Insulin signaling in clock neurons regulates sleep in Drosophila

Preference of position in the proximity of various sugars revealed by location analysis of Drosophila melanogaster

Feeding behaviors are determined by two main factors. One is the internal state, such as hunger or previous experiences; the other is external factors, such as sensory stimulation. During starvation, animals must balance food-seeking behavior with energy conservation. The fruit fly, Drosophila melanogaster, serves as a useful model for studying food selectivity and various behaviors related to food intake. However, few studies have directly connected food selectivity with other behaviors, such as locomotor activity and sleep. In this study, we report that flies exhibited a preference for specific positions and spent more time in the proximity of sweet sugars, such as sucrose and sucralose, but not non-sweet and nutritious sugars like xylitol and sorbitol. On the other hand, prolonged exposure to sorbitol increased the staying time of flies in the proximity of sorbitol. Additionally, after starvation, flies immediately exhibited a position preference in the proximity of sorbitol. These findings suggest that flies prefer the proximity of sweet food, and starvation alters their preference for nutritious food, which may be beneficial for their survival.

Large-language models facilitate discovery of the molecular signatures regulating sleep and activity

Sleep, locomotor and social activities are essential animal behaviors, but their reciprocal relationships and underlying mechanisms remain poorly understood. Here, we elicit information from a cutting-edge large-language model (LLM), generative pre-trained transformer (GPT) 3.5, which interprets 10.2-13.8% of Drosophila genes known to regulate the 3 behaviors. We develop an instrument for simultaneous video tracking of multiple moving objects, and conduct a genome-wide screen. We have identified 758 fly genes that regulate sleep and activities, including mre11 which regulates sleep only in the presence of conspecifics, and NELF-B which regulates sleep regardless of whether conspecifics are present. Based on LLM-reasoning, an educated signal web is modeled for understanding of potential relationships between its components, presenting comprehensive molecular signatures that control sleep, locomotor and social activities. This LLM-aided strategy may also be helpful for addressing other complex scientific questions.

Drosophila noktochor regulates night sleep via a local mushroom body circuit

We show that a sleep-regulating, Ig-domain protein (NKT) is secreted from Drosophila mushroom body (MB) α'/β' neurons to act locally on other MB cell types. Pan-neuronal or broad MB expression of membrane-tethered NKT (tNkt) protein reduced sleep, like that of an NKT null mutant, suggesting blockade of a receptor mediating endogenous NKT action. In contrast, expression in neurons requiring NKT (the MB α'/β' cells), or non-MB sleep-regulating centers, did not reduce night sleep, indicating the presence of a local MB sleep-regulating circuit consisting of communicating neural subtypes. We suggest that the leucocyte-antigen-related like (Lar) transmembrane receptor may mediate NKT action. Knockdown or overexpression of Lar in the MB increased or decreased sleep, respectively, indicating the receptor promotes wakefulness. Surprisingly, selective expression of tNkt or knockdown of Lar in MB wake-promoting cells increased rather than decreased sleep, suggesting that NKT acts on wake- as well as sleep-promoting cell types to regulate sleep.

Ecdysone-induced microRNA miR-276a-3p controls developmental growth by targeting the insulin-like receptor in Drosophila

Animal growth is controlled by a variety of external and internal factors during development. The steroid hormone ecdysone plays a critical role in insect development by regulating the expression of various genes. In this study, we found that fat body-specific expression of miR-276a, an ecdysone-responsive microRNA (miRNA), led to a decrease in the total mass of the larval fat body, resulting in significant growth reduction in Drosophila. Changes in miR-276a expression also affected the proliferation of Drosophila S2 cells. Furthermore, we found that the insulin-like receptor (InR) is a biologically relevant target gene regulated by miR-276a-3p. In addition, we found that miR-276a-3p is upregulated by the canonical ecdysone signalling pathway involving the ecdysone receptor and broad complex. A reduction in cell proliferation caused by ecdysone was compromised by blocking miR-276a-3p activity. Thus, our results suggest that miR-276a-3p is involved in ecdysone-mediated growth reduction by controlling InR expression in the insulin signalling pathway.

Sleep-associated insulin resistance promotes neurodegeneration

Lifestyle modification can lead to numerous health issues closely associated with sleep. Sleep deprivation and disturbances significantly affect inflammation, immunity, neurodegeneration, cognitive depletion, memory impairment, neuroplasticity, and insulin resistance. Sleep significantly impacts brain and memory formation, toxin excretion, hormonal function, metabolism, and motor and cognitive functions. Sleep restriction associated with insulin resistance affects these functions by interfering with the insulin signalling pathway, neurotransmission, inflammatory pathways, and plasticity of neurons. So, in this review, We discuss the evidence that suggests that neurodegeneration occurs via sleep and is associated with insulin resistance, along with the insulin signalling pathways involved in neurodegeneration and neuroplasticity, while exploring the role of hormones in these conditions.

A phosphorylation-deficient mutant of Sik3, a homolog of Sleepy, alters circadian sleep regulation by PDF neurons in Drosophila

Sleep behavior has been observed from non-vertebrates to humans. Sleepy mutation in mice resulted in a notable increase in sleep and was identified as an exon-skipping mutation of the salt-inducible kinase 3 (Sik3) gene, conserved among animals. The skipped exon includes a serine residue that is phosphorylated by protein kinase A. Overexpression of a mutant gene with the conversion of this serine into alanine (Sik3-SA) increased sleep in both mice and the fruit fly Drosophila melanogaster. However, the mechanism by which Sik3-SA increases sleep remains unclear. Here, we found that Sik3-SA overexpression in all neurons increased sleep under both light-dark (LD) conditions and constant dark (DD) conditions in Drosophila. Additionally, overexpression of Sik3-SA only in PDF neurons, which are a cluster of clock neurons regulating the circadian rhythm, increased sleep during subjective daytime while decreasing the amplitude of circadian rhythm. Furthermore, suppressing Sik3-SA overexpression specifically in PDF neurons in flies overexpressing Sik3-SA in all neurons reversed the sleep increase during subjective daytime. These results indicate that Sik3-SA alters the circadian function of PDF neurons and leads to an increase in sleep during subjective daytime under constant dark conditions.

rdgB knockdown in neurons reduced nocturnal sleep in Drosophila melanogaster

Recent studies revealed behaviorally defined sleep is conserved across broad species from insect to human. For evolutional analysis, it is critical to determine how homologous genes regulate the homologous function among species. Drosophila melanogaster shares numerous sleep related genes with mammals including Sik3, salt-inducible kinase 3, whose mutation caused long sleep both in mouse and fruit fly. The Drosophila rdgB (retinal degeneration B) encodes a membrane-associated phosphatidylinositol transfer protein and its mutation caused light-induced degeneration of photoreceptor cells. rdgB mutation also impaired phototransduction and olfactory behavior, indicating rdgB is involved in the normal neural transmission. Mammalian rdgB homologue, Pitpnm2 (phosphatidylinositol transfer protein membrane-associated 2) was discovered as one of SNIPPs (sleep-need index phosphoproteins), suggesting its role in sleep. Here, we show that rdgB is involved in sleep regulation in Drosophila. Pan-neuronal and mushroom body (MB) specific rdgB knockdown decreased nocturnal sleep. MB neurons play a dominant role, since the rescue of rdgB expression only in MB neurons in pan-neuronal knockdown reversed the sleep reducing effect of rdgB knockdown. These results revealed the sleep-related function of rdgB in Drosophila which may be conserved across species.

Neural pathways in nutrient sensing and insulin signaling

Nutrient sensing and metabolic homeostasis play an important role in the proper growth and development of an organism, and also in the energy intensive process of reproduction. Signals in response to nutritional and metabolic status is received and integrated by the brain to ensure homeostasis. In Drosophila, the fat body is one of the key organs involved in energy and nutrient sensing, storage and utilization. It also relays the nutritional status of the animal to the brain, activating specific circuits which modulate the synthesis and release of insulin-like peptides to regulate metabolism. Here, we review the molecular and cellular mechanisms involved in nutrient sensing with an emphasis on the neural pathways that modulate this process and discuss some of the open questions that need to be addressed.

The regulation of circadian rhythm by insulin signaling in Drosophila

Circadian rhythm is well conserved across species and relates to numerous biological functions. Circadian misalignment impairs metabolic function. Insulin signaling is a key modulator of metabolism in the fruit fly as well as mammals and its defects cause metabolic disease. Daily diet timing affects both circadian rhythmicities of behavior and metabolism. However, the relationship between the circadian clock and insulin signaling is still elusive. Here, we report that insulin signaling regulates circadian rhythm in Drosophila melanogaster. We found the insulin receptor substrate mutant, chico¹, showed a shorter free-running circadian period. The knockdown of insulin receptor (InR), or another signaling molecule downstream of InR, dp110, or the expression of a dominant-negative form of InR resulted in the shortening of the circadian period and diminished its amplitude. The impairment of insulin signaling both in all neurons and restricted circadian clock neurons altered circadian period length, indicating that the insulin signaling plays a role in the regulation of circadian rhythm in clock cells. Among 3 insulin-like ligands expressed in the brain, dilp5 showed the largest effect on circadian phenotype when deleted. These results suggested that insulin signaling contributes to the robustness of the circadian oscillation and coordinates metabolism and behavior.