Loss of Prm1 leads to defective chromatin protamination, impaired PRM2 processing, reduced sperm motility and subfertility in male mice [PRM1]

One of the key events during spermiogenesis is the hypercondensation of chromatin by substitution of the majority of histones by protamines. In humans and mice, protamine 1 (PRM1/Prm1) and protamine 2 (PRM2/Prm2), are expressed in a species-specific ratio. Using CRISPR-Cas9-mediated gene editing we generated Prm1-deficient mice and demonstrate, that Prm1+/- mice are subfertile while Prm1-/- are infertile. Prm1-/- and Prm2-/- sperm show high levels of reactive oxygen species (ROS)-mediated DNA damages and increased histone retention. In contrast, Prm1+/- sperm display only moderate DNA damages. The majority of Prm1+/- sperm were CMA3 positive indicating protamine-free DNA. This is not due to increased histone retention in Prm1+/- sperm. Additionally, we found that sperm from Prm1+/- and Prm1-/- mice contain high levels of incompletely processed PRM2. Further, the PRM1:PRM2 ratio is skewed from 1:2 in WT to 1:5 in Prm1+/- animals. Our results reveal that PRM1 is required for proper PRM2 processing to produce the mature PRM2 which, together with PRM1 is able to hypercondense DNA. Hence, the species specific PRM1:PRM2 ratio has to be precisely controlled in order to retain full fertility. Comparative testis gene expression profiling of PRM1 deficient mice compared to WT