Journal
DEVELOPMENTAL BIOLOGY
Volume 477, Issue -, Pages 219-231Publisher
ACADEMIC PRESS INC ELSEVIER SCIENCE
DOI: 10.1016/j.ydbio.2021.05.021
Keywords
Chordate; Larvacean; Endostyle; Thyroid; Gene knockdown; Evolution
Categories
Funding
- JSPS KAKENHI [20K07221]
- JSPS
- MEXT Japan [24870019, 26840079, 18K06256, 20H05946]
- Inamori Foundation
- Kato Memorial Research Foundation
- Sumitomo Foundation
- Japan Foundation for Applied Enzymology
- Grants-in-Aid for Scientific Research [20H05946, 20K07221, 18K06256, 24870019, 26840079] Funding Source: KAKEN
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The endostyle in basal chordates plays a crucial role in internal filter feeding and is homologous to the follicular thyroid in vertebrates. Genes like Nkx2-1 and FoxE are essential in establishing regionalization within the organ, with Nkx2-1 regulating glandular region and Nkx2-1/FoxE regulating thyroid-equivalent region. These findings highlight the importance of DV axial regionalization in organizing glandular and thyroid-related traits along the DV axis in the pharynx.
The endostyle is a ventral pharyngeal organ used for internal filter feeding of basal chordates and is considered homologous to the follicular thyroid of vertebrates. It contains mucus-producing (glandular) and thyroid-equivalent regions organized along the dorsoventral (DV) axis. Although thyroid-related genes (Nkx2-1, FoxE, and thyroid peroxidase (TPO)) are known to be expressed in the endostyle, their roles in establishing regionalization within the organ have not been demonstrated. We report that Nkx2-1 and FoxE are essential for establishing DV axial identity in the endostyle of Oikopleura dioica. Genome and expression analyses showed von Willebrand factor-like (vWFL) and TPO/dual oxidase (Duox)/Nkx2-1/FoxE as orthologs of glandular and thyroid-related genes, respectively. Knockdown experiments showed that Nkx2-1 is necessary for the expression of glandular and thyroid-related genes, whereas FoxE is necessary only for thyroid-related genes. Moreover, Nkx2-1 expression is necessary for FoxE expression in larvae during organogenesis. The results demonstrate the essential roles of Nkx2-1 and FoxE in establishing regionalization in the endostyle, including (1) the Nkx2-1-dependent glandular region, and (2) the Nkx2-1/FoxE-dependent thyroid-equivalent region. DV axial regionalization may be responsible for organizing glandular and thyroid-equivalent traits of the pharynx along the DV axis.
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