PCNA-BINDING TO DNA AT THE G1 S TRANSITION IN PROLIFERATING CELLS OF THE DEVELOPING CEREBRAL WALL/

Proliferating cell nuclear antigen is a nuclear protein essential to D NA synthesis in eukaryotic cells. It is known to form part of a multi- protein complex which binds to DNA from the outset of S-phase of the c ell cycle. We define in this analysis the interval of proliferating ce ll nuclear antigen binding to DNA (strictly speaking, the interval thr ough which proliferating cell nuclear antigen is stained immunohistoch emically after ethanol fixation) with respect to the stages of the cel l cycle in the intact mammalian brain. The epithelium of the developin g cerebral wall is favourable for such an analysis because nuclei at t he same stage of the cell division cycle are spatially aligned with ea ch other at the same depth of the epithelium. Therefore spatial locati on of a nucleus within the epithelium is a reliable indicator of the s tage of the cell cycle for that nucleus. Proliferating cell nuclear an tigen-DNA binding in this epithelium is initiated in the final 5% (26 min) of G1-phase and continues through the initial 35% (1.3 h) of S-ph ase. This phasic pattern of proliferating cell nuclear antigen-DNA bin ding, as revealed for the first time in the intact cerebral wall, appr oximates closely the phasic pattern as it has been characterized until now only in vitro in vertebrate cell lines. This analysis illustrates the potential of the cerebral proliferative epithelium for study of t he molecular events of the cell cycle under in vivo conditions of hist ogenetic regulation.