Adaptive evolution of osmoregulatory-related genes provides insight into salinity adaptation in Chinese mitten crab, <Emphasis Type="Italic">Eriocheir sinensis</Emphasis>

Osmoregulation is an important mechanism by which euryhaline crustaceans regulate osmotic and ionic concentrations. The Chinese mitten crab (Eriocheir sinensis) is a strong osmoregulating animal model among crustacean species, as it can maintain its hemolymph composition and survives well in either seawater or freshwater. Osmoregulation by E. sinensis during physiological adaptation has been studied extensively. However, the genetic basis of osmoregulation in E. sinensis for acclimating to changing salinities remains unclear. The current study investigated five genes involved in E. sinensis osmoregulation and compared them with a representative marine crab Portunus trituberculatus to test whether adaptive evolution has occurred changing salinity conditions. The results showed that carbonic anhydrase (CA), cytochrome P450 4C (CYP4C), glutamate dehydrogenase (GDH), and the Na⁺/H⁺ exchanger (NHE) have undergone positive selection (i.e., directional selection) in E. sinensis. Thus, the positive selection in CA and NHE suggests that E. sinensis has enhanced capacity for maintaining systemic acid-base balance and ion regulation. GDH and CYP4C also demonstrated positive selection in E. sinensis, suggesting that E. sinensis might have acquired an enhanced capacity to metabolize glutamate and synthesize ecdysteroids in response to a change in osmotic concentration. The present study provides new insight into the molecular genetic basis of salinity adaption in E. sinensis.     

Identification and expression pattern analysis of Piwi genes during the spermiogenesis of Portunus trituberculatus

The Piwi genes have an important role in stem cell development, gametogenesis and RNA interference in diverse organisms. So far, most of the studies have focused on the function of Piwis in vertebrates, but their function during spermiogenesis in invertebrates still remains largely unclear. In order to investigate the function of Piwis during spermiogenesis in the crab Portunus trituberculatus, we use RT-PCR and RACE to identify three Piwi complete cDNA sequences from the total RNA of the testis in P. trituberculatus. The deduced amino acid sequences of P. trituberculatus Piwi-1, Piwi-2 and Piwi-3 showed that each contains a well-conserved PAZ domain and PIWI domain. RT-PCR analyzed the tissue expression pattern of P. trituberculatus Piwi-1, Piwi-2 and Piwi-3 in the testis, heart, muscle, hepatopancreas and gill. All of the Piwis are found in germ cells of adult testis in P. trituberculatus by in situ hybridization, suggesting that these genes may play function during spermiogenesis in this species.