Development of Soft Palatal Musculature Characterized by the Uvula Muscle of Miniature Pig

Introduction: Surgical reconstruction is recommended for cleft palate patients. However, improper muscle reconstruction can cause scarring and velopharyngeal insufficiency. Understanding the developmental patterns of soft palatal musculature is crucial for improving treatments. Although mice are commonly used to investigate soft palate development, the uvula deficiency in mice limits their applicability. This study aims to compare the developmental characteristics of soft palate muscles in miniature pigs and mice at various stages to better understand the patterns in large mammals. Methods: Specimens of soft palate were collected from human embryos, miniature pigs and mice at different stages. Furthermore, comprehensive gross observations, Hematoxylin and Eosin staining, and immunohistochemical analyses for myosin heavy chain and Hypermethylated cancer 1 (Hic1) were conducted on multiple dissected sections. Results: Mature soft palatal musculature exhibited anatomical and histological similarities across the three species. Notably, miniature pigs exhibited the uvula structure and uvula muscle development comparable to humans. Embryonic day 40 (E40, equivalent to human embryonic week 11, E11w) represented the early developmental stage of the uvula muscle, characterized by scattered muscle cells not yet coalescing into multinucleated fibres. By E45 (aligned with human E12w), the muscle bundles reached maturity, exhibiting two oriented fibre bundles flanking the midline. Levator veli palatini muscle and palatopharyngeus of miniature pigs exhibited a distinct course pattern due to the presence of the uvula muscle. Hic1+ perimysial cells were observed at the extending edge of the developing palatopharyngeus of miniature pigs, indicating a potential guiding role in the migration of myogenic cells. Conclusion: Characterized by the uvula muscle, the spatiotemporal dynamic process of soft palatal musculature of miniature pigs was revealed. Miniature pigs exhibit a similar structure of the uvula muscle to that of humans and therefore serve as a promising model for researching soft palatal musculature development of large mammals in the future.