Molecular characterization of Rab7 and its involvement in innate immunity in red swamp crayfish Procambarus clarkii

Rab7 is a member of the Rab GTPases protein family, and it plays an essential role in regulating trafficking organelles in higher animals. However, recent studies showed that it also participated in the immune response and cytophagy against pathogens in invertebrates. In the present study, the full-length of Rab7 from Procambarus clarkii (PcRab7) was cloned, and its function during pathogen infection and phagocytosis of haemocytes was also explored. The results showed that the full-length of PcRab7 was 3639 bp, containing a 618 bp open reading frame encoding 155 amino acids. The predicted molecular weight and isoelectric point of PcRab7 were 23.2 kDa and 5.77, respectively. PcRab7 was widely expressed in various tissues including haemocytes, intestine, muscle, gill, and hepatopancreas, and the highest expression level was in haemocytes. The mRNA transcripts of PcRab7 in the main organs (gill, intestine, and hepatopancreas, and haemocytes) were significantly affected by white spot syndrome virus (WSSV) and Aeromonas veronii infection. Subsequently, the prokaryotic and eukaryotic expression vectors were successfully constructed, and polyclonal antibodies, which could specifically recognize the endogenous Rab7 protein, were also obtained. Furthermore, the phagocytosis rate of haemocytes against FITC-labeled A. veronii was significantly decreased when the PcRab7 was silenced, while the over-expression of Rab7 increased the phagocytosis rate of haemocytes. The abnormal expression of Rab7 protein could also affect the survival rate of P. clarkii infected with WSSV or A. veronii. These results could provide a basis for further study on the immunological function of PcRab7.