The Tousled-like kinases (TLK1 and TLK2, also designated PKU-β and PKU-α, respectively) are the human homologs of the Tousled gene from Arabidopsis thaliana, which encodes a Serine/Threonine kinase that is necessary for proper organ morphogenesis (1-5). Both TLKs contain a nuclear localization signal and a predicted coiled-coil region in the N-terminal domain (1-3). TLK is ubiquitously expressed, and is prevalent in mouse testis, especially in pachytene spermatocytes and round spermatids (1,2,6). It displays a propensity to dimerize through an interaction between its coiled-coil structure and is able to autophosphorylate, as well as phosphorylate exogenous substrates (1,3). TLK1 and TLK2 are regulated by the cell cycle, showing maximum activity during S phase. Subsequently, they are thought to regulate the development of multicellular organisms, including playing a key role in spermatogenesis, through a series of phosphorylations (1,3,6).