Analysis of l-glycerol-3-phosphate dehydrogenase mutants in Drosophila melanogaster: complementation for intracellular degradation of the mutant polypeptide

The Drosophila melanogaster enzyme glycerol-3-phosphate dehydrogenase 1 is required for oogenesis, embryonic development, and amino acid homeostasis

As the fruit fly, Drosophila melanogaster, progresses from one life stage to the next, many of the enzymes that compose intermediary metabolism undergo substantial changes in both expression and activity. These predictable shifts in metabolic flux allow the fly meet stage-specific requirements for energy production and biosynthesis. In this regard, the enzyme glycerol-3-phosphate dehydrogenase 1 (GPDH1) has been the focus of biochemical genetics studies for several decades and, as a result, is one of the most well-characterized Drosophila enzymes. Among the findings of these earlier studies is that GPDH1 acts throughout the fly lifecycle to promote mitochondrial energy production and triglyceride accumulation while also serving a key role in maintaining redox balance. Here, we expand upon the known roles of GPDH1 during fly development by examining how depletion of both the maternal and zygotic pools of this enzyme influences development, metabolism, and viability. Our findings not only confirm previous observations that Gpdh1 mutants exhibit defects in larval development, lifespan, and fat storage but also reveal that GPDH1 serves essential roles in oogenesis and embryogenesis. Moreover, metabolomics analysis reveals that a Gpdh1 mutant stock maintained in a homozygous state exhibits larval metabolic defects that significantly differ from those observed in the F1 mutant generation. Overall, our findings highlight unappreciated roles for GPDH1 in early development and uncover previously undescribed metabolic adaptations that could allow flies to survive the loss of this key enzyme.

Purification and characterization of the naturally occurring allelic variants of sn-glycerol-3-phosphate dehydrogenase in Drosophila melanogaster

The naturally occurring electrophoretic variants of sn-glycerol-3-phosphate dehydrogenase and a heterodimeric form of the enzyme resulting from a genetic cross of two variant strains of Drosophila were purified to homogeneity by a combination of DEAE-cellulose chromatography and 8-(6-aminohexyl)-amino-ATP-Sepharose affinity chromatography. Each purified protein was compared with respect to a number of physicochemical and kinetic properties. All forms of the enzyme were found to be similar, except for pI differences associated with the electrophoretic variation observed.

Naturally occurring genetic variation affecting the expression of sn-glycerol-3-phosphate dehydrogenase in Drosophila melanogaster

Genetic variation among second and third chromosomes from natural populations of Drosophila melanogaster affects the activity level of sn-glycerol-3-phosphate dehydrogenase (EC 1.1.1.8; GPDH) at both the larval and the adult stages. The genetic effects, represented by differences among chromosome substitution lines with coisogenic backgrounds, are very repeatable over time and are generally substantially larger than environmental and measurement error effects. Neither the GPDH allozyme, the geographic origin, nor the karyotype of the chromosome contributes significantly to GPDH activity variation. The strong relationship between GPDH activity level and GPDH-specific CRM level, as well as our failure to find any thermostability variation among the lines, indicates that most, if not all, of the activity variation is due to variation in the steady-state quantity of enzyme rather than in its catalytic properties. The lack of a strong relationship between adult and larval activity levels suggests the importance of stage- or isozyme-specific effects.

Analyses of genetic variants of L-glycerol-3-phosphate dehydrogenase in Drosophila melanogaster by two-dimensional gel electrophoresis and immunoelectrophoresis

A protein spot corresponding to L-glycerol-3-phosphate dehydrogenase (alpha-GPDH, E.C. 1.1.1.8, NAD+ oxidoreductase) has been identified on a two-dimensional gel (isoelectric focusing-SDS gel) containing up to 150 stained protein spots from a crude Drosophila homogenate. Preliminary identification of the alpha-GPDH in crude fly homogenates prior to electrophoresis and observing an intensity enhancement of the corresponding protein spot on the gels. When three purified electrophoretic variants (slow, fast, and ultrafast) were mixed and analyzed by two-dimensional gel electrophoresis, horizontal displacements of the three protein spots were observed. Immunoprecipitation of the enzyme prior to electrophoresis and gene mapping further confirmed the identity of the alpha GPDH protein spot. The alpha-GPDH spot can also be detected by autoradiography of a two-dimensional gel from a single fly extract, where it has been estimated to constitute 0.5-1% of the total soluble protein. Mutants which express no apparent alpha-GPDH activity were analyzed by two-dimensional gels and immunoelectrophoresis in an attempt to identify and characterize the inactive proteins. It is suggested that these techniques provide a powerful tool, for the analysis of CRM+-null activity mutants of a specific gene-enzyme system.