An atypical net^Ch86 allele isolated from a natural population of Drosophila melanogaster.

 

Weisman, N.Ya., and I.K. Zakharov.  Institute of Cytology and Genetics of Siberian Branch of the Russian Academy of Sciences, Novosibirsk, 630090, Russia; e-mail: weisman@bionet.nsc.ru

      The Drosophila wing is divided into several cells by longitudinal veins and crossveins. A number of genes are involved in the formation of normal vein patterns. The net (net, 2-0.0) gene of Drosophila melanogaster is one of the key players in the process of vein development. The known spontaneous and induced net gene mutations cause disruption of vein patterns in all but the first posterior wing cell. A variegated expression of mutant phenotype is observed in different net alleles. Almost all of the known net mutations are recessive to the wild type allele (Lindsley and Zimm, 1992).

      In our previous work, a number of net mutations differing in expression from the known net alleles have been found in natural populations of D. melanogaster (Weisman et al., 2001). An atypical net^Ch86 allele (Figure 1c) was isolated from a D. melanogaster line obtained from the Chernobyl population (Ukraine) in 1986. The net^Ch86 mutants demonstrate a lesser extent of vein disruptions than the flies homozygous for standard net^2-45 allele (Figure 1b). Segments of extra veins develop in marginal, submarginal, second and third posterior wing cells in net^Ch86 flies.  In contrast to previously described net mutations, up to 10% of net^Ch86 flies carry an extr

a vein in the distal part of the first posterior cells (sector C).

A	B	C
Figure 1. Wing vein patterns in Drosophila melanogaster: wild-type wing (A), phenotypic expression of net2-45 (B), and netCh86 (C) alleles.

 

      The net^Ch86 mutation is semi-dominant to the wild type net⁺ allele. In the progeny of crosses of net^Ch86 line with Oregon and Canton-S laboratory stocks, up to 20-30% of hybrid flies develop small extra veins in the second and third posterior cells.

Genetic analysis was carried out with the use of the following mutant D. melanogaster lines from the collection of the Laboratory of Genetics of Populations, Institute of Cytology and Genetics, Siberian Branch of the Russian Academy of Sciences:

       1.  Line homozygous for standard net^2-45 allele causing multiple wing vein disruptions;

       2.  Line Df(2)net⁶²/Cy carrying the deficiency for the net locus.

      In net^2-45/ net^Ch86 heterozygotes, the vein disruptions are similar to those of net^Ch86 homozygotes and less expressed than those of net^2-45 homozygotes. Up to 7% of heterozygotes carry an extra vein in the distal part of the first posterior wing cell. Thus, the allele net^Ch86 with a less expressed vein disruption as compared to the standard mutant allele net^2-45 is dominant to the latter. However, the net^Ch86 / Df(2)net⁶² heterozygotes develop severe vein disruptions in the form of nets and segments of veins including the extra vein in the first posterior sector.

      As previously mentioned, the net mutations with an extra vein in the first posterior cell are very rare. Among 2720 flies and 250 isofemale lines derived from D. melanogaster populations from the two regions of Russia – Altai (populations Askat and Belokurikha) and Udmurtia (populations Izhevsk, Karambai, and Pychas) - in the year 2000 as well as among 1398 flies and 200 isofemale lines from populations Pychas (Udmurtia), Bishkek (Kyrgizstan), Zvenigorodka (Cherkassy region, Ukraine), and Vladivostok (Russia) collected in the year 2001, no net mutations with an extra vein in the first posterior cell has been found (Weisman et al., 2001b).

      Some other genes involved in the development of wing cells and suppressing the vein development are expressed in the wing disk, such as blistered (bs), knot (kn), plexus (px) (Fristrom et al., 1994;  Lindsley and Zimm, 1992;  Mohler et al., 2000). Supposedly, the activity of these genes in different sectors of the wing may overlap. The differences in expression of natural net alleles can be, possibly, due to the different molecular lesions of net gene. Interactions of these net alleles with the modifiers of net and other genes involved in the wing pattern formation can locally divert the imaginal disk cells from normal differentiation pathway to the development into the vein cells.

      Acknowledgments:  The authors are grateful to S.V. Tcheressiz for English translation of the manuscript and to V.A. Prasolov for the photography.  The work is partially supported by the Russian Foundation for Basic Research (No. 02-04-49251).

      References:  Fristrom, D., P. Gotwals, S. Eaton, T.B. Kornberg, M. Sturtevant, E. Bier, and J.W. Fristrom 1994, Development 120: 2661;  Lindsley, D.L., and G.G. Zimm 1992, The Genome of Drosophila melanogaster. San Diego, CA, Academic Press Inc.;  Mohler et al., 2000, Development 127: 55;  Weisman, N.J., I.D. Erokhina, and I.K. Zakharov 2001a, Dros. Inf. Serv. 84: 117;  Weisman, N.Ya., I.D. Erokhina, and I.K. Zakharov 2001b, Dros. Inf. Serv. 84: 82.