The leptin system and its expression at different nutritional and pregnant stages in lined seahorse (Hippocampus erectus)

Abstract

Leptin is an essential hormone for the regulation of energy metabolism and food intake in vertebrate animals. To better understand the physiological roles of leptin in nutrient regulation in paternal ovoviviparous fish (family Syngnathidae), the present study cloned the full-length of leptin-a and leptin receptor (lepr) genes in lined seahorse (Hippocampus erectus). Results showed that there was a 576-bp intron between two exons in leptin-a gene but no leptin-b gene in seahorse. Although the primary amino acid sequence conservation of seahorse leptin-a was very low, the 3-D structure modeling of seahorse leptin-a revealed strong conservation of tertiary structure with other vertebrates. Seahorse leptin-a mRNA was highly expressed in brain, whereas lepr mRNA was mainly expressed in ovary and gill. Interestingly, both leptin-a and lepr mRNA were expressed in the brood pouch of male seahorse, suggesting the leptin system plays a role during the male pregnancy. Physiological experiments showed that the expression of hepatic leptin-a and lepr mRNA in unfed seahorses was significantly higher than that in those fed 100%, as well as 60%, of their food during the fasting stage, showing that seahorse might initiate the leptin system to regulate its energy metabolism while starving. Moreover, the expression of leptin-a in the brood pouch of pregnant seahorse was significantly upregulated compared with non-pregnant seahorse, whereas the expression of lepr was downregulated, suggesting that the leptin system might be involved in the male pregnancy. In conclusion, the leptin system plays a role in the energy metabolism and food intake, and might provide new insights into molecular regulation of male pregnancy in seahorse.

Temperature-induced physiological stress and reproductive characteristics of the migratory seahorse Hippocampus erectus during a thermal stress simulation

“…In the present study, increased feeding and defecation frequencies occurred in the 30°C treatment only during the first week, and the parameters then recovered in the following 3 weeks. The relatively stable leptin expression observed in the seahorses also suggested that thermal stress does not affect the appetite continually ( Zhang et al, 2016 ). Previous studies have also confirmed that in juvenile Hippocampus trimaculatus , H. erectus and adult H. guttulatus food intake is not sensitive to thermal stress ( Sheng et al, 2006 ; Aurélio et al, 2013 ).…”

“…For example, the members of the Hsp gene family (heat shock proteins, such as Hsp70 and Hsp60 ), which are strongly up-regulated to protect cells from thermal stress by inhibiting apoptosis and repairing proteins, are commonly considered useful genetic markers for evaluating stress response levels ( Sorger and Pelham, 1988 ; Feder and Hofmann, 1999 ). The leptin gene functions to balance energy expenses by inhibiting hunger, and higher leptin levels in fasting seahorses are involved in anorexic behavioral responses ( Schwartz et al, 2000 ; Pan et al, 2014 ; Zhang et al, 2016 ). In addition, thermal stress can disrupt the function of the fish reproductive brain–pituitary–gonad axis and alter gonad development and spawning behavior ( Miranda et al, 2013 ; Shahjahan et al, 2017 ).…”

The Roles of the Kisspeptin System in the Reproductive Physiology of the Lined Seahorse (Hippocampus erectus), an Ovoviviparous Fish With Male Pregnancy

“…All experiments were performed according to the standard procedure in our lab (Zhang et al, 2016; Qin et al, 2018). In brief, total RNA was extracted using TRIzol reagent (Invitrogen, United States) according to the manufacturer’s protocol.…”

Leptin signalling in teleost fish with emphasis in food intake regulation

“…Shortly after a lep gene was identified in pufferfish in 2005 (Kurokawa et al, 2005), orthologous gene sequences were described in several fish species from different orders. These include Anguilliformes (European and Japanese eel, respectively, Morini et al, 2015), Cypriniformes (zebrafish, Gorissen et al, 2009;common carp, Huising et al, 2006;grass carp, Li et al, 2010;white-clouds mountain minnow, Chen et al, 2016;Ya-fish, Yuan et al, 2014), Characiformes (red-bellied piranha, pirapitinga, Volkoff, 2015;pacu, Volkoff et al, 2017;cavefish, Jeffery, 2020), Siluriformes (yellow catfish, , Salmoniformes (brown trout, Angotzi et al, 2013;rainbow trout, Murashita et al, 2008;Atlantic salmon, Angotzi et al, 2013 andRønnestad et al, 2010;Arctic charr, Angotzi et al, 2013 andFrøiland et al, 2010), Pleuronectiformes (tongue sole, Xu et al, 2018), Beloniformes (medaka, Kurokawa and Murashita, 2009), Perciformes (Nile tilapia, Shpilman et al, 2014;striped bass, Won et al, 2012; orange-spotted grouper, Zhang et al, 2013;chub mackerel, Ohga et al, 2015; mandarin fish or Chinese perch, He et al, 2013 andYuan et al, 2016;Northern snakehead, Wen et al, 2020), and Syngnathiformes (lined seahorse, Zhang et al, 2016).…”