Siyu Liu

Translational control is essential for male germ cell development, yet how post-transcriptional regulation is coupled to chromatin remodeling during spermatogenesis remains poorly understood. Here, we show that the RNA-binding proteins PUMILIO1 (PUM1) and PUMILIO2 (PUM2) promote translation of mRNAs encoding chromatin regulators in the mouse testis. Conditional deletion of Pum1 and Pum2 in germ cells at multiple developmental stages results in spermatogenic failure, defective nuclear shaping, impaired histone-to-protamine exchange, and complete male sterility. Polysome profiling and ribosome sequencing reveal selective reductions in translation efficiency of chromatin regulators, including histone modifiers and nucleosome remodelers, in Pum1/2 -deficient testes. Mechanistically, PUM1/2 associate with DAZL and PABPC1 to form a germ cell–specific translational activation complex that enhances protein output with little impact on mRNA stability. Together, these findings redefine mammalian PUM proteins as context-dependent translational activators in the germline and uncover a post-transcriptional mechanism that links RNA regulation to chromatin dynamics during spermatogenesis.

Mitochondrial fatty acid β-oxidation (FAO) is essential for energy production and cellular homeostasis, yet its role in sperm function has remained unclear. Through whole-exome sequencing (WES) of 800 patients with asthenozoospermia, we identified biallelic Testis-Expressed Protein 44 (TEX44) variants in six individuals, all of whom exhibited defective mitochondrial sheath assembly and impaired sperm motility. Using Tex44 knockout mice, we show that TEX44 interacts with carnitine palmitoyltransferase 1B (CPT1B) to form a mitochondrial glue, anchoring adjacent mitochondria and facilitating the assembly of the sperm-specific mitochondrial sheath. In vitro, we show that purified TEX44 protein can modulate CPT1B enzymatic activity, limiting the conversion of long-chain fatty acids such as palmitic acid and myristic acid into acyl-carnitines, thereby reducing reactive oxygen species (ROS) production. Loss of TEX44 disrupts this regulatory mechanism, leading to unregulated FAO, excessive ROS generation, and severe oxidative damage to sperm DNA and flagellar structure. Additionally, germ cell-specific Cpt1b knockout mice exhibit phenotypes similar to TEX44 deficiency, including mitochondrial sheath defects and reduced sperm motility. These findings reveal a sperm-specific mechanism by which TEX44 regulates CPT1B activity to balance FAO and ROS generation, providing critical insights into energy metabolism, mitochondrial integrity, and male infertility.