Sperm mitochondria diaphorase activity--a gene mapping study of recombinant inbred strains of mice

In order to study the genetic control of semen quality parameters, we derived a set of recombinant inbred (RI) mice from crosses between two inbred strains, KE and CBA/Kw, which differ significantly in gamete quality and fertility parameters. In this work, we used male mice from the two parental strains and from ten RI strains to map genes controlling quantitative traits such as sperm mitochondrial diaphorase activity, and assessed the correlation between this trait, sperm motility and in vivo fertilization efficiency. We analyzed sperm mitochondrial dehydrogenase (diaphorase) activity (NADH-dependent NBT assay) cytochemically by means of computerized image densitometry and obtained values for four parameters: 1) integrated optical density (IOD) for all pixels of the midpiece, 2) mean optical density (MOD) for the midpiece pixels, 3) length of sperm midpiece and 4) area of sperm midpiece. Polymorphic microsatellite marker profiles were prepared for 20 mouse chromosomes in the ten RI strains. We used Map Manager QTX software to correlate the strain distribution patterns (SDPs) of the four measured parameters with the SDPs of the analyzed markers. Hypothetical genes modifying diaphorase activity were mapped to chromosomal region 19q43-19q47, containing, for example, Poll, Sfxn2, Cyp17a1 and Usmg5 genes. Chromosomal regions 18q44 and 18q49-18q80 also showed correlation with the SDPs of diaphorase activity. Katnal2, Me2 and StARD6 candidate genes were proposed from this region. Diaphorase activity in the mouse sperm midpiece did not correlate with in vivo fertilization efficiency, but was negatively correlated with the linearity and straightness of sperm movement.