DPhK-gamma, a putative Drosophila kinase with homology to vertebrate phosphorylase kinase gamma subunits: molecular characterisation of the gene and phenotypic analysis of loss of function mutants

Functional analysis of the glycogen binding subunit CG9238/Gbs-70E of protein phosphatase 1 in Drosophila melanogaster

The product of the CG9238 gene that we termed glycogen binding subunit 70E (Gbs-70E) was characterized by biochemical and molecular genetics methods. The interaction between Gbs-70E and all catalytic subunits of protein phosphatase 1 (Pp1-87B, Pp1-9C, Pp1-96A and Pp1-13C) of Drosophila melanogaster was confirmed by pairwise yeast two-hybrid tests, co-immunoprecipitation and pull down experiments. The binding of Gbs-70E to glycogen was demonstrated by sedimentation analysis. With RT-PCR we found that the mRNAs coding for the longer Gbs-70E PB/PC protein were expressed in all developmental stages of the fruit flies while the mRNA for the shorter Gbs-70E PA was restricted to the eggs and the ovaries of the adult females. The development specific expression of the shorter splice variant was not conserved in different Drosophila species. The expression level of the gene was manipulated by P-element insertions and gene deletion to analyze the functions of the gene product. A small or moderate reduction in the gene expression resulted in no significant changes, however, a deletion mutant expressing very low level of the transcript lived shorter and exhibited reduced glycogen content in the imagos. In addition, the gene deletion decreased the fertility of the fruit flies. Our results prove that Gbs-70E functions as the glycogen binding subunit of protein phosphatase 1 that regulates glycogen content and plays a role in the development of eggs in D. melanogaster.

Increased extracellular adenosine in Drosophila that are deficient in adenosine deaminase activates a release of energy stores leading to wasting and death

Extracellular adenosine is an important signaling molecule in neuromodulation, immunomodulation and hypoxia. Adenosine dysregulation can cause various pathologies, exemplified by a deficiency in adenosine deaminase in severe combined immunodeficiency. We have established a Drosophila model to study the effects of increased adenosine in vivo by mutating the main Drosophila adenosine deaminase-related growth factor (ADGF-A). Using a genetic screen, we show here that the increased extracellular adenosine in the adgf-a mutant is associated with hyperglycemia and impairment in energy storage. The adenosine works in this regard through the adenosine receptor as an anti-insulin hormone in parallel to adipokinetic hormone, a glucagon counterpart in flies. If not regulated properly, this action can lead to a loss of energy reserves (wasting) and death of the organism. Because adenosine signaling is associated with the immune response and the response to stress in general, our results mark extracellular adenosine as a good candidate signal involved in the wasting syndrome that accompanies various human pathologies.

The Drosophila bifocal gene encodes a novel protein which colocalizes with actin and is necessary for photoreceptor morphogenesis

Photoreceptor cells of the Drosophila compound eye begin to develop specialized membrane foldings at the apical surface in midpupation. The microvillar structure ultimately forms the rhabdomere, an actin-rich light-gathering organelle with a characteristic shape and morphology. In a P-element transposition screen, we isolated mutations in a gene, bifocal (bif), which is required for the development of normal rhabdomeres. The morphological defects seen in bif mutant animals, in which the distinct contact domains established by the newly formed rhabdomeres are abnormal, first become apparent during midpupal development. The later defects seen in the mutant adult R cells are more dramatic, with the rhabdomeres enlarged, elongated, and frequently split. bif encodes a novel putative protein of 1063 amino acids which is expressed in the embryo and the larval eye imaginal disc in a pattern identical to that of F actin. During pupal development, Bif localizes to the base of the filamentous actin associated with the forming rhabdomeres along one side of the differentiating R cells. On the basis of its subcellular localization and loss-of-function phenotype, we discuss possible roles of Bif in photoreceptor morphogenesis.