Comparative Histoanatomy of the Gorilla Vocal Fold.

OBJECTIVES: The layered structure of the human vocal fold is unique to humans and absent in animals. Previous studies suggested that the maculae flavae at the anterior and posterior ends of the human membranous vocal fold are involved in the formation of this layered structure and that they serve as a stem cell niche nurturing tissue stem cells. This study aimed to examine the comparative histoanatomy of the gorilla vocal fold. METHODS: Two larynges from Western gorillas (male) were examined using light (including immunohistochemistry) and electron microscopy. RESULTS: The gorilla's vocal fold lacked a vocal ligament and Reinke's space and did not exhibit a layered structure; however, similar to humans, it possessed anterior and posterior maculae flavae composed of cells and extracellular matrix aggregates (collagen fibers, elastic fibers, reticular fibers, hyaluronan), with cellular heterogeneity observed. Cells in the gorilla macula flavae expressed vimentin, an intermediate filament of mesoderm-derived mesenchymal cells, but not desmin (mesoderm-derived muscle cells) or cytokeratin (ectoderm-derived epithelial cells). SOX17, a marker of endoderm-derived cells, was not expressed. These findings suggest that cells in the gorilla macula flavae lack the triploblastic multipotency observed in humans. CONCLUSIONS: Although the extracellular matrices of the gorilla maculae flavae resemble that of humans and cellular heterogeneity was confirmed, the cells appear not to be derived from all three germ layers and lack multipotency. Thus, while gorillas-closely related to humans phylogenetically-possess maculae flavae at the anterior and posterior ends of membranous vocal folds, these cells demonstrate limited stemness compared to humans.