International Mammalian Genome Society

The 16th International Mouse Genome Conference (2002)


Oral Presentation

Wednesday 20 November

11:30 - 11:45 HRS

STRUCTURE AND EXPRESSION OF AN UNUSUAL AXONEMAL DYNEIN HEAVY CHAIN GENE, Dnahc8, A Mouse T Complex Distorter/Sterility 2 (Tcd/Tcs2) CANDIDATE

S Samant
Temple University School Of Medicine

Co-Authors: Pilder S.
Institutions: Temple University School of Medicine

Axonemal dynein heavy chains (axDHCs) are integral participants in flagellar motility. Indeed, homozygosity for the t haplotype allele of a testis-specifically expressed axDHC gene, Dnahc8, is linked to male sterility resulting from aberrant flagellar movement.  However, although no role for axDHCs in flagellar morphogenesis has been previously established, the near total loss of Dnahc8 expression is associated with male sterility via severe disruption of sperm flagellar ultrastructure. To gain a better understanding of the presumed roles of Dnahc8, we have studied the organization and expression of full-length Dnahc8+ and Dnahc8t transcripts. Two alternatively spliced Dnahc8 mRNAs are transcribed by both + and t alleles. Except for a completely divergent N-terminus, a strongly expressed isoform encodes a protein with significant homology throughout to the Chlamydomonas g outer arm axDHC, while a weakly expressed isoform codes for a protein with the same N-terminus and a severely truncated C-terminus. In situ hybridization studies demonstrate that both mRNA species accumulate exclusively in late meiosis, but each isoform shows spatial independence. Affinity-purified antisera raised against putative DNAHC8 peptides detect proteins > 500 kDa in both +/+ and t/t testis and sperm extracts, but not in extracts derived from males homozygous for a Chr 17 polymorphism carrying a Dnahc8 null allele. Additionally, DNAHC8t isoforms carry numerous potentially deleterious mutations in their N-terminal regions.  The cumulative data imply that Dnahc8 is a strong candidate for Tcd/Tcs2, and indicate that Dnahc8 may have acquired functional plasticity in the testis through the tightly controlled expression of alternate isoforms.


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