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Biomedical subjects

M Bownes

Publications and source records attributed to M Bownes.

At least 91 records · Page 5Linked to original sources
PubMed1981

Sex determining genes and vitellogenin synthesis in Drosophila melanogaster.

This study investigates the relationship between sexual phenotype and ability to synthesize vitellogenin (yolk proteins, YPs) in Drosophila. Various mutations were used to transform XX and XY animals into intersexes or pseudomales (Table 1). The presence or absence of YPs in the haemolymph and in the fat body was determined by SDS gel electrophoresis, fluorography, and precipitation of YPs with anti-YP antibody (see Fig.1). YPs were synthesized whenever the flies displayed at least some female morphological characteristics, regardless of their sex chromosome constitution (Table 1; Fig. 2). Pseudomales (definition see p. 1) did not produce detectable amounts of YPs despite their female XX-karyotype. Immature ovaries, transplanted into adult males or pseudomales, developed normally and synthesized YPs, but the fat bodies of the host males or pseudomales were not induced to synthesize YPs. Vitellogenesis was, however, induced in the fat bodies of males and pseudomales by injection of 20-hydroxyecdysone (ecdysterone) (Fig. 3). The results are interpreted to mean that the sexual pathways are controlled by a small number of key genes that regulate the synthetic activities of many sex-specific genes. However, the female-specific YP genes can be activated with ecdysterone although the genetic signals are set for male differentiation.

Animals↗
PubMed1981

Characterisation of a new tumorous-head mutant of Drosophila melanogaster.

A new homoeotic mutant, I127, showing abnormal growths in the head region including homoeotic transformation of eye to genitalia and antenna to leg, was isolated in a screen designed to find new alleles of the tumourous head (tuh-3), mutation. Similarities in the phenotype and genetics of the mutant, and complementation studies with tuh-I; tuh-3, suggest that I127 is indeed an allele of tuh-3. In combination with the first chromosome modifier tuh-1, the mutant is temperature-sensitive during the third larval instar, giving an increased penetrance of the tumorous head phenotype when reared at 25 degrees C as opposed to 18 degrees C. The isolation of further alleles at the tumorous-head locus are essential. The type of morphological defects which can result from mutations at this locus would enable us to establish if this is a complex locus, and if null mutations are lethal during development. The interactions of the tumorous-head gene with first chromosome modifiers and other homoeotic mutations will only be understood if we are able to induce a number of mutations at this locus, and as a consequence begin to elucidate the role of the wild-type gene product in normal development.

Alleles↗
PubMed1981

Staging the metamorphosis of Drosophila melanogaster.

A sequence of 51 visible changes is described during the course of metamorphosis in Drosophila melanogaster, and a series of 24 convenient stages is defined for use in the experimental analysis and exploitation of this part of the insect life cycle. The duration of each stage is estimated and times are suggested for batch collections of symphasic animals.

Animals↗
PubMed1980

Drosophila nuclei replicate in Xenopus eggs.

Nuclei isolated from a permanent cell line derived from Drosophila melanogaster embryos have been injected, along with a radioactive DNA precursor [3H]TTP, into Xenopus laevis eggs. In culture, less than 7% of the cells were in S phase. After a 90 min incubation, following injection into eggs, 99% of the nuclei were shown by autoradiography to have synthesized DNA. In a similar experiment, a density label BrdUTP was injected into eggs along with the nuclei. Subsequent analysis on caesium chloride gradients showed that this DNA synthesis was semi-conservative replication. Therefore we conclude that signals present in Xenopus egg cytoplasm can initiate and sustain true semi-conservative DNA replication in nuclei from an invertebrate organism.

Animals↗
PubMed1979

Acquisition of differentiative capacity in imaginal wing discs of Drosophila melanogaster.

The wing discs from larvae undergoing the moult from 1st to 2nd instar are able to differentiate some parts of the adult wing when forced to undergo a premature metamorphosis. The first structures which differentiate are parts of the wing hinge and the wing blade. As development proceeds and older discs are forced through metamorphosis, the capacity to differentiate moves out both proximally and distally until gradually all of the derivatives of a mature wing disc are formed. Individual structures often differentiate from young discs in an incomplete form and pattern elements, such as bristles or sensilla, are added as older discs are tested.

Animals↗
PubMed1978

Genetic analysis of vitellogenesis in Drosophila melanogaster: the identification of a temperature-sensitive mutation affecting one of the yolk proteins.

A number of female sterile mutations on the first and third chromosomes of Drosophila melanogaster have been screened for defects in the yolk proteins using polyacrylamide gel electrophoresis. Two new mutants were identified. 6m45 accumulates all three yolk proteins (YP1, YP2 and YP3) in the haemolymph but they are all absent from the ovaries suggesting it is a yolk-protein-uptake mutant. In contrast, 1163 is a temperature-sensitive mutation with a large reduction in the quantity of YP1 in the haemolymph and ovaries at 29 degrees C. Both mutants are autonomous in ovary transplant experiments.

Animals↗
PubMed1978

Developmental analysis of the tumorous head mutation in Drosophila melanogaster.

The extent and type of adult transformations in the tumorous head (tuh) mutation of Drosophila melanogaster were studied. The observations indicate homeotic transformations, duplications and deficiencies of eye antennal disc derivatives. Contrary to previous observations there is no transformation of eye to abdomen and the only homeotic transformations identifiable are antenna to leg and rostralhaut to genitalia. Embryonic and post-embryonic lethality was also examined. Specific anterior abnormalities were found in embryos leading to early death. The amount of embryonic lethality was not affected by increased temperature during oogenesis. When analysing the adult phenotype, however, the whole period of oogenesis was sensitive to pulses of increased temperature; the pulses however did not have to be restricted to any particular stage of oogenesis to be effective in increasing tuh penetrance. The increase in the penetrance of the adult transformations is also exhibited when eggs are moved from 25 degrees C to 29 degrees C from the 8th to the 12th hour of embryonic development. Experiments indicate that the tuh-3 gene is active before the 8th hour of embryogenesis.

Animals↗
PubMed1977

Developmental effects of exposing Drosophila embryos to ether vapour.

Drosophila embryos at precise developmental stages were exposed to ether vapour. The defects in the resulting embryos and adults were observed. Ether disrupted embroygenesis in specific ways, causing defects primarily at the anterior of the embryo and disorganizing the arrangement of the segments. Adults showed deficiencies and duplications of many imaginal disc and histoblast derivatives. Phenocopies of the bithorax mutation which transforms metathorax to mesothorax were observed. They were first induced at the syncytial blastoderm stage, had their peak of production at the cellular blastoderm, and were no longer observed after the anterior and posterior midgut were partially invaginated. It was observed that not only are the halter/wing transformations confined to the anterior compartment, but also leg 3 to leg 2 transformations only occurred in the anterior leg compartment.

Animals↗
PubMed1977

Accumulation and degradation of three major yolk proteins in Drosophila melanogaster.

In contrast to previous findings, three major yolk proteins have been identified in the oocytes and eggs of Drosophila melanogaster. They are also present as major proteins in the haemolymph of mature females and in trace amounts in the haemolymph of young females; the male haemolymph lacked all three proteins. Female fat body contained the three proteins and, surprisingly, trace amounts were also present in the male fat body. The accumulation and degradation of the three yolk proteins by oocytes and embryos was asynchronous suggesting that independent controls may exist.

Adipose Tissue↗
PubMed1977

Developmental effects of X-irradiation of early Drosophila embryos.

Drosophila embryos were treated at specific stages during early embryogenesis with various doses of X-irradiation. The lethality at various times during development was established and pattern defects in the adults noted. It was observed that the most sensitive stages of embryogenesis to X-ray-induced lethality were also the stages where most morphological defects were found in the adults which emerged. This suggests that presumptive larval and adult cells are sensitive to X-rays at the same stages of embryogenesis.

Animals↗
PubMed1977

Abnormal oogenesis and embryogenesis resulting from centrifuging Drosophila melanogaster females.

Females of Drosophila melanogaster were centrifuged at 2400 g and 4200 g for 3 h in a number of different orientations. The oocytes in various stages of vitellogenesis become separated into three layers; a centrifugal yolk layer, a central cytoplasmic layer, and a centripetal lipid layer. The direction of layering is related to the orientation of the female. The process of recovery of the ovaries was followed and the development of the eggs laid analysed. Many of the eggs laid over the subsequent 3 days die very early in development and fail to produce any differentiated structures. Some hatch into normal larvae and others produce defective embryos. The most common defect being a misarrangement of the segmentation. The differences in the kinds of experimentally inducible pattern aberrations in Drosophila and other diptera is discussed.

Animals↗
PubMed1976

Larval and adult abdominal defects resulting from microcautery of blastoderm staged Drosophila embryos.

Drosophila embryos were damaged by microcautery at the cellular blastoderm stage at the sites of presumptive histoblasts, identified from fate maps. The resulting adults were analyzed for abnormal abdominal structures in one series, and in two further series the pupal cases of the defective adults which hatched were also checked for irregularities in segmentation of the larva, both dorsally and ventrally. The relationships between the larval segmentation and adult pattern are described. A sample of pupal cases of morphologically normal flies hatching from microcautery were checked and showed that regulation only rarely occurred, i.e., abnormal larvae sometimes produced normal adults. Both tergite and sternite defects occurred, and duplications of parts of these structures were observed in both cases. In general, abnormal fusions, missing hemi-segments, and partial deletions were associated with larval defects and were therefore probably the result of damage to larval cells, or both larval cells and histoblasts. Duplications and partial segment deficiencies also resulted from apparantly normal pupal cases and were therefore probably the result of directly damaging the presumptive histoblast cells of the blastoderm. It is suggested that the various nests of histoblasts in each segment act as one morphogenetic field, with larval cells within the field.

Abdomen↗