dc.description.abstract |
The lymphatic vasculature is essential for maintaining tissue fluid homeostasis, immune
surveillance, and lipid absorption. Aberrant lymphatic vessel growth has been implicated in
cancer metastasis and graft rejection, while insufficient lymphatic development results in fluid
buildup known as lymphoedema. The correct patterning and development of lymphatic vessels
relies on lymphatic guidance structures and molecular cues; however, these are not well
defined. Zebrafish are influential in studying lymphatic development due to conserved
molecular mechanisms and the ability to directly observe vessel growth in live embryos. This
study focuses on a zebrafish lymphatic vessel within the inner ear (otic vesicle) termed the
otolithic lymphatic vessel (OLV). Previously, two mutants with abnormal OLV development
were identified from a forward genetic screen. The first mutant was mapped to loss-of-function
mutations in patched-1 (ptch1), a negative regulator of Hedgehog signalling. The ptch1 mutant
has a hyperbranched OLV and subtle otic vesicle defects. The second, unmapped mutant,
termed olvless, has reduced OLV growth, pigmentation, and severe otic vesicle defects. This
study aimed to identify the candidate mutation in olvless and validate the role of the disrupted
genes in OLV development. Morpholino-mediated knockdown of ptch1 phenocopied the OLV
and otic vesicle defects observed in the ptch1 mutant. Furthermore, the ptch1 mutant could be
rescued with cyclopamine, an inhibitor of Hedgehog-signalling. Additionally, overexpression
of the Hedgehog ligand sonic hedgehog, disrupted otic vesicle and OLV development.
Together this data confirmed that ptch1 is required for OLV development. Whole genome
sequencing mapped the olvless mutant to a likely null allele of SRY-box transcription factor 10
(sox10), a gene with known roles in both pigmentation and otic vesicle development.
Morpholino knockdown of sox10 impaired OLV growth, otic vesicle development and
pigmentation, suggesting that the olvless phenotype is caused by a loss of sox10. However,
wild type sox10 mRNA did not rescue the olvless mutant. In conclusion, this study validated
the ptch1 mutant and indicated that lack of sox10 function may cause the olvless phenotype.
Future studies will further validate the olvless mutant, determine how ptch1 and olvless are
involved in OLV development and use the mutants to uncover novel guidance mechanisms. |
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