Expression of EMAP II in the developing and adult mouse.

Endothelial monocyte-activating polypeptide II (EMAP II) is a chemoattractant for monocytes and granulocytes. EMAP II is translated as a precursor protein, proEMAP II, and is proteolytically cleaved to become the mature, biologically active cytokine. In this study we show that the EMAP II mRNA and the EMAP II precursor protein are constitutively expressed by all cell types analyzed in vitro, whereas the mature cytokine is only present in the supernatant of apoptotic cells. During mouse embryogenesis we found widespread expression of the EMAP II mRNA with transcripts being abundant in areas of tissue remodeling, where a large number of apoptotic cells could be detected by TUNEL staining. In the adult mouse, strong expression of the EMAP II mRNA is restricted to the brain, testis and thymus. Interestingly, prominent signals for EMAP II mRNA are found in local correlation with sites of apoptosis in thymus and testis but not in the brain. We propose that during development, the generation and release of the mature EMAP II may provide a mechanism for the recruitment of phagocytic cells to sites of programmed cell death. In the adult brain, the generation of mature EMAP II may contribute to the recruitment of monocytes and the immunosurveillance of this tissue.