Drop out: a third chromosome maternal-effect locus required for formation of the Drosophila cellular blastoderm.

drop out (dop) is a recessive maternal-effect locus identified in a screen for female-sterile mutations in Drosophila polytene region 71C-F. Phenotypic analyses of the dop mutation indicate that the gene is required for proper formation of the cellular blastoderm. In embryos derived from either homozygous or hemizygous dop mothers, cytoplasmic clearing, nuclear migration and division, and pole cell formation appear normal. However, developmental defects are observed prior to and during cellularization of the blastoderm. At the beginning of nuclear cycle 14, the distinct separation of the internal yolk mass and the cortical cytoplasm breaks down. Subsequently, a population of somatic nuclei located at the periphery of the syncytial blastoderm becomes irregularly spaced and nonuniform in their distribution. Despite a somewhat regular formation of the cortical actin network, cellularization in mutant embryos is extremely variable. Such embryos fail to gastrulate normally and produce variable amounts of defective cuticle. Overall, our analyses suggest that the dop gene functions in maintaining the separation of yolk and cortical cytoplasm and in stabilizing the distribution of somatic nuclei in the Drosophila syncytial blastoderm.     

Developmental genetics of the gastrulation defective locus in Drosophila melanogaster

The fs(1)gastrulation defective (dg) locus is one of the dorsal-group genes of Drosophila. Maternal expression of this gene is required for gastrulation movements and the differentiation of structures along the embryonic dorso-ventral axis. Twelve alleles of gd displayed a complex pattern of complementation, suggesting a direct interaction between subunits of a multimeric protein. Essential expression of the gd locus was strictly maternal with no zygotic contribution by the paternally derived allele. Clonal analysis revealed that expression of the gd locus was required in the germ line and that extreme dorsalization represented the null gd phenotype. Temperature-sensitive (ts) alleles displayed a ts period that included the last 4-5 hr of oogenesis and the first 1.5-2 hr of embryogenesis. Eggs from one ts allelic combination displayed reduced hatching when retained in the ovary at permissive temperatures, suggesting the loss of a labile egg component. This lability may also be responsible for the variable phenotypes displayed by offspring from individual females.     

Developmental requirements for the ecdysoneless (ecd) locus in Drosophila melanogaster

The ecdysoneless locus in Drosophila melanogaster has been defined previously by a single conditional mutation, I(3)ecd¹, that causes an ecdysteroid deficit and larval death at the restrictive temperature, 29°C, although the primary role of the mutation in developmental processes has been unclear. Gene dosage and complementation studies reported here for ecd¹ and five nonconditional lethal alleles indicate that the ecd locus plays prezygotic and postzygotic roles essential for normal embryonic development, the successful completion of each larval molt, adult eclosion, and female fertility. The ecd locus is also required for normal macrochaete differentiation. For each observed phenotype, the severity of mutational effects was correlated with ecd mutant genotypes. In all cases, ecd¹ homozygotes were least affected. Mutants heteroallelic for ecd¹ and any one of four nonconditional recessive mutations were more severely affected than ecd¹ homozy-gotes, revealing these as hypomorphic alleles. For all phenotypic effects, mutants heteroallelic for ecd¹ and a dominant mutation (ecd^3D) were most severely affected. These individuals died during embryogenesis at 29°C and developed no macrochaetes on the dorsal thorax when transferred to 29°C during the white prepupal stage. The ecd^3D mutation also caused female semisterility in heterozygotes. Ecdysteroid regulation has been implicated previously in all the developmental processes disrupted by these ecd mutations except for macrochaete differentiation. © 1993 Wiley-Liss, Inc.     

Developmental analysis of Drosophila position-specific antigens

The distributions of three position-specific (PS) antigens have been examined in different Drosophila tissues and at various developmental times, using both immunofluorescence and affinity purification procedures. In the imaginal discs the PS antigens show nonuniform and nonhomologous distributions, and the expression of the antigens in a particular disc region can vary during development. In general, PS antigen expression appears to correlate with morphogenetic events in the disc epithelia, suggesting that the antigens are involved in cell-cell recognition and/or adhesion processes. PS antigens are also found in many other tissues, and in embryos as early as the cellular blastoderm stage. Affinity-purified PS antigens from different tissues or stages appear to be similar, as judged by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The results are discussed in relation to Drosophila developmental events, with particular regard to the dorsoventral cell lineage restriction in the wing disc.     

Developmental analysis of the facets, a group of intronic mutations at the Notch locus of Drosophila melanogaster that affect postembryonic development

The activity of the Notch locus of Drosophila melanogaster during embryogenesis is necessary for the correct segregation of neural from epidermal lineages. The action of Notch is not confined to embryogenesis but is also essential for normal development during the postembryonic stages. Its action is pleiotropic, as revealed by the existence of several classes of mutations which affect various imaginal structures. Here, we examine a group of six recessive mutations, the facets (fa, fa3, fag, fag-2, fafx and fasw), which affect eye and optic lobe morphology and have been previously shown to be associated with the insertion of transposable elements into an intronic region of Notch. Using both somatic recombination and gynandromorph analysis, we find that their behavior in a mosaic analysis is not identical. While in the majority of alleles abnormal Notch function in the retina is sufficient to induce optic lobe abnormalities, in the case of fag-2, a considerable number of individuals having mosaic retinas exhibit normal optic lobe structure. All the facet alleles appear to behave in a cell-autonomous manner. A developmental analysis of the eye and optic lobe defects associated with the facet mutations support the contention that Notch may be involved not only in the formation of certain structures but also in their maintenance.     

Developmental genetic analysis of lethal alleles at the ewg locus and their effects on muscle development in Drosophila melanogaster

The recessive X-linked mutation erect wing (ewg), in Drosophila melanogaster, was characterized as a flightless behavioral mutant which specifically lacked the dorsal longitudinal flight muscles [1]. This mutation was mapped distal to the X chromosomal locus yellow, and further to the cytological segment 1 A 1 to 1 B2-3 [2]. Several lethal complementation groups have been mapped to this interval [3]. Our complementation tests show that ewg is allelic to one lethal complementation group in the region 1 A 1 to 1 B2-3. A further analysis of ewg and several lethal alleles isolated at this locus was undertaken in the present investigation. Most of the lethal alleles at this locus lead to a late embryonic or early larval lethal phase, indicating that the ewg⁺ gene product is necessary for the development of more than just the dorsal longitudinal flight muscles. Intragenic complementation was observed for some of the ewg lethal alleles. Genetic mosaics with ewg lethal alleles showed that mutant cell clones in cuticular structures are viable. Mosaic analysis is consistent with a mesodermal defect associated with the locus.     

Alcohol metabolism in Drosophila melanogaster: Uselessness of the most active aldehyde oxidase produced by the Aldox locus

Alcohol dehydrogenase is necessary for ethanol detoxification and metabolic utilization. It has been generally assumed that aldehyde oxidase (AO) produced by the Aldox locus (3–56.7) is necessary for a further transformation of acetaldehyde into acetate. We find that various mutant strains (ma-l or Aldox ⁿ) which do not produce an active enzyme show about the same tolerance to alcohol as do wild strains. This physiological paradox is probably to be explained by the discovery of another locus (not localized) which produced a small amount of AO in all tested strains. The adaptive significance of the genetically polymorphic Aldox locus is probably to be looked for in physiological pathways other than ethanol metabolism.     

Adult abnormalities resulting from a localized blastoderm defect in a maternal-effect mutant of Drosophila.

In the mutant mat(3)3 of Drosophila melanogaster, there is a temperature-sensitive maternal effect on blastoderm formation. When oogenesis occurs in homozygous mat(3)3 females at the fully restrictive temperature of 29°C, the embryonic progeny form a defective cellular blastoderm in which cells are either completely or partially missing from a posterior-dorsal region, and the embryos die before hatching. Transplantation tests for the presence in the embryos of primordial imaginal cells capable of developing into adult structures showed a relatively high yield of eye and antenna structures, an intermediate yield of labium structures, and low or zero yields of wing, haltere, and leg structures. These results are consistent with the fate mapping of the primordial imaginal cells by analysis of gynandromorph mosaics; the eye and antenna map in the fully cellular region of the mutant blastoderm, the labium near the border of the defective region, and the wing, haltere, and legs within the defective region. When oogenesis oocurs at a lower temperature, the lethal maternal effect in mat(3)3 is reversed, but there is a nonlethal effect on larval and adult progeny of the mat(3)3 females. Many of the adults are missing one or more cuticular structures, usually a leg, haltere, or abdominal segment, and many of the larvae are missing the corresponding imaginal discs from which the thoracic structures are derived. These selective effects on imaginal development appear to be caused by maternally induced blastoderm defects that are less extensive at the lower temperature of oogenesis.     

Germline autonomy of maternal-effect mutations altering the embryonic body pattern of Drosophila

Nine maternal-effect loci Drosophila melanogaster were tested in germline mosaics to determine whether the wildtype gene activity is required in somatic or germline components of the maternal ovary. Mutations in these loci affect the anterior-posterior or dorso-ventral body pattern. In all nine loci (torso, trunk, exuperantia, vasa, valois, staufen, tudor, dorsal, Toll) a mutant genotype in the germ cells is sufficient to produce all aspects of the mutant embryonic phenotype, even when those germ cells are surrounded by wildtype somatic tissues.     

Experimental phenocopy of a minute maternal-effect mutation alters blastoderm determination in embryos of Drosophila melanogaster

Maternal haploinsufficiency for a third chromosome Minute, M(3)i55, lowers rates of protein synthesis by approximately 30% during the syncytial nuclear cycles of early embryogenesis. The maternal effect of Mi55 also produces segmentation defects (denticle belt fusions) in the posterior abdomen of larvae. Furthermore, embryos from Minute mothers show abnormal expression patterns of the segmentation gene fushi tarazu (ftz) at the cellular blastoderm stage of embryogenesis. We developed a computer-aided analysis to describe the deviations in ftz expression which demonstrates that abnormally narrow ftz stripes occur in segment primordia that become fused in the larva. Unexpectedly, an abnormally wide ftz stripe occurs in segment primordia which do not develop abnormally. In addition, Mi55 produces a general narrowing of all ftz- interstripes. We phenocopied the Minute mutation by injecting wild-type embryos with cycloheximide concentrations which decreased protein synthesis rates to levels comparable with those of Minute embryos. Thus, a general decrease in protein synthesis during early embryogenesis leads to abnormal determination of posterior abdominal segment primordia.     

The relationship of relative gene dose to the complex phenotype of the daughterless locus in Drosophila

The daughterless (da) gene provides an essential maternally supplied component for Drosophila sex determination and dosage compensation. In this connection, it is required as a positive regulator of a female-specific master regulatory gene, Sex-lethal (Sxl). In addition, zygotic da gene function is required for male and female viability. Thus, the phenotype da is complex; it includes both maternal and zygotic aspects, as well as both sex-specific and nonsex-specific aspects. Assessment of wild-type da function has relied on the characterization of only a single leaky mutant da allele. In order to better understand the nature of this allele and the relationships between the various aspects of its complex phenotype, tandem duplications of both the mutant and wild-type da alleles were isolated and used in a dose study of this gene's function. Three conclusions were reached: 1) by the most stringent genetic criteria, the mutant da allele is a simple hypomorph, an allele with reduced but non-zero levels of wild-type functions; 2) since increased dose of da+ had no effect on viability or progeny sex ratio, this gene seems not to be a dose-sensitive element of the X/A ratio sex determination signal; and 3) expression of the maternal da+ allele does make a contribution to the nonsex-specific developmental processes that require zygotic da+ function; however, that contribution is clearly minor. In contrast, the zygotic genotype with respect to da appears to have no effect on the expression of Sxl+ in the zygote, the sex-specific process that requires maternal da+ function.