Conservation and divergence in the control of yolk protein genes in dipteran insects

Abstract

We have investigated the conservation of regulatory elements for sex- and tissue-specific gene expression in three dipteran species, Drosophila melanogaster, Musca domestica and Calliphora erythrocephala, using the yolk protein (yp) genes. Yolk proteins of the fruitfly, medfly, housefly and blowfly are very well conserved both in their sequence and their expression in ovarian follicle cells and in fat bodies of adult females. Furthermore, yp regulation by both hormonal and nutritional factors shows similar features in all four species. To study conservation of yp regulation in dipteran insects, we tested 5' flanking regions from one Musca yp gene and one Calliphora yp gene for enhancer functions in D. melanogaster. Two fragments of 823 and 1046 bp isolated from Musca and Calliphora yp genes, respectively, are able to direct correct expression of a reporter gene in the ovarian follicle cells of transformed Drosophila at specific stages during oogenesis. Surprisingly, these enhancers do not confer sex-specific reporter gene expression in the fat body, as expression was found in both sexes of the transformed flies. None-the-less by in vitro DNA/protein interaction assays, a 284-bp DNA region from the Musca yp enhancer was able to bind the Drosophila DOUBLESEX (DSX) protein, which in D.melanogaster confers sex-specific expression of yp. We speculate that the sex-determining pathway is not directly involved in yp regulation in Musca or Calliphora adult females, but depends instead on hormonal controls to achieve sex-specific expression of yp genes in the adult.

Evolution of cis-regulatory sequence and function in Diptera

“…Comparisons of cis-regulatory elements among Diptera demonstrate that enhancer activity can be maintained despite extensive sequence divergence (Martin et al, 1988;Magoulas et al, 1993;Tortiglione and Bownes, 1997;Wolff et al, 1999;Ludwig et al, 2000). This phenomenon has been most clearly illustrated in the stripe 2 enhancer of the even-skipped gene, described below.…”

“…Cis-regulatory sequences from other Dipteran species often retain their activity when introduced into D. melanogaster using transgenes. This is true for sequences taken from other Drosophila species, distantly related flies (including the house fly Musca domestica and the black fly Simulium vittatum) and even animals outside Diptera (Mitsialis and Kafatos, 1985;Martin et al, 1988;Langeland and Carroll, 1993;Magoulas et al, 1993;Lukowitz et al, 1994;Pan et al, 1994;Xiong and Jacobs-Lorena, 1995;Tortiglione and Bownes, 1997;Ludwig et al, 1998;Wolff et al, 1999;Wittkopp et al, 2002).…”

Sex determination in Drosophila melanogaster and Musca domestica converges at the level of the terminal regulator doublesex

“…Whether this regulation is direct or indirect remains to be examined. In support of a direct transcriptional control is the presence of sites in the upstream regions of the Musca vitellogenin genes which have been shown to bind Drosophila DSX protein in vitro (Tortiglione and Bownes 1997).…”

“…The sequence of this fragment, located between the DM domain (exon 3) and the female-specific domain (exon 4), displays a high degree of sequence similarity at the nucleotide level (68%) and at the amino acid level (82%) when compared to dsx sequences of D. melanogaster. With this fragment as a probe, two lambda clones (GEM11.14 and GEM11.18) were isolated from a genomic Musca DNA library (Tortiglione and Bownes 1997). An alignment of the phage insert sequences with the partial female cDNA sequence exposed an intron at exactly the same position as in Drosophila (Fig.…”

A repressible female-specific lethal genetic system for making transgenic insect strains suitable for a sterile-release program

“…However, it is possible that the Drosophila yp1 enhancer may not retain the correct tissue and sex specificity in other insects. Indeed, the regulatory regions from the housefly yolk protein genes show the correct tissue specificity but not sex specificity in Drosophila (35), suggesting that it might be necessary to isolate the yolk protein genes from the insect species of interest. Yolk protein genes have been isolated from a number of insect species including the medfly (36).…”