IMMUNOHISTOCHEMICAL LOCALIZATION OF THE CALCIUM CALMODULIN-DEPENDENT PROTEIN PHOSPHATASE, CALCINEURIN, IN THE MOUSE TESTIS - ITS UNIQUE ACCUMULATION IN SPERMATID NUCLEI

Immunohistochemical localization of a calmodulin-dependent protein pho sphatase, calcineurin, was studied in the mouse testis in relation to previous observations showing that calmodulin is unusually rich in spe rmatogenic stages from mid-pachytene spermatocytes to elongating sperm atids. The antibodies raised against calcineurin from scallop testis r eacted with subunit B, but not subunit A, of calcineurin isoforms from mouse brain and testis. Indirect immunofluorescence using these antib odies on the mouse testis revealed positive reactions only in the nucl ei of round or elongating spermatids: calcineurin started to accumulat e in nuclei from the acrosomal cap phase, peaked at the initial stage of nuclear elongation, and decreased thereafter. There was almost no s ignal in the cytoplasm; spermatogenic cells at other stages, including spermatogonia, spermatocytes, mature sperm, and other somatic cells i n the seminiferous tubules were totally negative. Immune-electron micr oscopy gave the same result, on the basis of measuring the density of immunogold particles. These results suggest a role for calcineurin in remodeling of the nuclear chromatin in metamorphosing spermatids.