DEVELOPMENT OF DAY-8 COLONY-FORMING UNIT-SPLEEN HEMATOPOIETIC PROGENITORS DURING EARLY MURINE EMBRYOGENESIS - SPATIAL AND TEMPORAL MAPPING

The ontogeny of the hematopoietic system in mammalian embryos occurs d uring the yolk sac (YS) and the fetal liver (FL) stages. Events leadin g to the establishment of hematopoiesis in the FL remain obscure. The appearance of colony-forming units-spleen (CFU-S) in the FL is precede d by a gradual increase of CFU-S in the YS and a more rapid increase i n the AGM region (area comprising dorsal aorta, gonads, and mesonephro s) during day 10 of development (Medvinsky et al, Nature 364:64, 1993) . By this time, the AGM CFU-S attain a high frequency equivalent to th at found in the adult bone marrow. The analogous area gives rise to ad ult hematopoiesis in amphibians and probably in birds. We present here a more complete picture of CFU-S development during transition from t he pre-liver to liver stage of hematopoiesis. (1) Dissectional analysi s of the mouse AGM region shows the presence of CFU-S both around the dorsal aorta and in the uro-genital ridges. (2) The embryonic gut also shows low but distinctive CFU-S activity. This initial intra-body pat tern of CFU-S distribution in murine embryogenesis parallels that foun d for primordial germ cells. (3) The beginning of definitive liver hem atopoiesis is accompanied by wide dissemination of CFU-S in the embryo nic tissues. (4) Comparision of spleen colonies arising from the AGM a nd YS has shown morphologic differences. In contrast to simple erythro id constitution of the YS colonies, a broader variety of cells are fou nd within the AGM-derived colonies that are similar to those derived f rom 11-day FL. These data suggest a lineage relationship for hematopoi etic progenitors between the AGM region and the FL. (C) 1996 by The Am erican Society of Hematology.