STK33 Phosphorylates Fibrous Sheath Protein AKAP3/4 to Regulate Sperm Flagella Assembly in Spermiogenesis.

Spermatogenesis defects are important for male infertility; however, the etiology and pathogenesis are still unknown. Herein, we identified two loss-of-function mutations of STK33 in seven individuals with non-obstructive azoospermia. Further functional studies of these frameshift and nonsense mutations revealed that Stk33-/KI male mice were sterile, and Stk33-/KI sperm were abnormal with defects in the mitochondrial sheath, fibrous sheath, outer dense fiber, and axoneme. Stk33KI/KI male mice were subfertile and had oligoasthenozoospermia. Differential phosphoproteomic analysis and in vitro kinase assay identified novel phosphorylation substrates of STK33, fibrous sheath components A-kinase anchoring protein 3 and A-kinase anchoring protein 4, whose expression levels decreased in testis after deletion of Stk33. STK33 regulated the phosphorylation of A-kinase anchoring protein 3/4, affected the assembly of fibrous sheath in the sperm, and played an essential role in spermiogenesis and male infertility.

Potential clinical value of in vitro spermatogenesis†.

Infertility has become the third most common disease threatening human health, immediately after tumors and cardiovascular diseases. Male infertility is primarily caused by spermatogenesis disorders that may be classified as either genetic or non-genetic. For part of non-genetic disorders, in vitro spermatogenesis can be induced by adjusting the microenvironment of the testis culture. Establishing the in vitro spermatogenic induction system helps to clarify the critical molecular mechanisms in spermatogonia self-renewal, spermatocyte meiosis, and sperm formation during spermatogenesis. In this review, we summarize recent advances in the field of in vitro sperm cells induction. Therefore, we hope to provide ideas and solutions for the clinical treatment of male infertility.

In vitro testicular organogenesis from human fetal gonads produces fertilization-competent spermatids.

Unlike most organs that mature during the fetal period, the male reproductive system reaches maturity only at puberty with the commencement of spermatogenesis. Robust modelling of human testicular organogenesis in vitro would facilitate research into mechanisms of and factors affecting human spermatogenic failure and male fertility preservation in prepubertal tumor patients. Here, we report successful recapitulation of human testicular organogenesis in vitro from fetal gonadal ridge. Our model displayed the formation of mature seminiferous epithelium and self-renewing spermatogonia. Remarkably, in vitro-derived haploid spermatids have undergone meiotic recombination, and showed increased genetic diversity as indicated by genetic analysis. Moreover, these spermatids were able to fertilize oocytes and support subsequent blastocyst formation. The in vitro testicular organogenesis system described here will play an important role in elucidating the regulation of human testis development and maintaining male fertility in prepubertal cancer patients.