PROTEIN EXPRESSION DURING MURINE THYMUS DIFFERENTIATION

Driven by our long-standing interest in identifying proteins of the im mune system and in characterizing processes involved in lymphocyte dif ferentiation, we studied protein expression in biosynthetically labele d fetal and newborn thymus by 2D gel electrophoresis. Autoradiographs of the gels were scanned with a densitometer and image analysis was pe rformed using the Kepler system. Calibrated polypeptide spot abundance s (volumes) were compared to assesses qualitative and quantitative cha nges of the spot volumes. Among over 300 proteins evaluated at GD (ges tation day) 13, 15, and 17, there were sets of proteins that increased and others that decreased in intensity. We could in addition recogniz e proteins that were completely absent at GD 13 and/or 15 and that app eared thereafter to gradually increase in intensity. Conversely, vario us polypeptide spots present at early stages (at GD 13 and 15) disappe ar later (at GD 17 or at birth). Among the proteins that increase in i ntensity prevail molecules with masses less than 35 kD, whereas a cons iderable portion of those that decrease in intensity are characterized by masses above 60 kD. Spots reported in this communication were not defined beyond tagging them with numbers, which is a prerequisite to f ollow them up in the proteinpaedia developed in our laboratory. The ne xt step will be to retrieve the coding sequences from the existing par titioned cDNA library (BW 5147) as well as from thymocyte subtraction libraries. We predict that among those polypeptides with varying inten sity, important regulatory proteins in thymus development will be foun d.