Techn. Universiẗat, Diss., 2005--München.

Universiẗat, Diss., 2007--Giessen.

Thesis (Ph. D.)--University of Chicago, Committee on Immunology, December 1997. / Includes bibliographical references. Also available on the Internet.

Frankfurt (Main), Univ., Diss., 2003.

Thesis (Ph. D.)--University of Hong Kong, 2006. / Also available online.

Thesis (M. Med. Sc.)--University of Hong Kong, 2006.

No description available.

Thesis (Ph. D.)--University of Missouri-Columbia, 2000. / Typescript. Vita. Includes bibliographical references (leaves 148-171). Also available on the Internet.

The Notch receptor is an evolutionarily highly conserved transmembrane protein essential to a wide spectrum of cellular systems. Notch is especially important to T-cell development, and its deregulation leads to leukemia. Although not well characterized, Notch signaling continues to play an integral role in peripheral T-cells, in which a unique mode of Notch activation can occur. In contrast to canonical Notch activation initiated by adjacent ligand-expressing cells, T-cell receptor (TCR)-stimulation is sufficient to induce robust Notch signaling. However, the interactions between these two pathways have not been defined. In this dissertation, we show that Notch activation occurs in peripheral T-cells within a few hours post TCR-stimulation and is required for optimal T-cell activation. Utilizing a panel of inhibitors against components of the TCR signaling cascade, we demonstrate that Notch activation is facilitated through initiation of protein kinase C-induced ADAM-metalloprotease activity. Moreover, internalization of Notch via endocytosis is indispensible for this process. Whereas ligand-mediated Notch stimulation relies on mechanical pulling forces that disrupt the autoinhibitory domain of Notch, we hypothesized that in T-cells in the absence of ligands, these conformational changes are induced through chemical adjustments in the endosome, causing alleviation of autoinhibition and receptor activation. Our data show that endocytosis is not only a prerequisite for TCR-induced Notch processing during normal T-cell function, but is essential even in Notch-mutated T-leukemia cells exhibiting constitutively active Notch signaling. Our work has also focused on signaling mechanisms of Notch following receptor activation. The Notch signal is transduced via cleavage of the intracellular portion of the receptor that subsequently translocates to the nucleus where it regulates gene transcription via interactions with its DNA-binding partner, RBPJκ. Utilizing RBPJκ-deficient T-cells, we show that, although Notch signaling is required, RBPJκ-dependent signaling is dispensable for peripheral T-cell proliferation and activation. Using retroviral constructs that encode modified, active forms of Notch restricted to the nucleus or cytoplasm, we provide evidence that Notch signaling may utilize RBPJκ-independent pathways for signal transduction. In conclusion, T-cells have evolved a unique method of Notch receptor activation, described for the first time in this dissertation, as well as novel mechanisms that facilitate downstream signaling.

Forebrain development is controlled by a set of transcription factors which are expressed in dynamic spatiotemporal patterns in the embryonic forebrain and are known to regulate complex gene networks. Pax6 is a transcription factor that regulates corticogenesis and mutations affecting Pax6 protein levels cause neurodevelopmental defects in the eyes and forebrain in both humans and mice. In previous studies, it was shown that the graded expression pattern of Pax6 protein, which is high rostro-laterally to low caudo-medially in the cerebral cortex, is critical for its control of cell cycle progression and proliferation of cortical progenitors. However the underlying mechanisms are still unclear. Based on a microarray analysis carried out in our laboratory, a number of cell cycle-related candidate genes that may be affected by Pax6 have been identified. One such gene, Cell division cycle associated 7 (Cdca7) is expressed in a counter-gradient against that of Pax6. In my current study, I found that Cdca7 mRNA expression in the telencephalon is upregulated in Pax6 null (Small eye) mutants and downregulated in mice that overexpress PAX6 (PAX77) across developing time points from E12.5 to E15.5. There are several potential Pax6 binding motifs located in the genomic locus upstream of Cdca7. However, by chromatin immunoprecipitation, it is showed that none of the predicted binding sites are physically bound by Pax6. Promoter luciferase assays using fragments combining five suspected binding motifs show that Pax6 is functionally critical. Cdca7 is also identified as a Myc and E2F1 direct target and is upregulated in some tumours but its biological role is not fully understood. Current work using in utero electroporation to overexpress Cdca7 around the lateral telencephalon, where Cdca7 expression levels are normally low, tested the effects on the proliferation and differentiation of cortical progenitor cells in this region. In E12.5 mice embryos, overexpression of Cdca7 protein causes fewer intermediate progenitor cells and post-mitotic neurons to be produced but these effects were not found in E14.5 embryos. This result implies that Cdca7 may affect cell fate decision during cortical development.