International Mammalian Genome Society

logo18th International Mouse Genome Conference

17-22 October 2004, Seattle, USA


Meehan TP, Justice MJ

Baylor College of Medicine, Houston, United States

Infertility is a problem affecting about 15% of couples with nearly equal numbers of male factor and female factor infertility.  The underlying defects in most of these cases remain unknown.  Over 200 mouse models exist for genes involved in infertility, however, since it is estimated that 5000 genes are involved in fertility, more research is needed to determine novel causes of infertility.  Towards this goal, we have utilized ENU mutagenesis coupled with a balancer chromosome.  Previously, we described the isolation and characterization of a novel male infertility locus on mouse chromosome 11 (Clark et al., 2004, BOR 70:1317-1324).  Three non-complementing mutant lines generated by ENU mutagenesis displayed reduced sperm counts and complete loss of sperm motility.  Additionally, defects were found in the ultrastructure of the sperm tail axoneme.  A candidate gene approach was utilized to determine the gene responsible for the defects.  Twenty-two infertile candidate genes are closely linked to the region of chromosome 11 containing the infertile locus.  Based on obtaining three alleles in one gene, we predicted that the mutated gene is large in size, therefore, we focused our investigation on Dnahc2, an uncharacterized member of the axonemal dynein heavy chain family which spans approximately 84 kb of genomic sequence.  Northern blot analysis and real-time RT-PCR revealed decreased Dnahc2 transcript levels in two of three lines.  Additionally, the infertility in the third mutant line shows tight linkage to Dnahc2 by fine structure mapping.  The predicted 79 exons of Dnahc2 result in an 11.7 kb transcript encoding a 3907 amino acid protein.  Sequencing of the Dnahc2 cDNA from mutant lines has revealed mutations in two lines.  One mutation results in a premature stop codon prior to the motor domain of the protein.  The other mutation is a Q to R transition in the fifth of six AAA (ATPases associated diverse cellular activities) domains.  This residue is conserved among other members of the dynein heavy chain family.  Together, these mutations demonstrate the critical role of Dnahc2 in sperm function, and will be useful for dissecting the action of the dynein motor in sperm flagella.

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