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Comparative analyses of cranial skeletogenesis and odontogenesis in basal Ray-finned fishes
Pospíšilová, Anna ; Černý, Robert (advisor) ; Přikryl, Tomáš (referee) ; Buchtová, Marcela (referee)
Skeletal (cartilaginous, bony, and dental) tissues undoubtedly exemplify the key innovation of vertebrates. Among all recent vertebrates, the most numerous and successful lineage is represented by the Ray-finned fishes that, accordingly, exhibit amazing variety of skeletal architectures and phenotypic adaptations. In order to depict fundamental principles of fish cranial skeletogenesis the developmental formation of skeletal architectures was described, compared and analyzed using members of early branching fish lineages, that exemplify very different strategies of skeletogenesis. While the Senegal bichirs and the Tropical gars are heavily armored forms with massive exoskeleton and hyperossified dental structures covering the whole oropharyngeal region, the European sterlets, on the contrary, possess mostly cartilaginous skeleton and reduce their dental structures during early development. Whole analysis is underpinned by the Northen pike, teleostean species with lightened skeletal architecture with comparable number of cranial elements. The present study represents the first complex comparative analysis of their skeletogenesis and odontogenesis. This allowed to define developmental strategies founding different lineage-specific skeletal architecture of vertebrates. Comparative description of...
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Role of transcription factors MEIS in the origin and development of the neural crest
Fábik, Jaroslav ; Machoň, Ondřej (advisor) ; Buchtová, Marcela (referee) ; Procházka, Jan (referee)
Unique to the vertebrate embryo, neural crest cells represent a multipotent cell population that migrates throughout the body and gives rise to a multitude of different types of cells and tissues. Cranial neural crest cells populate the developing pharyngeal arches and establish skeletogenic condensations that generate the future bones and cartilages of the face and neck. Moreover, these cells send out and receive signals from adjacent tissues of non-neural crest origin, such as the mandibular epithelium and muscle precursor cells. Such reciprocal interactions give rise to organs and structures, for instance, to the tongue. The aim of this work was to elucidate the roles of homeodomain-containing MEIS transcription factors in neural crest cells and in craniofacial development, by using a mouse model with conditional inactivation of Meis2 gene in neural crest cells. We show that transcription factor MEIS2 is expressed in the medial region of the developing mandible and in the developing tongue. Conditional Meis2 inactivation using the Wnt1-Cre2 mouse strain caused mandible and tongue hypoplasia, and ectopic bone formation at the expense of tongue development. These mandibular arch anomalies were accompanied by the loss of Hedgehog signaling in the mandibular epithelium, expanded RUNX2 expression in...
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Comparative development & evolution of adenohypophysis in basal fishes
Brezarová, Dominika ; Černý, Robert (advisor) ; Buchtová, Marcela (referee)
The pituitary is a master endocrine gland in the vertebrate head with many crucial roles in producing hormones and controlling secretion of other glands, and with long-standing controversies on its evolution and embryonic origin. Adenohypophysis (ADH), the front lobe of the pituitary, develops from the rostral placode that extensively migrates under the brain to connect the neurohypophysis, evagination of the ventral hypothalamus. Owing to its ectodermal placodal origin, ADH is commonly understood as a part of the vertebrate specific acquisition of our new head. Recently, however, an endodermal contribution to ADH was revealed in the teleost fish, supporting classic claims of a pre-vertebrate origin of this organ from an ancient chordate pharyngeal structure. In this work, early development of ADH was characterized in three species of basal fishes, bichirs, sturgeons, and gars, representing a possible stem-like pattern of early vertebrate craniogenesis. Interestingly, in all three species, both the early development and later migration of ADH is intimately linked with the pharyngeal domain in the rostral head. In sturgeon embryos, ADH migrates in between the brain and the pharyngeal domain, which further separates ADH from the forming mouth. In bichir embryos, ADH was additionally shown to get...
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Evolution of the gene regulatory network underlying the formation of the gastrula organizer
Macháčová, Simona ; Kozmikova, Iryna (advisor) ; Krylov, Vladimír (referee) ; Buchtová, Marcela (referee)
During gastrulation, the vertebrate embryo is organized from the clump of cells into a bilaterally symmetric body. This organization process is driven by the gastrula organizer. Its establishment is induced by maternal Wnt/β-catenin signaling and Nodal/Activin signaling localized in the presumptive dorsal region of the embryo. The regulative environment then triggers the expression of the organizer-specific genes which create morphogen gradients in the embryonic body and therefore give each cell positional information. However, the evolution of vertebrate organizer establishment remains vague. Here we aim to test the compatibility of the invertebrate cis-regulatory modules with the vertebrate gene regulatory network (GRN). We introduced fluorescent reporter genes under the control of the invertebrate regulatory sequence of organizer-specific genes into a vertebrate model to observe their behavior in the context of the vertebrate GRN. We found and functionally verified a 500 bp-long amphioxus sequence (an enhancer) that is necessary and sufficient to drive a correct Chordin gene expression in the gastrula organizer in zebrafish. Chordin is a prominent organizer-specific gene antagonizing Bone Morphogenetic Protein (BMP) signaling. We tested also other invertebrate genes for their compatibility with...
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Migration and morphogenesis of neural crest cells in the context of craniofacial development of selected ray-finned fishes
Štundl, Jan ; Černý, Robert (advisor) ; Buchtová, Marcela (referee) ; Machoň, Ondřej (referee)
Neural crest (NC) cells play a crucial role in vertebrate development and evolution. This cell population contributes to many new cell types such as chondrocytes and osteocytes of the head skeleton, neurons, pigment cells, cardiomyocytes, and many others. As such the neural crest is often considered as the fourth germ layer. This vertebrate-specific cell population emerges during formation of the neural tube. Whereas in the trunk region NC cells migrate as separate cells, cranial neural crest (CNC) cells extensively migrate in three discrete streams forming most of the head mesenchyme. In all vertebrates, CNC stereotypically follows the tripartite pattern of migration along the anteroposterior axis so that the most anterior (trigeminal) stream emerges first, followed by the hyoid and branchial CNC streams. In this work, I have studied representatives of all three lineages of non-teleost fishes (bichir, sturgeon, and gar) and also one species from the crown group of ray-finned fishes, the pike. The main question I addressed in my project was whether the CNC cells stereotypically follow a tripartite pattern of migration along the anteroposterior axis as is seen throughout vertebrates. Surprisingly, I found several alterations in the emergence of CNC cells and their migratory pattern in the studied...
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Pathogenesis of limbs in Sprouty2/Sprouty4 mice
Cimlerová, Markéta ; Hovořáková, Mária (advisor) ; Buchtová, Marcela (referee)
Sprouty proteins play the role of negative regulators of receptor tyrosine kinases (RTKs), including the fibroblast growth factor (FGF) signaling pathway. During embryonic development, this pathway is essential for the regulation of cell proliferation, migration, differentiation and apoptosis, and its activity is crucial for normal limb development. An integral part of this pathway are also FGF receptors (FGFR), of which, for example, FGFR3 significantly affects chondrocytes in the growth plate and its mutations lead to the development of chondrodysplastic syndromes. Sprouty proteins play important roles during the formation of body tissues in the process of organogenesis. It has been shown that Sprouty2 and Sprouty4 are involved in the formation of many organs, such as the brain, lungs, teeth, but also in the formation of limbs. Sprouty2 is a regulator of enchondral ossification, modulates signaling in osteoblasts and chondrocytes and is essential for normal chondrocyte proliferation and differentiation. Sprouty4 is expressed in the progress zone of the limb bud. Disruption of Sprouty2 and Sprouty4 gene expression leads to limb defects, which has been demonstrated, for example, in mouse or chicken embryos. In the presented work we deal with the development of the limbs of transgenic mice with...
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Ontogeny, evolution & homology of cement glands and attachment organs in lower vertebrates
Minařík, Martin ; Černý, Robert (advisor) ; Ráb, Petr (referee) ; Buchtová, Marcela (referee)
Aquatic larvae of many vertebrate lineages develop specialized, cranially located cement or attachment glands which allow them to remain attached to a substrate by means of polysaccharide secretion. The larvae can thus remain still and safe in well-oxygenated water out of reach of any predators until the digestive and locomotory apparatus fully develops. Xenopus cement gland is the most thoroughly studied example of this type of glands, since it was used as a model for the anteriormost patterning of the developing head. Based on shared expression patterns of key transcription factors and a similar ectodermal origin it has been repeatedly suggested that Xenopus cement gland is homologous to adhesive organs of teleosts and adhesive papillae of ascidians. The lack of comprehensive knowledge on this type of glands in other lineages however rendered any considerations of homology among such a distant lineages rather inconclusive. In the present work I have focused on a detailed study of the cement glands and other corresponding structures in three representatives of basal actinopterygian lineages: Senegal bichir (Polypterus senegalus), sterlet (Acipenser ruthenus), and tropical gar (Atractosteus tropicus). Using a combination of in vivo fate-mapping approaches with a Micro-CT imaging of cranial endoderm...
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Developmental morphogenesis of attachment organs in lower vertebrates
Minařík, Martin ; Černý, Robert (advisor) ; Buchtová, Marcela (referee)
Adhesive organs are widespread structures among vertebrate larvae. They allow the larvae to attach to a substrate, so that the time for the development of mouth or motoric apparatus could be prolonged. Similar structures in ascidians, larvaceans and lancelets are known too. Thus, it might be hypothesized that the presence of some type of adhesive gland could indeed represent the ancestral state for chordate larvae. Interestingly, however, whilst in most species these glands take their developmental origin in ectodermal layer, in bichir, a member of a primitive actinopterygian lineage, their origin was suggested to be endodermal already at the beginning of 20th century. Since then, however, the former study has become almost forgotten and even recent analyses do not come with new findings on this topic. Because of the essential importance of study of bichir cement glands for understanding the relationship between these structures among chordates, I have decided to focus on this subject. To obtain appropriate comparative data Xenopus, Weather loach and Ribbed newt embryos were included in this study as well. By using combination of immunohistochemical and histological techniques the endodermal origin of cement glands in bichir was proven and their morphogenesis was described into considerable details. The...
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Early craniofacial and dental morphogenesis in bichir, P. senegalus
Kráľovič, Martin ; Černý, Robert (advisor) ; Buchtová, Marcela (referee)
Polypterid fishes are considered the basal-most group of extant actinopterygians and thus may serve as a direct link for understanding the evolution of the first bony fishes. Their embryonic and larval material, however, is extremely scarce what makes it difficult to study their developmental patterns and processes. This work of mine is based on several successful breedings of the bichir Polypterus senegalus that allowed me to analyse development of some 70 specimens at key developmental stages. I have focused my attention to the early morphogenesis of teeth and dentition on several locations within a developmental context of oropharyngeal cavity. Oropharyngeal cavity develops quite differently when compared to other vertebrate species: it arises by means of a schizocoeliclike split of epithelial layers and, moreover, the earliest mouth cavity seems to be strongly constrained by the presence of cement (attachment) glands. Mouth opening proceeds by development of new, enigmatic structures that I have entitled the epithelial bridges (Kralovic et al., 2009) and that might represent the ectoderm-endoderm border often judged to be essential for tooth initiation and patterning. I have described a pronounced delay in initiation of pharyngeal teeth when compared to the oral teeth, probably as a direct consequence...
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