Takashi Koyama

Cells and organisms adjust their growth based on the availability of cholesterol, which is essential for cellular functions. However, the mechanisms by which cells sense cholesterol levels and translate these into growth signals are not fully understood. We report that cholesterol rapidly activates the master growth-regulatory TOR pathway in Drosophila tissues. We identify the nuclear receptor HR3, an ortholog of mammalian RORα, as an essential factor in cholesterol-induced TOR activation. We demonstrate that HR3 binds cholesterol and promotes TOR-pathway activation through a non-genomic mechanism acting upstream of the Rag GTPases while also restraining longer-term responses through genomic regulation. We also find that RORα is necessary for cholesterol-mediated TOR activation in human cells, suggesting that HR3/RORα-mediated signaling represents a conserved mechanism for cholesterol sensing that couples cholesterol availability to TOR-pathway activity. These findings advance our understanding of how cholesterol influences cell growth, with implications for cholesterol-related diseases and cancer.

Maintaining internal water balance, including ionic and osmotic balance, is critical for animal development and survival. In insects, internal water balance is regulated through the Malpighian tubules and the hindgut, which transport water and ions across their epithelia under the regulation of multiple peptide hormones. One of these, ion transport peptide (ITP), a member of the highly conserved crustacean hyperglycemic hormone superfamily among ecdysozoans, is an anti-diuretic hormone in insects, but its mechanism of action remains largely unclear. Here, we show that the short amidated isoform of ITP (saITP), secreted from brain neurosecretory cells, regulates water absorption via the receptor guanylyl cyclase (rGC) Gyc76C in the hindgut of the fruit fly Drosophila melanogaster . Both ITP and Gyc76C are evolutionarily conserved and are essential for larval survival in D. melanogaster , as mutation or knockdown of either gene results in early larval lethality. In Drosophila S2 cells, synthetic saITP increases intracellular cyclic GMP (cGMP) in a Gyc76C-dependent manner, an effect abolished by deletion of its putative ligand-binding domain. Using the fluorescent cGMP biosensor RedcGull in ex vivo -cultured hindguts, we found that saITP increases epithelial cGMP levels, and this response requires Gyc76C. Consistently, saITP promotes hindgut water reabsorption via Gyc76C. Thus, saITP acts via Gyc76C in a brain-hindgut neuroendocrine axis that regulates internal water balance during development. Our study provides new insight into the neuroendocrine control of osmoregulation in ecdysozoans and supports a broader role for rGCs in peptide-hormone signaling.

Sickness-induced sleep is a behavior conserved across species that promotes recovery from illness, yet the underlying mechanisms are poorly understood. Here, we show that interleukin-6-like cytokine signaling from the Drosophila gut to brain glial cells regulates sleep. Under healthy conditions, this pathway promotes wakefulness. However, elevated gut cytokine signaling in response to oxidative stress – triggered by immune and inflammatory responses in the intestine – induces sleep. The cytokines Unpaired 2 and –3 are upregulated by oxidative stress in enteroendocrine cells and activate JAK–STAT signaling in glial cells, including those of the blood–brain barrier (BBB). This activity maintains elevated sleep during oxidative-stress-induced intestinal disturbances, suggesting that the JAK–STAT pathway in glia inhibits wake-promoting signaling to facilitate sleep-dependent restoration under these conditions. We find that the enteric peptide Allatostatin A (AstA) enhances wakefulness, and during intestinal oxidative stress, gut-derived Unpaired 2/3 inhibits AstA receptor expression in BBB glia, thereby sustaining an elevated sleep state during gut inflammation or illness. Taken together, our work identifies a gut-to-glial communication pathway that couples sleep with intestinal homeostasis and disease, enhancing sleep during intestinal sickness, and contributing to our understanding of how sleep disturbances arise from gastrointestinal disturbances.

Sickness-induced sleep is a behavior conserved across species that promotes recovery from illness, yet the underlying mechanisms are poorly understood. Here, we show that interleukin-6-like cytokine signaling from the Drosophila gut to brain glial cells regulates sleep. Under healthy conditions, this pathway promotes wakefulness. However, elevated gut cytokine signaling in response to oxidative stress – triggered by immune and inflammatory responses in the intestine – induces sleep. The cytokines Unpaired 2 and -3 are upregulated by oxidative stress in enteroendocrine cells and activate JAK-STAT signaling in glial cells, including those of the blood-brain barrier (BBB). This activity maintains elevated sleep during oxidative-stress-induced intestinal disturbances, suggesting that the JAK-STAT pathway in glia inhibits wake-promoting signaling to facilitate sleep-dependent restoration under these conditions. We find that the enteric peptide Allatostatin A (AstA) enhances wakefulness, and during intestinal oxidative stress, gut-derived Unpaired 2/3 inhibits AstA receptor expression in BBB glia, thereby sustaining an elevated sleep state during gut inflammation or illness. Taken together, our work identifies a gut-to-glial communication pathway that couples sleep with intestinal homeostasis and disease, enhancing sleep during intestinal sickness, and contributes to our understanding of how sleep disturbances arise from gastrointestinal disturbances.

Animals select food based on hungers that reflect dynamic macronutrient needs, but the hormonal mechanisms underlying nutrient-specific appetite regulation remain poorly defined. Here, we identify tachykinin (Tk) as a protein-responsive gut hormone in Drosophila and female mice, regulated by conserved environmental and nutrient-sensing mechanisms. Protein intake activates Tk-expressing enteroendocrine cells (EECs), driving the release of gut Tk through mechanisms involving target of rapamycin (TOR) and transient receptor potential A1 (TrpA1). In flies, we delineate a pathway by which gut Tk controls selective appetite and sleep after protein ingestion, mediated by glucagon-like adipokinetic hormone (AKH) signalling to neurons and adipose tissue. This mechanism suppresses protein appetite, promotes sugar hunger and modulates wakefulness to align behaviour with nutritional needs. Inhibiting protein-responsive gut Tk prolongs lifespan through AKH, revealing a role for nutrient-dependent gut hormone signalling in longevity. Our results provide a framework for understanding EEC-derived nutrient-specific satiety signals and the role of gut hormones in regulating food choice, sleep and lifespan.

Tenebrionid beetles have been highly successful in colonising environments where water is scarce, underpinned by their unique osmoregulatory adaptations. These include a cryptonephridial arrangement of their organs, in which part of their renal/Malpighian tubules are bound to the surface of the rectum. Within the cryptonephridial tubules, an unusual cell type, the leptophragmata, plays a key physiological role underpinning water conservation. Nothing was known about the developmental mechanisms or evolution of these unusual renal cells. Here, we investigate mechanisms underpinning leptophragmata development in Tribolium castaneum. We find that leptophragmata express and require the Tiptop transcription factor, similar to secondary renal cells in Drosophila melanogaster, which express Teashirt and Tiptop, despite Drosophila lacking a crypronephridial arrangement. An additional transcription factor, Dachshund, is required to establish leptophragmata identity and to distinguish them from the secondary cells in the non-cryptonephridial region of renal tubule of Tribolium. Dachshund is also expressed in a sub-population of secondary cells in Drosophila. Leptophragmata, which are unique to the beetle lineage, appear to have originated from a specific renal cell type present ancestrally and to be specified by a conserved repertoire of transcription factors.

Obesity impairs tissue insulin sensitivity and signaling, promoting type-2 diabetes. Although improving insulin signaling is key to reversing diabetes, the multi-organ mechanisms regulating this process are poorly defined. Here, we screen the secretome and receptome in Drosophila to identify the hormonal crosstalk affecting diet-induced insulin resistance and obesity. We discover a complex interplay between muscle, neuronal, and adipose tissues, mediated by Bone Morphogenetic Protein (BMP) signaling and the hormone Bursicon, that enhances insulin signaling and sugar tolerance. Muscle-derived BMP signaling, induced by sugar, governs neuronal Bursicon signaling. Bursicon, through its receptor Rickets, a Leucine-rich-repeat-containing G-protein coupled receptor (LGR), improves insulin secretion and insulin sensitivity in adipose tissue, mitigating hyperglycemia. In mouse adipocytes, loss of the Rickets ortholog LGR4 blunts insulin responses, showing an essential role of LGR4 in adipocyte insulin sensitivity. Our findings reveal a muscle-neuronal-fat-tissue axis driving metabolic adaptation to high-sugar conditions, identifying LGR4 as a critical mediator in this regulatory network.

Sickness-induced sleep is a behavior conserved across species that promotes recovery from illness, yet the underlying mechanisms are poorly understood. Here, we show that interleukin-6-like cytokine signaling from the Drosophila gut to brain glial cells regulates sleep. Under healthy conditions, this pathway promotes wakefulness. However, elevated gut cytokine signaling in response to oxidative stress – triggered by immune and inflammatory responses in the intestine – induces sleep. The cytokines Unpaired 2 and -3 are upregulated by oxidative stress in enteroendocrine cells and activate JAK-STAT signaling in glial cells, including those of the blood-brain barrier (BBB). This activity maintains elevated sleep during oxidative-stress-induced intestinal disturbances, suggesting that the JAK-STAT pathway in glia inhibits wake-promoting signaling to facilitate sleep-dependent restoration under these conditions. We find that the enteric peptide Allatostatin A (AstA) enhances wakefulness, and during intestinal oxidative stress, gut-derived Unpaired 2/3 inhibits AstA receptor expression in BBB glia, thereby sustaining an elevated sleep state during gut inflammation or illness. Taken together, our work identifies a gut-to-glial communication pathway that couples sleep with intestinal homeostasis and disease, enhancing sleep during intestinal sickness, and contributes to our understanding of how sleep disturbances arise from gastrointestinal disturbances.

Tenebrionid beetles have been highly successful in colonising environments where water is scarce, underpinned by their unique osmoregulatory adaptations. These include a cryptonephridial arrangement of their organs, in which part of their renal/Malpighian tubules are bound to the surface of the rectum. This allows them to generate a steep osmotic gradient to draw water from within the rectum and return it to the body. Within the cryptonephridial tubules a seemingly novel cell type, the leptophragmata, is considered to play a key role in transporting potassium chloride to generate this osmotic gradient. Nothing was known about the developmental mechanisms or evolution of these unusual renal cells. Here we investigate the mechanisms underpinning development of the leptophragmata in the red flour beetle, Tribolium castaneum . We find that leptophragmata express and require a teashirt / tiptop transcription factor gene, as do the secondary renal cells of Drosophila melanogaster which lack a cryptonephridial arrangement. We also find an additional transcription factor, Dachshund, is required to establish leptophragmata identity and to distinguish them from the secondary cells in Tribolium’s non-cryptonephridial region of renal tubule. Dachshund is also expressed in a sub-population of secondary cells in Drosophila . So leptophragmata, which are unique to the beetle lineage, appear to have originated from a specific renal cell type present ancestrally, and specified by a conserved repertoire of transcription factors. Significance: Beetles are a highly successful insect group and represent a quarter of all known animal species. Their digestive/renal systems have undergone major evolutionary change compared to other insects, likely contributing to their success. A dramatic example is the cryptonephridial complex, an evolutionary innovation of the gut and renal system which integrate as a powerful water-conservation system; an adaptation for survival in arid conditions. An unusual renal cell type—the leptophragmata—underpin the functions of the complex, but their developmental and evolutionary origins are unknown. Here we reveal the developmental mechanism that establish leptophragmata identity and, by studying a species lacking a cryptonephridial complex, shed light on their evolutionary origin. More broadly, the work illuminates the evolution of novel cell types.