Comparison of RNA localization during oogenesis within Acipenser ruthenus and Xenopus laevis

The oocyte is a unique cell, from which develops a complex organism comprising of germ layers, tissues and organs. In some vertebrate species it is known that the asymmetrical localization of biomolecules within the oocyte is what drives the spatial differentiation of the daughter cells required for embryogenesis. This asymmetry is first established to produce an animal-vegetal (A-V) axis which reflects the future specification of the ectoderm, mesoderm, and endoderm layers. Several pathways for localization of vegetal maternal transcripts have already been described using a few animal models. However, there is limited information about transcripts that are localized to the animal pole, even though there is accumulating evidence indicating its active establishment. Here, we performed comparative TOMO-Seq analysis on two holoblastic cleavage models: Xenopus laevis and Acipenser ruthenus oocytes during oogenesis. We found that there were many transcripts that have a temporal preference for the establishment of localization. In both models, we observed vegetal transcript gradients that were established during either the early or late oogenesis stages and transcripts that started their localization during the early stages but became more pronounced during the later stages. We found that some animal gradients were already established during the early stages, however the majority were formed during the later stages of oogenesis. Some of these temporally localized transcripts were conserved between the models, while others were species specific. Additionally, temporal de novo transcription and also degradation of transcripts within the oocyte were observed, pointing to an active remodeling of the maternal RNA pool

Polyspermie u jeseterů dává vzniknout životaschopným mozaikám

Chapter 1 (General Introduction), Chapter 2 (Polyspermy produces viable haploid/diploid mosaics in sturgeon), Chapter 3 (First evidence of viable progeny from three interspecific parents in sturgeon), Chapter 4 (General discussion, English Summary, Czech Summary, Acknowledgements, List of Publications, Training and Supervision Plan during Study, Curriculum Vitae). The thesis is written in English, contains 71 pages. The results were published in two scientific journals. The actuality of work: The majority of sturgeons are critically endangered and at the same time they are producers of the most expensive food product - black caviar. Presently, sturgeon restoring and conservation are depended on artificial reproduction in hatcheries. However, the way of fertilization is not clear: monospermy, physiological or pathological polyspermy? Moreover, during last decades it was believed that under artificial fertilizations, can appear atypically divided embryos like 3 or 6 cells, which die prior hatching stage or sometimes develop into malformed shape fry with soon death due to deformations. Atypically divided embryos, their origin and the reason of appearance was not studied well. Investigation of fertilization aspects in economically significant and endangered fishes is extremely important. Requires attention and studies a hybridization abilities in sturgeons, as hybridization plays an important role in sturgeon evolution. The purposes of the study were: to find a way of fertilization in sturgeons (monospermy/polyspermy); to understand the reasons of atypical division of cells during artificial breeding; to investigate if atypically divided embryos are able to develop beyond the feeding stage, to analyze their ploidy; to classify the types of atypically divided embryos and their frequency; to investigate sturgeon hybridization plasticity, to produce first interspecific hybrid from three parents. Novelty and scientific originality: In this research two ways of fertilization were found in sturgeons: physiological polyspermy (fertilization typical for caudate amphibians) and karyogamy with an additional plasmogamy, which results in production of viable multiple-sperm mosaics with atypical division on the 2-4 cell stage and mosaic ploidy). Conducted research is important for avoiding of negative effect on sturgeon propagation programs, due to uncontrolled fertilization and releasing of multiple-sperm mosaics into the wild, which can cause appearance of sturgeons with irregular ploidy and induce a detrimental genetic effects on sturgeon populations. However, multiple-sperm mosaics, which were discovered in this study and their easy way of production can be used as a beneficial tool for a rapid manufacture of isogenic strains in sturgeons. In this study was shown that applying of just one part of body (blood, tail, etc.) for ploidy determination is not giving a full view of a real ploidy of the studied individual. A huge ability for hybridization and plasticity were described in sturgeon. It was possible to generate a first viable hybrids from three interspecific parents

Table1_Comparison of RNA localization during oogenesis within Acipenser ruthenus and Xenopus laevis.xlsx

The oocyte is a unique cell, from which develops a complex organism comprising of germ layers, tissues and organs. In some vertebrate species it is known that the asymmetrical localization of biomolecules within the oocyte is what drives the spatial differentiation of the daughter cells required for embryogenesis. This asymmetry is first established to produce an animal-vegetal (A-V) axis which reflects the future specification of the ectoderm, mesoderm, and endoderm layers. Several pathways for localization of vegetal maternal transcripts have already been described using a few animal models. However, there is limited information about transcripts that are localized to the animal pole, even though there is accumulating evidence indicating its active establishment. Here, we performed comparative TOMO-Seq analysis on two holoblastic cleavage models: Xenopus laevis and Acipenser ruthenus oocytes during oogenesis. We found that there were many transcripts that have a temporal preference for the establishment of localization. In both models, we observed vegetal transcript gradients that were established during either the early or late oogenesis stages and transcripts that started their localization during the early stages but became more pronounced during the later stages. We found that some animal gradients were already established during the early stages, however the majority were formed during the later stages of oogenesis. Some of these temporally localized transcripts were conserved between the models, while others were species specific. Additionally, temporal de novo transcription and also degradation of transcripts within the oocyte were observed, pointing to an active remodeling of the maternal RNA pool.</p

Image1_Comparison of RNA localization during oogenesis within Acipenser ruthenus and Xenopus laevis.pdf

The oocyte is a unique cell, from which develops a complex organism comprising of germ layers, tissues and organs. In some vertebrate species it is known that the asymmetrical localization of biomolecules within the oocyte is what drives the spatial differentiation of the daughter cells required for embryogenesis. This asymmetry is first established to produce an animal-vegetal (A-V) axis which reflects the future specification of the ectoderm, mesoderm, and endoderm layers. Several pathways for localization of vegetal maternal transcripts have already been described using a few animal models. However, there is limited information about transcripts that are localized to the animal pole, even though there is accumulating evidence indicating its active establishment. Here, we performed comparative TOMO-Seq analysis on two holoblastic cleavage models: Xenopus laevis and Acipenser ruthenus oocytes during oogenesis. We found that there were many transcripts that have a temporal preference for the establishment of localization. In both models, we observed vegetal transcript gradients that were established during either the early or late oogenesis stages and transcripts that started their localization during the early stages but became more pronounced during the later stages. We found that some animal gradients were already established during the early stages, however the majority were formed during the later stages of oogenesis. Some of these temporally localized transcripts were conserved between the models, while others were species specific. Additionally, temporal de novo transcription and also degradation of transcripts within the oocyte were observed, pointing to an active remodeling of the maternal RNA pool.</p