217. Interaction of cdyl (chromodomain y-chromosome like) with the nuclear transport protein importin α2

Abstract

Spermatogenesis is a unique, ordered process governed by the precise expression of a specific set of genes at each stage. Progression through successive stages requires the shuttling of proteins and transcription factors into and out of the nucleus to implement changes in gene transcription. Major factors that mediate nucleocytoplasmic transport are members of the importin superfamily, of which there are five and 20 different importin α and β genes, respectively, in mouse. We have previously demonstrated that several importins display distinct mRNA and protein expression patterns in adult mouse testis1 indicating that specific importins carry a specific cargo at discrete stages of spermatogenesis. Identification of importin cargoes in the testis should help describe the potential developmental switches critical to the spermatogenic process. We performed a yeast two-hybrid screen using full length importin α2 as bait and an adult mouse testis library, identifying nine target proteins. Some of these proteins include nuclear components that may be important in eliciting changes in the nuclear structure during spermatogenesis, as well as those involved in cell cycle regulation, homologous chromosome pairing and recombination, transcriptional regulation and guanine nucleotide biosynthesis. One key candidate is CDYL, which has been implicated in male infertility. It is a chromodomain-containing protein that is predominantly expressed during spermiogenesis and has been previously described to participate in hyperacetylation of histone H4, which is believed to facilitate protamine replacement of histones during spermiogenesis. Verification of CDYL-importin α2 interaction was demonstrated using co-immunoprecipation and co-transfection, while immunohistochemical staining of testis sections indicated colocalisation in the same cell types (mainly elongating spermatids). Importantly, preliminary experiments indicated that increasing CDYL nuclear accumulation by over-expressing importin α2 can increase histone H4 acetylation. Our hypothesis is that importin α2 is central in nuclear targeting of CDYL to facilitate its hyperacetylation role during protamine-histone exchange. (1)Hogarth et al. (2005). Dev. Dynamics (submitted).