TSSK1B (testis-specific serine kinase 1B) is a calcium/calmodulin-dependent protein kinase essential for male reproductive function. During spermatogenesis, TSSK1B is expressed in elongating spermatids and functions in late-stage spermatid development, particularly in cytoplasmic reconstruction and transformation of ring-shaped structures at the flagellar base 1. The kinase domain has evolved under negative selection in primates, reflecting its critical functional importance 1. Beyond reproductive function, TSSK1B serves as a negative regulator of the Hippo-YAP pathway through the LKB1-TSSK1B axis, directly phosphorylating YAP at Ser94 to suppress oncogenic transformation and cellular proliferation 2. TSSK1B mutations are associated with male infertility phenotypes including asthenoteratozoospermia and azoospermia 34. Deletions encompassing TSSK1B correlate with reproductive impairment 4, and altered TSSK1B expression is identified as a potential biomarker for non-obstructive azoospermia 5. Recently, rare variants in TSSK1B have been associated with altered mean platelet volume in β-thalassemia patients 6. TSSK1B has emerged as a validated therapeutic target for male contraception 7.