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The Broad Role of Nkx3.2 in the Development of the Zebrafish Axial Skeleton
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Organismal Biology, Evolution and Developmental Biology. (evolution and development)
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Organismal Biology, Evolution and Developmental Biology. (evolution and development)ORCID iD: 0000-0003-1815-7818
Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computerized Image Analysis and Human-Computer Interaction. Uppsala University, Science for Life Laboratory, SciLifeLab. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Visual Information and Interaction.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Applied Material Science.ORCID iD: 0000-0003-2709-9541
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

The transcription factor Nkx3.2 (Bapx1) is an important chondrocyte maturation inhibitor. Previous Nkx3.2 knock-down and overexpression studies in non-mammalian gnathostomes have focused on its role in primary jaw joint development, while little is known about the function of this gene in broader skeletal development. We generated CRISPR/Cas9 knockout of nkx3.2 in zebrafish and applied a range of techniques to characterize skeletal phenotypes at developmental stages from larva to adult, revealing fusions in bones of the occiput, the loss or deformation of bony elements derived from basiventral cartilages of the vertebrae, and an increased length of the proximal radials of the dorsal and anal fins. These phenotypes are reminiscent of Nkx3.2 knockout phenotypes in mammals, suggesting that the function of this gene in axial skeletal development is ancestral to osteichthyans. Our results highlight the broad role of nkx3.2 in zebrafish skeletal development and its context-specific functions in different skeletal elements.

Keywords [en]
nkx3.2, bapx1, zebrafish, jaw joint, axial skeleton, occipital, basiventral cartilage, fin radials, CRISPR/Cas9 mutant
National Category
Developmental Biology
Research subject
Biology with specialization in Evolutionary Organismal Biology
Identifiers
URN: urn:nbn:se:uu:diva-429682DOI: 10.1101/2020.12.30.424496OAI: oai:DiVA.org:uu-429682DiVA, id: diva2:1513804
Available from: 2021-01-01 Created: 2021-01-01 Last updated: 2023-01-09Bibliographically approved
In thesis
1. The role of Nkx3.2 and Gdf5 during zebrafish skeletal development
Open this publication in new window or tab >>The role of Nkx3.2 and Gdf5 during zebrafish skeletal development
2021 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The vertebrate skeleton is composed of bony and cartilaginous structures that are developed under the control of numerous genetic networks. The transcription factor Nkx3.2 and the signaling molecule Gdf5 play a fundamental role during joint development and chondrogenesis, a process whereby mesenchyme cells form precartilaginous condensations followed by chondrocyte differentiation. Mutations in these genes can lead to some rare human skeletal diseases and are furthermore thought to play a role during osteoarthritis, whereby the articular cartilage in synovial joints degrades. Both genes are fairly well studied in amniotes, but their full function and regulation are not completely understood. This thesis focuses on further characterization of Nkx3.2 and Gdf5 function, by using the zebrafish Danio rerio, a small vertebrate, as a model organism.

We generated a CRISPR/Cas9 nkx3.2 mutant zebrafish line and detected broad phenotypes in the axial skeleton. Nkx3.2 deficiency in knockout zebrafish confirms previously reported jaw joint loss, but also revealed new phenotypes in the occipital region, the Weberian apparatus, the vertebrae and some fins.

By identifying a cis-regulatory element of nkx3.2 in zebrafish, we were able to generate a transgenic zebrafish line labelling the developing jaw joint and jaw joint progenitor cells. This line enables detailed documentation of jaw joint development and paves the way for a better understanding of joint development. Knockout of this nkx3.2 enhancer sequence in zebrafish did not result in any phenotypic differences, indicating a redundant function. Besides the identification of a nkx3.2 enhancer in the zebrafish genome, we identified homologous nkx3.2 enhancer sequences in the genomes of multiple gnathostome species and found that they display a high degree of functional conservation.

To study the role of Gdf5, we generated a CRISPR/Cas9 gdf5 mutant line. gdf5 mutant zebrafish displayed abnormalities in endoskeletal elements of all median and the pectoral fins showing truncation of median fin endoskeletal elements and partial absence of pectoral fin radials.

Finally, we developed an optical projection tomography (OPT) based automated workflow to generate 3D reconstructions of in situ and skeletal-stained zebrafish embryos and larvae. The acquired imaging data of skeletal-stained larval zebrafish was subsequently used to quantify phenotypic differences between mutant and wild-type zebrafish groups. This technique allows for the identification of even subtle phenotypic differences at early stages of development.

To conclude, the work presented in this thesis provides further understanding of the role of Nkx3.2 and Gdf5 during skeletogenesis in zebrafish and contributes to the development of zebrafish imaging techniques. 

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2021. p. 53
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 2002
Keywords
Nkx3.2, Gdf5, zebrafish, jaw joint, joints, axial skeleton, appendicular skeleton, fin, enhancer conservation, CRISPR/Cas9, OPT
National Category
Biological Sciences
Identifiers
urn:nbn:se:uu:diva-430399 (URN)978-91-513-1110-4 (ISBN)
Public defence
2021-02-26, Ekmansalen, Evolutionsbiologiskt centrum, Norbyvägen 16, Uppsala, 14:15 (English)
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Supervisors
Available from: 2021-02-05 Created: 2021-01-10 Last updated: 2021-03-04

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Waldmann, LauraLeyhr, JakeZhang, HanqingÖhman, CarolineAllalou, AminHaitina, Tatjana

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Evolution and Developmental BiologyComputerized Image Analysis and Human-Computer InteractionScience for Life Laboratory, SciLifeLabDivision of Visual Information and InteractionApplied Materials SciencesApplied Material Science
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