Ser/Thr phosphatase type I isoforms PP1γ1 and PP1γ2 are alternately spliced transcripts of one gene, PPP1CC. Amino acid sequences of PP1γ1 and PP1γ2 are identical except at their extreme C‐termini. PP1γ1 is ubiquitous whereas PP1γ2 is abundant in testis. PPP1CC knockout male mice (‐/‐) are sterile due to impaired sperm morphogenesis. Fertility can be restored in PPP1CC (‐/‐) mice by testis specific transgenic expression of PP1γ2. The purpose of this study was to determine if PP1γ1 is equivalent to PP1γ2 in supporting spermatogenesis and male fertility. We generated four different transgenic rescue mice lines with cDNA containing the entire PP1γ1 coding sequence followed by various portions of its 3’UTR. Testis expression of PP1γ1 occurred only when the transgene lacked a 1Kb segment immediately following the stop codon of the PP1γ1 transcript. Levels of the PP1γ1 transgene in this line were comparable to PP1γ2 levels in PPP1CC (+/‐) testis. Spermatogenesis was restored in these PP1γ1 rescue mice, but males were sub‐fertile due to impaired sperm motility. Our studies suggest that PP1γ1 in mammals is excluded in differentiating spermatogenic cells due to alternate splicing and miRNA mediated instability of its transcript. Thus PP1γ2, the PP1 isoform in mammalian sperm, has isoform specific functions in supporting normal sperm motility and male fertility. Grant Funding Source : Supported by R15HD068971 and R15HD061869