A2-pancortins (Pancortin-3 and -4) are the dominant Pancortins during neocortical development

We have identified a novel mouse gene named pancortin that is expressed dominantly in the mature cerebral cortex. This gene produces four different species of proteins, Pancortin-1-4, sharing a common region in the middle of their structure with two variations at the N-terminal (A1 or A2 part) and C- terminal (C1 or C2 part) sides, respectively. In the present study, we showed that expression of mRNAs for A2-Pancortins (Pancortin species that contain the A2 part, i.e., Pancortin-3 and -4) is more dominant than that of mRNAs for A1-Pancortins (Pancortin species that contain the A1 part, i.e., Pancortin-1 and -2) in the prenatal mouse cerebral neocortex. Using western blot analysis, we found that substantial amounts of both A2-Pancortins were present in the prenatal cerebral neocortex and P19 cells after inducing neuronal differentiation. A2-Pancortins were still present in the cerebral neocortex of the adult, although their mRNAs were hardly detected. In contrast, the amount of A1-Pancortins did not increase after the third postnatal week in spite of their intense gene expression. Furthermore, we showed that recombinant Pancortin-3, one of the A2-Pancortins, was a secreted protein, in contrast to Pancortin-1 (one of the A1-Pancortins). These results suggest that A2-Pancortins are extracellular proteins essential for neuronal differentiation and that their molecular behavior is distinct from that of A1-Pancortins.