The Passover Locus in Drosophila Melanogaster: Complex Complementation and Different Effects on the Giant Fiber Neural Pathway

Drosophila melanogaster bearing the Passover mutation fail to jump in response to a light-off stimulus. Pas also disrupts some of the synapses between the neurons of the giant fiber system which mediate this escape behavior. We have mapped Pas to the 19E subdivision of the polytene X chromosome. Our genetic analyses reveal that deletions of either of two nonoverlapping regions fail to fully complement Pas. Heterozygotes of Pas with chromosomal deletions in the vicinity of polytene band 19E3 exhibit the full set of neuronal defects shown by Pas homozygotes. Alleles of the R-9-29 complementation group, which maps to band 19E3, exhibit a complex pattern of complementation with Pas. Heterozygotes combining the lethal R-9-29 alleles with Pas are all viable, some complement the neuronal defects of Pas, but most exhibit these defects. The viable shaking-B2 mutation also fails to complement Pas, the R-9-29 alleles or the 19E3 deficiencies. The R-9-29 locus may contain two functional domains, one required for viability the other for normal neuronal phenotype, trans-Heterozygotes bearing mutant alleles or a deficiency of the first region (19E3) together with deficiencies of the second region (19E5-6) also exhibit some of the neuronal defects shown by the Passover mutant. Deficiencies which delete the entire 19E3 to 19E6 interval do not produce this phenotype when heterozygous with a normal X chromosome. Thus normal function requires a cis-interaction between the two regions. These findings raise the possibility that the gene mutated by Pas is split or separated from a cis-activator by at least one other gene.     

Effects of mutations at thestambh A locus ofDrosophila melanogaster

We report novel findings on the cytogenetic location, functional complexity and maternal and germline roles of thestambh A locus ofDrosophila melanogaster. stmA is localized to polytene bands 44D1.2 on 2R.stmA mutations are of two types: temperature-sensitive (ts) adult and larval paralytic or unconditional embryonic or larval lethal. Twelve alleles reported in this study fall into two intragenic complementing groups suggesting thatstmA is a complex locus with more than one functional domain. Some unconditional embryonic lethal alleles show a ‘neurogenic’ phenotype of cuticle loss accompanied by neural hypertrophy. It is shown that embryos of ts paralytic alleles also show mild neural hypertrophy at permissive temperatures while short exposure to heat induces severe cuticle loss in these embryos.stmA exerts a maternal influence over heat-induced cuticle loss. Unconditional embryonic lethal alleles ofstmA are also germline lethal.     

Genetic and Developmental Analysis of the Locus vnd in DROSOPHILA MELANOGASTER

Genetic and developmental analysis of an X-linked vital locus vnd was undertaken. Embryos hemizygous for the original allele vnd did not hatch and exhibited a disorganized ventral nervous system (VNS). The mutation maps in the region 1B6-7 to 1B9-10, a subregion of an area previously shown to be essential to normal neural development. In this paper, we report isolation of five new alleles at the locus vnd. Genetic complementation analysis of all mutations at the vnd locus, with lethal alleles at adjacent loci, indicates that all lesions at the locus vnd affect only one vital gene function in the region. Four of the five alleles are embryonic lethal; one allele is subvital and behaves like an hypomorphic mutation. Hemizygous embryos for three of the four embryonic lethal alleles were inspected in histological sections; all exhibited disorganized VNS similar to the original allele. The developmental analysis in gynandromorphic genetic mosaics shows that (1) vnd+ gene function is not essential in most imaginal-disc cell derivatives, (2) only about 30% of the mosaic zygotes survive as adults, (3) mosaic zygotes with mutant tissue close to the head cuticle are least likely to survive, and (4) mutant tissue in the thoracic ganglion in the adult is not necessarily lethal. The mosaic data are consistent with the vnd+ gene function being necessary in neural cells derived from the anterioventral region of the blastoderm.     

The Interaction of Two Complex Loci, Zeste and Bithorax in DROSOPHILA MELANOGASTER

It has been found that certain alleles of the zeste locus (z(a) 1-1.0) have no phenotype of their own, but interact with certain alleles at the bithorax locus (bx 3-58.8). This interaction takes the form of an enhancement of the homeotic bx phenotype to a more extreme form-i.e., the metathorax is transformed into mesothorax in varying degrees depending on the bx allele used. This enhancement is somewhat reminiscent of the transvection effect described by Lewis (1954). The characterization of the interaction thus far has shown that the enhancement only effects bx alleles which arise spontaneously, whereas the origin of the z(a) allele is unimportant. The gene claret nondisjunctional was used for the production of gynandromorphs which showed that the enhancing ability of z(a), like the eye pigment change caused by z, is autonomous. The enhancement of one specific allele (bx(34e)), which is temperature-sensitive, has allowed a delineation of the temperature-sensitive period of the bithorax locus to a period extending from the middle of the second larval instar to the middle of the third larval instar. These results, as well as those of other enhancer and suppressor systems in Drosophila, have revealed the possibility of the involvement of heterocyclic compounds in the control of cell determination and fate in Drosophila melanogaster.     

Genetic basis of stage-specific melanism: a putative role for a cysteine sulfinic acid decarboxylase in insect pigmentation

Melanism, the overall darkening of the body, is a widespread form of animal adaptation to particular environments, and includes bookcase examples of evolution by natural selection, such as industrial melanism in the peppered moth. The major components of the melanin biosynthesis pathway have been characterized in model insects, but little is known about the genetic basis of life-stage specific melanism such as cases described in some lepidopteran species. Here, we investigate two melanic mutations of Bicyclus anynana butterflies, called Chocolate and melanine, that exclusively affect pigmentation of the larval and adult stages, respectively. Our analysis of Mendelian segregation patterns reveals that the larval and adult melanic phenotypes are due to alleles at different, independently segregating loci. Our linkage mapping analysis excludes the pigmentation candidate gene black as the melanine locus, and implicates a gene encoding a putative pyridoxal phosphate-dependant cysteine sulfinic acid decarboxylase as the Chocolate locus. We show variation in coding sequence and in expression levels for this candidate larval melanism locus. This is the first study that suggests a biological function for this gene in insects. Our findings open up exciting opportunities to study the role of this locus in the evolution of adaptive variation in pigmentation, and the uncoupling of regulation of pigment biosynthesis across developmental stages with different ecologies and pressures on body coloration.     

Taste,movement, and death: varying effects of new prospero mutants during Drosophila development

The PGal4 transposon inserted upstream of the pan-neural gene prospero (pros) causes several neural and behavioral defects in the Voila(1) strain. The precise excision of the transposon simultaneously rescued all these defects whereas its unprecise excision created new pros(V) alleles, including the null allele pros(V17). Here, we describe the relationship between the genetic structure of pros locus, larval locomotion, and larval gustatory response. These two behaviors showed varying degrees of variation depending upon the pros allele. We also found a good relation between behavioral alteration, the level of Pros protein in the embryo, and the degree of disorganization in the larval neuromuscular junction. These data suggest that the complete development of the nervous system requires a full complement of Pros, and that a gradual decrease in the levels of this protein can proportionally alter the development and the function of the nervous system.     

Recovery of Dominant, Autosomal Flightless Mutants of Drosophila Melanogaster and Identification of a New Gene Required for Normal Muscle Structure and Function

To identify further mutations affecting muscle function and development in Drosophila melanogaster we recovered 22 autosomal dominant flightless mutations. From these we have isolated eight viable and lethal alleles of the muscle myosin heavy chain gene, and seven viable alleles of the indirect flight muscle (IFM)-specific Act88F actin gene. The Mhc mutations display a variety of phenotypic effects, ranging from reductions in myosin heavy chain content in the indirect flight muscles only, to reductions in the levels of this protein in other muscles. The Act88F mutations range from those which produce no stable actin and have severely abnormal myofibrillar structure, to those which accumulate apparently normal levels of actin in the flight muscles but which still have abnormal myofibrils and fly very poorly. We also recovered two recessive flightless mutants on the third chromosome. The remaining five dominant flightless mutations are all lethal alleles of a gene named lethal(3)Laker. The Laker alleles have been characterized and the gene located in polytene bands 62A10,B1-62B2,4. Laker is a previously unidentified locus which is haplo-insufficient for flight. In addition, adult wild-type heterozygotes and the lethal larval trans-heterozygotes show abnormalities of muscle structure indicating that the Laker gene product is an important component of muscle.     

Co-Localization to Chromosome Bands 99e1-3 of the Drosophila Melanogaster Myosin Light Chain-2 Gene and a Haplo-Insufficient Locus That Affects Flight Behavior

Using overlapping synthetic deficiencies, we find that a haplo-insufficient locus affecting flight behavior and the myosin light chain-2 gene co-map to the Drosophila melanogaster polytene chromosome interval 99D9-E1 to 99E2-3. From screening over 9000 EMS-treated chromosomes, we obtained alleles of two complementation groups that map to this same interval. One of these complementation groups lfm(3)99Eb, exhibits dominant flightless behavior; thus, flightless behavior of the deficiency is in all likelihood due to hemizygosity of this single locus. Rescue of flightless behavior by a duplication indicates that the single allele, E38, of the Ifm(3)99Eb complementation group is a hypomorph. Based upon its map position and a reduction in concentration of myosin light chain-2 mRNA in heterozygotes, we propose that Ifm(3)Eb(E38) is a mutant allele of the myosin light chain-2 gene. Our genetic analysis also resulted in the identification of four dominant flightless alleles of an unlinked locus, l(3)nc99Eb, that exhibits dominant lethal synergism with Ifm(3)99Eb.     

Mutations in the Protein Phosphatase 1 Gene at 87b Can Differentially Affect Suppression of Position-Effect Variegation and Mitosis in Drosophila Melanogaster

The suppressor of position effect variegation (PEV) locus Su-var(3)6 maps to 87B5-10. The breakpoints of deficiencies that define this interval have been placed on a 250-kb molecular map of the region. The locus is allelic to the ck19 complementation group previously shown to encode a type 1 serine-threonine protein phosphatase (PP1) catalytic subunit. When introduced into flies by P element-mediated transformation, a 5.8-kb genomic fragment carrying this gene overcomes the suppressor phenotype of Su-var(3)6(01) and recessive lethality of all mutations of the locus. Four of the mutant alleles at the locus show a broad correlation between high levels of suppression of PEV, a high frequency of aberrant mitosis and low PP1 activity in larval extracts. However, some alleles with low PP1 activity show weak suppression of PEV with a high frequency of abnormal mitosis, whereas others show strong suppression of PEV with normal mitosis. The basis for these disparate phenotypes is discussed.     

The Drosophila gene abstrakt, required for visual system development, encodes a putative RNA helicase of the DEAD box protein family

The molecular mechanisms underlying axonal pathfinding are not well understood. In a genetic screen for mutations affecting the projection of the larval optic nerve we isolated the abstrakt locus. abstrakt is required for pathfinding of the larval optic nerve, and it also affects development in both the adult visual system and the embryonic CNS. Here we report the molecular characterization of abstrakt. It encodes a putative ATP-dependent RNA helicase of the DEAD box protein family, with two rare substitutions in the PTRELA and the RG-D motifs, thought to be involved in oligonucleotide binding: serine for threonine, and lysine for arginine, respectively. Two mutant alleles of abstrakt show amino acid exchanges in highly conserved positions. A glycine to serine exchange in the HRIGR motif, which is involved in RNA binding and ATP hydrolysis, results in a complete loss of protein function; and a proline to leucine exchange located between the highly conserved ATPase A and PTRELA motifs results in temperature-sensitive protein function. Both the broad requirement for abstrakt gene function and its ubiquitous expression are consistent with a molecular function of the abstrakt protein in mRNA splicing or translational control.     

Specificity of gene action during central nervous system development in Drosophila melanogaster: analysis of the lethal (1) optic ganglion reduced locus

A newly defined genetic locus designated lethal (1) optic ganglion reduced (l(1)ogre: 1-18.8, 6E1/2-6E4/5) is characterized. Four alleles have been isolated, one organismal viable and three organismal lethals. Histological analyses of these mutants at the light microscopic level have detected defects only in the developing and adult central nervous system (CNS). Examination of genetic mosaics suggests that the wild-type product of this locus may function specifically in the CNS. Analyses of staged material show that abnormalities first become apparent early in the larval period, indicating that the l(1)ogre+ gene product normally acts at or before this stage. No maternal effects were detectable. Determination of the temperature-sensitive period for lethality, of a temperature-sensitive heteroallelic combination, indicates that the l(1)ogre+ gene product also acts late in the larval period. These results show that the time of l(1)ogre+ gene action overlaps the period during which growth and assembly of the imaginal CNS occurs and are consistent with the hypothesis that l(1)ogre may act specifically in the imaginal CNS during its morphogenesis.     

Fitness costs of insecticide resistance in natural breeding sites of the mosquito Culex pipiens

Genetic changes conferring adaptation to a new environment may induce a fitness cost in the previous environment. Although this prediction has been verified in laboratory conditions, few studies have tried to document this cost directly in natural populations. Here, we evaluated the pleiotropic effects of insecticide resistance on putative fitness components of the mosquito Culex pipiens. Experiments using different larval densities were performed during the summer in two natural breeding sites. Two loci that possess alleles conferring organophosphate (OP) resistance were considered: ace-1 coding for an acetylcholinesterase (AChE1, the OP target) and Ester, a 'super locus" including two closely linked loci coding for esterases A and B. Resistance ace-1 alleles coding for a modified AChE1 were associated with a longer development time and shorter wing length. The pleiotropic effects of two resistance alleles Ester1 and Ester4 coding for the overproduced esterases A1 and A4-B4, respectively, were more variable. Both A1 and A4-B4 reduced wing length, although only A1 was associated with a longer preimaginal stage. The fluctuating asymmetry (FA) of the wing did not respond to the presence or to the interaction of resistance alleles at the two loci at any of the density levels tested. Conversely, the FA of one wing section decreased when larval density increased. This may be the consequence of selection against less developmentally stable individuals. The results are discussed in relation to the local evolution of insecticide resistance genes.     

Genetic dissection of itpr gene function reveals a vital requirement in aminergic cells of Drosophila larvae

Signaling by the second messenger inositol 1,4,5-trisphosphate is thought to affect several developmental and physiological processes. Mutants in the inositol 1,4,5-trisphosphate receptor (itpr) gene of Drosophila exhibit delays in molting while stronger alleles are also larval lethal. In a freshly generated set of EMS alleles for the itpr locus we have sequenced and identified single point mutations in seven mutant chromosomes. The predicted allelic strength of these mutants matches the observed levels of lethality. They range from weak hypomorphs to complete nulls. Interestingly, lethality in three heteroallelic combinations has a component of cold sensitivity. The temporal focus of cold sensitivity lies in the larval stages, predominantly at second instar. Coupled with our earlier observation that an itpr homozygous null allele dies at the second instar stage, it appears that there is a critical period for itpr gene function in second instar larvae. Here we show that the focus of this critical function lies in aminergic cells by rescue with UAS-itpr and DdCGAL4. However, this function does not require synaptic activity, suggesting that InsP(3)-mediated Ca(2+) release regulates the neurohormonal action of serotonin.     

Genetic dissection of the central pair microtubules of the flagella of Chlamydomonas reinhardtii

Mutations at two loci, which cause an altered mobility of the flagella, affected the central pair microtubule complex of Chlamydomonas reinhardtii flagella. The mutations at both loci primarily affected the C1 microtubule of the complex. Three alleles at the PF16 locus affected the stability of the C1 microtubule in isolated axonemes. This phenotype has allowed us to determine that at least ten polypeptides of the central pair complex are unique to the C1 microtubule. The motility defect was correlated with the failure to assemble three of these ten polypeptides in vivo. The structural gene product of the PF16 locus was a polypeptide with molecular weight 57,000 as shown by analysis of five intragenic revertants and by analysis of axonemes from dikaryon rescue experiments. Three alleles at the PF6 locus affected the assembly of one of the two projections of the C1 microtubule and this projection was formed by at least three polypeptide components, which are a subset of polypeptides missing in isolated pf16 axonemes. No structural gene product has been identified for the PF6 locus. The gene product is probably not one of the identified projection constituents as shown by analysis of dikaryon rescue experiments. Chemical extraction of isolated wild-type axonemes suggests that at least seven polypeptide components are unique to the C2 microtubule.     

Chalcone isomerase gene from rice (Oryza sativa) and barley (Hordeum vulgare): physical,genetic and mutation mapping

The barley and rice chalcone flavonone isomerase (Cfi) genes were isolated and identified by homology to the maize Cfi gene. Structure analysis indicated high similarity except that the barley gene lacked intron 3. The maize Cfi gene has been mapped to three loci, but only a single locus was detected in barley and rice. This explains the lack of observed mutants in maize while a single locus anthocyanin-less 30 (ant30), with four alleles ant30-245, ant30-310, ant30-272 and ant30-287 has been described in barley. Based on biochemical analysis it has been suggested that these mutants are in the Cfi gene resulting in absence of anthocyanin. In order to provide molecular evidence for or against this hypothesis we sequenced the four ant30 alleles and compared them to their respective wild-type alleles. The three sodium azide induced mutants ant30-245, ant30-272 and ant30-287 showed single base changes resulting in two non-sense and one mis-sense mutations affecting the protein function. The 1-nitroso-5,6-dihydrouracil induced mutant ant30-310 had one base substitution and a 25 bp deletion. These observations are in accordance with the conclusion that the ant30 phenotype is caused by mutations in the Cfi gene. The nature of the mutants induced is in line with the proposed mechanism of action for the mutagens used.     

Inositol Mutants of SACCHAROMYCES CEREVISIAE: Mapping the ino1 Locus and Characterizing Alleles of the ino1, ino2 and ino4 Loci

An extensive genetic analysis of inositol auxotrophic mutants of yeast is reported. The analysis includes newly isolated mutants, as well as those previously reported (Culbertson and Henry 1975). Approximately 70% of all inositol auxotrophs isolated are shown to be alleles of the ino1 locus, the structural gene for inositol-1-phosphate synthase, the major enzyme involved in inositol biosynthesis. Alleles of two other loci, ino2 and ino4, comprise 9% of total mutants, with the remainder representing unique loci or complementation groups. The ino1 locus was mapped by trisomic analysis with an n + 1 disomic strain constructed with complementing alleles at this locus. The ino1 locus is shown to be located between ura2 (11.1 cm) and cdc6 (21.8 cm) on chromosome X. An extended map of chromosome X of yeast is presented. Unlike most yeast loci, but similar to the his1 locus, the ino1 locus lacks allelic representatives that are suppressible by known suppressors. This finding suggests that premature termination of translation of the ino1 gene product may be incompatible with cell viability.     

Novel polymorphisms of goat growth hormone and growth hormone receptor genes and their effects on growth traits

In this study, the polymorphisms of growth hormone (GH) gene 5' promoter region and intron 8, exons 4 and 10 of growth hormone receptor (GHR) gene were analyzed in Xinong Saanen goats (SG) and Boer goats (BG). Two alleles (A and B) and three genotypes (AA, AB and BB) were detected at P1 locus of GH gene, and two alleles (G and T) and two genotypes (GG and GT) were detected at P4 locus of GHR gene by PCR-SSCP analysis. In addition, two single nucleotide polymorphisms (SNPs)-A73C (P1 locus) and G114T (P4 locus), were identified by DNA sequencing. The frequencies of alleles A and B in the two goat breeds were 0.61-0.62, and 0.39-0.38, respectively, and the frequencies of alleles G and T in the two goat breeds were 0.82-0.86, and 0.18-0.14, respectively. The SNP loci were in Hardy-Weinberg disequilibrium in both goat breeds (P<0.05). Polymorphisms of GH and GHR genes were shown to be associated with growth traits in BG breed. AA and GG genotypes were associated with superior growth traits in 1-, 2- and 3-month old individuals. Hence, AA and GG genotypes are suggested to be a molecular marker for superior growth traits in BG breed.