Bochum, Univ., Diss., 2004.

Bochum, Universiẗat, Diss., 2004.

Doctorat en Sciences médicales / info:eu-repo/semantics/nonPublished

Cytokinesis is the physical partition of one cell into two. In Chapter 1, I provide a brief introduction to cytokinesis and some of the proteins whose functions I parse out throughout my studies. In Chapter 2, I present work I’ve contributed to elucidate the role of polarity proteins in cytokinesis, as well as a look at the differential requirement for canonically essential cytokinetic proteins in the 4-cell embryo. In Chapter 3, I address a long-standing controversy in the field regarding the relationship between the Rac GAP protein Cyk-4 and the small GTPase Rac, and in particular the inhibitory role of Rac during cell division. My major body of work highlights the necessity not to close the books on the GAP activity of Cyk-4 and its inhibition of Rac. I show that Rac is unable to rescue cytokinesis failure in downstream Rho effectors whose loss weakens the contractile ring, suggesting it is not a promiscuous suppressor of cytokinesis. Additionally, I found that levels of non-muscle myosin-II and the actin binding domain of Utrophin were unchanged with loss of Cyk-4. From this, I infer that Cyk-4 is unlikely to be an activator of the RhoGEF Ect-2. These results emphasize the need to probe further into the cross-talk between these GTPases. In chapter 4, I show inconclusive data addressing the role of cell fate signaling in protection against cytokinesis failure. Overall, this thesis represents my contributions to the field, revealing the complexity involved in assuring successful completion of cytokinesis.

Eine intakte Darmbarriere ist überlebensnotwendig. Bei einigen Erkrankungen kann eine Störung der Darmbarriere zur Translokation von Bakterien aus dem Lumen des Darmes in den menschlichen Körper führen, die septische Entzündungsprozesse auslösen können. In dieser Arbeit untersuchten wir zum einen die Bedeutung der desmosomalen Adhäsion für die Darmbarriere und zum anderen die Rolle der Rho-GTPasen in der Regulation der Darmbarriere. Für unsere Untersuchungen charakterisierten wir Caco2 Zellen, von denen wir nachweisen konnten, dass sie ein geeignetes Modell für die Darmbarriere sind. Wir konnten zeigen, dass Caco2 Zellen 14 Tage nach ihrer Konfluenz einen vollständigen Schlussleistenkomplex ausbilden und funktionell ähnlich Permeabilitäseigenschaften, wie die Mukosa von Ratten ex vivo aufweisen. Um die Bedeutung der desmosomalen Adhäsion zu klären, applizierten wir einen gegen die Extrazellulärdomäne von Dsg2 gerichteten Antikörper. Dieser Antikörper war spezifisch in der Lage Dsg2 vermittelte Adhäsion zu blockieren. Nach Applikation des Dsg2 ED konnten wir eine Fragmentierung der Occludensproteine, sowie eine gestörte Barrierefunktion mit erhöhter Permeabilität und erniedrigtem transepithelialen Widerstand nachweisen. Damit konnten wir zeigen, dass die Dsg2 vermittelte Adhäsion essentiell für die Aufrechterhaltung der Darmbarriere ist. Des Weiteren untersuchten wir die Rolle der Rho-GTPasen. Wir veränderten die Aktivität der Rho-GTPasen durch Applikation von bakteriellen Toxinen, wie CNF-1, CNF-y, Toxin B, C3-TF und LT sowie Mediatoren, wie Y27632 und quantifizierten die Änderung anschließend durch die Aktivitätsmessung der Rho-GTPasen mittels GLISA. In Immunfluoreszenzen konnten wir zeigen, dass sowohl eine Steigerung als auch eine Erniedrigung der Aktivität von RhoA mit einer Fragmentierung der Occludensproteine einhergeht, während die Adherens Junktionen unbeeinflusst bleiben. Diese morphologische Veränderung korreliert mit einer signifikant erhöhten Permeabilität und einem erniedrigtem transepithelialem elektrischen Widerstand. Im Gegensatz dazu, konnten wir zeigen, dass eine Erhöhung der Aktivität von Rac1 und Cdc42 in der Immunfluoreszenz zu keinen sichtbaren Veränderungen führt, die funktionellen Ergebnisse, mit einem erhöhten transepithelialen elektischen Widerstand und einer erniedrigten Permeabilität auf eine Stabilisierung der Barriere hinweisen. Eine Erniedrigung der Aktivität von Rac1 und Cdc42 führt hingegen zu einer Destabilisierung der Barriere. Morphologisch führte die Verringerung der Aktivität von Rac1 durch LT zu einer Reduzierung der Occludensproteine an den Zellgrenzen und zu einer diffuseren Färbung des Adherens Junktionsprotein E- Cadherin. Zum anderen zeigte sich in diesem Fall eine deutliche Reduzierung der Barrierefunktion mit einem erniedrigten transepithelialen elektrischen Widerstand und einer erhöhten Permeabilität. Letzlich konnte diese Arbeit durch ihre Erkenntnisse einen Teil dazu beizutragen, dass die komplexe Regulation der Darmbarriere besser verstanden wird. Dieses bessere Verständnis soll künftig zur Entwicklung neuer Therapieoptionen für Patienten dienen, die unter den septischen Folgen einer Störung der Darmbarriere leiden. / The integrity of intestinal barrier function is essential. In some diseases intestinal barrier breakdown can lead to contamination by bacteria in the human body. In our research we investigated on the one hand the relevance of desmosomal adhesion and the role of Rho GTPases in regulation of intestinal barrier function. For our research we characterized Caco2 cells. We could reveal, that 14 days after confluence Caco2 cells form the "terminal bar" and show a barrier function similar to rat muccosa. To address the relevance ofdesmosomal adhesion we applied an antibody directed against the extracellular domain (Dsg2 ED) in order to test whether impaired Dsg2-mediated adhesion affects intestinal epithelial barrier functions in vitro. This antibody was capable to specifically block Dsg2 interaction. The application of Dsg2 ED led to a fragmentation in tight junction proteins and an impaired barrier function as revealed by an increase of permeability and a decrease of transepithelial electrical resistance. We could show that Dsg2 mediated adhesion is essential for intestinal barrier function. Second we investigated the role of the Rho-GTPases. We modulated the activity of Rho-GTPases by the application of bacterial toxins like CNF-1, CNF-y, toxin B, C3-TF and LT and mediators like Y27632. We could show that an increase as well as a decrease of RhoA activity led to a fragmentation of tight junction proteins as revealed by immunostaining. These morphologic changes correlated with a significant increase of permeability as well as a decreased transepithelial electrical resistance. Apart from that an increased activation of Rac1 and Cdc42 led to a stabilization of intestinal barrier function with an increase of transepithelial electrical resistance and a decrease in permeability. A destabilization of intestinal barrier function was shown after a reduction of Rac1 and Cdc42 activity. Under these conditions we could observe a fragmentation of tight junction and adherens junction proteins. Furthermore decreased Rac1 and Cdc42 activity led to an increased permeability and a decreased transepithelial electrical resistance. In the final analysis this publication led to new insights in the complex regulation of intestinal barrier functions and therefore can possible lead to new targets in the therapy of impaired intestinal barrier function.

Modulation of the actin-based cytoskeleton and transcription factor regulation are merely two essential functions in a wide array of cellular activities that the Rho family of small GTPases is responsible for mediating. Aberrations in, or loss of, Rho GTPase signaling has been found to lead to multiple pathologies, including both metastatic progression and lenticular differentiation leading to cataractogenesis. This study has examined the transcriptional regulation of the metastasis suppressor, KiSS-1. Although the mechanism by which KiSS-1 modulates an anti-metastatic effect is not entirely known, it is known that KiSS-1 mediates stress fiber formation, increased adhesion and reduced migratory and invasive properties through modulation of the Rho family of small GTPases. The loss of KiSS-1 that commonly occurs during metastatic progression, leads to a loss of proper Rho GTPase regulation. This study has examined how KiSS-1 is regulated in two tissue types, breast and skin, and how the loss of AP-2(alpha) and DRIP-130, respectively, leads to the progression of breast cancer and melanoma. In addition, this study has also looked at the importance of Rac1 expression and function in the lens epithelium. Activation of Rac1 and its downstream effector, SRF, have been shown to be key regulators in lens cell differentiation, possibly leading to lens opacification via its transcriptional control of the structural crystallins within the lens. The results of this dissertation research have made significant strides in understanding the nature of the anti-metastatic effects registered by the novel KiSS-1 peptide and its cognate GPCR. Additionally, it has shed light on the Rho family regulation of lens epithelial cell differentiation, indicating the elaborate involvement of Rac1 in mediating lens fiber development. In all, this research has determined previously unknown roles of small molecule GTPases in both the progression of metastasis, as well as in normal and abnormal lens cell differentiation.

The TWIST Collaboration has measured the Michel parameter rho in normal muon decay,u+ -> e+VeVu. In the standard model of particle physics,rho = 3/4. Deviations from this value require mixing of left- and right-handed muon and electron couplings in the muon-decay Lagrangian. We find rho = 0:75080+-0:00032(stat.)+-0:00097(syst.) +- 0:00023, where the last uncertainty represents the dependence of rho on the Michel parameter n. This result sets new limits on the WL - WR mixing angle in left-right symmetric models.

Modulation of the actin-based cytoskeleton and transcription factor regulation are merely two essential functions in a wide array of cellular activities that the Rho family of small GTPases is responsible for mediating. Aberrations in, or loss of, Rho GTPase signaling has been found to lead to multiple pathologies, including both metastatic progression and lenticular differentiation leading to cataractogenesis. This study has examined the transcriptional regulation of the metastasis suppressor, KiSS-1. Although the mechanism by which KiSS-1 modulates an anti-metastatic effect is not entirely known, it is known that KiSS-1 mediates stress fiber formation, increased adhesion and reduced migratory and invasive properties through modulation of the Rho family of small GTPases. The loss of KiSS-1 that commonly occurs during metastatic progression, leads to a loss of proper Rho GTPase regulation. This study has examined how KiSS-1 is regulated in two tissue types, breast and skin, and how the loss of AP-2(alpha) and DRIP-130, respectively, leads to the progression of breast cancer and melanoma. In addition, this study has also looked at the importance of Rac1 expression and function in the lens epithelium. Activation of Rac1 and its downstream effector, SRF, have been shown to be key regulators in lens cell differentiation, possibly leading to lens opacification via its transcriptional control of the structural crystallins within the lens. The results of this dissertation research have made significant strides in understanding the nature of the anti-metastatic effects registered by the novel KiSS-1 peptide and its cognate GPCR. Additionally, it has shed light on the Rho family regulation of lens epithelial cell differentiation, indicating the elaborate involvement of Rac1 in mediating lens fiber development. In all, this research has determined previously unknown roles of small molecule GTPases in both the progression of metastasis, as well as in normal and abnormal lens cell differentiation.

Thesis (Ph. D.)--University of Texas at Austin, 2003. / Vita. Includes bibliographical references. Available also from UMI Company.

Neuropathy is a major complication that affects nearly half of all patients with diabetes, greatly decreasing their quality of life. Patients experience a wide range of symptoms including pain, numbness, weakness and other morbidities. While its pathogenesis has been the focus of extensive research, there are still few effective treatment options available for this disease. The discovery of novel molecular targets underlying this diabetic neuropathy may lead to the development of new, more effective therapeutics. DLC2, a Rho GTPase-activating protein with specific activity for RhoA, was shown to be involved in pain signaling. Mice deficient for this protein (DLC2-/-) have increased RhoA activity in their peripheral nerves, and have heightened pain responses compared to wild type (DLC2+/+) in acute pain tests, displaying increased sensitivity to noxious thermal and inflammatory stimuli. DLC2-/- mice also show elevated blood glucose levels, lower body weight and increased sensitivity to blood glucose compared to wild type. Because of the hyperalgesia to acute pain displayed by DLC2-/- mice compared to wild type, and since the RhoA pathway is known to be involved in the pathogeneses and maintenance of diabetes and its complications, these mice were used to investigate more clinically relevant, chronic pain in a model of diabetic neuropathy. Streptozotocin (STZ), given in multiple low doses over five days (MLDS treatment), was used to induce diabetes in DLC2+/+ and DLC2-/- mice, and their pain responses were tested 8 weeks later. Diabetic DLC2-/- mice (DLC2-/--STZ) were hyperalgesic to thermal stimuli from the hot plate test compared to diabetic DLC2 wild type mice (DLC2+/+-STZ) and vehicle-treated controls of both genotypes (DLC2-/--Veh and DLC2+/+-Veh. Similar responses were seen from the von Frey filament test, where the DLC2-/--STZ group exhibited mechanical allodynia compared to the DLC2+/+-STZ group and both control groups. Dorsal root ganglia (DRG) were dissected from these four groups of mice for qPCR screening and protein analysis. DLC2-/--STZ mice showed significantly higher gene expression of the voltage-gated sodium channel Nav 1.9 compared to DLC2+/+-STZ mice, while there was a strong trend of increased levels in the DLC2-/--STZ group compared to both non-diabetic groups. Western blot analysis of the DRG from these mice shows increased levels of COX-2 expression of DLC2-/--STZ mice compared to DLC2+/+-Veh, and elevated levels of phosphorylated ERK (pERK) in DLC2-/--Veh and both diabetic groups compared to DLC2+/+-Veh. Overall, diabetic DLC2-/- mice have more severe painful diabetic neuropathy, with thermal hyperalgesia and mechanical allodynia. Increased RhoA activity and pERK, which are known to be involved in regulation, transcription and trafficking of sodium channels, may lead to increased Nav1.9 mRNA levels and activation. Localized mainly to nociceptors of the DRG, Nav1.9 is known to play a role in sensitizing neurons through lowering the threshold for action potentials, possibly leading to the observed heightened pain response. Additionally, elevated COX-2 levels in DLC2-/--STZ mice may lead to further deficits through activation of inflammatory responses. Future studies will further investigate how these mechanisms are involved in the altered pain response from diabetes. / published_or_final_version / Anatomy / Master / Master of Philosophy