), D. pseudoobscura (34), and D. virilis (38), but inverted in D. melanogaster. Similarly the orientation of ftz is also different between D. hydei and D. melanogaster (37).…”