Orientador: Sara Teresinha Olalla Saad / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Ciências Médicas / Made available in DSpace on 2018-08-26T18:19:15Z (GMT). No. of bitstreams: 1 XavierFerrucio_JulianaMartins_D.pdf: 4222784 bytes, checksum: e2845997ddb128f2d29a2cabc667da17 (MD5) Previous issue date: 2015 / Resumo: A hematopoiese, processo pelo qual a célula-tronco hematopoiética (CTH) dá origem a todas as células do sangue, é regulada através do seu contato com diversos tipos celulares que compõem o estroma da medula óssea, mantendo o balanço entre autorrenovação e diferenciação das CTHs, processos também regulados por vias de sinalização como a via Hedgehog e proteínas reguladoras de citoesqueleto como RhoGTPases. Sendo assim, os objetivos gerais do trabalho foram investigar a via Hedgehog na medula óssea de pacientes com síndromes mielodisplásica (SMD) e a função da ARHGAP21 na autorrenovação das CTH. Através de imunohistoquímica de bióspias de medula óssea de pacientes com SMD em comparação com anemia megaloblástica (usada como controle) observamos o aumento de células marcadas para os ligantes Sonic e Dessert Hedgehog e células positivas para c-Kit nas amostras de SMD. Em seguida, analisamos a expressão gênica dos membros da via Hedgehog em células totais de medula óssea de pacientes SMD e doadores normais. Não houve diferença na expressão de Patched (PTCH) em SMD em comparação com doadores saudáveis, porém quando as amostras são classificadas de acordo com a WHO 2008, observamos aumento significativo de PTCH nos pacientes com <5% de blastos na medula óssea (AR, ARSA e CRDM). As expressões tanto de GLI1 como de SUFU foram reduzidas nos pacientes SMD e no grupo de pacientes com ARSA, CRDM e CRDU quando comparados aos doadores normais. A expressão de SUFU também foi reduzida em grupo de pacientes SMD com > 5% de blastos na medula óssea (AREB-1 e 2). Observamos aumento de 7 vezes na expressão de SMO no grupo de SMD e de 14 vezes no grupo AREB-1 e 2 em comparação com doadores normais. Análises de sobrevida de Cox demonstraram que o aumento na expressão de SMO e a redução na expressão de PTCH são fatores independentes na sobrevida global dos pacientes com SMD. Além disso, confirmamos o aumento da ativação da via Hedgehog em células CD34+ de pacientes com SMD através do aumento da expressão dos alvos da via: GLI1, BMI1 e Nanog. Nossos dados indicam que a via Hedgehog está desregulada na medula óssea dos pacientes com SMD e o possível envolvimento dessa via na progressão da doença. Através do modelo murino Arhgap21+/- estudamos a importância dessa proteína na hematopoiese normal e observamos que esses animais apresentam redução nas diferenciações eritroide e megacariocítica juntamente com aumento da mobilização mielóide. Observamos ainda o aumento na frequência das CTHs de curta e longa duração na medula óssea dos heterozigotos. Esse aumento foi responsável pela maior recuperação no número de neutrófilos após indução de estresse hematopoiético nos animais Arhgap21+/-. Durante o transplante seriado de células de medula óssea observamos menor reconstituição após 4 semanas, juntamente com menor reconstituição a longo prazo nos animais que receberam células dos heterozigotos, sugerindo menor autorrenovação das CTHs nas células com redução da Arhgap21. O nicho medular dos animais Arhgap21+/- demonstrou redução no suporte inicial da hematopoiese o que foi relacionado à maior produção de ROS após irradição subletal dos heterozigotos. Juntos, esses resultados indicam que a ARHGAP21 tem importante papel na hematopoiese normal, pois participa de processos como a diferenciação, mobilização e autorrenovação das CTHs / Abstract: Hematopoiesis is a process by which hematopoietic stem cell (HSC) gives rise to all blood cells and it is regulated by HSC contact with different cell types that compose the bone marrow stroma and maintain the balance between HSC self-renewal and differentiation, processes that are also regulated by signaling pathways such as the Hedgehog and regulatory proteins of the cytoskeleton as RhoGTPases. The overall aims of this work were to investigate the Hedgehog pathway in myelodysplastic syndrome (MDS) bone marrow and the ARHGAP21 role in hematopoiesis. Immunohistochemistry assays revealed that MDS bone marrow biopsies showed increased Sonic and Dessert Hedgehog together with c-kit positive stained cells compared to megaloblastic anemia (used as control).We also analyzed gene expression of the Hedgehog pathway members in total cells from MDS bone marrow and healthy donors. There was no difference in Patched (PTCH) expression in MDS compared to healthy donors, however, when MDS samples were classified according to WHO 2008, we observed a significant increase in PTCH1 expression in MDS patients <5% bone marrow blast (RCUD, RCMD, ARSA). GLI1 and SUFU expressions were significantly reduced in the MDS patients and in the group of patients with RCUD, RCMD, ARSA, when compared to healthy donors. SUFU expression was also decreased in MDS patients > 5% bone marrow blast (RAEB-1 and RAEB-2) compared to controls. We also observed 7-fold increase of SMO transcripts in the MDS group and 14-fold increase in RAEB-1 and RAEB-2. Cox survival analyses showed that increased SMO and decreased PTCH expression were considered as independent factors influencing the survival of these patients. We also confirmed the enhanced Hedgehog activation in CD34+ cells from MDS patients through increased expression of the pathway targets: GLI1, BMI1 and Nanog. Together, our data indicate that the Hedgehog pathway is deregulated in MDS bone marrow and the possible role of that pathway in disease progression. Arhgap21+/- murine model study showed the importance of this protein in normal hematopoiesis as these animals showed alterations in erythroid and megakariocyte differentiation along with increased myeloid mobilization. We also observed increased short and long term HSC frequency in the heterozygous bone marrow. This increase was responsible for enhanced neutrophil reconstitution during induced hematopoietic stress in Arhgap21+/-. Serial bone marrow transplantation assay showed lower chimerism in peripheral blood 4 weeks after the transplant together with lower long term reconstitution in animals who received Arhgap21+/- bone marrow, indicating decreased HSC self-renew from heterozygous cells. Bone marrow niche of Arhgap21+/- animals showed a reduction in initial support hematopoiesis and this result was correlated with the increased ROS production from Arhgap21+/- bone marrow after sublethally irradiation. Taken together, our data indicate that ARHGAP21 has an important role in hematopoiesis regulating process such as differentiation, mobilization and self-renewal of HSC / Doutorado / Biologia Estrutural, Celular, Molecular e do Desenvolvimento / Doutora em Fisiopatologia Médica

Axon pathfinding is an important process required for the establishment of proper neuronal connections during development. An increasing number of secreted and membrane-anchored molecules have been identified as axon guidance cues, which can act as positive or negative factors to increase or decrease the growth of axons and influence the direction of axonal growth. These axon guidance factors present in the extracellular environment interact with receptors present on the growth cone, a structure located at the tip of the axon which functions as the motor unit for the axon. Upon binding to their receptors on the growth cone, the guidance factors then elicit an intracellular signaling cascade within the axon that ultimately influences the direction of axon growth, often through a direct, non-transcriptional mechanism. In this dissertation, we show that Sonic hedgehog (Shh) acts as an axon guidance factor for chick retinal ganglion cell (RGC) axons in a concentration-dependent manner. At a low concentration, Shh functions as a positive factor that induces axon growth and attractive turning while, at a high concentration, Shh functions as a negative factor that induces axon retraction and repulsive axon turning. We further characterized the effects of Shh on macropinocytosis, a fluid-phase type of endocytosis, in the axons. A high concentration of Shh significantly increased macropinocytosis in the axons. Macropinocytosis resulted in the generation of large, dextran-positive, clathrinindependent vesicles in the axonal growth cones, prior to growth cone collapse, axon retraction and repulsive axon turning. These vesicles were found to require dynamic F-actin, nonmuscle myosin II and dynamin for their formation but were formed independently of PI3 kinase signaling. Interestingly, a low concentration of Shh had an opposite effect on macropinocytosis. A low concentration of Shh and soluble laminin decreased macropinocytosis and additionally increased the turnover of these vesicles within the axons, suggesting positive axon guidance factors can additionally regulate downstream processing or maturation of these vesicles. The effect of Shh on regulating the motility of macropinosomes within the axons was investigated. A low concentration of Shh appeared to increase the motility of these vesicles along axonal microtubules in a cAMPdependent manner. However, a high concentration of Shh did not appear to affect the motility of the macropinosomes, suggesting that it likely plays a more predominant role in the formation of these vesicles within the growth cone. When we began this work, a large body of research existed describing the effects of guidance factors on regulating the cytoskeleton during axon motility. However, the role of membrane trafficking events during axon growth and guidance were very poorly characterized. Since we began this project, an increasing number of reports have shown that endo- and exocytosis are important for axon growth and, here, we show that macropinocytosis induced by negative axon guidance factors plays a critical role in growth cone collapse, axon retraction and repulsive axon turning. Positive axon guidance factors also affect macropinocytosis within the axons and additionally regulate their maturation, suggesting that membrane trafficking events mediated by axon guidance factors are important for regulating axon growth and pathfinding.

The normal regulation of the Hedgehog (Hh) pathway is essential for embryonic development, stem cell maintenance, and gametogenesis for both vertebrates and invertebrates, whereas the aberrant pathway regulation can cause various developmental defects and cancers. Hence, it is important to understand the precise mechanism of how the Hh pathway is regulated. Much of our understanding of the Hh pathway comes from studies in Drosophila but applies also to vertebrates. In Drosophila, Hh signal transduction terminates with regulation of the transcriptional activator, Cubitus interruptus (Ci). In the absence of Hh signaling, Ci is 1) processed to a repressor form via the Costal2 (Cos2) complex and suppresses the transcription of Hh target genes or 2) inhibited by binding to Cos2 and Suppressor of Fused (Su(fu)). Once the cells receive Hh ligand, however, 1) Ci processing is inhibited and 2) inhibition by Su(fu), and possibly Cos2, is countered by Fused (Fu) kinase, which ultimately transforms Ci into an activator form that goes into the nucleus and induces the transcription of Hh target genes. How Fu alleviates Su(fu) inhibition and facilitates the activation of Ci is not well understood, and it was only discovered recently that Ci is the direct target of Fu phosphorylation. Many studies of Hh signaling have been conducted under artificial conditions, where proteins are often overexpressed, leading to findings that sometimes do not reflect in vivo events, where relative protein stoichiometry is important. For this dissertation, I investigated how Ci activation is regulated by Su(fu) and Fu using CRISPR/Cas to generate different Ci variants expressed at physiological levels in fly wing discs. I looked at how different regions of Ci, including known phosphorylation sites, contribute to the regulation of Ci activity. From this study, I propose that different sets of Ci phosphorylation events mediated by Fu are responsible for changes in Ci-Su(fu) interactions, by altering Ci-Su(fu) interfaces, but also by changing intramolecular Ci-Ci interactions and thereby transforming Ci to an active conformation, leading to target gene activation in response to Hh.

The role of Indian hedgehog (Ihh) signalling in the regulation of endochondral bone formation is well established. Ihh controls the rate of bone growth by negatively regulating differentiation and positively regulating growth plate chondrocyte proliferation. It has been well documented also that mutations resulting in constitutive activation of signalling through FGFR3 in chondrodysplasia, lead to a significant decrease in this important signalling factor accompanied by reduced proliferation of the chondrocytes and a dwarf phenotype. / In an attempt to rescue the chondrodysplasia phenotype hedgehog agonist Hh-Ag 1.4 was injected subcutaneously into mice with achondroplasia (ACH) or with severe achondroplasia with developmental delay and acanthosis negricans (SADDAN) with mixed results. / Administration of a hedgehog agonist in SADDAN mice led to a significant up-regulation of both Ptch and Gli1, as measured by quantitative PCR, indicating that Hh-Ag 1.4 does indeed stimulate hedgehog signalling in vivo. Also, in situ hybridization for Ihh seems to show a down regulation of native Ihh expression in pre-hypertrophic chondrocytes, possibly due to the activation of the negative PTHrP feedback loop. In our study, Hh-Ag 1.4 treatment resulted in an increased growth plate length and reduced size of the hypertrophic zone. The cortical bone flanking the growth plate in mice injected with Hh-Ag 1.4 was 2-3 times thicker than in control mice, which may be attributed to the positive effect of increased Ihh signalling in osteoblastogenesis. Contrary to our expectations, there was also a noticeable reduction in chondrocyte proliferation in mice treated with the agonist. / Overall, the effect on the growth of long bones was not beneficial and the treatment with high doses of Hh-Ag 1.4 did not result in an amelioration of the chondrodysplastic phenotype.

Glial cells maintain homeostasis that is essential to neuronal function. Injury to the nervous system leads to the activation and proliferation of glial cells and pericytes, which helps to wall off the damaged region and restore homeostatic conditions. Sonic hedgehog is a mitogen which is implicated in injury-induced proliferation of glial cells and pericytes. The mitogenic effects of sonic hedgehog require primary cilia, but the few reports on glial or pericyte primary cilia do not agree about their abundance and did not address effects of injury on these cilia. Primary cilia are microtubule-based organelles that arise from the centrosome and are retracted before cells divide. Depending on cell type, proteins concentrated in cilia can transduce several mitotic, chemosensory, or mechanosensory stimuli. The present study investigated effects of stab wound injury on the incidence and length of glial and pericyte primary cilia in the area adjacent to the injury core. Astrocytes, polydendrocytes and pericytes were classified by immunohistochemistry based on cell-type markers. In normal adult mice, Arl13b immunoreactive primary cilia were present in a majority of each cell type examined: astrocytes, 98±2%; polydendrocytes, 87±6%; and pericytes, 79±13% (mean ± SEM). Three days post-injury, cilium incidence decreased by 24% in astrocytes (p< 0.008) and 41% in polydendrocytes (p< 0.002), but there was no significant effect in pericytes. Polydendrocytes labeled with the cell cycle marker Ki67 were less likely to have cilia compared to resting, Ki67- polydendrocytes. Considering post-injury rates of proliferation for astrocytes and polydendrocytes, it appears that resorption of cilia due to cell cycle entry may account for much of the loss of cilia in polydendrocytes but was not sufficient to account for the loss of cilia in astrocytes. Under normal conditions, astrocytes rarely divide, and they maintain non-overlapping territories. However, three days after injury, there was a 7-fold increase in the number of paired mirror-image astrocytes (p< 0.018), which are most likely daughter cells from astrocytes that recently divided. Cilia incidence tended to decrease in these pairs compared to single astrocytes (p< 0.057) in injured mice. This is the first systematic investigation of cilia of astrocytes, polydendrocytes, and pericytes in the brain. Moreover, the examination of effects of brain injury on cilia adds to the understanding of injury-induced proliferation in these cells.

No description available.

Leiomioma (LMU) e leiomiossarcoma (LMSU) são tumores mesenquimais que se desenvolvem no útero e apresentam comportamento clínico variável. Ambos são neoplasias do miométrio (MM), com mesmo padrão de diferenciação celular, porém com progressão clínica completamente diferente. Até o momento, existe grande controvérsia quanto aos fatores relacionados ao surgimento dessas neoplasias e uma possível malignização de um leiomioma pré-existente. Foi demonstrado que a ativação da via de sinalização do Sonic hedgehog (SHH) está relacionada ao desenvolvimento de diversos tipos de tumor, uma vez que a mesma desempenha importante papel na proliferação e diferenciação celular. O objetivo desse trabalho foi avaliar o padrão de expressão transcricional e protéica de moléculas envolvidas na via do SHH em LMU e LMSU. Foram avaliados a expressão de 106 genes, por PCR em tempo real, e de sete proteínas (SHH, PTCH 1, SMO, SUFU GLI 1-3 e HHIP 1), por imunoistoquímica, em 176 amostras (20 MM, 103 LMU - incluindo 16 leiomiomas não convencionais/LMA e 37 LMSU). Os resultados mostraram que a expressão gênica e protéica foram similares nas amostras de LMAU e LMSU. A expressão de AXIN 2, FZD 2, CCND 1, FZD 6, ESR 1 e IFT 52 foi associada com a sobrevida livre de doença; FZD3, FZD 8 e WISP1 com sobrevida cancer específica nas pacientes com LMSU. As proteínas SMO, SUFU, GLI 1 e GLI 3 não foram expressas nas amostras de MM. SHH e SUFU mostraram correlação com sobrevida livre de doença nas pacientes com LMSU. De modogeral, o perfil de expressão das proteínas (exceto HHIP 1 e GLI 2), foi crescente entre as amostras de MM, LMU, LMAU e LMSU. Esse dado corrobora a hipótese de malignização dos leiomiomas. Adicionalmente, algumas das proteínas avaliadas têm sido alvos terapêuticos em pacientes com câncer. Assim, no futuro, novos tratamentos podem ser propostos para as mulheres com esse tipo de neoplasias / Leiomyoma (LMU) and leiomyosarcoma (LMSU) are uterine mesenchymal tumors with variable clinical behavior. Both are myometrial (MM) neoplasms that show the same pattern of cell differentiation, but with completely different clinical progression. To date, there are controversies about these neoplasias devolopement-related factors and a possible malignant transformation of a pre-existing leiomyoma. It was demonstrated that activation of the Sonic Hedgehog (SHH) signaling pathway is related to the development of several tumors, due to its activity in the cell proliferation and differentiation. The aim of this study was to evaluate the transcriptional and protein expression profile of the SHH pathway molecules in LMU and LMSU. It was evaluated 106 genes, by quantitative real time PCR, and seven proteins (SHH, PTCH 1, SMO, SUFU, GLI 1-3 and HHIP 1), by immunohistochemistry, in 176 samples (20 MM, 103 LMU - including 16 unconventional leiomyoma /LMAU and 37 LMSU). The results show that the gene and protein expression were similar for LMAU and LMSU samples. The gene expression of AXIN 2, FZD 2, CCND 1, FZD 6, ESR 1 and IFT 52 was associated with disease free survival; and FZD3, FZD 8 and WISP1 with cancer specific survival in patient with LMSU. No SMO, SUFU, GLI 1 and GLI 3 protein expression was observed in the MM samples. SHH and SUFU proteins were correlated with disease-free survival in patients with LMS. LMU, LMAU and LMSU samples displayed increased expression of all SHH proteins (except HHIP 1 and GLI 2). These data corroborate with the leiomyoma malignant transformation hypothesis. Moreover, some proteins evaluated have been used as therapeutic target for cancer patients. In the near future, new treatment strategies might be proposed for women with these neoplasias

Leiomioma (LMU) e leiomiossarcoma (LMSU) são tumores mesenquimais que se desenvolvem no útero e apresentam comportamento clínico variável. Ambos são neoplasias do miométrio (MM), com mesmo padrão de diferenciação celular, porém com progressão clínica completamente diferente. Até o momento, existe grande controvérsia quanto aos fatores relacionados ao surgimento dessas neoplasias e uma possível malignização de um leiomioma pré-existente. Foi demonstrado que a ativação da via de sinalização do Sonic hedgehog (SHH) está relacionada ao desenvolvimento de diversos tipos de tumor, uma vez que a mesma desempenha importante papel na proliferação e diferenciação celular. O objetivo desse trabalho foi avaliar o padrão de expressão transcricional e protéica de moléculas envolvidas na via do SHH em LMU e LMSU. Foram avaliados a expressão de 106 genes, por PCR em tempo real, e de sete proteínas (SHH, PTCH 1, SMO, SUFU GLI 1-3 e HHIP 1), por imunoistoquímica, em 176 amostras (20 MM, 103 LMU - incluindo 16 leiomiomas não convencionais/LMA e 37 LMSU). Os resultados mostraram que a expressão gênica e protéica foram similares nas amostras de LMAU e LMSU. A expressão de AXIN 2, FZD 2, CCND 1, FZD 6, ESR 1 e IFT 52 foi associada com a sobrevida livre de doença; FZD3, FZD 8 e WISP1 com sobrevida cancer específica nas pacientes com LMSU. As proteínas SMO, SUFU, GLI 1 e GLI 3 não foram expressas nas amostras de MM. SHH e SUFU mostraram correlação com sobrevida livre de doença nas pacientes com LMSU. De modogeral, o perfil de expressão das proteínas (exceto HHIP 1 e GLI 2), foi crescente entre as amostras de MM, LMU, LMAU e LMSU. Esse dado corrobora a hipótese de malignização dos leiomiomas. Adicionalmente, algumas das proteínas avaliadas têm sido alvos terapêuticos em pacientes com câncer. Assim, no futuro, novos tratamentos podem ser propostos para as mulheres com esse tipo de neoplasias / Leiomyoma (LMU) and leiomyosarcoma (LMSU) are uterine mesenchymal tumors with variable clinical behavior. Both are myometrial (MM) neoplasms that show the same pattern of cell differentiation, but with completely different clinical progression. To date, there are controversies about these neoplasias devolopement-related factors and a possible malignant transformation of a pre-existing leiomyoma. It was demonstrated that activation of the Sonic Hedgehog (SHH) signaling pathway is related to the development of several tumors, due to its activity in the cell proliferation and differentiation. The aim of this study was to evaluate the transcriptional and protein expression profile of the SHH pathway molecules in LMU and LMSU. It was evaluated 106 genes, by quantitative real time PCR, and seven proteins (SHH, PTCH 1, SMO, SUFU, GLI 1-3 and HHIP 1), by immunohistochemistry, in 176 samples (20 MM, 103 LMU - including 16 unconventional leiomyoma /LMAU and 37 LMSU). The results show that the gene and protein expression were similar for LMAU and LMSU samples. The gene expression of AXIN 2, FZD 2, CCND 1, FZD 6, ESR 1 and IFT 52 was associated with disease free survival; and FZD3, FZD 8 and WISP1 with cancer specific survival in patient with LMSU. No SMO, SUFU, GLI 1 and GLI 3 protein expression was observed in the MM samples. SHH and SUFU proteins were correlated with disease-free survival in patients with LMS. LMU, LMAU and LMSU samples displayed increased expression of all SHH proteins (except HHIP 1 and GLI 2). These data corroborate with the leiomyoma malignant transformation hypothesis. Moreover, some proteins evaluated have been used as therapeutic target for cancer patients. In the near future, new treatment strategies might be proposed for women with these neoplasias

The Hedgehog (Hh) family of proteins are secreted growth factors that play an essential role in the embryonic development of all organisms and the main components in the pathway are conserved from insects to humans. These proteins affect patterning and morphogenesis of multiple tissues. Therefore, mutations in the Hh pathway can result in a wide range of developmental defects and oncogenic diseases. Because the main components in the pathway are conserved from insects to humans, Drosophilahas been shown to provide a genetically tractable system to gain insight into the processes that Hh is involved in. In this study, the roles of Hh cholesterol modification and endocytosis during gradient fonnation are explored in the Drosophila larval wing imaginal disc. To exclude the possibility of looking at a redistribution of preexisting Hh instead of Hh movement, a spatially and temporally regulated system has been developed to induce Hh expression. Functional Hh-GFP with and without the cholesterol-modification was expressed in a wild-type or shi-tslendocytosis mutant background. The Gal80 system was used to temporally express (pulse) the Hh-GFP transgenes to look at the rate of Hh gradient formation over time and determine whether this process was affected by cholesterol modification and/or endocytosis. Hh with and without cholesterol were both largely detected in punctate structures and the spreading of the different forms of Hh was quantified by measuring distances of these particles from the expressing cells. Hh without cholesterol showed a greater range of distribution, but a lower percentage of particles near the source. Loss of endocytosis blocked formation of intracellular Hh particles, but did not dramatically alter its movement to target cells. Staining for Hh, its receptor Ptc and cortical actin revealed that these punctate structures could be classified into four types of Hh containing particles: cytoplasmic with and without Ptc, and cell surface with and without Ptc. Cholesterol is specifically required for the formation of cytoplasmic particles lacking Ptc. While previous studies have shown discrepancies in the localization of Hh following a block in endocytosis, Hh with and without cholesterol is detected at both apical and basolateral surfaces, but not at basal surfaces. In the absence of cholesterol and endocytosis, Hh particles can be observed in the extracellular space. Through three-dimensional reconstruction and quantitative analysis, this study concludes that the cholesterol modification is required to restrict Hh movement. In addition, the cholesterol modification promotes Ptc-independent internalization. This study also observes that Dynamin-dependent endocytosis is necessary for internalization but does not play an essential role in Hh distribution. The data in this thesis supports the model in which Hh movement occurs via planar diffusion.

During development, axons respond to a variety of guidance cues in the environment to navigate to the proper targets. Sonic hedgehog (Shh), a classical morphogen, has been shown to function as a guidance factor that directly acts on the growth cones of various types of axons. We previously found that Shh affects retinal ganglion cell (RGC) axonal growth and navigation in a concentration-dependent manner. However, the signaling pathways that mediate such events are still unclear. In this thesis, we show that high concentrations of Shh induce growth cone collapse and repulsive turning of the chick RGC through rapid increase of Ca2+ in the growth cone, and specific activation of PKCα and Rho signaling pathways. We further found that integrin linked kinase (ILK) acts as an immediate downstream effector of PKCα. PKCα directly phosphorylates ILK in vitro at two previously unidentified sites threonine-173 and -181. Inhibition of PKCα, Rho, and ILK by pharmacological inhibitors and/or dominant-negative approaches abolished the negative effects of high-concentration of Shh. We provide evidence that Rho likely functions downstream of PKC and suggest that PKC, Rho and ILK may cooperatively mediate the negative effects of high concentrations of Shh. Furthermore, retroviral expression of dominant-negative constructs of PKCα (DN-PKCα) and ILK-double mutants (ILK-DM) resulted in misguidance of RGC axons at the optic chiasm in vivo. These results demonstrate that new signaling pathways composed of PKCα, Rho, and ILK play an important role in Shh-induced axonal chemorepulsion. In contrast, we show that attractive axonal turning in response to low concentrations of Shh is independent of PKCα, but requires the activity of cyclic nucleotides cAMP. Taken together, our results suggest that the opposing effects of Shh on axon guidance are mediated by different signaling pathways.