Relationship between abundance and localization of maternal messenger RNA and egg quality in artificially matured Japanese eel Anguilla japonica

Abstract

Artificial maturation and ovulation of Japanese eel do not always result in the production of good-quality eggs. The molecular basis for compromised egg quality in artificially matured Japanese eel remains unknown. In this study, we investigated the relationship between the localization of six maternal transcripts, grip2, dazl, sybu, trim36, pou5f3 and npm2, and egg quality in artificially matured Japanese eel oocytes and eggs. We observed that localization of these messenger RNAs (mRNAs) in oocytes from the perinucleolus stage to the migratory nucleus stage is not associated with egg quality. In contrast, in ovulated eggs, we observed two different mRNA localization patterns, which we designated type A (mRNA localized in the cortex) and type B (mRNA distributed more centrally). Furthermore, individuals containing many type B eggs tended to have low fertilization and hatching rates, but this was not reflected in the target gene mRNA levels. Our results suggest that the loss of quality in eggs from artificially matured Japanese eel is caused by abnormal mRNA localization even if there is no difference in mRNA levels.