Genomic organisation of the human and mouse CatSper4 genes. (a) Gene structure of human and mouse CatSper4 genes on human chromosome 1p35.3 and mouse chromosome 4 band D3 respectively. Horizontal line represent human genome assembly NCBI 31 and mouse genome assembly NCBI 03, filled boxes represent coding regions, un-filled boxes represent non-coding regions. (b) Comparison of exon boundaries between human and mouse genes, exons are shaded alternately. Predicted transmembrane regions are underlined, the pore forming region is underlined with a dashed line.