Human securin, also known as pituitary tumor transforming gene, plays a critical role during cell division. Ubiquitination of securin during the metaphase to anaphase transition releases its binding partner separase, which cleaves the cohesins holding sister chromatids together. We recently demonstrated reduced securin expression in human fetal versus adult brain, and dissected its role in affecting the proliferation of human embryonal CNS precursor NTERA-2 (NT-2) cells. We have now investigated separase in this context. In 61 fetal and 12 adult human brain samples, we found dramatically increased separase levels throughout fetal brain ontogeny, coincident with significantly reduced securin levels. Separase mRNA was 70.1-fold (p<0.001, n=14) and 86.6-fold (p<0.001, n=21) increased in early and late first trimester fetal brain respectively. Similarly, levels were 144.4-fold (p<0.001, n=20) and 40-fold (p<0.001, n=6) induced during the early and late part of the second trimester respectively. mRNA encoding securin and separase correlated negatively during fetal life (R2=0.1, P=0.015), whereas a positive correlation was evident in adult samples (R2=0.6, P=0.005). Protein expression for both genes was consistent with mRNA data. Using retinoic acid treatment, we differentiated NT-2 cells into post-mitotic neurones and examined securin and separase expression. Securin mRNA expression was 10.9-fold (P<0.001, n=4) higher, and separase mRNA 96% (P<0.001, n=4) reduced, in differentiated compared with undifferentiated NT-2 cells. In MTT assays, low (0.5 micrograms/well of 6 well plate) transient expression of securin (P<0.001, n=4) and separase (P<0.001, n=4) significantly induced cell proliferation, whereas high levels (3 micrograms/well) of securin inhibited cell turnover (P=0.005, n=4). Based on our in vivo and in vitro findings, we propose a model for human neural development. High separase and low securin expression in fetal brain promotes the rapid cell proliferation characteristic of ontogeny, whereas low separase and high securin in adult brain prevents cell division in mature neurons.
22 - 24 Mar 2004
British Endocrine Societies