Differential Expression of Ovarian Cathepsins B, D and L during Oocyte Growth in Scad

抄録

In pelagic egg-spawning marine fish, sequential processing of a hepatically derived vitellogenin occurs concomitant with oocyte growth within the follicles. This process consists of yolk formation during early oocyte growth and yolk degradation during late oocyte growth. Since ovarian cathepsins B, D and L have been suspected of being involved in both events, the present study determines their different expression during oocyte growth in round scad Decapterus maruadsi. By adopting specific substrates and inhibitors in newly established assays, the activities of scad ovarian cathepsins B, D and L had been assessed as CA074-sensitive Z-Arg-Arg-MCA hydrolysis, pepstatin-sensitive MOCAc-Gly-Lys-Pro-Ile-Leu-Phe-Phe-Arg-Leu-Lys(Dnp)-Arg-NH₂ hydrolysis and Z-Phe-Phe-CHN₂-sensitive Z-Phe-Arg-MCA hydrolysis, respectively. All ovarian cathepsins were expressed at the highest level in early growing oocytes. With oocyte growth, the expression of cathepsin L decreased significantly, while that of cathepsins B and D showed only marginal variation. The results indicate that highly expressed ovarian cathepsins B and D play roles in yolk degradation during late oocyte growth in scad.