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Recently, the research team led by Prof. LI Jun from the Institute of Oceanology of the Chinese Academy of Sciences (IOCAS) reported the latest research findings on the developmental pattern and continuous replacement regulation mechanism of the beak-like teeth in the important cultured fish, spotted knifejaw (Oplegnathus punctatus). The beak-like healing teeth are a special type of jaw teeth that can regrow in O. punctatus after wear and tear.

The study was published in the international academic journal International Journal of Biological Macromolecules (IF=8.2, Top Journal) on Aug. 9. The research findings also have been selected for the "2023 International Research Awards on New Science Inventions".

The O. punctatus is an economically significant marine aquaculture species newly developed in recent years in China (priced at 240 RMB /kg). It possesses a distinct beak-like tooth phenotype, allowing it to feed on hard-shelled foods such as oysters and sea urchins. The research team has pioneered the artificial breeding technology of the O. punctatus in China. They have established a large-scale seedling production technology (1 million tails/year) and a land-sea relay aquaculture model that integrates factory-scale closed-loop water culture with cage culture, greatly expanding the scale of O. punctatus aquaculture.

Through preliminary breeding observations, researchers found that the jaw teeth of O. punctatus are fused with the upper and lower jaw bones, forming a robust parrot-like beak-shaped dental structure, with gaps between teeth filled with calcified material. How are these unique beak-like teeth arranged and fused? Is the developmental pattern of beak-like teeth similar to fish species with teeth that grow separately? What are the regulatory mechanisms behind their development? Could this phenomenon affect the feeding habits and digestive system function of O. punctatus? To explore the formation mechanism of the beak-like tooth in O. punctatus, guide precise feeding in factory-scale aquaculture, and develop effective attractants, researchers conducted this study.

This study comprehensively employed techniques such as morphological anatomy, scanning electron microscopy, and microCT 3D scanning imaging to systematically investigate the developmental characteristics of the healing-type beak-like teeth in O. punctatus. For the first time, a "nested" arrangement pattern of healing teeth in O. punctatus was discovered, with a dental formula (4, 15-16, 10-1). The key developmental time points of the beak-like teeth were determined (28 dph, initiation of primary tooth germination; 40 dph, appearance of replacement teeth and start of dental fusion; 45 dph, commencement of ossification; 50 dph, completion of healing).

Furthermore, through integrated analyses involving genomics and transcriptomics, among other disciplines, a total of 11 key genes (bmp2, bmpr2, smad1, wnt5a, msx, axin2, fgfr1a, fgfr2, pitx2, ptch1, cyp27a1) closely associated with the development of O. punctatus' beak-like teeth were identified, along with crucial regulatory pathways (Wnt, BMP, FGF, SHH). These genes and pathways collaboratively regulate the interaction between dental epithelium and mesenchyme during the pre-fusion, fusion, and post-fusion stages of O. punctatus' dental fusion, promoting sustained proliferation and differentiation of enamel-forming cells and odontoblasts.

Additionally, the study found that the cyp27a1 gene, closely associated with vitamin D metabolism and calcium accumulation, is localized in the upper jawbone and base of the beak-like teeth of O. punctatus. During the rapid healing phase of the teeth, it accelerates its expression, promoting vitamin D metabolism, thereby regulating the differentiation of cells within the dental bud, as well as the mineralization of enamel and dentin in O. punctatus' teeth. This provides a calcium foundation for the healing and development of beak-like teeth.

"The study first reveals a 'nested' arrangement pattern of beak-like healing teeth in O. punctatus, while determining the developmental timing of beak-like teeth and key time points of dental mineralization," said MA Yuting, first author of the study.

"The study further unveils the regulatory mechanisms of beak-like healing teeth development," said Dr. XIAO Yongshuang, corresponding author of the study. "The research findings on the beak-like healing teeth of O. punctatus provide a new model for a deeper understanding of fish dental development and adaptive evolution."

"This research enriches the theoretical and regulatory understanding of fish dental development and offers insights into the adaptive evolution and regenerative capabilities of biological teeth," added Prof. LI.

This work was supported by grants from the National Key Research and Development Program, National Natural Science Foundation of China, Key Deployment Projects of Center for Ocean Mega-Science, Chinese Academy of Sciences, and CARs for Marine Fish Culture Industry.

Fig. 1 External morphology of O. punctatus' beak-like tooth and feeding habits.

Fig. 2 3D reconstruction of beak-like healing tooth in O. punctatus based on micro-CT scanning.

Fig. 3 Regulatory mechanism of development and formation of healing-type tooth in O. punctatus.

Yuting Ma, Yongshuang Xiao*, Zhizhong Xiao, Jun Li*. (2023). Morphological characteristics of beak-like tooth in spotted knifejaw (Oplegnathus punctatus) and mechanisms of dental development regulation by the Wnt, BMP, FGF and SHH signalling pathways. International Journal of Biological Macromolecules.

(Text by XIAO Yongshuang)

Media Contact:

ZHANG Yiyi

Institute of Oceanology

E-mail: zhangyiyi@qdio.ac.cn 

(Editor: ZHANG Yiyi)