The serglycin proteoglycan is expressed in most hematopoietic cells and is packaged into secretory vesicles for constitutive or regulated secretion. We have now shown serglycin mRNA expression in undifferentiated murine embryonic stem (ES) cells and in embryoid bodies, and synthesis and secretion in undifferentiated ES cells. Serglycin was localized to ES cell cytoplasm by immunostaining. Serglycin mRNA is expressed in tal-1((-/-)) ES cells and embryoid bodies; tal-1((-/-)) mice cannot produce hematopoietic cells. Thus, ES serglycin expression is probably not associated with hematopoiesis. Serglycin expression was increased by treatment of ES cells with retinoic acid (RA) and dibutyryl cAMP (dbcAMP). The serglycin core protein obtained from control ES culture medium after chondroitinase digestion appears as a doublet. Only the lower Mr band is present in serglycin secreted from RA-treated and the higher Mr band in RA+dbcAMP-treated cells, suggesting that core protein structure is affected by differentiation.

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