The role of the zebrafish tbx5 paralogues during eye, pectoral fin and heart development.
Tbx5 is a transcription factor expressed in the developing eyes, heart and upper limbs. Mutations in human TBX5 cause Holt-Oram syndrome (HOS), a condition characterised by heart and upper limb malformations. In zebrafish, a novel tbx5 gene (tbx5b), which emerged from the teleost specific genome dup...
| Autor: | |
|---|---|
| Formato: | tesis doctoral |
| Estado: | Versión publicada |
| Fecha de publicación: | 2018 |
| País: | España |
| Recursos: | CBUC, CESCA |
| Repositorio: | TDR. Tesis Doctorales en Red |
| OAI Identifier: | oai:www.tdx.cat:10803/650832 |
| Acesso em linha: | http://hdl.handle.net/10803/650832 |
| Access Level: | acceso abierto |
| Palavra-chave: | Peix zebra Pez cebra Zebra danio Morfogènesi Morfogénesis Morphogenesis Ciències Experimentals i Matemàtiques 575 |
| Resumo: | Tbx5 is a transcription factor expressed in the developing eyes, heart and upper limbs. Mutations in human TBX5 cause Holt-Oram syndrome (HOS), a condition characterised by heart and upper limb malformations. In zebrafish, a novel tbx5 gene (tbx5b), which emerged from the teleost specific genome duplication, is co-expressed with its paralogue (tbx5a). To understand tbx5 paralogues function and relationship in the different tissues where they are expressed (i.e. eye, heart and pectoral fin) in zebrafish, downregulation by morpholino oligonucleotides (MO) injection has been performed. The results reveal that tbx5 genes are essential for the development of these organs, where they have different requirements and relationships to ensure proper dorsoventral (DV) retina axis organization, the establishment of cardiac laterality and the induction and sustained outgrowth of the pectoral fin. In the retina, tbx5 genes role is redundant and both paralogues knock-down causes a reduction of the dorsal retina identity, concomitant with an expansion of the ventral retina markers expression, that results in defective DV patterning and subsequent thinner retinotectal projections. In contrast, tbx5a and tbx5b have gene-specific functions during pectoral fin development: tbx5a is required for the initiation of pectoral fin outgrowth, whereas tbx5b is later responsible for the sustained outgrowth of the pectoral fin. In the case of heart morphogenesis, both paralogues cooperate in the same pathway. In addition, our results uncover a novel role for tbx5 paralogues in the establishment of heart asymmetry in zebrafish embryos in both asymmetric events (i.e. cardiac jogging and looping) and an earlier role for tbx5a during the directional migration and of the cardiac precursors in the midline. Further analysis of the role of tbx5a during the establishment of left-right (LR) asymmetry shows that the expression of left-side markers from the Nodal signalling pathway expressed in the lateral plate mesoderm (LPM) is also randomized. Laterality defects during zebrafish development in tbx5a morphant are also found in neural and visceral laterality, suggesting an early role of tbx5a in LR establishment. Strikingly, tbx5a knock-down in the DFCs/KV (dorsal forerunner cells / Kupffer’s vesicle) lineage, the organ responsible for LR asymmetry generation, also results in cardiac jogging randomization. Furthermore, our results show an early tbx5a expression during gastrulation and an altered expression pattern for charon and a reduction on bmp4 expression levels around the KV at 10SS. In addition, a reduction on Bmp signalling levels in tbx5a DFC-specific morphants is detected, which is consistent with the identification of a putative binding site for Tbx5 that is conserved in high vertebrates for bmp2b and bmp4. Finally, the analysis of tbx5a morphants also show that they have a reduced KV. Overall, we propose a model in which tbx5 is required during zebrafish early development to achieve a proper KV size that will ensure a robust directional flow within the KV and Bmp signalling in the KV itself and its surroundings. These signalling cues ensure the correct activation of the Nodal signalling pathway and are subsequently transmitted to the LPM to guide organ primordia to their final position along the LR axis. |
|---|