Teleost fish comprise a diverse group, among which seahorses exhibit a unique morphology. The characteristic spines and brood pouches found in seahorses contain distinct epithelial cells—called flame cone cells—covered in a mucous cap.
However, these cells were not found in the barbed pipefish Urocampus nanus or the seaweed pipefish Syngnathus schlegeli, a close relative of the seahorse, belonging to the Syngnathidae lineage. While research has hypothesized the function of flame cone cells, their evolutionary origins remain a mystery.
Now, a group of scientists led by Assoc. Prof. Mari Kawaguchi and Prof. Shigeki Yasumasu from the Department of Materials and Life Sciences at Sophia University has identified an “orphan” gene—a gene with no known homologous sequence in other species or lineages—in the seahorse Hippocampus abdominalis. They believe that this gene, called the proline-glycine rich (pgrich) gene, is involved in the development of flame cone cells in the brood pouch. Their findings are published in the journal Cell and Tissue Researchon May 25, 2023.
In expanding the reason behind the continuation of this investigation, Dr. Kawaguchi said, “Seahorses have interesting morphology, and males carry embryos in their brood pouches.
The team first matched histological staining with electron microscopy to confirm that flame cone cells were present in the outer epithelium of the brood pouch of H. abdominalis, but not in U. nanus or S. schlegeli. Next, in situ hybridization and immunohistochemical methods revealed that the pgrich gene is expressed and its protein is localized in flame cone cells on the surface of the body.
The amino acid sequences of the protein product of the pgrich gene, PGrich show partial similarity to the translated amino acid sequence taken from the antisense strand–the noncoding part–of the larger pipefish elastin gene. Through sequence analyses, the team discovered several transposable elements around the pgrich gene. They suggest that the pgrich gene may have evolved from the elastin gene in pipefish and subsequently acquired a new function in the formation of flame cone cells, unique to seahorses.
As the team continues to piece together the evolution of the seahorse brood pouch, Dr. Kawaguchi concluded, “The evolutionary history of the pgrich gene may provide clues as to how the orphan gene came about and how the brood pouch developed in this generation. Seahorses are popular in home aquariums, and understanding these phenomena can contribute to the appeal of these fish.”
More information:
Mari Kawaguchi et al, Orphan gene expressed in flame cone cells uniquely found in seahorse epithelium, Cell and Tissue Research (2023). DOI: 10.1007/s00441-023-03779-1
Provided by Sophia University
Citation: Study identifies gene conferring novel function in seahorse brood pouch (2023, July 24) retrieved on July 25, 2023 from https://phys.org/news/2023-07-gene-conferring-function-seahorse-brood.html
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