HGF-HGFR-STAT signaling axis regulates haemocyte proliferation in oyster Crassostrea gigas

As a pleiotropic growth factor, hepatocyte growth factor (HGF) involves in the division and growth of multifarious cells through binding hepatocyte growth factor receptor (HGFR). In the present study, a homologue of HGF (CgHGF-like) and HGFR (CgHGFR) with conserved domain features were identified in oyster Crassostrea gigas. The mRNA transcripts of CgHGF-like and CgHGFR were detected in all tested tissues, and both showed the highest expression level in haemocytes. Their mRNA expression in haemocytes were significantly increased after Vibrio splendidus stimulation. Immunofluorescence assay showed that the positive signals of CgHGF-like and CgHGFR were mainly located in the cytoplasm and membrane of haemocytes, respectively. Recombinant protein CgHGF-like and CgHGFR-SEMA showed in vitro interaction by Bio-layer interferometry assay. In the CgHGF-like-RNAi and CgHGFR-RNAi oysters, the percent of haemocytes with EdU positive signals, as well as the mRNA expression levels of CgGATA, CgSCL and CgRUNX all significantly down-regulated in haemocytes after V. splendidus stimulation. The positive signals of CgSTAT were observed in the haemocyte nucleus after V. splendidus stimulation, however, the nuclear translocation of CgSTAT was suppressed in CgHGF-like-RNAi and CgHGFR-RNAi oysters. These results collectively indicated that CgHGF-like might interact with CgHGFR to regulate haemocyte proliferation by activating CgSTAT during the immune response, suggesting its important roles in haemocyte proliferation of oyster C. gigas.