Chitinase gene responses and tissue sensitivity in an intertidal mud crab (Macrophthalmus japonicus) following low or high salinity stress

Changes in salinity affect the physiological status of the marine habitat including that of the intertidal mud crab Macrophthalmus japonicus. Chitinases play significant biological roles in crustaceans such as morphogenesis, nutrient digestion, and pathogen defense. In this study, the osmoregulatory function of three chitinase gene transcripts was determined compared to seawater (SW, 31 ± 1 psu) in M. japonicus gills and hepatopancreas under different salinities (10, 25, and 40 psu) for 1, 4, and 7 days. In SW-exposed crab, quantitative real-time PCR analysis showed chitinase 1 (Mj-chi1) and chitinase 4 (Mj-chi4) transcripts constitutively expressed in all the tested tissues with strong expression in hepatopancreas, but chitinase 5 (Mj-chi5) showed highest expression in stomach. When exposed to different salinities, Mj-chi1 showed significant up-regulation at day 4 whereas Mj-chi4 showed late up-regulation (day 7) at all the salinities in hepatopancreas. In the gills, early up-regulation (day 1) in Mj-chi1 and time-dependent late up-regulation (day 7) in Mj-chi4 at high salinity were observed. These results indicate the possibility of using Mj-chi4 as a marker against salinity changes. Moreover, our results further suggest that Mj-chi1 and Mj-chi4 transcriptions were significantly affected by changes in salinity; however, Mj-chi5 in gills was less affected by salinity and showed no effect in hepatopancreas. Thus, chitinase transcription modulations in the gills are more sensitive than hepatopancreas to salinity stress. Further, present data indicate the possible existence of different physiological roles among chitinase gene families, which need to be clarified in more detail by future biochemical and physiological functional studies.