Regulated expression of p14 (cofactor A) during spermatogenesis

The correct folding of tubulins and the generation of functional alpha beta -tubulin heterodimers require the participation of a series of recently des cribed molecular chaperones and CCT (or TRiC), the cytosolic chaperonin con taining TCP-1. p14 (cofactor A) is a highly conserved protein that forms st able complexes with beta-tubulin which are not apparently indispensable alo ng the in vitro beta-tubulin folding route. Consequently, the precise role of p14 is still unknown, though findings on Rbl2p (its yeast homologue) sug gest p14 might play a role in meiosis and/or perhaps to serve as an excess beta-tubulin reservoir in the cell. This paper investigates the in vivo pos sible role of p14 in testis where mitosis, meiosis, and intense microtubula r remodeling processes occur. Our results confirm that p14 is more abundant ly expressed in testis than in other adult mammalian tissues. Northern blot , Western blot, in situ hybridization, and immunocytochemical analyses have all demonstrated that p14 is progressively upregulated from the onset of m eiosis through spermiogenesis, being more abundant in differentiating sperm atids. The close correlation observed between the mRNA expression waves for p14 and testis specific tubulin isotypes beta 3 and alpha 3/7, together wi th the above results, suggest that p14 role in testis would presumably be a ssociated to beta-tubulin processing rather than meiosis itself. Additional in vitro beta 3-tubulin synthesis experiments have shown that p14 plays a double role in beta-tubulin folding, enhancing the dimerization of newly sy nthesized beta-tubulin isotypes as well as capturing excess beta-tubulin mo nomers. The above evidence suggests that p14 is a chaperone required for th e actual beta-tubulin folding process in vivo and storage of excess beta-tu bulin in situations, such as in testis, where excessive microtubule remodel ing could lead to a disruption of the a-p balance. As seen for other chaper ones, p14 could also serve as a route to lead excess beta-tubulin or replac ed isotypes towards degradation. Cell Motil. Cytoskeleton 43:243-254, 1999. (C) 1999 Wiley-Liss, Inc.