A Genetic Analysis of the Suppressor 2 of Zeste Complex of Drosophila Melanogaster

The zeste(1) (z(1)) mutation of Drosophila melanogaster produces a mutant yellow eye color instead of the wild-type red. Genetic and molecular data suggest that z(1) achieves this change by altering expression of the wild-type white gene in a manner that exhibits transvection effects. There exist suppressor and enhancer mutations that modify the z(1) eye color, and this paper summarizes our studies of those belonging to the Suppressor 2 of zeste complex [Su(z)2-C]. The Su(z)2-C consists of at least three subregions called Psc (Posterior sex combs), Su(z)2 and Su(z)2D (Distal). The products of these subregions are proposed to act at the level of chromatin. Complementation analyses predict that the products are functionally similar and interacting. The alleles of Psc define two overlapping phenotypic classes, the hopeful and hapless. The distinctions between these two classes and the intragenic complementation seen among some of the Psc alleles are consistent with a multidomain structure for the product of Psc. Psc is a member of the homeotic Polycomb group of genes. A general discussion of the Polycomb and trithorax group of genes, position-effect variegation, transvection, chromosome pairing and chromatin structure is presented.     

Genetic Analysis of the Claret Locus of Drosophila Melanogaster

The claret (ca) locus of Drosophila melanogaster comprises two separately mutable domains, one responsible for eye color and one responsible for proper disjunction of chromosomes in meiosis and early cleavage divisions. Previously isolated alleles are of three types: (1) alleles of the claret (ca) type that affect eye color only, (2) alleles of the claret-nondisjunctional (cand) type that affect eye color and chromosome behavior, and (3) a meiotic mutation, non-claret disjunctional (ncd), that affects chromosome behavior only. In order to investigate the genetic structure of the claret locus, we have isolated 19 radiation-induced alleles of claret on the basis of the eye color phenotype. Two of these 19 new alleles are of the cand type, while 17 are of the ca type, demonstrating that the two domains do not often act as a single target for mutagenesis. This suggests that the two separately mutable functions are likely to be encoded by separate or overlapping genes rather than by a single gene. One of the new alleles of the cand type is a chromosome rearrangement with a breakpoint at the position of the claret locus. If this breakpoint is the cause of the mutant phenotype and there are no other mutations associated with the rearrangement, the two functions must be encoded by overlapping genes.     

Genetic Analysis of Stellate Elements of Drosophila Melanogaster

Repeated elements are remarkably important for male meiosis and spermiogenesis in Drosophila melanogaster. Pairing of the X and Y chromosomes is mediated by the ribosomal RNA genes of the Y chromosome and X chromosome heterochromatin, spermiogenesis depends on the fertility factors of the Y chromosome. Intriguingly, a peculiar genetic system of interaction between the Y-linked crystal locus and the X-linked Stellate elements seem to be also involved in male meiosis and spermiogenesis. Deletion of the crystal element of the Y, via an interaction with the Stellate elements of the X, causes meiotic abnormalities, gamete-genotype dependent failure of sperm development (meiotic drive), and deposition of protein crystals in spermatocytes. The current hypothesis is that the meiotic abnormalities observed in cry(-) males is due to an induced overexpression of the normally repressed Ste elements. An implication of this hypothesis is that the strength of the abnormalities would depend on the amount of the Ste copies. To test this point we have genetically and cytologically examined the relationship of Ste copy number and organization to meiotic behavior in cry(-) males. We found that heterochromatic as well as euchromatic Ste repeats are functional and that the abnormality in chromosome condensation and the frequency of nondisjunction are related to Ste copy number. Moreover, we found that meiosis is disrupted after synapsis and that cry-induced meiotic drive is probably not mediated by Ste.     

A Genetic Analysis of Hermaphrodite, a Pleiotropic Sex Determination Gene in Drosophila Melanogaster

Sex determination in Drosophila is controlled by a cascade of regulatory genes. Here we describe hermaphrodite (her), a new component of this regulatory cascade with pleiotropic zygotic and maternal functions. Zygotically, her(+) function is required for female sexual differentiation: when zygotic her(+) function is lacking, females are transformed to intersexes. Zygotic her(+) function may also play a role in male sexual differentiation. Maternally, her(+) function is needed to ensure the viability of female progeny: a partial loss of her(+) function preferentially kills daughters. In addition, her has both zygotic and maternal functions required for viability in both sexes. Temperature sensitivity prevails for all known her alleles and for all of the her phenotypes described above, suggesting that her may participate in an intrinsically temperature-sensitive process. This analysis of four her alleles also indicates that the zygotic and maternal components of of her function are differentially mutable. We have localized her cytologically to 36A3-36A11.     

Genetic Analysis of Chromosome Region 63 of Drosophila Melanogaster

The salivary chromosome region including cytological division 63 of Drosophila melanogaster was genetically analyzed in order to (1) characterize this previously unstudied region and (2) attempt to isolate mutations in the hsp82 gene. Seven deletions which span this region were isolated, including four which remove the hsp82 gene. A Minute mutation was mapped to this region and this Minute was used to isolate duplications in the 63 region. These duplications map the Minute to 63B8-C1. F2 screens were initiated using deletions which remove the hsp82 gene. Over 15,000 chromosomes were screened, yielding 40 lethal mutations which comprise 14 complementation groups. Several of these mutations map outside the 63 region and appear to give second site interaction with the Minute locus. Four loci, including the Minute gene, are candidates for hsp82 mutations by cytogenetic mapping. These loci were tested for complementation with a P element carrying the hsp82 gene. However, none of the mutations was rescued.     

Mitochondrial DNA in the Drosophila Melanogaster Complex

Mitochondrial DNA in the complex Drosophila melanogaster was among the first studied in metazoans. The variability of the molecule was extensively studied using restriction enzymes, gene sequence and recently sequence of the whole coding region. Within the complex, seven major haplotypes have been described, one (me) in D. melanogaster, three in D. simulans (siI, siII, siIII), two in D. mauritiana (maI, maII), and one in D. sechellia (se). The molecular distance between the haplotypes is comprised between 1 and 5%, except for siII and maI, which are virtually identical. The nucleotide diversity within each of these haplotypes is very low, varying from 0 to 0.0005. Most of the cytoplasms are infected by the bacterium Wolbachia and different bacterial strains infect cytoplasms harboring different mtDNA types. mtDNA polymorphism is discussed in relation with Wolbachia, nuclear polymorphism and speciation events.     

A Genetic Analysis of Male-Predominant Pheromones in Drosophila Melanogaster

Chemical signals from males play an important role in stimulating Drosophila melanogaster females to mate, and male-predominant pheromones may influence a female's choice of mates. Male-predominant pheromones also inhibit courtship, thereby functioning as antiaphrodisiacs. Interstrain variation in the ratio of two male-predominant pheromones (7-tricosene and 7-pentacosene) has been reported, but the genetic basis for this potentially important variation has not been examined. In a series of crosses between strains that differ radically in the amounts of 7-tricosene and 7-pentacosene, we have identified both X-linked and autosomal contributions to interstrain variation in the amounts of these compounds. The X-linked loci act as enhancers for production of the compound predominant in the strain from which the X chromosome originated. Autosomal factors for each of the two compounds appear to segregate as high vs. low, with incomplete dominance of high 7-tricosene over low, and low 7-pentacosene over high. A significant negative correlation between the quantities of 7-pentacosene and 7-tricosene in the F2 and backcross progeny, but not in the F1s or parentals, indicates linkage between autosomal loci regulating the expression of each compound. However, the phenotypic distributions of the backcross progeny indicate that additional unlinked loci are also directly involved in the production of these two hydrocarbons.     

Developmental Genetic Analysis of Contrabithorax Mutations in Drosophila Melanogaster

A developmental analysis of the Contrabithorax (Cbx) alleles offers the opportunity to examine the role of the Ultrabithorax (Ubx) gene in controlling haltere, as alternative to wing, morphogenesis in Drosophila. Several Cbx alleles are known with different spatial specificity in their wing toward haltere homeotic transformation. The molecular data on these mutations, however, does not readily explain differences among mutant phenotypes. In this work, we have analyzed the "apogenetic" mosaic spots of transformation in their adult phenotype, in mitotic recombination clones and in the spatial distribution of Ubx proteins in imaginal discs. The results suggest that the phenotypes emerge from early clonality in some Cbx alleles, and from cell-cell interactions leading to recruitment of cells to Ubx gene expression in others. We have found, in addition, mutual interactions between haltere and wing territories in pattern and dorsoventral symmetries, suggesting short distance influences, "accommodation," during cell proliferation of the anlage. These findings are considered in an attempt to explain allele specificity in molecular and developmental terms.     

A Genetic Analysis of Intersex, a Gene Regulating Sexual Differentiation in Drosophila Melanogaster Females

Sex-type in Drosophila melanogaster is controlled by a hierarchically acting set of regulatory genes. At the terminus of this hierarchy lie those regulatory genes responsible for implementing sexual differentiation: genes that control the activity of target loci whose products give rise to sexually dimorphic phenotypes. The genetic analysis of the intersex (ix) gene presented here demonstrates that ix is such a terminally positioned regulatory locus. The ix locus has been localized to the cytogenetic interval between 47E3-6 and 47F11-18. A comparison of the morphological and behavioral phenotypes of homozygotes and hemizygotes for three point mutations at ix indicates that the null phenotype of ix is to transform diplo-X animals into intersexes while leaving haplo-X animals unaffected. Analysis of X-ray induced, mitotic recombination clones lacking ix(+) function in the abdomen of diplo-X individuals indicates that the ix(+) product functions in a cell-autonomous manner and that it is required at least until the termination of cell division in this tissue. Taken together with previous analyses, our results indicate that the ix(+) product is required to function with the female-specific product of doublesex to implement appropriate female sexual differentiation in diplo-X animals.     

Identification and Genetic Analysis of Wunen, a Gene Guiding Drosophila Melanogaster Germ Cell Migration

We describe a novel genetic locus, wunen (wun), required for guidance of germ cell migration in early Drosophila development. Loss of wun function does not abolish movement but disrupts the orientation of the motion causing the germ cells to disperse even though their normal target, the somatic gonad, is well formed. We demonstrate that the product of this gene enables a signal to pass from the soma to the germ line and propose that the function of this signal is to selectively stabilize certain cytoplasmic extensions resulting in oriented movement. To characterize this guidance factor, we have mapped wun to within 100 kb of cloned DNA.     

Genetic Analysis of the Additional Sex Combs Locus of Drosophila Melanogaster

Additional sex combs (Asx) is a member of the Polycomb group of genes, which are thought to be required for maintenance of chromatin structure. To better understand the function of Asx, we have isolated nine new alleles, each of which acts like a gain of function mutation. Asx is required for normal determination of segment identity. AsxP1 shows an unusual phenotype in that anterior and posterior homeotic transformations are seen in the same individuals, suggesting that AsxP1 might upset chromatin structure in a way that makes both activation and repression of homeotic genes more difficult. Analysis of embryonic and adult phenotypes of Asx alleles suggests that Asx is required zygotically for determination of segment number and polarity. The expression pattern of even-skipped is altered in Asx mutant embryos, suggesting that Asx is required for normal expression of this gene. We have transposon-tagged the Asx gene, and can thus begin molecular analysis of its function.     

Genetic Analysis of the Enhancer of Zeste Locus and Its Role in Gene Regulation in Drosophila Melanogaster

The Enhancer of zeste [E(z)] locus of Drosophila melanogaster is implicated in multiple examples of gene regulation during development. First identified as dominant gain-of-function modifiers of the zeste1-white (z-w) interaction, mutant E(z) alleles also produce homeotic transformations. Reduction of E(z)+ activity leads to both suppression of the z-w interaction and ectopic expression of segment identity genes of the Antennapedia and bithorax gene complexes. This latter effect defines E(z) as a member of the Polycomb-group of genes. Analysis of E(z)S2, a temperature-sensitive E(z) allele, reveals that both maternally and zygotically produced E(z)+ activity is required to correctly regulate the segment identity genes during embryonic and imaginal development. As has been shown for other Polycomb-group genes, E(z)+ is required not to initiate the pattern of these genes, but rather to maintain their repressed state. We propose that the E(z) loss-of-function eye color and homeotic phenotypes may both be due to gene derepression, and that the E(z)+ product may be a general repressing factor required for both examples of negative gene regulation.     

Genetic Analysis of Chromosomal Region 67a-D of Drosophila Melanogaster

In an effort to (1) characterize the 67 interval of chromosome 3 of Drosophila melanogaster genetically and (2) isolate mutations of the 67B1 small heat shock protein (hsp) gene cluster specifically, we undertook a mutational analysis of the 67A-D subinterval. Using a deficiency of the 67A2 to 67D11-13 region, Df(3L)AC1, we screened 8700 diepoxybutane-treated chromosomes and 7800 ethyl methanesulfonate-treated chromosomes for visible and lethal mutations throughout this interval and recovered 74 independent recessive lethal mutations, but no visible mutations. One of the lethal mutations, d29A6, was identified as an overlapping deficiency extending from 66F3 to 67B1. An additional 6000 diepoxybutane-treated chromosomes were screened for lethality over d29A6, yielding another four lethal mutations within the 67A2-B1 subinterval. These 78 lethal mutations, along with two others isolated in other laboratories, define 23 essential loci--6 within the 67A2-B1 subinterval and 17 within the 67A2 to D11-13 subinterval. Many of these loci appear to be required for imaginal development only, exhibiting late larval to pharate adult lethal phases. Examination of the 67A2-B1 lethal complementation groups for (1) earlier onset of lethality following a heat shock, (2) missing or altered small hsps on two-dimensional protein gels, and (3) restoration of viability by transformed wild-type copies of the small hsp genes indicates that none of these mutations affect the small hsps. On the basis of this analysis and the known homology of the genes, we conclude that the small hsps are functionally equivalent.