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cDNAs were cloned for the murine and human orthologues of Chlamydomonas PF20, a component of the alga axoneme central apparatus that is required for flagellar motility. The mammalian genes encode transcripts of 1.4 and 2.5 kb that are highly expressed in testis. The two transcripts appear to arise from alternative transcription start sites. The murine Pf20 gene was mapped to chromosome 1, syntenic with the location of the human gene on chromosome 2. An antibody generated against an N-terminal sequence of mouse Pf20 recognized a 71-kDa protein in sperm and testis extracts. Immunocytochemistry localized Pf20 to the tails of permeabilized sperm; electron microscope immunocytochemistry showed that Pf20 was located in the axoneme central apparatus. A murine Pf20-green fluorescent protein fusion protein expressed in Chinese hamster ovary cells accumulated in the cytoplasm. When coexpressed with Spag6, the mammalian orthologue of Chlamydomonas PF16, Pf20 was colocalized with Spag6 on polymerized microtubules. Yeast two-hybrid assays demonstrated interaction of the Pf20 WD repeats with Spag6. Pf20 was markedly reduced in sperm collected from mice lacking Spag6, which are infertile due to a motility defect. Our observations provide the first evidence for an association between mammalian orthologues of two Chlamydomonas proteins known to be critical for axoneme structure and function.

Background— Circadian rhythmicity of many aspects of cardiovascular function—blood pressure, coagulation and contractile function—is well established, as is diurnal variation in important clinical events, such as myocardial infarction and stroke. Here, we undertake studies to globally assess circadian gene expression in murine aorta. Methods and Results— Aortae from mice were harvested at 4-hour intervals for 2 circadian cycles (48 hours). Gene expression was assessed by expression profiling and subjected to a gene ontology bioinformatics analysis. Three hundred thirty transcripts exhibited a circadian pattern of oscillation in mouse aorta, including those intrinsic to the function of the molecular clock. In addition, many genes relevant to protein folding, protein degradation, glucose and lipid metabolism, adipocyte maturation, vascular integrity, and the response to injury are also included in this subset of roughly 7000 genes screened for circadian oscillation. Conclusions— Detection of functional cassettes of vascular genes that exhibit circadian regulation in the mouse will facilitate elucidation of the mechanisms by which the molecular clock may interact with environmental variables to modulate cardiovascular function and the response to therapeutic interventions.