Expression and function of APRIL and GDF-5 in the developing hippocampus

Neurite size and morphology are key determinants of the functional properties of neurons. In this thesis, it is described for the first time the expression of APRIL (A Proliferation-Inducing Ligand, TNFSF13) in the nervous system. APRIL is a member of the tumour necrosis factor superfamily and one of its receptors BCMA (B-Cell Maturation Antigen, TNFRSF17) are coexpressed in pyramidal neurons throughout the fetal and postnatal mouse hippocampus. The effect of APRIL on axon elongation is inhibited by the expression of a truncated BCMA receptor in the neurons, suggesting that BCMA mediates this effect. APRIL promotes rapid phosphorylation of ERK1/2, Akt and GSK-3β in cultured pyramidal neurons, and pharmacological inhibition of either MEK1/2 or PI3K, upstream activators of ERK1/2 and Akt/GSK-3β signalling, respectively, completely inhibits the axon growth-promoting action of APRIL. These findings reveal that APRIL selectively enhances axon growth from developing hippocampal pyramidal neurons by a mechanism that depends on BCMA and activation of ERK1/2 and Akt/GSK-3β signalling. In this thesis, it is also shown that GDF-5 (growth-differentiation factor 5), a member of the transforming growth factor-β superfamily with a wellcharacterized role in limb morphogenesis, is a key regulator of the growth and elaboration of pyramidal neuron dendrites in the developing hippocampus. Pyramidal neurons co-express GDF-5 and its preferred receptors bone morphogenetic protein receptor-IB and bone morphogenetic protein receptor-II during development. In culture, GDF-5 substantially increased dendrite, but not axon, elongation from these neurons by a mechanism that depends activation of Smads1/5/8 and upregulation of the Hes5 transcription factor. In vivo, the apical and basal dendritic arbors of pyramidal neurons throughout the hippocampus were very markedly stunted in both homozygous and heterozygous Gdf-5 null mutants, indicating that dendrite size and complexity are exquisitely sensitive to the level of endogenous GDF-5 synthesi

Exploring The Role Of FGFR2c Misregulation In Syndromic Craniosynostosis

Craniosynostosis is a common feature of craniofacial birth defects, and is characterised by premature fusion of the cranial sutures in the developing calvarium. Pathogenic FGFR2 signalling is a major cause of syndromic craniosynostosis and is caused by activating mutations within the FGFR2 gene. In particular, mutations affecting the IIIc isoform (i.e. FGFR2c-C342Y) contribute to coronal synostosis, a common phenotype in human Crouzon syndrome. This study aims to address the downstream effects of misregulated FGFR2c signalling in vivo. Conditional overexpression of Fgfr2c (R26RFgfr2cV5/+; βactinCRE/+) results in craniofacial hypoplasia without coronal synostosis, which is in contrast to Fgfr2cC342Y/+, a well-studied mouse model for human Crouzon syndrome. Assessment of the coronal suture reveals that R26RFgfr2cV5/+; βactinCRE/+ and Fgfr2cC342Y/+ have opposing phenotypes, where the former display insufficient osteoblast activity. However, biochemical examination of RAS-MAPK activity in embryonic sutures of Fgfr2cC342Y/+ and R26RFgfr2cV5/+; βactinCRE/+ demonstrates upregulated pERK expression. The opposing phenotypes seen between Fgfr2cC342Y/+ and R26RFgfr2cV5/+; βactinCRE/+ mice suggested the possibility that Fgfr2c overexpression on the Fgfr2cC342Y/+ (R26RFgfr2cV5/+;βactinCRE/+;Fgfr2cC342Y/+) genotype may serve to ameliorate the Crouzon phenotype. This study reports that the Crouzon phenotype was only partly spared in R26RFgfr2cV5/+;βactinCRE/+;Fgfr2cC342Y/+ mice, together with a partial rescue of the coronal suture. The latter was due to delayed calvarial ossification as well as reduced osteoblast activity. Therefore, this study demonstrated that an intricate balance would be required for FGF signalling in order to correct calvarial bone and suture morphogenesis, and that increasing the expression of the wild-type FGFR2c isoform may be a viable method to prevent or delay craniosynostosis progression. In addition, this study has uncovered a novel role for cartilage in craniosynostosis development and has performed comparative expression-profiling (RNAseq) on the E16.5 coronal suture of Fgfr2cC342Y/+ and WTs to uncover novel genes potentially involved in syndromic craniosynostosis. Further elucidation of the highly complex FGFR2c signalling pathway remains to be deciphered in order to improve our understanding of normal craniofacial development and its related pathologies, while providing a framework for the innovation of novel therapeutic strategies

The Retina in Health and Disease

Vision is the most important sense in higher mammals. The retina is the first step in visual processing and the window to the brain. It is not surprising that problems arising in the retina lead to moderate to severe visual impairments. We offer here a collection of reviews as well as original papers dealing with various aspects of retinal function as well as dysfunction. New approaches in retinal research are described, such as the expression and localization of the endocannabinoid system in the normal retina and the role of cannabinoid receptors that could offer new avenues of research in the development of potential treatments for retinal diseases. Moreover, new insights are offered in advancing knowledge towards the prevention and cure of visual pathologies, mainly AMD, RP, and diabetic retinopathy