@phdthesis{01HNAMNJQDM1KS659V59ET6XQB,
  abstract     = {{In Chapter I it has been introduced that the advent of CRISPR/Cas9 made it possible to alter the Xenopus genome. The Xenopus species has a remarkable history. Initially used as a pregnancy test, Xenopus laevis has gone on to make significant contributions to the field of cell and developmental biology. The large Xenopus embryos develop externally, making them convenient for micro-injections. The advent of CRISPR/Cas9made it possible to modify the Xenopus genome and generate genetic models. As Xenopus laevis is allotetraploid, its diploid sister species Xenopus tropicalis has been introduced and has gained interest as a model organism for CRISPR/Cas9-mediated disease modelling. 
Inherited retinal diseases (IRDs) are a group of disorders characterized by degeneration and dysfunction of the retinal cell types, more specifically the photoreceptor cells and the retinal pigment epithelium (RPE). IRDs are clinically and genetically heterogeneous, and more than 290 disease genes have been associated with IRDs. With the identification of these disease genes and associated mutations, it is important to understand how these genes function in biological processes and what the consequences are of gene dysfunction. Therefore, the overall goal of this doctoral work was to generate Xenopus tropicalis IRD disease models that could benefit retinal research and patients suffering from IRDs.
In Chapter II, an rcbtb1-/- Xenopus tropicalis IRD model was generated using CRISPR/Cas9 and subsequent breeding. Via this genetic Xenopus model, we hoped to discover more about the exact function of the rcbtb1 gene. The Xenopus retina was thoroughly examined by histology, light microscopy and 3D electron microscopy (3D-EM). This is the first time that 3D-EM and subsequent reconstructions have been performed on a Xenopus model. This histological examination revealed dystrophic changes at the level of the RPE, characterized by vacuolization, spreading of the pigment granules, loss of apical-basal cell polarity, loss of cuboidal cell structure and a general disorganization of the RPE layer. Our data suggest that the RPE is involved as tissue of origin in the pathogenesis of rcbtb1-/- and is an important finding that may improve the examination, diagnosis and follow-up of these patients.
In Chapter III, an ush2a-/- Xenopus tropicalis IRD model was generated using CRISPR/Cas9 and subsequent breeding. The generation of this ush2a-/- model was aimed at providing an ush2a model with a penetrant retinitis pigmentosa (RP) phenotype, as this was lacking in the Ush2a-/- mice and zebrafish models available at the start of this thesis. We observed a thinning of the photoreceptor layer from the age of 10 months on and one animal was completely devoid of rods, coinciding with the early disease symptoms seen in human RP patients.
In Chapter IV, Xenopus tropicalis was used to investigate a potential dual role for the disease gene SF3B2 both during early development and in postnatal life. We showed that two distinct missense variants affecting residue Tyr806 lead to isolated autosomal dominant RP, whereas loss-of-function variants lead to syndromic evelopmental phenotypes characterized by craniofacial and/or skeletal defects.
In addition to IRD, Xenopus tropicalis can also be used for evolutionary studies. In Chapter V, we describe a hoxc13-/- Xenopus tropicalis model that lacks pigmented black claws. We show that hoxc13 regulates claw-specific keratins 34 & 59. Similarly, HOXC13 has been shown to be involved in the control of hair keratin expression in humans. This chapter provides important insights into the molecular composition and transcriptional regulation of amphibian skin appendages. In contrast to the previous assumption that claws of clawed frogs and claws of amniotes and hair of mammals have evolved independently, we suggest here that they have evolved in a homologous manner.
Overall, this dissertation demonstrates once again that Xenopus tropicalis is a suitable animal model for disease modelling, here specifically for IRD and evolutionary research. This work has resulted in several Xenopus tropicalis models that have helped to understand the pathogenesis of IRD and the origin of skin appendages.}},
  author       = {{Carron, Marjolein}},
  language     = {{eng,dut}},
  pages        = {{252}},
  publisher    = {{Ghent University. Faculty of Medicine and Health Sciences}},
  school       = {{Ghent University}},
  title        = {{Modelling of rare diseases and developmental processes in Xenopus tropicalis : from retinal degeneration to epidermal  structures}},
  year         = {{2023}},
}