Constitutive activation of NF-kappaB and T-cell leukemia/lymphoma in Notch3 transgenic mice.

The multiplicity of Notch receptors raises the question of the contribution of specific isoforms to T-cell development. Notch3 is expressed in CD4(-)8(-) thymocytes and is down-regulated across the CD4(-)8(-) to CD4(+)8(+) transition, controlled by pre-T-cell receptor signaling. To determine the effects of Notch3 on thymocyte development, transgenic mice were generated, expressing lck promoter-driven intracellular Notch3. Thymuses of young transgenics showed an increased number of thymocytes, particularly late CD4(-)8(-) cells, a failure to down-regulate CD25 in post-CD4(-)8(-) subsets and sustained activity of NF-kappaB. Subsequently, aggressive multicentric T-cell lymphomas developed with high penetrance. Tumors sustained characteristics of immature thymocytes, including expression of CD25, pTalpha and activated NF-kappaB via IKKalpha-dependent degradation of IkappaBalpha and enhancement of NF-kappaB-dependent anti-apoptotic and proliferative pathways. Together, these data identify activated Notch3 as a link between signals leading to NF-kappaB activation and T-cell tumorigenesis. The phenotypes of pre-malignant thymocytes and of lymphomas indicate a novel and particular role for Notch3 in co-ordinating growth and differentiation of thymocytes, across the pre-T/T cell transition, consistent with the normal expression pattern of Notch3.

Signals involved in gamma/delta T cell versus alpha/beta T cell lineage commitment.

In seeking an explanation for the complexity of tissue development, biologists are obliged to explain lineage commitment, the events that dictate whether or not a progenitor cell will differentiate into one cell type or another. Such explanations have been sought across a broad spectrum of biological systems, although in no case has a full under- standing been developed. For immunologists, attention has been focused on the lineage commitment of a T cell progenitor to becoming either a gammadelta T cell or an alphabeta T cell. In this review, we compare the signals that thymocytes may receive from the pre T cell receptor (preTCR) with signalling from TCRgammadelta. These signals may determine, co-determine, facilitate, or cement the alphabeta/gammadelta lineage decision, in concert with signals from additional molecules, such as Notch and cytokine receptors. Elucidating the pleiotropic signalling events, particularly those elicited by the preTCR, may in the near future contribute to a molecular definition of lineage commitment.

Absence of a significant mixed lymphocyte reaction in a marsupial (Monodelphis domestica).

Previously we reported preliminary results suggesting that the marsupial Monodelphis domestica fails to exhibit a mixed lymphocyte reaction with allogeneic lymphocytes. To test whether this observation is simply a matter of a response too weak to detect, but capable of being augmented by immunization, we performed mixed lymphocyte culture tests on 23 of these animals that had been immunized with lymphocytes. Despite the fact that all recipients were sensitized to the lymphocytes of the donors, none of the animals had a substantial mixed lymphocyte response. Significant stimulation was noted with the mitogen concanavalin A; thus, the T cells were immunologically competent. It seems likely that the failure of this species to exhibit a significant mixed lymphocyte response is due to T cells whose ontogeny differs from that of the T cells of eutherian mammals.

Intrathymic delta selection events in gammadelta cell development.

The major pathway of gammadelta cell development is shown to be regulated by in-frame rearrangements at the T cell receptor (TCR) delta locus. Such "delta selection" occurs at or around the same point in thymocyte development as selection for in-frame rearrangements at the TCRbeta locus. However, there are at least two major differences with beta selection: first, delta selection commonly involves selection on the cognate TCR chain, gamma, suggesting that there is no "preTgamma" chain of major biological significance; second, most gammadelta-selected thymocytes differentiate rather than proliferate. Nonetheless, some delta selection events seemingly facilitate thymocyte expansion, similar to alphabeta T cell development. In these cases, TCRgamma selection is less obvious. Furthermore, the capacity of individual gamma chains to facilitate gammadelta selection is shown to vary with developmental age. The results further clarify early T cell development at the beta selection/delta selection stage and place clear constraints on models of cell fate determination.

Fate of allogeneic skin transplantations in a marsupial (Monodelphis domestica).

Previously we reported that the South American gray short-tailed opossum, Monodelphis domestica, had an MHC class-I locus similar to that of eutherian species. In addition to the detection of lymphocyte antigens by cytotoxic antisera, we concluded that this marsupial rejected allogeneic skin grafts, as would be expected of animals with MHC class-I polymorphism. However, this conclusion was based on a limited number of skin transplants that were assayed for only a short period. Here we report the results of 22 reciprocal skin grafts made between individuals of known genetic relationships. On the basis of gross inspection of the grafts and histologic examination, we found that the average time of the onset of graft rejection was about 19 days and that the average time for complete graft rejection was about 31 days. In general, it took longer for the onset of graft rejection among pairs of genetically related animals than among less related animals. These results indicate unequivocally that this marsupial species has a high degree of class-I polymorphism and rejects allogeneic skin transplants in a manner similar to but more slowly than eutherian mammals.

Enhanced growth of mice lacking the cyclin-dependent kinase inhibitor function of p27(Kip1).

SUMMARY: Disruption of the cyclin-dependent kinase-inhibitory domain of p27 enhances growth of mice. Growth is attributed to an increase in cell number, due to increased cell proliferation, most obviously in tissues that ordinarily express p27 at the highest levels. Disruption of p27 function leads to nodular hyperplasia in the intermediate lobe of the pituitary. However, increased growth occurs without an increase in the amounts of either growth hormone or IGF-I. In addition, female mice were infertile. Luteal cell differentiation is impaired, and a disordered estrus cycle is detected. These results reflect a disturbance of the hypothalamic-pituitary-ovarian axis. The phenotypes of these mice suggest that loss of p27 causes an alteration in cell proliferation that can lead to specific endocrine dysfunction.

Productive T-cell receptor beta-chain gene rearrangement: coincident regulation of cell cycle and clonality during development in vivo.

Productive gene rearrangement at the T-cell receptor (TCR) beta-chain locus facilitates formation of the "pre-TCR," a molecular complex that is important for the subsequent development of alpha beta T cells. The transition of thymocytes from a population of cells undergoing TCRbeta chain genes to a population enriched in cells with productively rearranged TCRbeta chain genes is known as "beta selection." This is the first point in alpha beta T-cell development at which the products of an activated TCR locus define cell phenotype. Toward an understanding of these events, this study has focused on a set of thymocytes defined by cell surface phenotype as HSA+ CD44low CD25+, in which the bulk of TCRbeta gene rearrangement occurs. The analysis of this set, presented here, allows its novel subdivision into two subsets that are respectively strong candidates for cells immediately prior to and immediately following TCRbeta selection. Cells that have passed beta selection differ from the preceding cells by several criteria, including hyperphosphorylation of Rb, increased expression of cyclins A and B, down-regulation of p27, increased CDK2 activity, an induction of cdc2 activity, and progression through DNA synthesis. Consistent with these changes being attributable to productive TCRbeta chain gene rearrangement, the identified "beta-selected" subset is not detected in mutant mice that cannot assemble a pre-TCR. Interestingly, there is a coincident selective and transient down-regulation of the protein RAG2, on which TCR gene rearrangement obligatorily depends. Together, these findings demonstrate that productive TCR gene rearrangement is associated with events that can ensure thymocyte expansion and monoclonality.

Perioperative nursing. Designing, implementing a baccalaureate elective.

The clinical faculty of the affiliated teaching hospitals felt the initial course offering was beneficial to students and institutions alike. The course served as a foundation for the students' entry into perioperative nursing practice, and served to shorten the amount of time institutions invest in orientation. In conclusion, we recognize the importance of offering a perioperative nursing educational opportunity at the baccalaureate level. With increased student interest, we are looking forward to continuing the course and implementing the refinements as recommended.