Dissecting the molecular mechanisms regulating proliferation, antigen responsiveness, and differentiation of CD4⁺ T lymphocytes : a central role for the mammalian target of Rapamycin (mTor)

The intracellular events that regulate lymphocyte proliferation upon antigen encounter and the ability of the cells to respond to subsequent stimulation and to differentiate into effector cells remain largely to be understood. Several studies have linked T cell proliferation with the maintenance of antigen responsiveness and with the ability of the cells to differentiate and to acquire proper effector functions. The aim of my Ph.D. research project was to investigate the role of the TCR, CD28, and IL-2 generated intracellular events dictating CD4+ T lymphocyte proliferation and differentiation. In a model of CD3-induced clonal anergy, we have shown that antigen responsiveness was uniquely regulated by an IL-2/IL-2R-induced signalling event, which was delivered independently of IL-2-driven cell proliferation, and which was Rapamycin-sensitive. This indicates that proliferation and antigen responsiveness are independently regulated and that the latter specifically requires intact signalling through mTor, the mammalian target of Rapamycin. Moreover, we have shown that proper activation of p70S6k, one the known target of mTor, might play a crucial role in the maintenance of T lymphocyte responsiveness. We have also investigated the role of mTor in a model of in vitro antigen driven naive T cell differentiation. In this model, blocking mTor activity by the addition of Rapamycin during T cell activation, allowed comparable T cell expansion, but completely prevented polarization of effector cells. Together our results indicate that the intracellular events that dictate T cell proliferation are distinct from the intracellular signals that modulate the functional phenotype of activated T lymphocytes and suggest that, while mTor-dependent signalling is dispensable for T cell proliferation, it is primarily involved in the acquisition of proper T cell effector functions

Extracellular HMGB1, a signal of tissue damage, induces mesoangioblast migration and proliferation

High mobility group box 1 (HMGB1) is an abundant chromatin protein that acts as a cytokine when released in the extracellular milieu by necrotic and inflammatory cells. Here, we show that extracellular HMGB1 and its receptor for advanced glycation end products (RAGE) induce both migration and proliferation of vessel-associated stem cells (mesoangioblasts), and thus may play a role in muscle tissue regeneration. In vitro, HMGB1 induces migration and proliferation of both adult and embryonic mesoangioblasts, and disrupts the barrier function of endothelial monolayers. In living mice, mesoangioblasts injected into the femoral artery migrate close to HMGB1-loaded heparin-Sepharose beads implanted in healthy muscle, but are unresponsive to control beads. Interestingly, α-sarcoglycan null dystrophic muscle contains elevated levels of HMGB1; however, mesoangioblasts migrate into dystrophic muscle even if their RAGE receptor is disabled. This implies that the HMGB1–RAGE interaction is sufficient, but not necessary, for mesoangioblast homing; a different pathway might coexist. Although the role of endogenous HMGB1 in the reconstruction of dystrophic muscle remains to be clarified, injected HMGB1 may be used to promote tissue regeneration

Xotx5b, a new member of the Otx gene family, may be involved in anterior and eye development in Xenopus laevis

We describe the cloning, expression pattern and functional overexpression analysis of Xotx5b, a new member of the Otx gene family in Xenopus laevis. Early expression of Xotx5b resembles that of Xotx2, being detected in the organizer region at early gastrula stage, and, shortly after, also in anterior neuroectoderm. During neurula stages Xotx5b exhibits a changing and dynamic pattern of expression. After neural tube closure, Xotx5b is expressed in the eye and pineal gland, both involved in photoreception. Overexpression of Xotx5b has a similar effect to that of Xotx2, producing posterior truncations and inducing ectopic cement gland and neural tissue in whole embryos. In animal cap assays, Xotx5b and Xotx2 are both able to activate XAG, to strongly suppress the expression of the epidermal marker XK81, and to reciprocally activate each other. Finally, in einsteck transplantation assays, Xotx5b is able to respecify a tail/trunk organizer to a head organizer