We identified a novel nuclear protein, NF-|jiNR, that binds to multiple sites flanking the immunoglobulin heavy-chain enhancer. The expression of NF-|jiNR shows a unique developmental pattern; the activity is present in all cells representing early stages of B-cell development, but is absent from more mature cells that express a high level of immunoglobulin heavy chains. NF-|iNR also is present in most cell lines outside of the B-cell lineage (e.g., T cells, macrophages, and fibroblasts). The binding sites for NF-|jiNR correlate very well with cisacting negative regulatory elements of the heavy-chain enhancer defined previously. Indeed, when the segments bound by NF-^.NR are deleted from the enhancer, it is now found to function as a positive transcription element in T cells and macrophages. Taken together, these results suggest that NF-|jiNR may function as a negative regulator of enhancer function. The observation that the segments bound by NF-ftNR correspond to the segments bound to the nuclear matrix suggests an intriguing model not only of how enhancers might function but also of how negative regulation might occur.

Over an average period of seven years 2,900 cases of benign breast lesions diagnosed by biopsy between 1948 and 1973 in the Department of Pathology, Kaiser Foundation Hospital, Oakland, were followed for breast cancer development. When classified according to traditional diagnostic categories, the cancer incidence per 1,000 person-years varies between 2.7 and 7.9 and appears to be elevated in comparison to expectations obtained from the Third National Cancer Survey, San Francisco Bay Area. Two thousand four hundred biopsies were also scored by the Black-Chabon method. There is an upward trend in the breast cancer incidence as the atypia score rises, a finding which confirms conclusions from a retrospective case-control study by Black et al.

Mouse embryonic stem (ES) cells have the potential to differentiate into embryoid bodies in vitro and mimic normal embryonic development. The "ES fetus" is a specific development at a late stage seen under our culture conditions. We have established several mixed populations from ES fetuses by using combinations of retroviruses carrying different oncogenes (v-abl, v-raf, c-myc), interleukins 2 and 3, and Con A. Six groups ofmixed populations were characterized by immunophenotyping. For some groups, transfer of cells into sublethally irradiated mice resulted in the development of macrophages, mature T and B lymphocytes, and plasma cells of donor origin. Thus, these mixed populations may contain immortalized precursors of hematopoietic lineages. These mixed populations should be valuable for defining hematopoietic stem cells and their committed progenitors.

Mouse embryonic stem (ES) cells can differentiate in culture to late stages of many cell lineages. have found culture conditions that are favorable for development in vitro of ES cells into hematopoietic cells at a stage equivalent to day 11-14 of fetal liver development. describe here: (1) the growth conditions necessary for maintenance of ES cells in an undifferentiated state, and the conditions that allow differentiation of cystic embryoid bodies that contain precursors of most hematopoietic cell lineages, including lymphoid cells; (2) the development of lymphoid vessels from ES fetuses in vivo ; (3) the characterization of lymphoid, erythroid, megakaryoid, and myeloid cells from ES fetuses; and (4) the cloning of cell lines representing lymphoid, myeloid lineage cells from differentiated ES cells.

Mouse embryonic stem cells (ES) were allowed to differentiate in a liquid culture system. After 23 weeks, complex cystic embryoid bodies developed. These bodies were composed of several structures identified as cardiac muscle and yolk sac blood islands as well as cupshape compartments containing a mixed population of hematopoietic stem cells. When these cystic embryoid bodies were implanted into adult mice, either subcutaneously or under the kidney capsule, they developed into various tissues. These included bone, blood vessels, cardiac muscle, nerves, and skin with hair follicles. In addition, highly differentiated, complicated tissues resembling intestinal epithelium with mucus glands or salivary glandular tissue were derived. The ES tissues from these in uitro developed embryoid bodies developed quickly within 2 to 3 weeks of implantation. This is in contrast to a minimal of 6 weeks for teratocarcinomas derived from embryonic carcinoma cells and/or the direct implantation of undifferentiated embryonic stem cells. Moreover, we found that there are different types of tissue developed upon different sites of implantation. The data suggest a local environment andlor growth factors are influential for ES tissue development. This system provides a possible means to purify and identify stem cells that give rise to specific tissues, and to study the factors regulating the commitment of these stem cells.0 1993 Wiley-Liss, Inc.