Studies on the sex-specific lethals of Drosophila melanogaster. A third chromosome male-specific lethal mutant

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1 Jpn. J. Genet. (1981) 56, pp SHORT PAPER Studies on the sex-specific lethals of Drosophila melanogaster. III. A third chromosome male-specific lethal mutant BY Satoko UCHIDA, Takahisa UENOYAMA and Kugao OISHI' Department of Biology, Faculty of Science, Kobe University, Nada, Kobe 657 (Received July 21, 1981) ABSTRACT A recessive male-specific lethal mutant of Drosophila melanogaster is described. The mutant, mle (3)13f, which is the first to be described on the third chromosome, is located at Homozygous males show delayed development and die during the larval stages. The mutant shows no interactions with sex-transformation mutants, tra-2, tra-2otj`', tra, or dsx: thus only single-x individuals are killed regardless of the phenotypic sex. Sex-specific lethal mutations in Drosophila melanogaster have received some attention in recent years (Belote and Lucchesi 1980b and the references therein). Results obtained so far reveal several interesting features : (1) Only a few genetic loci are related to or involved in the mechanisms of sex-determination. Thus, for example, sonless (snl) kills normal males almost completely and also kills Xf X ; tra/tra transformed "males" to some extent (Colaianne and Bell 1972). A male-specific lethal mutant, Sx1M#1, has a sex-transforming effect (Cline 1979). The majority of sex-specific lethals, however, shows no such effects. (2) A few are female-specific but the majority are male-specific in their actions. (3) Several male-specific lethals on the second chromosome and a single female-specific lethal on the X have all proven to have profound effects on the expression of X-linked genes such that dosage compensation is not seen (Belote and Lucchesi 1980a; Lucchesi and Skripsky 1981). These latter lethals may provide a means to dissect the regulatory mechanisms of dosage compensation. Obviously the recovery of more sex-specific lethals would be beneficial. Although numbers of sex-specific lethals have been reported on the X and the second chromosome [in the case of second chromosome the number appears to be approaching saturation as alleles of some loci are repeatedly obtained (Belote and Lucchesi 1980b; Uenoyama, Uchida and Oishi in preparation) ], no 1) To whom correspondence should be addressed.

2 524 S. UCHIDA, T. UENOYAMA and K. OIsHI Table 1. Results of crosses for mapping mle (3)132. Total of 197 extracted chromosome/ TM3 F1 progeny from the cross, mwh red e1132>< Pr/TM3, were individually mated to Pr! TM3, and each extracted chromosome was made homozygous in F3 by crossing F2 extracted chromosome if TM3 females and males such lethals have been reported on the third and fourth chromosome. Belote and Lucchesi (1980b) reported that they failed to recover any sex-specific lethals from more than 6,000 EMS-treated third chromosomes while obtaining four from about 7,000 second chromosomes similarly treated. Here, we wish to describe a recessive male-specific lethal mutant on the third chromosome. A third chromosome (named X132) extracted from a natural population of Drosophila melanogaster at Katsunuma, Yamanashi Prefecture, was found to be male-specific lethal when homozygous. When female parents were homozygous, both female and male homozygous progeny flies were killed. The stock was kindly given to us by its discoverer, Dr. T. K. Watanabe of the National Institute of Genetics, Mishima. Heterozygous females of the genotype mwh red e/132 were crossed with Pr/ TM3 (Sb Ser) males: TM3 is a balanced lethal chromosome marked with two dominant genes. For mutants mentioned without reference, see Lindsley and Grell One hundred and ninety-seven F1 progeny were taken, extracted chromosome 1-197/ TM3, and crossed individually to Pr! TM3. Extracted chromosomes i/ TM3 females and males in the F2 were crossed and each was made homozygous in the F3. Table 1 shows the results with respect to the male-specific lethal mutant, mle(3) 132, which is calculated to be between mwh (3-0.0) and red (3-53.6) at The maternal lethal effect of X132 noted above was separated from the male-specific lethal (non-maternal) erect. In each of the 197 lines, homozygous F3 females were crossed with heterozygous male sibs and the progeny examined. Results (not presented) showed that the maternal effect lethal, l(3) l32mat, was located between red and e (3-70.7). No

3 Sex-specific lethal of Drosophila 525 Table 2. Viability at various developmental stages in progenies of two kinds of crosses * See text for details. further pursuit was attempted. Using a recombinant chromosome thus obtained, mle(3) 132 red, two crosses were made. When homozygous females were crossed with heterozygous (over TM3) males, F1 progeny were consisted of 455 heterozygous females, 441 heterozygous males, 430 homozygous females, and 0 homozygous males. When mothers were heterozygous (over TM3), the progeny were 495, 474, 229, and 0 in the above order. The gene, mle(3) 132, is lethal specifically for males. Using the recombinant chromosome, we next examined the lethal stage. Homozygous (cross 1) and heterozygous (over TM3, cross 2) females were crossed with heterozygous males, and flies were transferred to fresh culture bottles every 6 hours. Numbers of eggs laid were counted and the development of these eggs followed (Table 2). Third instar larvae (at about 100 hours following the egg collection) were examined to see whether they were females or males (on the basis of gonad size) and whether they were homozygous or heterozygous mle(3) 132 (on the basis of the red color of Malpighian tubules). Heterozygous females and males as well as homozygous females showed normal development and appeared at expected ratios. Homozygous males at this stage, however, were found to be much smaller in size and in cross 1 in reduced number. Most of these males (more transparent in appearance than the normal larvae) were found to be second instar larvae and some in crass 1 to be even first instar, on the basis of their mouth-hook morphology (Bodenstein 1965). Many died as second instar larvae around the time other genotypes pupariated. Some larvae, however, did manage to survive through this

4 526 S. UCHIDA, T. UENOYAMA and K. OISHI Table 3. Numbers of various genotypes in Fl progeny of a cross: X/X; tra-2/sm1; mle (3)132 red/tm6 x X/B8 Y; tra-2/sm1; mle (3)132 red/ TM6 * Disregarding the interactions between mle(3)132 and tra-2. stage becoming third instar ; these kept growing and eventually were the size of normal late third instar larvae. They lived for as long as 17 days, but none pupariated. Some of these observations are based on separate experiments as larvae were sacrificed to examine the mouth-hook morphology. Whether the lethality of mle (3)132 exerts its effect on the sexual phenotype was examined by using sex-transformation mutants, tra-2 (Watanabe 1975) and its allele tra-2orf (Fujihara et al. 1978), tra (Sturtevant 1945), and dsx (Hildreth 1965). As tra and dsx are both on the third chromosome, they were incorporated into the chromosome carrying mle(3) 132 by recombination, respectively. No interactions were observed : Homozygous mle (3)132 tra and mle (3)132 dsx died only when they were single-x individuals regardless of the phenotypic sex (data not shown). The genes tra-2 and tra-2otf were combined with mle (3)132 red by using SM1 (a balanced lethal second chromosome) and TM6 (a balanced lethal third chromosome). The results for tra-2 are shown in Table 3. Chromosomal females transformed into phenotypic males were not killed when homozygous for mle(3)132 and appeared at an expected ratio. However, a few homozygous mle (3)132 chromosomal males, both heterozygous and homozygous for tra-2, did also appear in this cross. Essentially the same results were obtained with tra-2otf (data not shown). Crosses were repeated with tra-2 as well as with tra'2otf, and such survivors were always produced. We had never observed such survivors in the original stocks, recombinant stocks, and in stocks also homozygous for tra or dsx, as long as these stocks were maintained over TM3. The reason for the appearance of these homozygous males requires further investigation. Finally mle(3) 132 was combined with a second chromosome male-specific lethal, mle (2) 27 (an allele of msl -2 of Belote and Lucchesi 1980b; Uenoyama, Uchida and Oishi in preparation). No interactions were observed : Double

5 Sex-specific lethal of Drosophila 527 heterozygous males appeared at an expected ratio, and males homozygous either for mle (2) 2T or mle (3)132, as well as those double homozygotes did not appear. Thus it appears that the third chromosome male-specific lethal mutant, mle (3)132, is very similar in its action to those already reported on the second chromosome. Whether the mutant has any effect on dosage compensation remains to be seen. Attempts are now being made to recover more sex-specific lethals on the third chromosome. We thank Dr. T. K. Watanabe for the original stock and for discussion. We also thank Dr. M. Yamamoto, National Institute of Genetics and Dr. D. Kankel, Yale University for reading the manuscript. REFERENCES BELOTE, J. M. and LUCCHESI, J. C. (1980a) Control of X chromosome transcription by the maleless gene in Drosophila. Nature 285, BELOTE, J. M, and LUCCHESI, J. C. (1980b) Male specific lethal mutations of Drosophila melanogaster. Genetics 94, BODENSTEIN, D. (1965) The postembryonic development of Drosophila. In Biology of Drosophila (ed. M. Demerec), pp Hafner Publishing Company, New York and London. CLINE, T. W. (1979) A male-specific lethal mutation in Drosophila melanogaster that transforms sex. Develop. Biol. 72, COLAIANNE, J. J. and BELL, A. E. (1972) The relative influence of sex of progeny on the lethal expression of the sonless gene in Drosophila melanogaster. Genetics 72, FUJIHARA, T., KAWABE, M. and OISHI, K. (1978) A sex-transformation gene in Drosophila melanogaster. J. Heredity 69, HILDRETH, P. E. (1965) Doublesex, a recessive gene that transforms both males and females of Drosophila melanogaster. Genetics 51, LINDSLEY, D. L. and GRELL, E. H. (1968) Genetic variations of Drosophila melanogaster. Carnegie Inst, of Washington, Publ. No LUCCHESI, J. C, and SKRIPSKY, T. (1981) The link between dosage compensation and sex differentiation in Drosophila melanogaster. Chromosoma 82, STURTEVANT, A. H. (1945) A gene in Drosophila melanogaster that transforms females into males. Genetics 30, WATANABE, T. K. (1975) A new sex-transforming gene on the second chromosome of Drosophila melanogaster. Jpn. J. Genet. 50,