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Comparative and evolutionary analyses of neurulation in non-teleost fishes
Matějková, Tereza ; Černý, Robert (advisor) ; Pergner, Jiří (referee)
Neurulation, i. e. formation of a neural tube, is a crucial event in embryogenesis of each vertebrate. This developmental process is rather stereotypical, generally comprising a transformation of a neural plate into a neural tube. In the majority of vertebrate groups, neurulation classically occurs by a folding process of bending neural folds, whereas in bony fishes (Teleostei), representing a crown group of ray-finned fishes (Actinopterygii), the neurulation occurs rather differently by a solid neural keel. The three stem groups of ray- finned fishes - bichirs, sturgeons and gars - might thus serve as unique models for understanding of evolutionary changes in the pattern of vertebrate neurulation. For that reason, detailed developmental series of bichir (Polypterus senegalus), sturgeon (Acipenser ruthenus) and gar (Atractosteus tropicus) were used, and their morphogenetic processes of neurulation were compared. I present here description of the outer morphology, and analyses of tissue and cellular changes, with a focus on intrinsic forces within the neural plate like apical constriction and convergent extension, as well as on some extrinsic forces. I also try to discuss possible mechanisms of an evolutionary transition from the bending of the neural plate to the neurulation via the neural keel,...
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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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The prechordal plate during embryogenesis of the vertebrate head
Marková, Kristýna ; Černý, Robert (advisor) ; Soukup, Vladimír (referee)
The prechordal plate is generally described as a population of axial mesendodermal cells that is formed during early embryonic development, in the rostral- most area of the vertebrate head. The population of the prechordal plate cells is specific for vertebrate, and evolution of the vertebrate head was one of the key steps during vertebrate evolution. During vertebrate embryogenesis, the prechordal plate cells are pushed by the growth of the forebrain, until only some small population remains in front of the notochord, which later differentiate into mesodermal cells. The precise morphogenesis of this prechordal mesoderm, differs across vertebrates, but in most vertebrates produces a pair of head cavities, which are called premandibular. Within the organogenesis of vertebrates, extrinsic eye muscles are formed from these mesodermal cells and cavities. The prechordal plate, however is also referred to as one of the important centers that control the formation of the vertebrate head during early embryogenesis, since its removal or inhibition of important signals caused various disorders and embryonic dead. This thesis aims to summarize the information on the formation and function of the prechordal plate cells during vertebrate embryogenesis. Key words: prechordal plate; prechordal mesoderm; head...
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The trabecular cartilage as a key structure for development and evolution of the anterior vertebrate cranium
Horáčková, Agáta ; Černý, Robert (advisor) ; Němec, Pavel (referee)
Anterior part of the skull is in embryos composed of two rod-like cartilages called trabeculae cranii. The final shape of the skull of jawed vertebrates is affected by the manner of composition of trabeculae. There are two types of arrangement of vertebrate skull: the platybasic, which is probably the original one, and the tropibasic, which has developed independently in birds, bony fishes and mammals. Jawless vertebrates (lampreys and hagfishes) also have cartilaginous elements called trabeculae, but there are doubts about homology of these structures between groups of jawed and jawless vertebrates. The trabeculae initially became interesting elements because of their possible position in premandibular segment as a former premandibular branchial arch. The two theories of origin of jaws, which do not assume there ever were any branchial arches before the mandibular, strictly disagree in the question of the nature of the trabeculae cranii.
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The embryonic formation of the primary mouth in vertebrates
Psutková, Viktorie ; Černý, Robert (advisor) ; Soukup, Vladimír (referee)
The primary mouth develops during early embryogenesis at the anterior end of the forming head and it is created from the ectoderm and the endoderm that directly juxtapose. The primary mouth is the first connection of the digestive system with the outside, which is undoubtedly a crucial step for further development of an organism. In most vertebrates, the primary mouth is getting opened by perforation of a thin septum, the oral membrane. The oral membrane is formed from the ectoderm and the endoderm, when the ectoderm pushes against endoderm. Surprisingly, developmental formation of the primary mouth is not identical in all vertebrates and we can commonly recognize three main developmental modes. In the most vertebrates clades, the primary mouth forms via the so called stomodeal invagination, which is often exemplified in the frog Xenopus leavis. The primary mouth of salamanders and lungfishes forms via the so called stomodeal collar and the primary mouth of teleost fishes forms via the so called stomodeal wedge. Moreover, in the hagfishes, the development of the primary mouth seems similar to the stomodeal invagination, but with some substantial differences in later formation. The particular mode of the primary mouth formation probably depends on the course of embryonic development and spatial...
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Asymetric segregation of cell determinants in embryos with regulatory development
Chramostová, Kamila ; Krylov, Vladimír (advisor) ; Černý, Robert (referee)
Asymmetric segregation of cell determinants specific the cell fates in early embryonic development. In C. Elegans somatic and germ cells are separeted in early development. On the basis of the first five asymmetric divisions AB, MS, C, E, D, P4 are found. In this specifications, par genes and genes responsible for the specification of blastomers are involved. P granules are segragated to P4 cells. Xenopus as a representative of amphibians, belonging to a group with regulative embryogenesis , exhibit features of mosaic development like C. Elegans. Maternal RNAs in germ plasm determine germ cells already in oocyte. These RNAs are transported through two distinct pathways. METRO pathways is used for a transportation of mitochondrial cloud RNA. It is specific for Xcat-2, Xpat, XIsirt, Xdazl. Vg1 and VegT RNAs are involved in the second pathway called Vg1 . This RNA contribute to the specification of mesoderm and endoderm. Although mammals reveal regulative development they also exhibit some features of the mosaic embryos. As an example, in the mouse embryo, overexpressing cadherin leads to compaction at the 8 -cell stage. Then the cells of embryo are polarized. Polarized internal cells give rise to ICM. Conversely, the outer nonpolarized cells give rise to TE. Specific factor for TE is Cdx2, for ICM is...
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Characterization of cranial skeletogenesis and odontogenesis in basal Ray-finned fishes
Pospíšilová, Anna ; Černý, Robert (advisor) ; Přikryl, Tomáš (referee)
Skeletal tissues represent a key novelty of vertebrates, moreover, structural diversification and phenotypic adaptation of cartilaginous, bony and dental elements determine life strategies of each vertebrate lineage. Ray-finned fishes (Actinopterygii) constitute the most diverse vertebrate group with striking diversity in skeletogenesis and skeletal systems. In this thesis, comparative developmental analyses of craniofacial skeletal tissues and structures in bichirs (Polypteriformes) and sturgeons (Acipenseriformes), was analysed. These basal lineages differ essentially in their strategy of skeletogenesis. Bichirs represent heavily armoured forms with massive exoskeleton, they also comprise thick ganoid scales and dental structures that cover the whole oropharynx. Sturgeons, on the contrary, are primarily cartilaginous fishes with rather reduced skeleton and with teeth that are completely lost during larval development. Skeletogenesis was studied on a unique series of embryonic and larval stages of the Senegal bichir (Polypterus senegalus) and the sterlet (Acipenser ruthenus) by whole-mount staining of their cartilage and mineralized tissues followed by fluorescent microscopy visualisation. Growth dynamics of their skeletal systems was described and compared; expansion of their bony surfaces during ontogeny...
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Developmental and structural analysis of similarities among calcified and keratinized tooth structures in mouth of vertebrates
Karpecká, Zuzana ; Černý, Robert (advisor) ; Hovořáková, Mária (referee)
Calcified teeth comprise the hardest vertebrate tissues (enamel and dentine) and they undoubtedly represent a key evolutionary advantage for their users. Nevertheless, teeth have been lost many times and they were often replaced by keratinised structures, such as rhamphoteca of birds or of turtle beaks, or labial tooth structures and scratching laminae of many aquatic vertebrates. This thesis is intended to analyse levels of similarities among keratinised teeth and structures of three phylogenetically distinct lineages of amniotes and to compare them to morphogenesis of true teeth. Detailed developmental and structural characteristics of oral apparatus possessing keratinous teeth of lampreys, Loricarid cathfishes and frog tadpoles were identified and distinguished. Keratinous structures of cathfishes include only horny projections from single cell surface (unculi), whereas in frog tadpoles both horny jaw sheet and unicellular labial teeth composed by cell columns were found; the lamprey oral apparatus consists of multicellular teeth and laminae instead. Disparate phenotypes of these keratinous structures can, however, developmentally derive from a general process of keratinization: morphological disparities arise by distinct gradual accretion of keratinous layers and collumns during development. My...
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Identification and characterization of main genetic components involved in phototransduction and vision of the cubozoan jellyfish Tripedalia cystophora
Liegertová, Michaela ; Kozmík, Zbyněk (advisor) ; Černý, Robert (referee) ; Kostrouch, Zdeněk (referee)
(English) Many of the metazoan phyla sense light by an opsin-based photopigment present in a photosensitive receptor cell (photoreceptor), with Cnidaria being arguably the earliest branching phylum containing a well-developed and complex visual system (advanced eyes morphologically similar to those of vertebrate). The evolutionary history of phototransduction and visual components (ranging from light-sensing opsins to structural genes of the lenses) is a long standing question. In this work, we decided to address this issue by applying a comprehensive multidisciplinary approach combining modern molecular biology methods with bioinformatics. Comprehensive genome-wide inspection of a cubozoan jellyfish Tripedalia cystophora, was complemented with gene expression analyses, together with functional (cell culture based assays) and behavioural (pharmacogenetics) testing. First, genome analysis uncovered the presence of a surprisingly large number of opsin genes with distinct tissue- and stage-specific expression. Our extensive phylogenetic analysis classified cubozoan opsins as a sister group to c-type opsins and documented a lineage-specific expansion of opsin gene repertoire. Functional tests in cell cultures provided evidence for the use of Gs-cAMP signalling pathway only in a small subset of opsins,...
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