A knock-in mouse model for male fertility: basis for the mammal-specific protein phosphatase isoform PP1y2 in sperm

Kent State University, Kent OH

Investigators

Abstract

Spermatogenesis and the development of fertility competent sperm involve complex processes in the testis, epididymis and female reproductive tract. These physiological processes of sperm formation and development are difficult if not impossible to be recapitulated and studied in vitro. Mouse models amenable to genetic manipulation are essential for understanding the basis for male gamete function. Considerable progress has been made in identifying signaling proteins essential for sperm function which include components of cyclic AMP metabolism, proteins controlling sperm intracellular pH and calcium levels of sperm in the epididymis and in the female reproductive tract. Numerous gene knock out approaches targeting the signaling proteins involved in metabolism and in the action of second messengers result in male infertility. Yet the mechanistic basis for normal and disrupted sperm function remains largely unknown. We discovered that a protein phosphatase PP12, which is one of two paralogs from one gene Ppp1cc, is highly expressed in testis and present in sperm. The other paralog, PP11, is expressed in brain and several somatic cells and tissues and cells. Two other genes encode the PP1 and PP1 isoforms. These four PP1 isoforms are highly conserved between themselves and across species. The isoform PP12 is present only in placental mammals suggesting an essential role for it in the unique features of mammalian sperm function. It is notable that sperm from other species contain one of the protein phosphate isoforms PP11, PP1 or PP1. The targeted knock out of Ppp1cc results in male infertility. Transgenic expression of PP12, but not PP11, driven by a testis specific promoter restores fertility in the Ppp1cc null mice, highlighting the essential requirement for PP12. In this proposal we will examine a mouse line we have generated where the Ppp1cc gene is edited by Crispr/Cas9 to express PP11 alone in testis. Determination of the impaired functions in PP11 bearing mice and sperm should lead to the identification of key proteins essential for normal sperm function. Male infertility is responsible for about 10% of infertile couples. Identification of the causes and treatments for male infertility are limited. A number of factors can affect male infertility: major factors are likely environmental or genetic. This mouse model bearing the non-mammalian PP1 isoform in sperm should also be valuable in not only understanding the significance of the presence of PP12 in all mammals but also in understanding the biochemical basis for fertility and infertility in man.