Mediolateral somitic origin of ribs and dermis determined by quail-chick chimeras.

Somites are transient mesodermal structures giving rise to all skeletal muscles of the body, the axial skeleton and the dermis of the back. Somites arise from successive segmentation of the presomitic mesoderm (PSM). They appear first as epithelial spheres that rapidly differentiate into a ventral mesenchyme, the sclerotome, and a dorsal epithelial dermomyotome.

Kinetics and repertoire selection of T cells derived from the early waves of fetal thymus colonization after thymus grafting in allogeneic nude recipients.

The survival of T cells derived from the early waves of thymus colonization by haemopoietic cell precursors was investigated by grafting thymus from B6.Thy1.1 day 14 embryos (E14) (first wave) or E17 or newborn thymus (subsequent waves) into allogeneic athymic BALB/c (Thy1.

Abnormal T cell selection on nod thymic epithelium is sufficient to induce autoimmune manifestations in C57BL/6 athymic nude mice.

To investigate the role of primary T cell repertoire selection in the immunopathogenesis of autoimmune diseases, pure thymic epithelium (TE) from nonobese diabetic (NOD) embryos was grafted into non autoimmune prone newborn C57BL/6 athymic mice. The results show that NOD TE selects host T cell repertoires that establish autoimmunity in otherwise nondiabetic animals. Thus, such chimeras regularly show CD4 and CD8 T cell-mediated insulitis and sialitis, in contrast with syngeneic or allogeneic chimeras produced with TE from nonautoimmune strains.

On the mechanisms of thymic epithelium induced tolerance.

We have devised a model in which nude mice are T cell reconstituted at birth by subcutaneous grafts of embryonic thymic epithelium (TE) removed from 10 days allogeneic embryos. The TE is colonized by the nude mouse hemopoietic cells which differentiate into T cells. Such T cell-reconstituted nude mice are able to reject third party skin graft and are tolerant to skin of their own haplotype but also the TE H-2 type.

Bone morphogenetic protein-2 (BMP-2) inhibits muscle development and promotes cartilage formation in chick limb bud cultures.

Bone morphogenetic proteins (BMPs) induce ectopic cartilage and bone when implanted intramuscularly in adult rats. Expression data suggest that BMPs signal skeletal development in embryos. An important question is which cells are targets of BMP signaling in adult and embryonic tissues.