Characterization, tissue distribution of resistin gene and the effect of fasting and refeeding on resistin mRNA expression in Siberian sturgeon (Acipenser baerii)

Characterization of Leptin and Leptin Receptor Gene in the Siberian Sturgeon (Acipenser baerii): Molecular Cloning, Tissue Distribution, and Its Involvement in Feeding Regulation

Leptin is an adipokine known as a regulator of feeding and metabolism in mammals. Previous studies on fish have revealed its role in food intake regulation in limited teleosts. However, its specific function in Siberian sturgeon, an ancient Chondrostei fish, remains poorly understood. This study represents the first successful cloning of sequences for leptin and leptin receptors in Siberian sturgeon, achieved using RT-PCR. The predicted leptin sequence in this species consists of 168 amino acids that exhibit low identity with other fish species, except within the Acipenseriformes order. Tissue distribution analysis revealed a high expression of Siberian sturgeon leptin mRNA in the liver and lepr mRNA in the hypothalamus. Fasting differentially affected the expression of leptin and lepr mRNA, with decreased levels in the hypothalamus and increased levels in the liver (leptin: 3-15 days; lepr: 6-15 days). Recombinant Siberian sturgeon leptin (Ssleptin) was produced via E. coli expression, and intraperitoneal injection (100 ng/g BW) significantly inhibited food intake. The anorectic effect was correlated with changes in hypothalamic gene expression, including downregulation of orexigenic factors (agrp, orexin, npy, and ghrelin) and upregulation of anorexigenic factors (pomc, mch, and insulin). Meanwhile, the peripheral administration of Ssleptin promoted the expression of resistin in the liver and concurrently increased cck and pyy mRNA levels in the valvular intestine. Furthermore, Ssleptin injection stimulated the expression of hypothalamic lepr, jak2, akt, and ampkα2 mRNA. These findings suggest that leptin plays a significant role in the feeding control of Siberian sturgeon and provide new insights into the evolutionary function of leptin in fish.

Exploration of Appetite Regulation in Yangtze Sturgeon (Acipenser dabryanus) During Weaning

Yangtze sturgeon is an endangered fish species. After weaning, some Yangtze sturgeon fry refuse to consume any food, which causes a low survival rate during the artificial breeding period. This study showed that the body length and body weight of failed weaning Yangtze sturgeons were significantly lower than those of successful weaning sturgeons. Since the brain is the center of appetite regulation, RNA-seq of the brain was employed to analyze the differentially expressed genes and their biological functions in successfully and unsuccessfully weaned fry. After that, 82,151 unigenes and 3222 DEGs were obtained. Based on the results of RNA-seq, appetite factors, including POMC, CART, NPY and AgRP, were cloned, and then a weaning experiment was designed to explore the changes in appetite after feeding a microcapsule diet (weaning group). The results showed that, during the weaning period, the expression of CART was increased on the 1st and 3rd days but decreased on the 5th, 6th, 8th and 10th days. The expression of AgRP was downregulated on the 1st and 3rd days but upregulated on the 5th, 6th, 8th and 10th days. These findings indicate that appetite was suppressed in the early and middle periods but enhanced in the latter period of weaning and that CART may play an important role in the appetite-suppressing effect.

Resistin gene expression: Novel study in dromedary camel (Camelus dromedarius)

Resistin, an adipocyte-specific hormone involved in insulin resistance and adipocyte differentiation, was initially identified in adipose tissue and macrophages. The physiological role of this molecule in camels remains largely unexplored. This study analysed for the first time blood and tissue levels of resistin as well as expression of resistin gene by real time PCR in adipose tissue (hump, visceral & epididymal) and different muscles (gastrocnemius, heart and caecum) in dromedary camels. The results revealed that resistin concentration was significantly (P<0.01) higher in epididymal adipose tissue as compared to other tissues and the lowest concentration was detected in serum. Additionally, the differential mRNA expression levels of resistin gene showed the highest expression level in epididymal adipose tissue as compared to other tissues. In conclusion, the results demonstrated for the first time that resistin was expressed in different tissues of dromedary camels. These data underscore an important facet of the physiological role of resistin as a factor involved in insulin resistance and glucose metabolism in camels.

Recent advances in the crosstalk between adipose, muscle and bone tissues in fish

Control of tissue metabolism and growth involves interactions between organs, tissues, and cell types, mediated by cytokines or direct communication through cellular exchanges. Indeed, over the past decades, many peptides produced by adipose tissue, skeletal muscle and bone named adipokines, myokines and osteokines respectively, have been identified in mammals playing key roles in organ/tissue development and function. Some of them are released into the circulation acting as classical hormones, but they can also act locally showing autocrine/paracrine effects. In recent years, some of these cytokines have been identified in fish models of biomedical or agronomic interest. In this review, we will present their state of the art focusing on local actions and inter-tissue effects. Adipokines reported in fish adipocytes include adiponectin and leptin among others. We will focus on their structure characteristics, gene expression, receptors, and effects, in the adipose tissue itself, mainly regulating cell differentiation and metabolism, but in muscle and bone as target tissues too. Moreover, lipid metabolites, named lipokines, can also act as signaling molecules regulating metabolic homeostasis. Regarding myokines, the best documented in fish are myostatin and the insulin-like growth factors. This review summarizes their characteristics at a molecular level, and describes both, autocrine effects and interactions with adipose tissue and bone. Nonetheless, our understanding of the functions and mechanisms of action of many of these cytokines is still largely incomplete in fish, especially concerning osteokines (i.e., osteocalcin), whose potential cross talking roles remain to be elucidated. Furthermore, by using selective breeding or genetic tools, the formation of a specific tissue can be altered, highlighting the consequences on other tissues, and allowing the identification of communication signals. The specific effects of identified cytokines validated through in vitro models or in vivo trials will be described. Moreover, future scientific fronts (i.e., exosomes) and tools (i.e., co-cultures, organoids) for a better understanding of inter-organ crosstalk in fish will also be presented. As a final consideration, further identification of molecules involved in inter-tissue communication will open new avenues of knowledge in the control of fish homeostasis, as well as possible strategies to be applied in aquaculture or biomedicine.