Biology subjects

Julick, C. R.

Publications and source records attributed to Julick, C. R..

4 recordsLinked to original sources

bioRxiv2019

Lactate and glycerol-3-phosphate metabolism cooperatively regulate growth and redox balance during Drosophila melanogaster larval development

The dramatic growth that occurs during Drosophila larval development requires rapid conversion of nutrients into biomass. Many larval tissues respond to these biosynthetic demands by increasing carbohydrate metabolism and lactate dehydrogenase (dLDH) activity. The resulting metabolic program is ideally suited to synthesize macromolecules and mimics the manner by which cancer cells rely on aerobic glycolysis. To explore the potential role of Drosophila dLDH in promoting biosynthesis, we examined how dLdh mutations influence larval development. Our studies unexpectantly found that dLdh mutants grow at a normal rate, indicating that dLDH is dispensable for larval biomass production. However, subsequent metabolomic analyses suggested that dLdh mutants compensate for the inability to produce lactate by generating excess glycerol-3-phosphate (G3P), the production of which also influences larval redox balance. Consistent with this possibility, larvae lacking both dLDH and G3P dehydrogenase (GPDH1) exhibit developmental delays, synthetic lethality, and aberrant carbohydrate metabolism. Considering that human cells also generate G3P upon Lactate Dehydrogenase A (LDHA) inhibition, our findings hint at a conserved mechanism in which the coordinate regulation of lactate and G3P synthesis imparts metabolic robustness upon growing animal tissues.

developmental biology↗

bioRxiv2018

Genetic variation for ontogenetic shifts in metabolism underlies physiological homeostasis in Drosophila

Organismal physiology emerges from metabolic pathways and structures that can vary across development and among individuals. Here we tested whether genetic variation at one level of physiology can be buffered at higher levels during development by the inherent capacity for homeostasis in physiological systems. We found that the fundamental scaling relationship between mass and metabolic rate, as well as the oxidative capacity per mitochondria, differed significantly across development in the fruit fly Drosophila. However, mitochondrial respiration rate was maintained across development at similar levels. Furthermore, genotypes clustered into two types--those that switched to aerobic, mitochondrial ATP production before the second instar and those that relied on anaerobic production of ATP via glycolysis through the second instar. Despite genetic variation for the timing of this metabolic shift, second-instar metabolic rate was more robust to genetic variation than was the metabolic rate of other instars. We also found that a mitochondrial-nuclear genotype with disrupted mitochondrial function both increased aerobic capacity more through development and relied more heavily on anaerobic ATP production relative to wildtype genotypes. By taking advantage of both ways of making ATP, this genotype maintained mitochondrial respiratory capacity, but also generated more free radicals and had decreased mitochondrial membrane potential, potentially as a physiological-defense mechanism. Taken together, the data revealed that genetic defects in core physiology can be buffered at the organismal level via physiological compensation and that natural populations likely harbor genetic variation for distinct metabolic strategies in development that generate similar organismal outcomes.

genetics↗

bioRxiv2017

Energy demand and the context-dependent effects of genetic interactions

Genetic effects are often context dependent, with the same genotype differentially affecting phenotypes across environments, life stages, and sexes. We used an environmental manipulation designed to increase energy demand during development to investigate energy demand as a general physiological explanation for context-dependent effects of mutations, particularly for those mutations that affect metabolism. We found that increasing the photoperiod during which Drosophila larvae are active during development phenocopies a temperature-dependent developmental delay in a mitochondrial-nuclear genotype with disrupted metabolism. This result indicates that the context-dependent fitness effects of this genotype are not specific to the effects of temperature and may generally result from variation in energy demand. The effects of this genotype also differ across life stages and between the sexes. The mitochondrial-nuclear genetic interaction disrupts metabolic rate in growing larvae, but not in adults, and compromises female, but not male, reproductive fitness. These patterns are consistent with a model where context-dependent genotype-phenotype relationships may generally arise from differences in energy demand experienced by individuals across environments, life stages, and sexes.\n\nIMPACT SUMMARYGenetic effects on traits are often context dependent, such that a genotype that improves fitness under one context may have no effect or even a deleterious effect in another context. The external environment is a common context that affects the degree to which a genotype determines a phenotype, but the internal environment of an organism (e.g., its genetic background, sex or life stage) also provides an important context that may modify the phenotypic expression of a genotype. Here we combine new data on the phenotypic effects of a well-characterized genetic interaction between the mitochondrial and nuclear genomes of the fruit fly Drosophila with prior observations to support a model of energy demand as a general explanation for context-dependent genetic effects, particularly for mutations that affect metabolism. We show that the magnitude of fitness effects of this genetic interaction correlates positively with the degree of energy demand among developmental treatments that accelerate growth rate, across developmental stages that differ in the cost of growth, and between sexes with potentially different costs of reproduction. These internal and external contexts create variable demands on energy metabolism that will impact the efficacy of natural selection acting on metabolic mutations in populations.

evolutionary biology↗

bioRxiv2017

Maternal loading of a small heat shock protein increases embryo thermal tolerance in Drosophila melanogaster

Maternal investment is likely to have direct effects on offspring survival. In oviparous animals whose embryos are exposed to the external environment, maternal provisioning of molecular factors like mRNAs and proteins may help embryos cope with sudden changes in the environment. Here we sought to modify the maternal mRNA contribution to offspring embryos and test for maternal effects on acute thermal tolerance in early embryos of Drosophila melanogaster. We drove in vivo overexpression of a small heat shock protein gene (Hsp23) in female ovaries and measured the effects of acute thermal stress on offspring embryonic survival and larval development. We report that overexpression of the Hsp23 gene in female ovaries produced offspring embryos with increased thermal tolerance. We also found that brief heat stress in the early embryonic stage (0 to 1 hour-old) caused decreased larval performance later in life (5 to 10 days-old), as indexed by pupation height, as well as increased development time to pupation. Maternal overexpression of Hsp23 protected embryos against these heat-induced larval defects. Our data demonstrate that transient products of single genes have large and lasting effects on whole-organism environmental tolerance. Further, our results suggest that maternal effects have a profound impact on offspring survival in the context of thermal variability.\n\nSUMMARY STATEMENTA gene-specific maternal effect confers thermal tolerance to offspring embryos in the fruit fly Drosophila melanogaster.

evolutionary biology↗