Comparative approaches to the study of physiology: Drosophila as a physiological tool

The astrocyte-enriched gene deathstar plays a crucial role in the development, locomotion, and lifespan of D. melanogaster

The Drosophila melanogaster brain is a complex organ with various cell types, orchestrating the development, physiology, and behaviors of the fly. While each cell type in Drosophila brain is known to express a unique gene set, their complete genetic profile is still unknown. Advances in the RNA sequencing techniques at single-cell resolution facilitate identifying novel cell type markers and/or re-examining the specificity of the available ones. In this study, exploiting a single-cell RNA sequencing data of Drosophila optic lobe, we categorized the cells based on their expression pattern for known markers, then the genes with enriched expression in astrocytes were identified. CG11000 was identified as a gene with a comparable expression profile to the Eaat1 gene, an astrocyte marker, in every individual cell inside the Drosophila optic lobe and midbrain, as well as in the entire Drosophila brain throughout its development. Consistent with our bioinformatics data, immunostaining of the brains dissected from transgenic adult flies showed co-expression of CG11000 with Eaat1 in a set of single cells corresponding to the astrocytes in the Drosophila brain. Physiologically, inhibiting CG11000 through RNA interference disrupted the normal development of male D. melanogaster, while having no impact on females. Expression suppression of CG11000 in adult flies led to decreased locomotion activity and also shortened lifespan specifically in astrocytes, indicating the gene's significance in astrocytes. We designated this gene as 'deathstar' due to its crucial role in maintaining the star-like shape of glial cells, astrocytes, throughout their development into adult stage.

Using Drosophila to uncover the role of organismal physiology and the tumor microenvironment in cancer

Cancer metastasis causes over 90% of cancer patient fatalities. Poor prognosis is determined by tumor type, the tumor microenvironment (TME), organ-specific biology, and animal physiology. While model organisms do not fully mimic the complexity of humans, many processes can be studied efficiently owing to the ease of genetic, developmental, and cell biology studies. For decades, Drosophila has been instrumental in identifying basic mechanisms controlling tumor growth and metastasis. The ability to generate clonal populations of distinct genotypes in otherwise wild-type animals makes Drosophila a powerful system to study tumor-host interactions at the local and global scales. This review discusses advancements in tumor biology, highlighting the strength of Drosophila for modeling TMEs and systemic responses in driving tumor progression and metastasis.

Neuroendocrine Regulation of Reproductive Dormancy in the Fruit Fly Drosophila melanogaster: A Review of Juvenile Hormone-Dependent Regulation

Animals can adjust their physiology, helping them survive and reproduce under a wide range of environmental conditions. One of the strategies to endure unfavorable environmental conditions such as low temperature and limited food supplies is dormancy. In some insect species, this may manifest as reproductive dormancy, which causes their reproductive organs to be severely depleted under conditions unsuitable for reproduction. Reproductive dormancy in insects is induced by a reduction in juvenile hormones synthesized in the corpus allatum (pl. corpora allata; CA) in response to winter-specific environmental cues, such as low temperatures and short-day length. In recent years, significant progress has been made in the study of dormancy-inducing conditions dependent on CA control mechanisms in Drosophila melanogaster. This review summarizes dormancy control mechanisms in D. melanogaster and discusses the implications for future studies of insect dormancy, particularly focusing on juvenile hormone-dependent regulation.

A multicomponent screen for feeding behaviour and nutritional status in Drosophila to interrogate mammalian appetite-related genes

OBJECTIVE

More than 300 genetic variants have been robustly associated with measures of human adiposity. Highly penetrant mutations causing human obesity do so largely by disrupting satiety pathways in the brain and increasing food intake. Most of the common obesity-predisposing variants are in, or near, genes expressed highly in the brain, but little is known of their function. Exploring the biology of these genes at scale in mammalian systems is challenging. We sought to establish and validate the use of a multicomponent screen for feeding behaviour phenotypes, taking advantage of the tractable model organism Drosophila melanogaster.

METHODS

We validated a screen for feeding behaviour in Drosophila by comparing results after disrupting the expression of centrally expressed genes that influence energy balance in flies to those of 10 control genes. We then used this screen to explore the effects of disrupted expression of genes either a) implicated in energy homeostasis through human genome-wide association studies (GWAS) or b) expressed and nutritionally responsive in specific populations of hypothalamic neurons with a known role in feeding/fasting.

RESULTS

Using data from the validation study to classify responses, we studied 53 Drosophila orthologues of genes implicated by human GWAS in body mass index and found that 15 significantly influenced feeding behaviour or energy homeostasis in the Drosophila screen. We then studied 50 Drosophila homologues of 47 murine genes reciprocally nutritionally regulated in POMC and agouti-related peptide neurons. Seven of these 50 genes were found by our screen to influence feeding behaviour in flies.

CONCLUSION

We demonstrated the utility of Drosophila as a tractable model organism in a high-throughput genetic screen for food intake phenotypes. This simple, cost-efficient strategy is ideal for high-throughput interrogation of genes implicated in feeding behaviour and obesity in mammals and will facilitate the process of reaching a functional understanding of obesity pathogenesis.

Analysis of various physiological salines for heart rate, CNS function, and synaptic transmission at neuromuscular junctions in Drosophila melanogaster larvae

Drosophila serves as a playground for examining the effects of genetic mutations on development, physiological function and behavior. Many physiological measures that address the effects of mutations require semi-intact or cultured preparations. To obtain consistent physiological recordings, cellular function needs to remain viable. Numerous physiological salines have been developed for fly preparations, with emphasis on nervous system viability. The commonly used saline drifts in pH and will cause an alteration in the heart rate. We identify a saline that maintains a stable pH and physiological function in the larval heart, skeletal neuromuscular junction, and ventral nerve cord preparations. Using these common assays, we screened various pH buffers of differing concentrations to identify optimum conditions. Buffers at 25 mM produce a stable heart rate with minimal variation in pH. Excitatory junction potentials evoked directly on larval muscles or through sensory-CNS-motor circuits were unaffected by at buffers at 25 mM. The salines examined did not impede the modulatory effect of serotonin on heart rate or neural activity. Together, our results indicate that the higher buffer concentrations needed to stabilize pH in HL3 hemolymph-like saline do not interfere with the acute function of neurons or cardiac myocytes.