Objective To investigate the mechanisms underlying regional heterogeneity in the elevating patterns of palatal shelf during mammalian craniofacial development.

Methods Using a mouse model of embryonic palatal development, we acquired coronal multi-plane slices of the palatal shelves before elevation (early E13.5), during elevation (late E13.5), and after elevation (early E14.5). Hematoxylin and eosin (HE) staining was performed to compare the morphological changes and spatial correlations between the palate and tongue. Immunofluorescence staining of myosin heavy chain 1 (MYH1), a marker found in slow muscle fibers and responsible for muscle contraction and movement, was performed to observe the tongue muscle development characteristics at different stages. We also observed changes in the palatal shelf elevating patterns at early E13.5 in the absence of the tongue through HE-stained in vitro palate organ culture. Further immunofluorescence staining of tenascin-C, an extracellular matrix protein, was performed to evaluate the effect of the tongue on the elevating pattern of the palatal shelf along the anterior-posterior axis.

Results HE staining results of the coronal multi-plane slices showed that during the elevation period, from the posterior toward anterior, the coronal height of the tongue decreased, lateral inclination and flattening increased, but the sagittal length of the tongue increased. The elevating pattern of the palatal shelf changed from slow remodeling to rapid flipping, and MYH1 was abundantly expressed in both the internal and external muscle bundles of the tongue during this period. According to findings from in vitro cultivation of palatal organs, the posterior part of the palatal shelf elevated without forming new lateral lingual protrusions in the absence of the tongue. The regional expression pattern of tenascin-C was consistent with that observed before elevation. The posterior palate exhibited an elevation pattern similar to that of the anterior region.

Conclusion The tongue may play a crucial role in shaping the posterior morphological remodeling and distinct elevation patterns of the palatal shelf.