According to Shenzhen BGI Genomics Co., Ltd. (BGI), on March 29, in collaboration with the Qingdao BGI Research Institute of Oceanography, researchers from China's Ocean University utilized BGI's independently developed spatiotemporal transcriptomics technology, Stereo-seq, combined with single-cell transcriptome sequencing, to map high-quality spatial resolution single-cell atlas of the internal columnar organ of the tunicate. This comprehensive mapping decoded the cell types and potential functional features of the pharyngeal organs of marine animals, providing crucial information for uncovering the potential evolutionary origins of vertebrate pharyngeal organs. The related research findings were published in Science Advances.
Primitive chordates possess a unique pharyngeal organ called the internal column. In cephalochordates and tunicates, the internal columnar organ is located on the ventral side of the adult, while in vertebrates, the internal columnar organ of the larval stage of the larvacean tadpole exists only during development and metamorphosis to form the thyroid follicles.
Previous studies commonly believed that the internal columnar organ of primitive chordates serves as an auxiliary organ for animal filter feeding and is a precursor organ in the evolution of vertebrate thyroid organs. Recent research has found that the endoderm of the pharyngeal region in deuterostomes plays a central role in pharyngeal organ development. However, whether there is continuity in the evolutionary development of pharyngeal organs between vertebrates and primitive chordates has not been thoroughly studied.
In this study, the team integrated two complementary technologies, spatial and single-cell transcriptomics, to construct the first high-quality spatial resolution single-cell atlas of the internal columnar organ of the tunicate. By combining morphological and gene expression characteristics, they further elucidated the diversity of cell populations and functions in the internal columnar organ.
Within the tunicate's internal columnar organ, the team discovered a cell population resembling a lymphoid-like region and identified a population of hair cell-like cells located in the dense tissue area of the internal column, which exhibited high similarity in gene expression characteristics to vertebrate inner ear hair cells. Simultaneously, the team revealed the coexistence characteristics of cells in different mature states within the internal column thyroid-like region.
Furthermore, researchers compared the single-cell atlas of the tunicate with relevant single-cell transcriptome data of vertebrates. The results showed that as a chordate, the tunicate's internal column shares gene expression similarities with various vertebrate pharyngeal organs.
This study marks the first application of cutting-edge spatial transcriptomics technology in the field of evolutionary developmental biology of marine animals, enabling the high-throughput identification of cell population compositions of evolutionarily unique pharyngeal organs. It provides a good methodological reference for understanding the tissues and organs of various important evolutionary marine organisms and also offers high-quality data support for understanding the origin of pharyngeal organs.
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