CELL TYPE-DEPENDENT AND DIFFERENTIATION STAGE-DEPENDENT EXPRESSION OFPML DOMAINS IN RAT, DETECTED BY MONOCLONAL-ANTIBODY HIS55

Using mouse monoclonal antibody (mAb) HIS55, we identified a nuclear a ntigen (ag) that exhibited a staining pattern of discrete foci. Such f oci could be detected in cells of many mammalian species. These nuclea r foci were not associated with nuclear membrane, nucleoli, or mitotic chromosomes. In isolated rat liver nuclei, HeLa cells, and normal hum an and rat lymph nodes, staining of HIS55 colocalized with that of 5E1 0. 5E10 recognizes PML nuclear domains, multimolecular complexes of un known function containing the product of PML gene and at least two oth er components. HIS55 foci were expressed widely in many tissues but th e expression level varied in a cell type-specific manner, with the num ber of HIS55 nuclear foci ranging from 0 (as in neurons) to over 100 ( as in megakaryocytes) and the size ranging from fine (as in cortical t hymocytes) to very large (as in urethra epithelium). HIS55 ag expressi on level also varied among cells of the same lineage, as observed in e mbryonic development of rat and in the hemopoietic system of adult rat . The expression level of HIS55 foci roughly correlated with the overa ll rate of protein synthesis of cells, supporting a role of PML domain s as transcription regulatory units. The expression of HIS55 foci, how ever, did not correlate with the growth index of cell populations. Our observations on normal tissues agreed with the hypothesis that PML do main expression is regulated by external, possibly site-dependent fact ors. We further supported this by demonstrating that PML domains in ra t ventral prostate epithelia were upregulated upon castration. (C) 199 5 Academic Press, Inc.