Analysis of a newly-isolated temperature sensitive maternal effect mutation of Drosophila melanogaster.

A mutation located near the tip of the X chromosome in Drosophila melanogaster has been isolated, and its developmental effects described. This mutation (1(1)ts-1 is temperature sensitive, and at permissive temperature (18 degrees C) develops normally. However, zygotes from females raised or aged at restrictive temperature (28 degrees C) never hatch, regardless of the embryonic genotype. Midgut formation is abnormal in lethal zygotes and dorsal closure is probably incomplete. Temperature shift experiments have shown that the zygotic lethality is governed by a temperature sensitive period in oocytes of stage seven or older. If viable 1(1)ts-1 embryos are shifted to restrictive temperatures, they develop as far as the pupal stage, but never eclose. The temperature sensitive period for pupal lethality includes the last 2.5 days of pupal development and does not involve a maternal effect.     

Localized defects of blastoderm formation in maternal effect mutants of Drosophila

In the three maternal effect lethal mutant strains of D. melanogaster described in this report, the homozygous mutant females produce defective eggs that cannot support normal embryonic development. The embryos from these eggs begin to develop for the first 2 hr after fertilization in an apparently normal way, forming a blastula containing a cluster of pole cells at the posterior end and a layer of syncytial blastoderm nuclei. During the subsequent transition from a syncytial to a cellular blastoderm, cell formation in the blastoderm is either partially or totally blocked. In mutant mat(3)1 no blastoderm cells are formed, indicating that there are separate genetic controls for pole cells and blastoderm cells. The other two mutants form an incomplete cellular blastoderm in which certain regions of the blastoderm remain noncellular. The noncellular region in mutant mat(3)3 is on the posterior-dorsal surface, covering about 30% of the total blastoderm. In mutant mat(3)6 blastoderm cells are formed only at the anterior and posterior ends, separated by a noncellular region that covers about 70% of the total blastoderm. The selective effects on blastoderm cell formation in the three mutants emphasize the importance of components present in the egg before fertilization for the transition from a syncytial to a cellular blastoderm.The genes defective in the three mutants are essential only for oogenesis and not for any other period of development, as indicated by a strict dependence of the lethal phenotypes on the maternal genotypes. Heterozygous embryos from the eggs of homozygous mutant females die, whereas homozygous mutant embryos from the eggs of heterozygous females develop into viable adults.One of the mutants, mat(3)3, has a temperature-sensitive phenotype. Homozygous mat(3)3 females maintained at a restrictive temperature of 29°C show the lethal maternal effect. However, at a permissive temperature of 20°C the females produce viable adult progeny. The temperature-sensitive period in mat(3)3 females occurs during the last 12 hr of oogenesis, consistent with the maternal effect phenotype of the mutant.     

Germ line dependence of the deep orange maternal effect in Drosophila

Pole cell transplantations were used to determine the tissue specificity of maternal effects in Drosophila. The deep orange maternal effect is shown to be germ line autonomous. A cytoplasmic injection assay was used to determine when the dor⁺ substance could be detected in the developing oocyte. The dor⁺ substance is present during the early stages of vitellogenesis but could not be detected in the yolk of the embryo after blastoderm cellularization.     

Competition between cleavage nuclei in Drosophila

Distribution of tissues of XX and XO genotype in gynandromorphs resulting from elimination of unstable ring X-chromosome during initial cleavage divisions was studied. Predominantly XX-nuclei proved to give rise to cell nuclei in tissues of cranial and caudal regions of mosaics. XX nuclei are proposed to be more migrationally active than XO nuclei.     

Localization and possible functions of Drosophila septins.

The septins are a family of homologous proteins that were originally identified in Saccharomyces cerevisiae, where they are associated with the "neck filaments" and are involved in cytokinesis and other aspects of the organization of the cell surface. We report here the identification of Sep1, a Drosophila melanogaster septin, based on its homology to the yeast septins. The predicted Sep1 amino acid sequence is 35-42% identical to the known S. cerevisiae septins; 52% identical to Pnut, a second D. melanogaster septin; and 53-73% identical to the known mammalian septins. Sep1-specific antibodies have been used to characterize its expression and localization. The protein is concentrated at the leading edge of the cleavage furrows of dividing cells and cellularizing embryos, suggesting a role in furrow formation. Other aspects of Sep1 localization suggest roles not directly related to cytokinesis. For example, Sep1 exhibits orderly, cell-cycle-coordinated rearrangements within the cortex of syncytial blastoderm embryos and in the cells of post-gastrulation embryos; Sep1 is also concentrated at the leading edge of the epithelium during dorsal closure in the embryo, in the neurons of the embryonic nervous system, and at the baso-lateral surfaces of ovarian follicle cells. The distribution of Sep1 typically overlaps, but is distinct from, that of actin. Both immunolocalization and biochemical experiments show that Sep1 is intimately associated with Pnut, suggesting that the Drosophila septins, like those in yeast, function as part of a complex.     

Homoeosis in Drosophila: Evidence for a maternal effect of the polycomb locus

When heterozygous, dominant mutant alleles of the Polycomb locus are associated with a variety of adult homoeotic effects. Zygotes homozygous for these alleles die as late embryos showing homoeotic transformation of head, thoracic, and abdominal segments. This study shows that embryos homozygous for Pc³ are more extreme than those homozygous for Pc¹ or Pc². Moreover, Pc¹/Pc³ heterozygotes are more extensively transformed if their mothers were Pc³/ + than if they were Pc¹/ +; this effect does not depend on zygotic genetic background and must be maternal in nature. Embryos homozygous for Pc³ are less extreme if they arise from Pc³/ + / + than from Pc³/ + mothers. These results strongly suggest that the Polycomb locus acts maternally as well as zygotically to affect early determinative decisions.     

A possible maternal effect in the abnormal hyporesponsiveness to specific alloantigens in offspring born to neonatally tolerant fathers

Newborn CBA mice were inoculated i.p. with 1 X 10(8) adult (CBA X A)F1 lymphoid cells with 5 X 10(7) F1 hybrid lymphoid cells thereafter inoculated i.v. at 14-day intervals. The mice were subsequently grafted with A/J tail skin at 24 days of age. At 8 wk of age, individual tolerant males with intact skin grafts were each mated with similar tolerant skin-grafted females or with 8-wk-old control normal CBA females. Approximately 0.4 ml of peripheral blood from 7-wk-old progeny born to these crosses, along with the blood from age-matched progeny born to normal CBA incrosses, were used for in vitro mixed leukocyte cultures (MLC). All progeny received skin grafts of (CBA X A)F1 tail skin at 7 1/2 wk of age. In this study, we show i) that MLC hyporesponsiveness to histocompatible cells is an acquired phenotype expressed by lymphoid cells of the progeny of tolerant male mice, and ii) that these progeny also show delayed rejection of (CBA X A)F1 skin grafts. The continued breeding of the first generation animals established that a similar transmission of hyporesponsiveness can be observed in the second generation progeny. When putatively normal females, however, which had borne several litters after mating with neonatally tolerant males, were mated with "normal" (nontolerant) males; their offspring also exhibited a specific hyporesponsiveness in MLC to the initial tolerizing allodeterminants. This suggests that there may ultimately be a maternally derived origin for the transmission of characters from tolerant males.     

A genetic maternal effect on egg surface in Tribolium castaneum.

Females homozygous for an autosomal recessive gene, wd, produce "weird" eggs that are dry when laid. The wd gene has some important population consequences and also provides a very useful example of a genetic maternal effect for laboratory courses.     

Dynamics of maternal morphogen gradients in Drosophila

The first direct studies of morphogen gradients were done in the end of 1980s, in the early Drosophila embryo, which is patterned under the action of four maternally determined morphogens. Since the early studies of maternal morphogens were done with fixed embryos, they were viewed as relatively static signals. Several recent studies analyze dynamics of the anterior, dorsoventral, and terminal patterning signals. The results of these quantitative studies provide critical tests of classical models and reveal new modes of morphogen regulation and readout in one of the most extensively studied patterning systems.     

Complementation and maternal effect in insulin-dependent diabetes.

The marker association segregation chi-square (MASC) method was applied to a sample of 416 Caucasians affected with insulin-dependent diabetes mellitus (IDDM), for which information on the parental and sibship status was available, as well as HLA typing. We show that the model which best explains all the observations assumes a cis or trans complementation of two tightly linked genes within the HLA region, an additional maternal effect, and other familial factors. The HLA molecule corresponding to the complementation of Arg52(+) and Asp57(-) has been recently proposed as explaining susceptibility to IDDM. However, this hypothesis does not account for the overall observations made on the HLA marker in IDDM patients and their relatives. The MASC method may also be applied to evaluate the risk for relatives of an affected individual (the "index"). For example, the risk for a sib depends not only on the parental status and on the number of HLA haplotypes he shares with the index, but also on which haplotype the index himself inherited from his mother and father.