Molecular characterization of diploid YY sperm related to its developmental advantages

Previously, we have reported diploid YY male fish obtained by the combination of androgenetic technology and distant hybridization and described its special reproductive characteristics producing unreduced and diploid homogametes. The above diploid sperm displayed developmental advantages, forming all-male offspring, and directly developing into individuals without chromosome doubling during androgenesis. However, the related molecular advantages of YY fish sperm have not been reported. In this study, we firstly compared the semen of two kinds of male fish (XY and YY), both obtained by androgenetic technology with the autotetraploid fish sperm. Morphological features exhibited by electron microscope revealed that YY fish sperm is normal, while partial XY fish sperm has defects with uncompacted nucleus or cell degradation. Moreover, a comparison of global transcriptomes showed that the expression of genes related to immunity and energy production was increased in YY fish semen, while genes related to meiosis and spermiogenesis were highly expressed in XY fish semen. Then, we compared the semen of YY fish and red crucian carp (RCC), in which the sperm has normal structure but the different developmental potential for different ploidy. Epigenetic analysis revealed that di/tri- methylation on histone H3 lysine 9 (H3K9me2/3) exhibited higher levels in YY fish semen than in RCC semen. Consisting with the variation of H3K9me2/3, expression of histone methylase gene setdb1b increased, while demethylase gene kdm4a decreased in YY fish semen. Taken together, this is the first time reported the molecular dominance of diploid sperm of YY fish, which will be helpful for the following practice aquaculture breeding application.