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A M Handler

Publications and source records attributed to A M Handler.

27 records · Page 2Linked to original sources
PubMed1989

Ecdysteroid receptors in Drosophila melanogaster adult females.

Ecdysteroid receptors were identified and partially characterized from total cell extracts of whole animals and dissected tissues from Drosophila melanogaster adult females. Binding studies indicated the presence of two ecdysteroid binding components having high affinity and specificity consistent with receptors previously identified in embryos and larvae. The highest affinity binding component in 3- to 4-day females had a dissociation constant of 9.2 x 10(-10) M and a maximal binding concentration of approximately 90 pmol/g protein, with a lower affinity component having a dissociation constant of 2.94 X 10(-9) M. Receptors at similar concentrations were also observed in abdominal walls containing adult fat body, with relatively lower receptor levels observed in ovaries. These results indicate that the observed ecdysteroid hormone concentrations in adult females can account for a physiological stimulatory effect on yolk protein synthesis in adult fat body.

Animals↗
PubMed1988

Mobility of P elements in drosophilids and nondrosophilids.

The mobility properties of the Drosophila melanogaster P element in drosophilid and nondrosophilid species has been determined using a P-element mobility assay that is conducted transiently in insect embryos. P elements are mobilizable in all drosophilids tested, including species outside the genus Drosophila but not in the related Tephritidae (order: Diptera), although the P-element gene necessary for mobility, transposase, is transcribed. These results show that without modifications P elements will not serve as general insect gene vectors and suggest that nonconserved host-encoded factors participate in the transposition of P elements. Our methods will be generally useful for analyzing the cis- and trans-acting factors required for P-element mobility in vivo and could be used to analyze the mobility properties of other transposable elements in insects.

Journal Article↗
PubMed1985

Sex-specific regulation of yolk protein gene expression in Drosophila.

Many of the genes in the regulatory hierarchy controlling sex determination in Drosophila melanogaster are known. Here we examine how this regulatory hierarchy controls the expression of the structural genes encoding the female-specific yolk polypeptides. Temperature shift experiments with a temperature-sensitive allele of the sex determination regulatory gene transformer-2 (tra-2) showed that tra-2+ function is required in the adult for both the sex-specific initiation and maintenance of YP synthesis. Control of the YP genes by this regulatory hierarchy is at the level of transcription, or transcript stability. The results of temperature shift experiments with abdomens isolated from tra-2ts homozygotes support the notion that the tra-2+ function acts in a cell-autonomous manner to control YP synthesis. These results provide a paradigm for the way this regulatory hierarchy controls the terminal differentiation functions for sexually dimorphic development.

Animals↗
PubMed1977

Endocrine control of vitellogenesis in Drosophila melanogaster: effects of the brain and corpus allatum.

The endocrine control of yolk deposition in Drosophila melanogaster was studied by ligation and transplantation techniques. Endocrine events associated with the initiation of vitellogenesis were found to be synchronized with eclosion rather than the completion fo adult development. Decapitation experiments showed that a cephalic event occurring at about the time of eclosion is necessary for each animal to initiate vitellogenesis. The morphogenetic effect of the head could be replaced by a juvenile hormone analog (JHA). In addition to the cephalic event, a thoracic factor is required for each follicle to initiate vitellogenesis, since preparation of isolated abdomens before 16 hours after eclosion prevented vitellogenesis. In abdomens isolated after this time, no early vitellogenic stages were formed. The suppression of vitellogenesis in isolated abdomens was reversed by implanting corpora allata or by treating these preparations with JHA, but not by implanting corpora cardiaca. Ovaries that were artificially induced to mature by treating isolated abdomens with JHA still displayed the normal complement of ovarian proteins after electrophoresis in polyacrylamide gels. These results show that a circadian clock triggers vitellogenesis via a cephalic signal at eclosion, which in turn triggers events in the thorax or abdomen. The cephalic signal can be superseded by juvenile hormone, whose presence is necessary for each follicle to become vitellogenic.

Animals↗