Variation in sex-, stage- and tissue-specific expression of the amylase genes in Drosophila ananassae

The Amylases of Insects

Alpha-amylases are major digestive enzymes that act in the first step of maltopolysaccharide digestion. In insects, these enzymes have long been studied for applied as well as purely scientific purposes. In many species, amylases are produced by multiple gene copies. Rare species are devoid of Amy gene. They are predominantly secreted in the midgut but salivary expression is also frequent, with extraoral activity. Enzymological parameters are quite variable among insects, with visible trends according to phylogeny: Coleopteran amylases have acidic optimum activity, whereas dipteran amylases have neutral preference and lepidopteran ones have clear alkaline preference. The enzyme structure shows interesting variations shaped by evolutionary convergences, such as the recurrent loss of a loop involved in substrate handling. Many works have focused on the action of plant amylase inhibitors on pest insect amylases, in the frame of crop protection by transgenesis. It appears that sensitivity or resistance to inhibitors is finely tuned and very specific and that amylases and their inhibitors have coevolved. The multicopy feature of insect amylases appears to allow tissue-specific or stage-specific regulation, but also to broaden enzymological abilities, such as pH range, and to overcome plant inhibitory defenses.

Cloning and expression analysis of the Bombyx mori α-amylase gene (Amy) from the indigenous Thai silkworm strain, Nanglai

α-Amylase is a common enzyme for hydrolyzing starch. In the silkworm, Bombyx mori L. (Lepidoptera: Bombycidae), α-amylase is found in both digestive fluid and hemolymph. Here, the complete genomic sequence of the Amy gene encoding α-amylase from a local Thai silkworm, the Nanglai strain, was obtained. This gene was 7981 bp long with 9 exons. The full length Amy cDNA sequence was 1749 bp containing a 1503 bp open reading frame. The ORF encoded 500 amino acid residues. The deduced protein showed 81-54% identity to other insect α-amylases and more than 50% identity to mammalian enzymes. Southern blot analysis revealed that in the Nanglai strain Amy is a single-copy gene. RT- PCR showed that Amy was transcribed only in the foregut. Transgenic B. mori also showed that the Amy promoter activates expression of the transgene only in the foregut.

Origin and evolution of the Amyrel gene in the alpha-amylase multigene family of Diptera

Alpha-amylase genes often form multigene families in living organisms. In Diptera, a remote paralog, Amyrel, had been discovered in Drosophila, where this gene is currently used as a population and phylogenetic marker. The putative encoded protein has about 40% divergence with the classical amylases. We have searched the presence of the paralog in other families of Diptera to track its origin and understand its evolution. Amyrel was detected in a number of families of Muscomorpha (Brachycera-Cyclorrapha), suggesting an origin much older than previously thought. It has not been found elsewhere to date, and it is absent from the Anopheles gambiae genome. The intron-exon structures of the genes found so far suggest that the ancestral gene (before the duplication which gave rise to Amyrel) had two introns, and that subsequent, repeated and independent loss of one or both introns occurred in some Muscomorpha families. It seems that the Amyrel protein has experienced specific amino acid substitutions in regions generally well conserved in amylases, raising the possibility of peculiar, functional adaptations of this protein.

Amyrel, a paralogous gene of the amylase gene family in Drosophila melanogaster and the Sophophora subgenus

We describe a gene from Drosophila melanogaster related to the alpha-amylase gene Amy. This gene, which exists as a single copy, was named Amyrel. It is strikingly divergent from Amy because the amino acid divergence is 40%. The coding sequence is interrupted by a short intron at position 655, which is unusual in amylase genes. Amyrel has also been cloned in Drosophila ananassae, Drosophila pseudoobscura, and Drosophila subobscura and is likely to be present throughout the Sophophora subgenus, but, to our knowledge, it has not been detected outside. Unexpectedly, there is a strong conservation of 5' and 3' flanking regions between Amyrel genes from different species, which is not the case for Amy and which suggests that selection acts on these regions. In contrast to the Amy genes, Amyrel is transcribed in larvae of D. melanogaster but not in adults. However, the protein has not been detected yet. Amyrel evolves about twice as fast as Amy in the several species studied. We suggest that this gene could result from a duplication of Amy followed by accelerated and selected divergence toward a new adaptation.

Metabolic evolution in alpha-amylases from Drosophila virilis and D. repleta, two species with different ecological niches

alpha-Amylases from Drosophila virilis and D. repleta were partially purified by ion exchange chromatography. The two amylases share common characteristics for pH and cations effects, although with slight differences. D. virilis has optimal activity at pH 6.6 and D. repleta at pH 7.2. Calcium, sodium, and potassium cations activate amylolytic activity in both species but Ba2+ has an activation effect in D. repleta only. In contrast, there are major differences in thermal offbility and kinetics among amylases of the two species. D. virilis amylase is much more stable at high temperature and the optimal temperatures are very different between the two species, respectively, 45 degrees C and 30 degrees C for D. virilis and D. repleta. alpha-Amylase activity using different substrates is greater on starch than on glycogen in both species and still higher on amylose for D. virilis, the nonfungus feeder species. alpha-Amylase of D. repleta, the mycophagous species, has a better affinity to amylopectin and glycogen. Such differences in substrate specificity suggest adaptation to different resources in these species living in different habitats. Metabolic evolution seems to have occurred through a "tradeoff" between kinetic effectiveness and the nature of substrate, with a higher Vmax on amylose for D. virilis and a lower K(m) on glycogen for D. repleta.

Genetic relationships between the mutations spade and Sternopleural and the wingless gene in Drosophila development

In Drosophila melanogaster, there are cases in which gene products contributing to the same developmental event may derive from closely adjacent transcription units and may even share cis-regulatory sequences. Correct recognition of such genomic organization is central to an understanding of developmental mechanisms. The adult phenotypes of combinations between the mutations spade, Sternopleural, and wingless suggest that they are lesions in functionally related genes within the same chromosomal region. wingless mutations fail to complement the recessive mutation spade. The spade mutation, as previously shown, behaves as a lesion in a regulatory site of wingless, sited 5' to the transcription unit, and is concerned with particular postembryonic functions of wingless. While showing wingless-like phenotypes in combination with Sternopleural, even lethal alleles of wingless complement the recessive lethality of Sternopleural alleles. Mutations in Sternopleural increase the severity of wingless phenotypes in many wingless-dependent processes during postembryonic development, and this interaction can occur when the only functional copies of Sp or wg are located in either opposing chromosomes or the same chromosome. This is inconsistent with previous attempts to define Sp as a regulatory allele of wg and explain the phenotypes that result from combinations of Sp and wg by means of transvection. We have analyzed a new EMS-induced allele of Sternopleural that is more severe than the original allele, which also argues for Sp being a separate, mutable genetic locus rather than a regulatory allele of wg. Finally, we have a revertant of Sternopleural (Sp[Rv1]) that behaves as a genetic null allele of wg, but causes ventral-to-dorsal transformations in combination with wg(P), which is not observed in combinations of wg null alleles with wg(P). Because wg(P) is the result of an inversion and because inversions inhibit transvection, the increased severity observed in Sp(Rv1)/wg(P) in comparison to wg(null)/Sp(Rv1) animals cannot be explained by an absence of transvection. Therefore, the two Sternopleural mutations most reasonably define an independent gene located 3' to the wingless gene and having strong functional synergism with it.