One action of cyclosporin A thought to be central to many of its immunosuppressive effects is its ability to inhibit the early events of T lymphocyte activation such as lymphokine gene transcription in response to signals initiated at the antigen receptor. Cyclosporin A was found to specifically inhibit the appearance of DNA binding activity of NF-AT, AP-3, and to a lesser extent NF-kappa B, nuclear proteins that appear to be important in the transcriptional activation of the genes for interleukin-2 and its receptor, as well as several other lymphokines. In addition, cyclosporin A abolished the ability of the NF-AT binding site to activate a linked promoter in transfected mitogen-stimulated T lymphocytes and in lymphocytes from transgenic mice. These results indicate that cyclosporin A either directly inhibits the function of nuclear proteins critical to T lymphocyte activation or inhibits the action of a more proximal member of the signal transmission cascade leading from the antigen receptor to the nucleus.

Serving as the primary conduit for communication between the nucleus and the cytoplasm, nuclear pore complexes (NPCs) impact nearly every cellular process. The extent to which NPC composition varies and the functional significance of such variation in mammalian development has not been investigated. Here we report that a null allele of mouse nucleoporin Nup133, a structural subunit of the NPC, disrupts neural differentiation. We find that expression of Nup133 is cell type and developmental stage restricted, with prominent expression in dividing progenitors. Nup133-deficient epiblast and ES cells abnormally maintain features of pluripotency and differentiate inefficiently along the neural lineage. Neural progenitors achieve correct spatial patterning in mutant embryos; however, they are impaired in generating terminally differentiated neurons, as are Nup133 null ES cells. Our results reveal a role for structural nucleoporins in coordinating cell differentiation events in the developing embryo.

A severe immunodeficiency involving a complete loss of T lymphocytes and natural killer cells was observed in independent lines of transgenic mice containing >30 copies of the human CD3E gene (pL12). T-cell natural killer (NK)-mice could also be generated by using a gene fragment pL12A1 (without exons 4A and 5) coding for the CD3-e transmembrane region and its 55-amino acid nonenzymatic cytoplasmic tail. The abnormally small thymus gland in the homozygous transgenic animals, which was 41% the size of a wild-type thymus, contained only a few (2-4%) prethymocytes with a Thy-l+Pgp-1+IL-2Ra-CD3-4-8-phenotype. In mice with lower copy numbers of the transgene thymocyte development was blocked at the Thy-l+Pgp-1lIL-2Ra+CD3-4-8-stage, and normal NK activity was detected. Mice generated with high-copy numbers of a transgene pL12A2 (pL12A1 minus exons 6), coding for a truncated protein from which the CD3-E extracellular domain, its transmembrane region, and most of its cytoplasmic region were absent, contained normal numbers of T lymphocytes and NK cells. These transgene effects suggested that recruitment of signal-transduction molecules by the cytoplasmic tail of this protein played an important role in the abrogation of both lineages. Taken together these observations support the notion that T lymphocytes and NK cells stemmed from a common precursor.Antigen CD3-e plays a dual role in the six-polypeptide-chain T-cell antigen receptor: initiator of receptor assembly within the endoplasmic reticulum and transducer of the signal generated by antigen recognition (1-3). More recently it has become clear that incomplete CD3 complexes, which are T-cell receptor (TCR)-ac, -(-, -y-, and -8-, can be detected on the surface of CD4-8-thymocytes. These extremely low levels of cell-surface CD3-y, -8, and -E are potentially functionally competent because antibodies directed at CD3-e trigger one of its signal-transduction pathways and drive differentiation from CD4-8-to CD4+8+ thymocytes in the absence of TCR gene rearrangements (4). Intracellular CD3-E protein was found in human natural killer (NK) cells (5) and more recently, studies using cultured human fetal thymus and fetal liver clones revealed that CD3-E could also be found in NK cell precursors (6, 7

Fate-mapping experiments in the mouse have revealed that the primitive streak can be divided into three functional regions: the proximal region gives rise to germ cells and the extra-embryonic mesoderm of the yolk sac; the distal region generates cardiac mesoderm and node-derived axial mesendoderm; and the middle streak region produces the paraxial, intermediate and lateral plate mesoderm of the trunk. To gain insight into the mechanisms that mediate the assembly of the primitive streak into these functional regions, we have cloned and functionally identified the gene disrupted in the amnionless (amn) mouse, which has a recessive, embryonic lethal mutation that interferes specifically with the formation and/or specification of the middle primitive streak region during gastrulation. Here we report that the gene Amn encodes a novel type I transmembrane protein that is expressed exclusively in the extra-embryonic visceral endoderm layer during gastrulation. The extracellular region of the Amn protein contains a cysteine-rich domain with similarity to bone morphogenetic protein (BMP)-binding cysteine-rich domains in chordin, its Drosophila melanogaster homolog (Short gastrulation) and procollagen IIA (ref. 3). Our findings indicate that Amn may direct the production of trunk mesoderm derived from the middle streak by acting in the underlying visceral endoderm to modulate a BMP signaling pathway.