Spag16, an axonemal central apparatus gene, encodes a male germ cell nuclear speckle protein that regulates SPAG16 mRNA expression.

Spag16 is the murine orthologue of Chlamydomonas reinhardtii PF20, a protein known to be essential to the structure and function of the "9+2" axoneme. In Chlamydomonas, the PF20 gene encodes a single protein present in the central pair of the axoneme. Loss of PF20 prevents central pair assembly/integrity and results in flagellar paralysis. Here we demonstrate that the murine Spag16 gene encodes two proteins: 71 kDa which is found in all murine cells with motile cilia or flagella, and 35 kDa representing the C terminus of duanyu1842G16L, which is expressed only in male germ cells, and is predominantly found in specific regions within the nucleus that also contain SC35, a known marker of nuclear speckles enriched in pre-mRNA splicing factors. expression precedes expression of Mice homozygous for a knockout of alone are infertile, but show no abnormalities in spermatogenesis. Mice chimeric for a mutation deleting the transcripts for both duanyu1842G16L and duanyu1842G16S have a profound defect in spermatogenesis. We show here that transduction of duanyu1842G16S into cultured dispersed mouse male germ cells and BEAS-2B human bronchial epithelial cells increases duanyu1842G16L expression, but has no effect on the expression of several other axoneme components. We also demonstrate that the Spag16L promoter shows increased activity in the presence of The distinct nuclear localization of duanyu1842G16S and its ability to modulate Spag16L mRNA expression suggest that duanyu1842G16S plays an important role in the gene expression machinery of male germ cells. This is a unique example of a highly conserved axonemal protein gene that encodes two protein products with different functions.

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