A MATERNAL-EFFECT SEX-TRANSFORMATION MUTANT OF THE HOUSEFLY, MUSCA DOMESTICA L. ABSTRACT

Transcription

1 Copyright by th Gntics Socity of Amrica A MATERNAL-EFFECT SEX-TRANSFORMATION MUTANT OF THE HOUSEFLY, MUSCA DOMESTICA L. HIROAKI INOUE AND TOSHIKI HIROYOSHI Dpartmnt of Gntics, Osaka Univrsity Mdical School, 3-57 Nakanoshima 4-chom, Kita-ku, Osaka 530, Japan Manuscript rcivd April 24, 1985 Rvisd copy accptd Octobr 24, 1985 ABSTRACT A matrnal-ffct sx-transformation mutant, transformr (tra), of th housfly is dscribd. It is locatd on autosom 4 in clos linkag with th Ba locus. Normally, th sx of Musca domstica is dtrmind by th prsnc or absnc of an pistatic factor, M. Whn producd by traltra mothrs, a larg fraction of th traltra gnotypic fmal progny carrying no M factors ar transformd to dvlop into intrsxs or frtil phnotypic mals. Th &a/+ progny ar also transformd, but lss frquntly. Aging of th mothrs incrass th frquncy of sx-transformd flis. Whn producd by tra/+ mothrs, traltra progny (but not +/&a) occasionally undrgo sx transformation. Thus, tra+ is activ both matrnally and zygotically. Gnotypic mals carrying th M factor ar not affctd by th tra mutant. It is concludd that th tra+ gn product is rquird for fmal dtrmination and/or diffrntiation. A modl is proposd to xplain actions of all th known sx-dtrmination gns in M. domstica, and it is discussd in rlation to sx-dtrmination mchanisms in svral othr insct spcis. EX dtrmination involvs a sris of intgratd dvlopmntal vnts S which dirct individual ggs to choos btwn altrnativ pathways of sxual diffrntiation. In many bisxual spcis, sx is dtrmind ithr by th chromosom constitution or by th action of a singl gn. Th formr mchanism includs th balanc systm rportd in Drosophila (BRIDGES 1925) and in th nmatod Canorhabditis lgans (MADL and HERMAN 1979), as wll as th diplohaploidy systm rportd in many Hymnoptran spcis (rviwd by ROTHENBUHLER 1975; CASSIDY 1975). Th lattr mchanism, trmd homohtrozygosity or pistatic systm, has provd to b applicabl to most spcis of Lpidoptra (.g., TAZIMA 1964; CASPARI and GOTTLIEB 1975) and many spcis of Diptra (ENGELMANN 1970), as wll as to svral vrtbrats including mammals (OHNO 1979). In numrous spcis, singl gn mutations hav bn discovrd which caus partial or complt transformation of sxual phnotyps. In Drosophila mlanogastr, such sx-transformation mutants fall into at last six loci, Sxl, tra, tra-2, ix, dsx and hr (rviwd by BAKER and BELOTE 1983). Similar mutants, tra-i, tra-2, tra-3, fm-1 (=isx-i), fm-2, fm-3 and hr-1, hav also bn dscribd in C. lgans (HODGKIN and BRENNER Gntics 112: March, 1986

2 470 H. INOUE AND T. HIROYOSHI 1977; NELSON, LEW and WARD 1978; HODGKIN 1980, 1985). In th mammalian systm, P in goats causs X /X PIP gnotypic fmals to dvlop into intrsxs (HAMERTON t al. 1969), and Tfm in mic causs somatic clls of XY qnotypic mals to undrgo fmal sxual diffrntiation (LYON and HAWKES 1970). Ths sx-transformation mutants hav bn usd to lucidat th gntic control of sx dtrmination and/or diffrntiation. In th housfly, Musca domstica L., svral diffrnt systms of sx dtrmination hav bn rportd. In th standard strains, flis hav fiv pairs of autosoms and a pair of htrochromatic sx chromosoms, XX in th fmal and XY in th mal (STEVENS 1908; PERJE 1948). Th sx is dtrmind by th prsnc or absnc of th Y chromosom, which carris an pistatic maldtrmining factor, im, whras th X chromosom plays no important rol in sx dtrmination (HIROYOSHI 1964; RUBINI and PALENZONA 1967). In som laboratory and natural strains, howvr, both fmals and mals hav th XX chromosom complmnt, and th prsnc or absnc of a spcial autosom that carris an autosomal mal-dtrmining factor, AM, dtrmins sx (AM systm). Th occurrnc of A" chromosoms hav so far bn dmonstratd in at last four linkag groups (SULLIVAN 1958; WAGONER 1969; HIROYOSHI and INOUE 1979), and th locations of AM factors hav rcntly bn dtrmind (INOUE, FUKUMORI and HIROYOSHI 1983; INOUE and HIROYOSHI 1984). Th Y chromosomal and th autosomal M factors can b rgardd as a polymorphism. Thrfor, th prsnc or absnc of th M factor appars to b th primary signal for sx dtrmination in ths mal-htrogamtic strains. Furthrmor, in som othr strains, both fmals and mals hav th M factor(s) in th homozygous stat, and th prsnc or absnc of a hologynically inhritd fmal-dtrmining factor, F, dtrmins sx (fmal-htrogamtic or F systm) (RUBINI 1967; WAGONER 1969; MCDONALD t al. 1978; INOUE and HIROYOSHI 1982). Bsids ths sx factors, a dominant matrnal-ffct mutant, Arrhnognous (Ag), found in a laboratory strain, causs th gnotypic fmal progny carrying nithr M nor F to dvlop into frtil phnotypic mals (VANOSSI-ESTE 197 I ; VANOSSI-ESTE and ROVATI 1982). Th us of ths phnotypic mals allowd th stablishmnt of a uniqu strain in which th sx is dtrmind undr th control of matrnal gnotyp (sx prdtrmination systm). Coxistnc of multipl sx-dtrmining systms within a spcis is of particular intrst, bcaus it may b an volutionary link btwn a varity of sx-dtrmining systms found in rlatd spcis. Th dominant gns, M, F and Ag, ar valuabl bcaus thy may shd light on th mchanism of sx dtrmination in M. domstica. Matrnal-ffct mutations idntify gns in which wild-typ products ar synthsizd during oognsis and ar utilizd by th dvloping zygot. Thy hav bn usd as valuabl tools for lucidating how and whn thir wild-typ gn products rgulat th xprssion of zygotic gns in dvlopmnt. In spit of th abundanc of matrnal-ffct mutations so far idntifid in a varity of spcis, only a fw xampls ar known which caus th altration of sxual phnotyps. In C. lgans, a matrnal-ffct mutant, tra-3, causs th gnotypic hrmaphrodit progny to dvlop into stril phnotypic mals

3 HOUSEFLY SEX DETERMINATION 47 1 (HODGKIN and BRENNER 1977). Dominant matrnal-ffct gns, fmal sxralizr (F') in th monognic blowfly, Chrysomya rujfacis (ULLERICH 1973, 1980) and Ag in M. domstica (VANOSSI-ESTE 1971), ar of particular intrst bcaus thy produc frtil sx-transformd progny. W dscrib hr a nw matrnal-ffct sx-transformation mutant of M. domstica. Th mutant, transformr (tra), is similar to Ag in its action, but it is a rcssiv mutant on autosom 4. A possibl rol of th wild-typ gn product of th tra locus is discussd in rlation to othr sx-dtrmining gns. MATERIALS AND METHODS Th mutant to b dscribd was first notd as an occasional apparanc of "sonlss" FUKUMORI mals in a laboratory IIIM strain, + bwb g +/Bx2 + + M (Nagai) (HIROYOSHI, and INOUE 1982). Bcaus rcombination usually dos not tak plac in mals of th housfly, th Bx2 + + M chromosom carrying th sol M factor in this strain should b inhritd holandrically, sgrgating bwb g fmals and Bx' mals in vry gnration. Howvr, various typs of rcombinant flis which rsultd from xcptional mal crossing ovr wr occasionally rcovrd from this strain. Morovr, bwb g mals wr also rcovrd at a frquncy of 0.22% (40 of 18,300). Ths flis, surprisingly, producd no mal progny whn outcrossd to fmals from th convntional XX-XY strain and, thus, wr dnotd sonlss. Whn individually matd with th bwb g sib fmals, all but on of ths bwb g mals producd only a fw, if any, mal progny. This xcptional mal producd 16% (54 of 339) mals in th F,, and th subsqunt sibmatings using ths F1 flis producd approximatly 10-30% mals and 5-10% intrsxs in latr gnrations. Th bwb g mal progny still showd th sonlss charactr in th outcross matings. Most likly th sonlss mals wr phnotypic mals carrying no M factor, which rsultd from a fmal-to-mal sx transformation. This uniqu strain, usd in th prsnt study, was namd Sonlss-81 (Snl'l). Examinations of xtrnal morphology of flis wr don with a disscting microscop. Extrnal morphology of trminal sgmnts including th fifth strnit, gnitalia and analia was usd for sxing, bcaus distinct sxual dimorphisms ar sn in ths sgmnts. Flis wr classifid as fmals or mals if thy had normally dvlopd trminalia charactristic to ach sx, or as intrsxs if thir trminalia consistd of both fmal and mal parts. Trminology of trminal sgmnts was basd on th nomnclatur dscribd by WEST (195 1). All photographs wr takn undr a disscting microscop quippd with a ring-shapd flash lamp. Gntic markrs usd wr R1 (Rolld wings, autosom l), Mk (Mashd ys, 2), Bx2 (an alll of Bx, Badx wings, 3; hraftr dnotd simply as Bx), bwb (brown body, 3), g (grn ys, 3), Ba (Bald abdomn, 4) and Lp (Loop wing vins, 5). Dtaild dscriptions of ths markrs and thir linkag rlationships ar givn by HIROYOSHI (1977). Flis wr rard at 25 k 1" undr uncrowdd conditions, according to th mthod dscribd by HIROYOSHI (1977), unlss othrwis notd. RESULTS Inhritanc of th sx-transformation gn, tru: As dscribd abov, mals of th Snl" strain nvr producd mal progny whn outcrossd to fmals from th convntional XX-XY strains, although thy producd approximatly 10-30% mals and 5-10% intrsxs in th intrastrain matings. To xamin what sx ratios th Snl" fmals produc, 15 bwb glbwb g fmals from th SnZH' strain wr matd with + bwb +/Bx + M mals from a laboratory IIIM strain, bwb/bx M (Nagai) (hraftr dnotd tstr), and thn ggs laid by individual fmals wr collctd at 3-day intrvals for 9 days. As a control,

4 ~ ~~ 472 H. INOUE AND T. HIROYOSHI TABLE 1 Sgrgations from individual crosss btwn + bwb g +/+ bwb g + fmals from th Snl'" strain and + bwb + +/Bx + + M mals from th tstr strain Bw+ bwb Bx bwb' TR Fmals Crosa (no.) P f 6 " P o p s BrBx+ (a)b Typ I Typ a Phnotypic mals carrying no M factor. * TR(%) rprsnts a prcntag of sx-transformd flis (intrsxs and phnotypic mals) in th Bx+ bwh gnotypic fmal progny. 23 bwblbwb fmals takn from th tstr strain wr similarly xamind. Th advantag of using tstr mals instad of th convntional XY mals is that th mal-dtrmining factor, M, of th tstr mals is markd with a dominant mutation, Bx, so that w can asily distinguish th gnotypic fmal and mal progny. From ths crosss, thrfor, Bx+ bwb flis would b rcovrd as fmals, whras Bx bwb+ flis ar rcovrd as mals. Th control fmals all producd bwb fmals and Bx mals, as xpctd. In contrast, two typs of sgrgation data wr obtaind from th SnP' fmals (Tabl 1). Svn fmals (typ 1) producd bwb fmals and Bx mals, as xpctd, whras th rmaining 8 fmals (typ 2) producd not only th xpctd bwb fmals and Bx mals but also bwb mals and som bwb intrsxs. Th ratio of th numbr of Bx gnotypic mals to th numbr of Bx+ gnotypic fmals was similar btwn typ 1 fmals and typ 2 fmals ( us ). Apart from th ffct of Bx mutant on viability, thr was no slctiv dath with rspct to on gnotypic sx whn comparing typ 1 and typ 2 fmals. Th bwb mals producd by th typ 2 fmals provd to b sonlss in subsqunt outcross matings. Ths combind rsults suggst that som of th gnotypic fmal progny producd by th typ 2 fmals did not dvlop into fmals but wr transformd into intrsxs or phnotypic mals. It is probabl that this sx transformation is causd by a matrnal-ffct mutant carrid by th Snl" fmals, and hraftr, w rfr to transformation rat [TR(%)] to xprss th proportion of gnotypic fmal progny of an individual fmal which undrgo sx transformation.

5 HOUSEFLY SEX DETERMINATION 473 Inhritanc of this hypothtical sx-transformation gn was xamind as follows. First, bwblbwb fmals takn from th tstr strain wr matd with bwb glbwb g mals from th Snl" strain. Som of th F1 fmals wr backcrossd to bwb glbwb g mals from th Snl" strain and wr individually allowd to lay ggs in ordr to dtrmin whthr thy producd sx-transformd progny. Thr of th 11 F1 fmals producd sx-transformd progny, but at xtrmly low frquncis, % (s blow, Zygotic xprssion of th tra locus). Scond, th rmaining F1 fmals wr matd with th tstr mals, + bwb +/Bx + M, and wr individually allowd to lay ggs in ordr to chck whthr thy producd sx-transformd flis. Non of th F1 fmals (0 of 23) producd sx-transformd progny, Third, th F2 fmals obtaind from th backcross wr matd with th tstr mals, and thir offspring wr similarly xamind. Som of th FP fmals (10 of 29) did produc sx-transformd flis at frquncis ranging from 18.5 to 98.7%. It is concludd that th sx transformation is causd by a rcssiv matrnal-ffct mutant, hr namd transformr (tra), th ffct of which is xtrmly variabl, causing gnotypic fmal progny to dvlop into normal fmals, intrsxs or compltly transformd frtil mals. Linkag analysis of tru: Th linkag group of tra was dtrmind by using fiv dominant mutations, RE (autosom l), Mlz (2), Bx (3), Ba (4) and Lp (5). For this purpos, it is ncssary to us traltra fmals. Th following matings wr mad to idntify such fmals. In,a linkag tst for autosom 1, for strain wr xampl, +/+; + bwb g +/+ bwb g + fmals from th Snl" matd with +/R1; + bwb + +/Bx + + M mals. Th progny +/RI; + bwb g +/+ bwb + + phnotypic mals must b tra/+, bcaus such flis ar rcovrd only from traltra mothrs. Ths mals wr backcrossd to fmals from th Snl" strain. Ths fmals wr individually allowd to lay ggs and wr chckd to s if thy producd both fmal and mal progny, or only fmal progny. In th F2, fmals wr takn from culturs in which many mal sibs wr simultanously rcovrd, nsuring that thir mothr was traltra. Ths fmals, RI' or R1, wr matd with + bwb +/Bx + M mals and wr individually allowd to lay ggs in ordr to chck whthr thy producd sx-transformd flis. If tra is locatd on autosom 1, th F2 fmals, R1+ and R1, obtaind from this schm should hav th traltra and tra/re chromosoms, rspctivly. Similar procdurs wr usd in othr linkag tsts, xcpt that in th linkag tst for autosom 3, + +/MK M(IIM); +/Bx mals wr usd instad of th +/R1; + bwb +/Bx + M(III') mals. Rsults, givn in Tabl 2, clarly dmonstrat that tra is locatd on autosom 4. Nxt, w carrid out xprimnts to dtrmin th map distanc btwn Ba and tra. For this purpos, w stablishd a nw strain, Snls2, in which tra is homozygously fixd. This was accomplishd by crossing + tra/+ tra fmals and + tra/ba + phnotypic mals obtaind from th linkag xprimnts dscribd abov. Thn, + tra/+ tra phnotypic mals takn from th Snls2 strain wr matd with Ba +/+ tra fmals, and th rsulting Ba +/+ tra fmals backcrossd to th + tra/+ tra mals. Th FP fmals, Ba+ or Ba, wr matd with tstr mals and wr individually allowd to lay ggs to chck whthr

6 ~ 474 H. INOUE AND T. HIROYOSHI TABLE 2 Linkag analyss of tra: FL fmals carrying a Sn1" strain-drivd chromosom(s), dsignatd tru, in ithr htrozygous or homozygous stat wr matd with tstr mals to chck whthr thy produc sx-transformd flis No. of F2 fmals No. of FP fmals Prsumptiv that producd that producd no I.in!ag gnotyp of sx-transformd sx-transfoi-md group Fs fmals flis flis J tralr traltra 8 8 I1 tra/mk 3 4 traltra 3 7 I11 tralbx 8 2 I v traltra 6 7 tralba 0 19 v traltra 20 0 trallp 5 8 tra/tra 9 11 For mating procdurs, s txt. TABLE 3 Zygotic ffct of tra Phnotyp (:l-os\ (0 x 6) of progny P : 1+6 TR(%Y 1 traltra X tralba ' 38 Bd : 25 2 Raltra X traltra : Ba : 0 0 * TR(%) rprsnts th frquncy of sx-transformd flis. * Significant at th 5% lvl (x2 = 5 882). thy producd sx-transformd flis. Of th 227 Ea' * and 205 Ba fmals xamind, only on rcombinant Ba fmal which producd sx-transformd progny was idntifid. Th rcombination frquncy btwn Ba and tra is thus -0.2%. Zygotic xprssion of th tru locus: Th zygotic ffct of tra was xamind by using + tra/ba + and + tra/+ tra phnotypic mals (Tabl 3). In ths crosss, only fmal progny would b xpctd to appar unlss sx-transformation taks plac. Whn producd by + tra/+ tra mothrs (cross l), + tra/ + tra progny wr sx transformd much mor frquntly than + tra/ba + (26.6% us. 15.3%, x2 = 5.822, P C 0.05), dmonstrating th partial rscu of tra matrnal ffct by th tra+ sprm. Whn producd by Ba +/+ tra mothrs (cross 2), sx transformation took plac, but only in + tra/+ tra progny and at an xtrmly low frquncy. Ths rsults dmonstrat that th tra locus is xprssd not only during oognsis but also zygotically. Effct of fmal ag on xprssivity of tru: In all of th xprimnts

7 TR (%I HOUSEFLY SEX DETERMINATION ,11 12,13 Fmal ag (Day) FIGURE 1.-Effct of aging on xprssivity of tra matrnal ffct. Frquncis of sx-transformd flis [TR(%)] in daily broods of individual bwb glbwb g; traltra fmals wr xamind bp mating with th tstr mals. A closd circl rprsnts TR(%) of ach fmal, and an opn circl rprsnts that of th poold progny. dscribd abov, th frquncy of sx-transformd progny from traltra fmals was always lowr in th first 3-day brood as compard with thos rcovrd from th latr broods, suggsting that th matrnal ag affcts th xprssion of th mutant. To confirm this fact, th frquncy of sx-transformd flis was xamind by daily collction of ggs producd by ach of 14 traltra fmals, although thy did not lay ggs vry day. Du to a lowrd fcundity in agd fmals, ggs laid by th 10- to 13-day-old fmals wr poold for vry 2 days. Rsults ar shown in Figur 1. All fmals producd th first gg masss on th fifth day aftr mrgnc. Among thm only two producd sx-transformd flis. Th ovrall frquncy of sx-transformd flis in th poold progny of th 6-day-old mothrs was still lowr than th frquncy of thos producd by th sam mothrs during 7 to 13 days (17.7% vos %). Ths rsults suggst that th xprssion of tra is wak whn th carrir fmals ar young. Extrnal morphology of tra-transformd flis: Th xprssion of th ma-

8 476 H. INOUE AND T. HIROYOSHI FIGURE 2.-Vntral viws of fmal (a), intrsx (b, c, d) and mal () phnotyps of gnotypic fmal progny producd by a singl traltra fmal. Th gnotyp of ths flis was fro/+. Abbrviations: pf, primary forcps on th fifth strnit; c, crci. S txt for xplanations. trnal sx-transforming ffct of tru is xtrmly variabl in that nontransformd frtil fmals, intrsxs and phnotypic frtil mals ar usually rcovrd from th sam trultru mothr. In th tstr strain, th had-frons (th width of had/th width of frons) ratio in th fmals is 3.2 f 0.1 (man +- SE, N = 20) and that of th mal is (N = 26). Similar valus ar obsrvd in th Snl" strain; i.., 3.2 f 0.1 (N = 21) for th nontransformd fmals and (N = 15) for th sx-transformd phnotypic mals. Sx-transformd phnotypic mals also rsmbld gnotypic mals in othr quantitativ charactrs, such as body siz, body pigmntation and bristl lngth. Intrsxs showd a sris of intrmdiat phnotyps in ths charactrs. Rmarkabl sxual dimorphisms ar sn in th trminalia, including both gnitalia and analia. Figur 2 shows vntral viws of abdomns of a nontransformd fmal, intrsxs and a sx-transformd phnotypic mal. No morphological diffrncs ar obsrvd ithr btwn nontransformd fmals and normal XX fmals or btwn phnotypic mals and normal XY mals. Th nontransformd fmal (Figur 2a) has long bristls on th nonsclrotizd fifth strnit. Th sgmnts 6-11 form a mmbranous ovipositor with nonsclrotizd trgits and strnits dnominatd dorsal and vntral chitinous rods, rspctivly. Ths sgmnts ar usually intrudd into th body cavity,

9 HOUSEFLY SEX DETERMINATION 477 and only a pair of button-shapd crci, appndags of th sgmnt 11, can b sn. Th phnotypic mal (Figur 2) has short bristls on th fifth strnit, which bars a pair of havily sclrotizd primary forcps. Th sgmnts 6-8 ar sclrotizd to form mal-typ gnitalia. Intrsxs show a sris of intrmdiat sxual phnotyps. Thr xampls ar shown hr. A fmal-lik intrsx (Figur 2b) has th fifth strnit which bars only a right half of primary forcps. Th sgmnts 6 and 7 form a fmal-typ mmbranous ovipositor, but th sgmnt 8 is partially sclrotizd to form a rudimntary mal-typ gnitalia. Th trminal sgmnt bars no crci. An intrmdiattyp intrsx (Figur 2c) has narly complt fmal-typ fifth strnit, xcpt for a pigmntd patch in th lft rgion. Th sgmnt 6 is mmbranous, but th sgmnts 7 and 8 ar havily sclrotizd to form mal-typ gnitalia. A mal-lik intrsx (Figur 2d) has th partially sclrotizd fifth strnit. Th sgmnts 6 to 8 form mal-typ gnitalia, although th rotation of ths sgmnts is incomplt. DISCUSSION Th tra mutant is a rcssiv matrnal-ffct mutant that causs th gnotypic fmal progny carrying no M factors to follow th mal pathway of sxual diffrntiation to varying dgrs. Th mutant is locatd on autosom 4 nar th Ba locus. Th xprssivity of tra is not complt, and th phnotyps of th gnotypic fmal progny rang from th normal fmal, through various dgrs of intrsxuality, to th compltly transformd frtil mal. Th mutant also has a zygotic ffct, such that th gnotypic fmal progny producd by traltra mothrs ar transformd much mor frquntly whn thy ar traltra than whn thy ar tra/+. Morovr, th traltra progny of +lira mothrs can undrgo sx transformation, although at vry low frquncis. A similar mutant, Arrhnognous (Ag), has bn idntifid on autosom 1 (VANOSSI-ESTE 1971 ; VANOSSI-ESTE and ROVATI 1982). Th prsnt rsults suggst that (1) th tra+ gn product is ncssary for fmal dtrmination and/or diffrntiation and that (2) th tra locus is xprssd during oognsis and also in zygots. It is notd also that th tra ffct is mor pronouncd in agd mothrs (Figur 1). A similar aging ffct has bn rportd for Ag (VANOSSI-ESTE and ROVATI 1982). This suggsts that changs in th physiological condition of mothrs, th activity of th rproductiv systm for xampl, may affct th xprssivity of ths matrnal-ffct mutations. Production and/or storag of th tra+ gn product may not procd constantly but, rathr, in a sporadic mannr in tim and spac, so that individual ggs may rciv various amounts of th product. Th fact that intrsxs with a mal had and a fmal gnitalia, or vic vrsa, occasionally wr obsrvd suggsts that th tra+ product may not always b distributd vnly in th gg cytoplasm. It is known that sx in M. domstica is dtrmind in a cll autonomous mannr (MILANI 1975). Th xprssivity of tra is not affctd by tmpratur, bcaus th frquncy of sx-transformd flis is similar at thr diffrnt tmpraturs, 17, 25 and 31 O (data not shown). It has bn said that Musca and Drosophila, although thy ar both Diptr-

10 478 H. INOUE AND T. HIROYOSHI Matrnal sx-dtrmining gns f ZYgOll. -" tra', Ag I Zygotic sx-dtrmining gns I Gn products stord in - gg cytoplasm F * gn i. OFF M gn I M product 0 turn5 off F gn c=l_ (constitutiv mutant) FIGURE 3.-A 4 i? a modl for th control of sx dtrmination in Musca domstica. I? ans, hav compltly diffrnt sx-dtrmination mchanisms: th pistatic systm in th formr and th balanc systm in th lattr (ENGELMANN 1970). W should lik to mphasiz, howvr, that thy may, in fact, shar a common gntic systm for th control of sx dtrmination. In M. domstica, th prsnc or absnc of th M factor instructs th mal or fmal pathway, rspctivly, of sxual diffrntiation. Sinc matrnal-ffct mutants, Ag (VANOSSI- ESTE 1971) and tra (this study), ar abl to produc frtil phnotypic mals carrying no M factors, th M factor itslf is not ssntial for mal diffrntiation, although it dtrmins malnss. This indicats that th M factor controls th xprssion of anothr gn(s) involvd in sx dtrmination and/or diffrntiation. Th fmal-dtrmining factor F, a fourth chromosomal dominant, causs gnotypic mals carrying on or mor M factors to dvlop as frtil fmals (RUBINI 1967; MCDONALD t al. 1978). Th matrnal ffct of Ag is compltly rscud by th F gn (ROVATI and VANOSSI-EST= 1978). Th pistatic rlationship of F and tra could not b xamind bcaus tra is closly linkd with th F locus. Hr, w prsnt a modl xplaining th actions of th known sx-dtrmining gns in M. domstica (Figur 3). Th tra+ gn is activ both matrnally and zygotically. Th matrnal tra+ product may b ncssary to turn on th F+ gn, and th zygotic tra' product may b rquird to maintain th turndon stat of th F+ gn. Th Ff gn, whn turnd on, lads both somatic and grm clls to follow th fmal diffrntiation pathway. Various M loci may simply rprsnt polymorphic variations of th M factor, th rol of which is to turn off th F+ gn. Thus, th F mutation may b simply a constitutiv mutant. Gnotypic fmal progny of traltra mothrs may hav various amounts of th matrnally synthsizd tra+ product, somtims sufficint and somtims insufficint, to turn on th F+ gn: flis thn dvlop as fmals, intrsxs or phnotypic mals, dpnding on th amount of I;" gn product

11 HOUSEFLY SEX DETERMINATION 479 or th numbr of clls xprssing F+. Whn ths flis carry th M factor, F+ gn is turnd off irrspctiv of th amount of tra" product, and thn flis dvlop as mals. Th rason that th mutant of M factor has not bn rportd is probably bcaus th loss-of-function would simply lad flis to diffrntiat as normal fmals and, hnc, b unnoticd. Loss-of-function mutants of th F+ gn hav not bn rportd. Th modl dscribd abov may b rgardd as similar to th sx dtrmination mchanism nvisagd in D. mlanogastr (CLINE 1978, 1983a,b, 1984; BAKER and BELOTE 1983). Whn th XA ratio is 1.O, th SxP gn is activatd in th prsnc of matrnally synthsizd da+ gn product. Th Sxl+ product, in turn, activats th tra' and tra-2+ gns, and thir products thn caus th dsx+ gn to tak th fmal mod of xprssion and fmal diffrntiation nsus. Whn th XA ratio is 0.5, th Sxl+ gn is not activatd, hnc tra+ and tra-2+ ar not activatd, and dsx' rmains in th basal mal mod of xprssion, which lads to mal diffrntiation. Th countrparts of tra+, F+ and M in M. domstica may b found in D. mlanogastr as da+, Sxl+ and th XA ratio (=0.5), rspctivly. W not that, whras th tra matrnal-ffct phnotyp in M. domstica is sx transformation, th da matrnal-ffct phnotyp in D. mlanogastr is sx-spcific lthality (i.., no sx-transformd progny ar obsrvd). This is probably bcaus with da th sx-transformd fmals ar also "transformd" with rspct to thir lvls of X-linkd gn activitis (i.., thy xhibit mal-lik dosag compnsation), and this is lthal to diplo-x flis. This xplanation is consistnt with th obsrvation that som partially transformd flis from da/da mothrs can b rcovrd if th flis carry mal-spcific lthal mutations (.g. mllml), which would prvnt X chromosom hyprtranscription (CLINE 1984). At prsnt, quivalnts for th control gns, tra+, tra-2+ and dsx+, in D. mlanogastr hav not bn idntifid in M. domstica. Th abov similaritis may rprsnt not mr coincidncs but th ral rlatdnss of th two Diptran spcis. It should b mntiond hr that, in M. domstica, thr is no dosag compnsation. Th htrochromatic sx chromosoms, X and Y, hav no major gns xcpt for th M factor on th Y. In D. mlanogastr, gns rsponsibl for dosag compnsation ar known also to play important rols in sx dtrmination (SKRIPSKY and LUCCHESI 1982; BAKER and BELOTE 1983; UENOYAMA 1984; CLINE 1984). It is important to not that all th sx transformation mutants so far idntifid in D. mlanogastr do not caus sx transformation in grm-lin clls, thus producing stril sx-transformd flis (BAKER and BELOTE 1983). Thus, ths mutations ar dtrimntal mutations that cannot b usd dirctly as matrials for th volution of sx-dtrmining systms. In contrast, all of th sx-transformation mutants so far known in M. domstica ar capabl of producing frtil sx-transformd flis. Ths mutations apparntly hav ld to th stablishmnt of multipl sx-dtrmining systms in this spcis. Th F factor has stablishd th fmal htrogamty, i.., F/+; M/M fmals and +/ +; M/M mals, in som natural populations (WAGONER 1969; RUBINI, HEE- MART and FRANCO 1977; INOUE and HIROYOSHI 1982). A similar fmal ht-

12 480 H. INOUE AND T. HIROYOSHI rogamtic strain has bn rportd in a local rac of Chironomus tntuns (THOMPSON 1971), in which th prsnc or absnc of M dtrmins sx in normal strains, as in M. domstica. It is tmpting to spculat that th sam basic gntic mchanism is involvd in th fmal htrogamty rportd in many spcis of Lpidoptra (TAZIMA 1964; CASPARI and GOTTLIEB 1975). Th authors would lik to thank K. OISHI of Kob Univrsity and J. M. BELOTE of Univrsity of California for critical rading of th manuscript. Thanks ar also givn to R. WADA for xcllnt tchnical assistanc. This study was supportd by Grant-in-Aids ( , and ) from th Ministry of Education, Scinc and Cultur, Japan. LITERATURE CITED BAKER, B. S. and J. M. BELOTE, 1983 Sx dtrmination and dosag compnsation in Drosophila mlanogastr. Annu. Rv. Gnt. 17: BRIDGES, C. B., 1925 Sx in rlation to chromosoms and gns. Am. Nat CASPARI, E. W. and F. J. GOTTLIEB, 1975 Th Mditrranan mal moth, Ephstia kuhnilla. pp In: Handbook of Gntics, Vol. 3, Editd by R. C. KING. Plnum Prss, Nw York. CASSIDY, J. D., 1975 Th parasitoid wasps, Habrobracon and Mormonilla. pp In: Handbook of Gntics, Vol. 3, Editd by R. C. KING. Plnum Prss, Nw York. CLINE, T. W., 1978 Two closly linkd mutations in Drosophila mlanogastr that ar lthal to opposit sxs and intract with daughtrlss. Gntics 90: CLINE, T. W., 1983a A cryptic sx-transforming matrnal ffct of daughtrlss in D. mlanogastr is rvald by th intraction of Sx-lthal and mallss. Gntics 100 (Suppl): s13. CLINE, T. W., 1983b Th intraction btwn daughtrlss and Sx-lthal in triploids: a lthal sx-transforming matrnal-ffct linking sx dtrmination and dosag compnsation in Drosophila mlanogastr. Dv. Biol. 95: CLINE, T. W., 1984 Autorgulatory functioning of a Drosophila gn product that stablishs and maintains th sxually dtrmind stat. Gntics 107: ENGELMANN, F., 1970 Th Physiology of Insct Rproduction. Intrnational Sris of Monographs in Pur and Applid Biology Zoology Division, Vol. 44. Prgamon Prss, Nw York. HAMERTON, J. L., J. M. DICKSON, C. E. POLLARD, S. A. GRIEVES and R. V. SHORT, 1969 intrsxuality in goats. J. Rprod. Frtil. 7 (Suppl): Gntic HIROYOSHI, T., 1964 Sx-limitd inhritanc and abnormal sx ratio in strains of th housfly. Gntics 50: HIROYOSHI, T., 1977 Som nw mutants and rvisd linkag maps of th housfly, Musca domstica L. Jpn. J. Gnt. 52: HIROYOSHI, T., Y. FUKUMORI, and H. INOUE, 1982 Mal crossing-ovr and location of th mal dtrmining factor on th third chromosom in a IIIM strain of th housfly. Jpn. J. Gnt. 57: HIROYOSHI, T. and H. INOUE, HODGKIN, J. A., On th IM-chromosom of th housfly. Jpn. J. Gnt. 54: Mor sx-dtrmination mutants of Canorhabditis lgans. Gntics 96: HODGKIN, J. A., 1985 Mals, hrmaphrodits and fmals: sx dtrmination in Canorhabditis lgans. Trnds in Gnt. 1: HODGKIN, J. A. and S. BRENNER, 1977 Mutations causing transformation of sxual phnotyp in th nmatod Canorhabditis lgans. Gntics 86:

13 HOUSEFLY SEX DETERMINATION 48 1 INOUE, H., Y. FUKUMORI and T. HIROYOSHI, 1983 Mapping of autosomal mal-dtrmining factors of th housfly, Musca domstica L., by mans of sx-rvrsal. Jpn. J. Gnt. 58: INOUE, H. and T. HIROYOSHI, 1982 A mal-dtrmining factor on autosom 1 and occurrnc of mal-rcombination in th housfly, Musca domstica L. Jpn. J. Gnt. 57: INOUE, H. and T. HIROYOSHI, 1984 Mapping of autosomal mal-dtrmining factors of th housfly, Musca domstzca L., by using a fmal-dtrmining factor. Jpn. J. Gnt. 59: LYON, M. F. and S. G. HAWKES, 1970 Natur 227: MADL, J. E. and R. K. HERMAN, 1979 Gntics An X-linkd gn for tsticular fminization of th mous. Polyploids and sx dtrmination in Canorhabditis lgans. MCDONALD, I. C., P. EVENSON, C. A. NICKEL and 0. A. JOHNSON, 1978 Hous fly gntics: isolation of a fmal dtrmining factor on chromosom 4. Ann. Entomol. Soc. Am. 71: MILANI, R., 1975 Th housfly, Musca domstica. pp In: Handbook of Gntics, Vol. 3, Editd by R. C. KING. Plnum Prss, Nw York. NELSON, G. A., K. K. LEW and S. WARD, 1978 Intrsx, a tmpratur-snsitiv mutant of th nmatod Canorhabditis lgans. Dv. Biol OHNO, S., 1979 Major &%-Dtrmining Gns. Monographs on Endocrinology, Vol. 11. Springr Vrlag, Nw York. PERJE, A. M., 1948 Studis on th sprmatognsis in Musca domstica. Hrditas 34: ROTHENBUHLER, W. C., 1975 Th hony b, Apis mllijira. pp In: Handbook of Gntics, Vol. 3, Editd by R. C. KING. Plnum Prss, Nw York. ROVATI, C. and S. VANOSSI-ESTE, 1978 Dtrminazion dl ssso in Musca domstica L.-Sopprssion dll fftto matrno dl fattor Ag (arrnogno) ad opra dl fattor di fmminilita F. Boll. Zool. 45: 240. RUBINI, P. G., 1967 Ultriori ossrvazioni sui dtrminanti sssuali di Musca domstica L. Gnt. Agrar. 21: RUBINI, P. G., C. V. HEEMART and M. G. FRANCO, 1977 Rapport0 sssi anomalo in una popolazion natural di Musca domstica L. su basi gnich. Gnt. Agrar. 31: RUBINI, P. G. and D. PALENZONA, 1967 Rspons to slction for high numbr of htrochromosoms in Musca domstica L. Gnt. Agrar. 21: SKRIPSKY, T. and J. C. LUCCHESI, 1982 Intrsxuality rsulting from th intraction of sxspcific lthal mutations in Drosophila mlanogastr. Dv. Biol STEVENS, N. M., 1908 A study of th grm clls of crtain Diptra with rfrnc to th htrochromosoms and phnomnon of synapsis. J. Exp. Zool SULLIVAN, R. L., 1958 Gnt. 2: 282. TAZIMA, Y., 1964 Sx limitation of svral loci in th housfly. Proc. 10th Int. Congr. Th Gntics of th Silkworm. Logos Prss, London. THOMPSON, K. H., 1971 Mal and fmal htrogamty in populations of Chironomus tntans (Diptra: Chironomida). Can. Entomol. 103: UENOYAMA, T., 1984 Studis on th sx-spcific lthals of Drosophila mlanogastr. VIIl. Enhancmnt and supprssion of Sxl xprssion by ml(3)132. Jpn. J. Gnt ULLERICH, R. H., 1973 Di gntisch Grundlag dr Monogni bi dr Schmissflig, Chrysomya rufifaczs. Mol. Gn. Gnt. 125:

14 482 H. INOUE AND T. HIROYOSHI ULLERICH, F. H., 1980 Analysis of th prdtrmining ffcts of a sx ralizr by ovary transplantations in th monognic fly, Chrysomya ruffacis. Wilhlm Roux Arch. 188: VANOSSI-ESTE, S., 1971 Zool. 38: 566. VANOSSI-ESTE, S. and C. ROVATI, 1982 domstica L. Boll. Zool. 49: Nuovi quilibri nlla dtrminazion dl ssso in Musca domstica L. Boll. Inhritanc of th arrhnognic factor Ag of Musca WAGONER, D. E., 1969 Prsnc of mal dtrmining factor found on thr autosoms in th housfly, Musca domstica. Natur 223: WEST, L. S., 1951 York. Th HousJy. Comstock Publishing Associats (Cornll Univrsity Prss) Nw Communicating ditor: V. G. FINNERTY