Developmental studies on two ecdysone deficient mutants ofDrosophila melanogaster

Summary This paper describes two ecdysone-deficient, recessive-lethal mutants,lethal(1)giant ring gland (grg) andlethal(1)suppressor of forked ^mad-ts (mad-ts: Jürgens and Gateff 1979) and compares their ecdysteroid titers with that of the wild-type. Mutant larvae show a much reduced ecdysteroid content, amounting to 1/10 to 1/30 of the wild-type values, but never a true titer peak. They fail to pupate and die after 1–3 weeks. Ecdysteroid feeding elicits different responses in the larvae of the two mutants.mad-ts larvae pupate within 24 h, thus showing that their low ecdysteroid titer is directly connected to their inability to pupate.mad-ts resembles the mutantlethal (3)ecdysone-1 ^ts (Garen et al. 1977). Thegrg mutant larvae, on the other hand, fail to pupate after 20-hydroxyecdysone feeding as well as injection. The primary defect of thegrg mutant is not entirely clear. Thegrg larval salivary gland cells appear to possess normal ecdysteroid receptors. Furthermore, the low ecdysteroid titer ingrg is not the result of an increased ecdysteroid catabolism. The primary defect in the mutant may lie in the malfunctioning neurosecretory cells which do not show neurosecretion in histological preparations. Further support for this notion comes from electronmicrographs of the enlargedgrg ring glands which, in contrast to the wild-type, do not possess nerve endings.In the wild-type three ecdysteroid peaks were found: one shortly before puparium formation, the second at approximately 12 h and the third at about 30 h after pupation. The ecdysteroid titer peak in late third instar, wild-type larvae is mainly due to the presence of 20-dydroxyecdysone as shown by radioimmunoassays after thin layer chromatography and derivatization followed by gas liquid chromatography and mass spectroscopy. In addition, a number of unidentified polar and apolar metabolites were also present.     

Genes involved in the activation of the bithorax complex ofDrosophila

Summary We have studied the genetic properties and developmental effects of several mutations, in eight different loci, which alter the specification of embryonic segments. All of the changes are related to the transformations caused by mutants of the bithorax complex.Several properties: the interactions of these mutants with different mutants of the bithorax complex, the interactions between themselves, the effect of changing dosages of their wildtype alleles and their response to ether induction of phenocopies permit one to distinguish between those mutations which affect activation of the bithorax genes in early embryogenesis and those which affect expression of the bithorax genes during development. This paper deals mainly with the Rg-bx locus and its interactions with other loci which affect segment specification.In particular two loci show genetic and developmental characteristics which seem to conform to those expected for a repressor coding gene (Polycomb) and for an inducer synthesizing gene (Rg-bx) active in a negative control system of the genes in the bithorax complex. A model for the interaction of the wildtype products of these genes to determine the segmental characteristics of both the thorax and abdomen is proposed.     

Enhancer of bithorax: a mutation ofDrosophila melanogaster

A recessive lethal mutation ofDrosophila melanogaster which as heterozygote enhances the phenotype of several mutant combinations of thebithorax-complex (BX-C) is described here; it is calledEnhancer of bithorax (E(bx)²). The linkage group and the map position of this mutation have been determined; it maps on the third chromosome at - 1.65 map units. It has been cytologically localised to the region 61A1-6. This locus is a possible candidate for positive control of BX-C.     

Behavioral analysis ofDrosophila mutants displaying abnormal male courtship

We describe six recessive autosomal male sterile mutations inDrosophila, generated by mobilization of single P-elements, exhibiting abnormal male courtship behavior. Detailed analysis of courtship behavior elicited by virgin wild type females indicated that five of the six mutants are affected in the early steps of courtship. The sixth mutant is blocked at the step of attempted copulation which occurs later in the courtship sequence. All of the mutants have normal olfactory responses and normal locomotor activity. No defect in the visual modality has been observed for the five mutants affected in the initiation of courtship. The mutant blocked at attempted copulation lacks the ‘on’ and ‘off’ transients, but this appears to be due to genetic background rather than the mutation itself. Abnormal spermatogenesis was observed in five of the mutants. Spermatogenic defects vary and include lesions in the proliferation of the germline, in meiosis, and in the differentiation and maturation of the spermatids into motile sperm.     

Genetic analysis of viable and lethalfused mutants ofDrosophila melanogaster

Summary Fused is a segmentation gene belonging to the segment-polarity class. Mutations at thefused locus are known to display pleiotropic effects, causing zygotically determined anomalies of ovaries and of some adult cuticular structures, and maternally determined embryonic segmentation defects. In order to determine the amorphic phenotype offused and to study the genetical basis of its pleiotropy, newfused alleles (18 viable and 11 lethal) were isolated. The phenotype of these mutants and of others already known are described, taking into account zygotic and maternal effects. The main results provided by this analysis are as follows. Firstly, allfused alleles show the whole complex fused phenotype, and a good correlation is observed between the strength of the wing and segmentation defects, suggesting that a single function is involved in both processes. Secondly, all embryonic and larval lethals carry deficiencies which allow us to localizefused between the 17C4 and 17D2 bands of the X-chromosome. Thirdly, the 24 viable and 2 pupal lethals examined behave as point mutants, as shown cytologically or by Southern blot analysis. However, only one of them, the pupal lethalfu ^mH63 was proven to carry a nullfused allele, since it displays in germ-line clones a strong maternal phenotype and a very low zygotic rescue, similar to those of the small deficiencyDf(1)fu ^z4. The phenotype of the amorphic mutant indicates that zygotic ezpression offused is required for normal metamorphosis, while maternal expression is necessary for a normal segmentation pattern, since a complete loss offused expression during oogenesis cannot be compensated zygotically.     

Rudimentary mutants ofDrosophila melanogaster

Summary The X-linkedrudimentary (r) mutants ofDrosophila melanogaster are pyrimidine auxotrophs and require exogenous pyrimidines (Nørby, 1970; Falk, 1976). We have established a set ofrudimentary cell lines that are derived from embryos, homozygous for eitherr ¹ orr ³⁶. The enzymatic activities of the pyrimidine synthesizing enzymes were measured in the mutant lines. We have further investigated the nutritional requirements of the mutant cells in vitro by using a pyrimidine free culture medium.Ther ¹ cell lines were found to express 3–7%dihydroorotase (DHOase) activity as compared to a wildtype cell line. Reducedaspartate transcarbamylase (ATCase) activity was measured in somer ¹ cell lines whereas wildtypecarbamylphosphate synthetase (CPSase) activity is expressed in allr ¹ cell lines. Ther ³⁶ cell line expresses wildtype activity ofDHOase andCPSase. ATCase activity was found to be reduced to 10% of the wildtype activity.The mutant cell lines do not proliferate in pyrimidine free minimal medium and cell proliferation is obtained by the addition of crude RNA. Proliferation of ther ¹ cells is restored by the supplementation of the minimal medium withdihydroorotate whereas proliferation of ther ³⁶ cells is restored by supplementation with eitherdihydroorotate orcarbamylaspartate.The results demonstrate that therudimentary phenotypesr ¹ andr ³⁶ are expressed at the cellular level and that the two mutant cell types behave as cellular pyrimidine auxotrophs in vitro.     

Sugar-hydrolysing enzymes in gustatory mutants ofDrosophila

The distribution of the isozymes of α-glucosidase in different parts ofDrosophila melanogaster was examined. Two of the eight glucosidase bands are associated with tarsi. The gustatory mutations in the genesgustB andgustC greatly reduce tarsal glucosidase activity, but the enzyme deficiency is not correlated with inability to taste sugars.     

Dietary fatty acid effects on morphogenesis in bithorax mutants

Three bithorax alleles of Drosophila melanogaster were tested to determine if dietary additions of fatty acids would alter their gene expression. For the bx¹ allele, myristic, oleic, and linoleic acids were all effective in reducing gene expression while fatty acid supplementation was ineffective with the bx³ and bx^34e alleles. For bx¹ the nutritionally sensitive period was found to occur in the first 48 h of larval life.     

Autonomous cellular differentiation of homoeotic bithorax mutants of Drosophila melanogaster

Various mixtures of imaginal disc cells from wild-type and from homoeotic bithorax mutants have been studied in an in vivo Drosophila cell culture system. These mutants effect specific types of segmental transformations, e.g., bithorax-3 (bx³) transforms the anterior region of the metathorax (MT) into a region resembling the anterior mesothorax (MS), while postbithorax (pbx) transforms the posterior MT into a posterior MS-like region. In cell mixtures, wild-type haltere-disc cells segregate from wild-type wing-disc cells. On the other hand, bx³ and pbx haltere-disc cells integrate with wild-type cells derived from anterior and posterior regions, respectively, of wing discs. The behavior of these and other tested mutants of the bithorax series indicates in all cases studied that (1) the effects of the mutants are cell-autonomous, and (2) cellular affinities are determined by the genetic constitution rather than the segmental origin of the cells.     

Larval adipose tissue of homoeotic bithorax mutants of Drosophila.

In the homoeotic bithorax mutant combination bx³$\text{pbx}\text{Ubx}{}^{105}$ of Drosophila melanogaster, the metathoracic segment is transformed to a mesothoracic segment and the adult flies have an extra pair of wings in place of the paired halteres [Lewis, E. B. (1963). Amer. Zool.3, 33–56]. The morphology of the larval fat body, the number of cells in the fat body, and the distribution pattern of kynurenine autofluorescent materials (KAF+) in this tissue were compared in the homoeotic mutant and a wild-type strain. The mutant has an additional mass of adipose cells anterior to the posterior margin of the ventral commissure of the fat body. However, the total number of adipose cells in the two strains as well as the limits of the KAF+ cell population do not differ. Therefore, the bithorax transformation in the larval fat body involves rearrangement of the same cell population as that in the normal strain. This study suggests (1) that the bithorax mutant genes affect the pattern of cell segregation and/or migration of preblastoderm nuclei during embryogenesis and (2) that the larval fat body of Drosophila has a segmental origin.     

Developmental homeostasis in X-rayed populations ofDrosophila pseudoobscura

An experiment was designed to study the effects of various dosages of X-ray irradiation on different gene-arrangements (AR and CH) of the third chromosome ofD. pseudoobscura, with respect to quantitative characters.Egg production showed an insignificant decline at 1500r and an increasingly strong reduction by 3000 and 4500r. Other characters studied (emergence, longevity, body size and weight) generally showed the same trend.Irradiation of both gene-arrangements usually gave more reduction in fitness characters than did irradiation of one gene arrangement alone. Irradiation caused an increase in phenotypic variability as expressed by coefficients of variation.Heterosis in F₁ was observed for most of the characters studied, and a breakdown of heterosis in F₂. Heterosis was enhanced by irradiation at higher dosages.Relative indices of general performance indicate that the adaptive values decreased with the increase in radiation dosages. In all cases the heterozygous genotypes are the fittest while the CH/CH homozygote was the least fit.The present work was carried out during the author's tenure of a Fellowship (PHS Grant No. CRT-5013) given by the Roscoe B. Jackson Memorial Laboratory, Bar Harbor, Maine, U.S.A.     

Gradients of differentiation in wild-type and bithorax mutants of Drosophila

We present evidence to show that differentiation in wing cells to produce hairs is synchronous over the distal 90% of the wing surface (approximately 28,000 cells). In spite of this synchrony within such a large area a temporal gradient exists between zones (in general anterior to posterior) on the animal surface with rather sharp boundaries in between. In order to evaluate the basis for the gradient we studied two mutants which carry different combinations of the genes of the bithorax complex. These were examined with respect to the temporal aspects of sensitivity to heat shock induction of the multihair phenocopy on wings and the time of initiation of the program of protein synthesis that is related to hair formation. Results show that the gradient observed is based on predetermined properties within specific areas of tissue rather than on the position of the cells in the animal.