Molecular expression of Ly6k, a putative glycosylphosphatidyl-inositol-anchored membrane protein on the mouse testicular germ cells.

Ly6k, a putative mouse glycosylphosphatidyl-inositol (GPI)-anchored membrane protein is specifically associated with a unique germ-cell marker, TEX101. Although a human orthologue LY6K has been proposed as a novel cancer/testis antigen, its molecular nature is largely obscure, because its characteristics have been gleaned mainly from qualitative studies of gene structure. The aim of this study is to characterize molecular nature of Ly6k more precisely, especially, to focus on the molecular expression during testicular development. The present study have shown that: (1) Ly6k was strongly observed in testis, but faint expression was broadly noticed in other tissues; (2) Ly6k was weakly detected in testes from 18-day postcoitus to 1-day postpartum (dpp), with a plateau starting around 8-dpp; and (3) testicular Ly6k showed two-peak expression at around 14-dpp and 24-dpp, then exhibited stable expression from 6-week after birth onward. Western blot and immunohistochemical analyses revealed that Ly6k exists in at least two forms: a GPI-anchored form (17kDa) and a water-soluble (non-membrane) form (12kDa), and the 17-kDa mature form is expressed in the testicular germ cells beginning approximately 10days after birth. This information is essential for the molecular classification of Ly6k, and may help uncover the detailed physiological role of Ly6k in gametogenesis, or cancer biology.