Differential subcellular localization of neural isoforms of the catalytic subunit of calmodulin-dependent protein phosphatase (calcineurin) in central nervous system neurons: Immunohistochemistry on formalin-fixed paraffin sections employing antigen retrieval by microwave irradiation

We examined the immunohistochemical distribution of the two mammalian isoforms of calcineurin catalytic subunits, Aα and Aβ, in central nervous system (CNS) tissues of cows, rats, and humans. Cryostat sections and paraffin sections of paraformaldehyde-fixed tissues were stained with anti-peptide antibodies for each isoform. The same localization pattern was observed in both cryostat and paraffin sections. In the latter, the intensity of the staining was dramatically enhanced by microwave irradiation. Calcineurin isoforms were localized in a variety of nerve cells but not in neuroglial cells. Their differential expression as the Aα isoform in the nucleus and the Aβ isoform in the cytoplasm was present in a variety of CNS nerve cells, most distinctively in Purkinje cells of the cerebellum and pyramidal cells of the cerebrum, irrespective of species. These results suggest that each isoform has distinct intracellular sites of action in CNS neurons and that the phenomenon has been conserved during mammalian evolution.