Abstract
The Chinese mitten crab Eriocheir sinensis lives in saline or fresh water during different life stages and exhibits a complex life history, making it an ideal model to study the salinity adaptation of euryhaline animals. In this study, RNA-seq techniques, and determinations of free amino acids (FAAs), monoamine neurotransmitters, and Na+/K+ pump activity, were employed to understand the osmoregulatory mechanism in Chinese mitten crab. A total of 15,138 differentially expressed genes were obtained from 12 transcriptome libraries. GO enrichment analysis revealed that the mRNA expression profiles were completely remodeled from 12 to 24 h after salinity stress. The neuroendocrine system was activated under stimulation, and the monoamine neurotransmitters including dopamine (DA) and serotonin (5-HT) were released to modulate osmoregulation. Furthermore, the Na+/K+ pump in crab hemocytes was significantly inhibited post salinity stress, resulting in increased intracellular ion concentrations and osmotic pressure to sustain the osmotic balance. Moreover, six key FAAs, including alanine (Ala), proline (Pro), glycine (Gly), glutamate (Glu), arginine (Arg), and aspartate (Asp), were overexpressed to modulate the extracellular osmotic balance during salinity adaptation. Interestingly, the immune genes were not enriched in the GO analysis, implying that the immune system might not contribute fundamentally to the tolerance upon fluctuating ambient salinity in the Chinese mitten crab. These results collectively demonstrated that the Chinese mitten crab had evolved an efficient regulation mechanism by modulating the FAAs production and Na+/K+ pump activity to sustain the osmotic balance independent of the immune system, in which the neuroendocrine modulation, especially generated by the monoamine neurotransmitter, played an indispensable role.
Highlights
The Chinese mitten crab, Eriocheir sinensis, has a unique life cycle
After removing the non-coding RNA, the remaining clean reads in each library were mapped to a transcriptome of E. sinensis downloaded from NCBI database, and the successfully mapping rates ranged from 59.16 to 85.94% (Table 1)
The Chinese mitten crab has evolved a successful osmoregulation mechanism to cope with drastic salinity changes ranging from saline water to fresh water, making it a suitable model for the study of salinity adaptation
Summary
The Chinese mitten crab, Eriocheir sinensis, has a unique life cycle. The adults grow in freshwater, while their mating activities take place in brackish water and the larvae hatch in the nearshore area (Li et al, 2014). The superb osmoregulatory capacity of the Chinese mitten crab in some way recapitulates the evolution processes of the ancient creatures, making it an ideal model to study the evolution transition of life from oceans to lands (Li et al, 2014). It is able to transport Na+ out of the cells and K+ into the cells on the opposite of their respective concentrations (Skou and Esmann, 1992; Sun et al, 2012) It is the basic modulator of ion transport across the cell membrane in euryhaline crabs (Neufeld et al, 1980). Investigation has been extended to understand the key modulators and pathways regulating the FAAs’ production and specific ion channel activity in crustaceans (Huong et al, 2001)
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