Chromatin structure is influenced by histone modification, and this may help direct chromatin behavior to facilitate transcription, DNA replication, and DNA repair. Chromatin condensation and DNA fragmentation are the classic nuclear features but remain poorly characterized. It is highly probable that nucleosomal structure must be altered to allow these features to become apparent, but data to support this construct are lacking. We report here that in response to apoptotic signals from a death receptor (CD95 and tumor necrosis factor-␣) or mitochondrial (staurosporine) apoptotic stimulus, the core nucleosomal histones H2A, H2B, H3, and H4 become separated from DNA during apoptosis in Jurkat and HeLa cells and are consequently detectable in the cell lysate prepared using a non-ionic detergent. The timing of this histone release from DNA correlates well with the progression of apoptosis. We also show expression of a caspase cleavageresistant form of ICAD (ICAD-DM) in Jurkat and HeLa cells abolished DNA fragmentation and also dramatically reduced histone release in apoptotic cells. However, we demonstrate that apoptotic histone release is not an inevitable consequence of CAD/DFF-40-mediated DNA destruction as DNA fragmentation but not histone release occurs efficiently in tumor necrosis factor-␣-and etoposide-treated NIH3T3 cells. Furthermore, in an in vitro apoptotic assay, incubation of apoptotic Jurkat cellular extract with non-apoptotic Jurkat nuclei led to nuclear DNA fragmentation without obvious histone release. Taken together, these data demonstrate that CAD/DFF-40 functions indirectly in mediating nucleosomal destruction during apoptosis.

T1D (Type 1 Diabetes) is an autoimmune disorder caused by the immune-mediated destruction of insulin-producing beta cells in the pancreas. There are direct mechanisms that have been demonstrated to cause final beta cell demise, such as the pathways triggered by Fas engagement and Perforin release. However, focus should be placed on other indirect mechanisms, such as pro-inflammatory cytokines present in the beta cell niche early on, that progressively debilitate and alter beta cells from earlier phases of T1D progression, rendering them as helpless targets of the immune system at the end. Though beta cells may resist adverse stimuli in early phases of the autoimmune process, the complicity of both, direct and indirect deleterious mechanisms, leads to beta cell death. In an effort to identify those indirect mechanisms that chronically besiege beta cells from the T1D-prone NOD mouse model, we used the microarray technology. We have identified several candidate genes the expression of which is altered in the NOD islet prior to T1D onset. Several of these genes are related to cell cycle progression and are downregulated due to the insulitic attack to the islet. One of these genes is cyclin D-3, a Dtype cyclin that interacts with either Cdk4 or Cdk6 to promote G1/S cycle progression. We have reported that cyclin D3 protects beta cells against cytokine-induced apoptosis and is required for proper beta cell function in a cell-cycle independent fashion. Cdk11 is also affected by inflammation in islet cells and is a cyclin-dependent kinase which is involved in transcription, mitosis and apoptosis. The natural partners of Cdk11 are L-type cyclins. We have examined whether the immune function is affected in the relative absence of Cdk11.