Cancer associated variant expression and interaction of CIZ1 with cyclin A1 in differentiating male germ cells

• Published in: Journal of cell science Vol. 125; no. Pt 10; p. 2466
• Main Authors: Greaves, Erin A., Copeland, Nikki A., Coverley, Dawn, Ainscough, Justin F. X.
• Format: Journal Article
• Language: English
• Published: England 15.05.2012
• Subjects: Alternative Splicing; Animals; Cell Proliferation; Cyclin A1 - genetics; Cyclin A1 - metabolism; Gene Expression Regulation, Developmental; Gene Expression Regulation, Neoplastic; Male; Mice; Mice, Inbred C57BL; Neoplasms - genetics; Neoplasms - metabolism; Neoplasms - physiopathology; Nuclear Proteins - genetics; Nuclear Proteins - metabolism; Protein Binding; Protein Isoforms - genetics; Protein Isoforms - metabolism; Protein Structure, Tertiary; Spermatogenesis; Spermatogonia - cytology; Spermatogonia - growth & development; Spermatogonia - metabolism
• ISSN: 0021-9533; 1477-9137; 1477-9137
• DOI: 10.1242/jcs.101097

CIZ1 is a nuclear matrix associated DNA replication factor unique to higher eukaryotes, for which alternatively spliced isoforms have been associated with a range of disorders. In vitro the CIZ1 N-terminus interacts with cyclins E and A via distinct sites, enabling functional cooperation with cyclin A-Cdk2 to promote replication initiation. C-terminal sequences anchor CIZ1 to fixed sites on the nuclear matrix imposing spatial constraint on cyclin dependent kinase activity. Here we demonstrate that CIZ1 is predominantly expressed as predicted full-length product throughout mouse development, consistent with a ubiquitous role in cell and tissue renewal. CIZ1 is expressed in proliferating stem cells of the testis, but is notably down-regulated following commitment to differentiation. Significantly, CIZ1 is re-expressed at high levels in non-proliferative spermatocytes prior to meiotic division. Sequence analysis identifies at least seven alternatively spliced variants at this time, including a dominant cancer-associated form and a set of novel isoforms. Furthermore, we show that in these post-replicative cells CIZ1 interacts with the germ cell specific cyclin, A1, that has been implicated in DNA double-strand break repair. Consistent with this role, antibody depletion of CIZ1 reduces the capacity for testis extract to repair digested plasmid DNA in vitro. Together, the data imply novel post-replicative roles for CIZ1 in germ cell differentiation that may include meiotic recombination, a process intrinsic to genome stability and diversification.