NDLI: Pitx controls amphioxus asymmetric morphogenesis by promoting left-side development and repressing right-side formation

Content Provider	Springer Nature : BioMed Central
Author	Xing, Chaofan Pan, Rongrong Hu, Guangwei Liu, Xian Wang, Yiquan Li, Guang
Abstract	Background Left-right (LR) asymmetry is an essential feature of bilateral animals. Studies in vertebrates show that LR asymmetry formation comprises three major steps: symmetry breaking, asymmetric gene expression, and LR morphogenesis. Although much progress has been made in the first two events, mechanisms underlying asymmetric morphogenesis remain largely unknown due to the complex developmental processes deployed by vertebrate organs. Results We here addressed this question by studying Pitx gene function in the basal chordate amphioxus whose asymmetric organogenesis, unlike that in vertebrates, occurs essentially in situ and does not rely on cell migration. Pitx null mutation in amphioxus causes loss of all left-sided organs and incomplete ectopic formation of all right-sided organs on the left side, whereas Pitx partial loss-of-function leads to milder phenotypes with only some LR organs lost or ectopically formed. At the N1 to N3 stages, Pitx expression is gradually expanded from the dorsal anterior domain to surrounding regions. This leads to activation of genes like Lhx3 and/or Prop1 and Pit, which are essential for left-side organs, and downregulation of genes like Hex and/or Nkx2.1 and FoxE4, which are required for right-side organs to form ectopically on the left side. In Pitx mutants, the left-side expressed genes are not activated, while the right-side genes fail to decrease expression on the left side. In contrast, in embryos overexpressing Pitx genes, the left-side genes are induced ectopically on the right side, and the right-side genes are inhibited. Several Pitx binding sites are identified in the upstream sequences of the left-side and right-side genes which are essential for activation of the former and repression of the latter by Pitx. Conclusions Our results demonstrate that (1) Pitx is a major (although not the only) determinant of asymmetric morphogenesis in amphioxus, (2) the development of different LR organs have distinct requirements for Pitx activity, and (3) Pitx controls amphioxus LR morphogenesis probably through inducing left-side organs and inhibiting right-side organs directly. These findings show much more dependence of LR organogenesis on Pitx in amphioxus than in vertebrates. They also provide insight into the molecular developmental mechanism of some vertebrate LR organs like the lungs and atria, since they show a right-isomerism phenotype in Pitx2 knockout mice like right-sided organs in Pitx mutant amphioxus. Our results also explain why some organs like the adenohypophysis are asymmetrically located in amphioxus but symmetrically positioned in vertebrates.
Related Links	https://bmcbiol.biomedcentral.com/counter/pdf/10.1186/s12915-021-01095-0.pdf
Ending Page	20
Page Count	20
Starting Page	1
File Format	HTM / HTML
ISSN	17417007
DOI	10.1186/s12915-021-01095-0
Journal	BMC Biology
Issue Number	1
Volume Number	19
Language	English
Publisher	BioMed Central
Publisher Date	2021-08-20
Access Restriction	Open
Subject Keyword	Life Sciences
Content Type	Text
Resource Type	Article
Subject	Ecology, Evolution, Behavior and Systematics Structural Biology Biochemistry, Genetics and Molecular Biology Plant Science Biotechnology Physiology Agricultural and Biological Sciences Cell Biology Developmental Biology
Journal Impact Factor	4.4/2023
5-Year Journal Impact Factor	5.4/2023

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