[Truncated abstract] It is becoming increasingly obvious that cell signalling pathways are more complicated than we originally perceived. Research is revealing that, not only is there a multitude of new proteins involved in signalling cascades, but also that previously identified proteins may have additional, alternate roles in intracellular trafficking. Gonadotropin-releasing hormone (GnRH) in conjunction with its receptor (GnRHR), the primary regulator of reproduction in all species, is no exception. In the past few years it has become readily accepted that the classic linear GnRHR-Gαq/11 signalling pathway is not universal and that this receptor is involved in a far greater range of cellular activities than was previously considered. In particular, it is widely accepted that continuous administration of GnRH analogs results in an inhibition of growth of a number of reproductive-derived tumours and that this may, in part, be mediated by direct activation of GnRHs expressed on these cells. However, it is not fully understood how the GnRHR mediates these growth effects or whether such effects are unique to reproductive-derived cancer cells. Research within this thesis aimed to determine how the presence or absence of this receptor in different cell types might affect the ability of GnRH to directly mediate growth effects. We demonstrate that continuous treatment with a GnRH agonist (GnRHA) induces an anti-proliferative effect in a gonadotropederived cell line (LβT2) and also in HEK293 cells stably expressing either the rat or human GnRHR. The anti-proliferative effect was time- and dose-dependent and was specifically mediated via the GnRHR, as co-treatment of the GnRHRexpressing cell lines with a GnRH antagonist blocked the growth suppressive effect induced by GnRHA treatment. Cell cycle analysis revealed that the GnRHA treated HEK/GnRHR cell lines induced an accumulation of cells in the G2/M phase while a G0/G1 arrest was observed in LβT2 cells. Previous identification by our group of a potential interaction between the GnRHR and the transcription factor E2F4, an integral cell cycle regulatory protein, prompted further investigation as to the nature of this interaction. Bioluminescence energy transfer (BRET) was utilised to demonstrate that the GnRHR also interacts with E2F5, another member of the E2F family of cell cycle proteins that shares a high level of homology to E2F4. In addition, it was determined that the interaction between human GnRHR and E2F4, detected using BRET, was influenced by cell density.

[Truncated abstract] Olfactory ensheathing glia (OEG) have been demonstrated to improve functional and anatomical outcomes after injury to the nervous system and are currently being trialled clinically. This thesis presents the investigation of two important issues in OEG biology. The first study (Chapter 2) investigates effects of different members of the neuregulin (NRG) family of molecules on the proliferation of OEG, as a means of quickly obtaining large numbers of cells for clinical or experimental use. We report that NRG-1β, but not NRG- 2α or NRG-3, has a significant proliferative effect. Furthermore, we report for the first time that use of different mitogens (forskolin and pituitary extract) commonly used to expand these cells in vitro, can have a significant effect on the responsiveness of OEG to added NRG in subsequent mitogenic assays. OEG grown initially with forskolin and pituitary extract exhibited increased basal proliferation rates in comparison to OEG originally expanded without these factors, and this increased rate of proliferation was sustained for at least 6 days following their withdrawal from the culture medium. We also report for the first time the expression pattern of ErbB2, ErbB3 and ErbB4 receptors on p75-selected OEG, and investigate their contribution to the NRG mitogenic effect by the use of inhibitory ErbB antibodies. Our second study (Chapter 3) seeks to clarify the role of OEG in promoting myelination of central nervous system neurons. In this study we have investigated the myelinating ability of OEG derived from embryonic (EEG), postnatal (PEG) and adult tissue (AEG) both in vitro and in vivo. OEG selected by p75-immunopanning were co-cultured with dissociated cultures of TrkA-dependant embryonic dorsal root ganglion (DRG) neurons. EEG, but not AEG or PEG, successfully myelinated DRG neurons in the presence of serum and/or ascorbate. AEG also failed to myelinate GDNF-dependant embryonic DRG cultures, and growth factor-independent adult DRG cultures. Transplantation of OEG into lysolecithin demyelinated spinal cord demonstrated distinct ultrastructural differences between transplants of OEG derived from animals of different ages. Furthermore, we demonstrate that clearance of degraded myelin from the lesion site appears to be more effective when animals are transplanted with EEG rather than AEG or Schwann cell preparations. These results suggest that myelinating potential of OEG in vitro and behaviour of these cells following transplantation in vivo are developmentally regulated.

Diss. (sammanfattning) Stockholm : Karolinska institutet, 2007. / Härtill 4 uppsatser.

Diss. (sammanfattning) Stockholm : Karol. inst., 2005. / Härtill 4 uppsatser.

Diss. (sammanfattning) Stockholm : Karolinska institutet, 2005. / Härtill 4 uppsatser.

Diss. (sammanfattning) Göteborg : Göteborg University, 2007. / Härtill 4 uppsatser.

Thesis (Ph. D.)--University of Sydney, 2008. / Submitted in fulfilment of the requirements for the degree of Doctor of Philosophy to the Department of Clinical Ophthalmology and Eye Health, Faculty of Medicine. Title from title screen (viewed Apr. 8, 2009) Includes bibliography. Also available in print form.

Thesis (Ph. D.)--University of Hong Kong, 2008. / Includes bibliographical references (leaves 169-208) Also available in print.

Thesis (Ph.D.)--University of Alabama at Birmingham, 2009. / Title from first page of PDF file (viewed on June 11, 2009). Includes bibliographical references.

Thesis (Ph.D.)--University of Alabama at Birmingham, 2008. / Title from first page of PDF file (viewed on June 24, 2009). Includes bibliographical references.