Co-translational targeting defect caused by Srp68 knockout leads tomeiotic arrest during spermatogenesis in mice

Co-translational targeting by the signal recognition particle delivers nascent secretory and membrane proteins into the endoplasmic reticulum, yet its role in mammalian germ cells remains unclear. Here, we found that SRP68 is indispensable for spermatogenesis in mice. Conditional Srp68 deletion in germ cells results in defective synapsis and double-strand break repair, leading to meiotic prophase I arrest and male infertility. Proteomic profiling revealed that SRP68-deficient spermatocytes exhibit significant reduced endoplasmic reticulum (ER)-associated signal peptide-containing proteins, accompanied by structural disorganization. Additionally, multiple factors involved in ER–mitochondrial contact are decreased in SRP68-deficient spermatocytes, leading to mitochondrial calcium ion depletion, depolarized membrane potential, and insufficient ATP production. These findings demonstrate that SRP68-dependent co-translational targeting is essential for meiotic progression, providing a basis for interpreting ER-related causes of male infertility. Overall design: We performed Smart-seq2 on FACS-isolated leptotene/zygotene spermatocytes from control and SKO mice at postnatal day 12 .For Smart-seq2, cell lysis, mRNA reverse transcription, and cDNA amplification were performed using the Discover-sc WTA Kit V2 (Vazyme, N711). Following this, cDNA fragmentation and adapter ligation were carried out with the TruePrep Flexible DNA Library Prep Kit for Illumina (Vazyme, TD504). All procedures were conducted in strict accordance with the manufacturer's protocols. The Smart-seq2 library sequencing was performed by Novogene on Illumina platforms, generating 150 bp paired-end reads.