Fig 1.
Panel A: Schema of frontal sections for morphometric analysis of the middle cranial base. The parameters are shown in the schema. Panel B: A schematic illustration of discectomy. The measurement point of the condylar neck as 1.3 mm inferior to the top of the condylar head. The distance between the condylar neck and the temporalis muscle (yellow arrow). Panels C and D: The mean gestation in C57BL6J and BALB/cA mice was 18.5 days. Panel E: Crown-rump length (CRL) at E12.5, E15.5, and P0. There is no significant difference between the two strains in this respect (Table 1).
Table 1.
Crown-rump length of mice (mean ± SD).
Fig 2.
Comparative anatomy of two mice strains at E15 and P0.
Panels A and D show the superior view of the middle cranial base, and the lower side of the figures correspond to the anterior side of the head. Panels B and E show the anterior view of the middle cranial base. Panels C and F are frontal sections. Panels G-L and P-U show high magnification views, including the inferior part of the hypophyseal cartilage (4) and tensor veli palatini (T). Morphological differences are apparent in the middle cranial base of the two mouse strains at E15.5 and P0 (panels A-L, P-U). The inferior part of the hypophyseal cartilage (4) has a small spine that is longer in BALB/cA mice than that in C57BL6J (panels G, J, M, P, S, and V). The anterior part of the tensor veli palatini (T) in BALB/cA mice is smaller than that in C57BL6J (panels H, K, N, Q, T, and V).1. Anterior part of the hypophyseal cartilage; 2, 3. ala temporalis cartilage; 4. Inferior part of the hypophyseal cartilage. M, masseter; MA, medial pterygoid; L, lateral ptergoid; T, tensor veli palatine; TG, trigeminal ganglion; asterisk. newly formed muscle. Scale bar = 500 μm (panels C, F), 100 μm (panels H, I, K, L, Q, R, T, U).
Fig 3.
Comparative anatomy of two mice strains at P10.
All panels show high magnification views including the inferior part of the hypophyseal cartilage (S) and the tensor veli palatini (T). Panels B and E (C and F) show the anterior (posterior) part of the TVP. The TVP angle between the line connecting the most inferior point with the superomedial point and a horizontal line are different between the C57BL6J mice (74.3° ± 3.0°) and BALB/cA mice (105.2° ± 5.2°) (panels A, B, D, E, and G; arrow heads). The shapes of the inferior spine (S) show differences (panels B, E, and H). Although the cross-sectional areas (CSAs) of the anterior TVPs show no differences (panels B, E, and H), the CSAs of the posterior TVPs differed significantly (panel C, F, and H).M. medial pterygoid; MP. medial pterygoid process; S. inferior spine of the hypophyseal cartilage; T. tensor veli palatini, asterisk. newly formed muscle. Scale bar = 100 μm.
Fig 4.
Comparable primordial muscles in C57BL6J and BALB/cA mice.
Panels A, B, E, F, I, J show the frontal sections at E12.5. Panels C and D (G and H, K and L) show high magnification view of panels A and B (E and F, I and J). Yellow dots indicate anlage of the TVP (panels C, D, G, H, K, and L). Panels A, B, E, F, I, J (C, D, G, H, K, and L) show same magnification level. The TVP first appears medial to the medial pterygoid (M) at E12.5 (panels A, B, E, F, I, and J). The desmin-positive TVP (FITC) is located lateral to the Sox9-positive inferior spine (S) (Rhodamine) (panels A, B, E, F, I, J). The anterior TVP in the C57BL6J mice had a larger CSA than that in the BALB/cA mice (P < 0.05) (panel M). There were no differences in the primordial muscle size between the C57BL6J and BALB/cA mice in the middle (P = 0.79) or posterior (P = 0.24) parts of the TVP (panels N and O). L. lateral pterygoid; M. medial pterygoid; MA. masseter; S. inferior spine of the hypophyseal cartilage; T. tensor veli palatini; Scale bar = 100 μm.
Fig 5.
Development and growth of the TVP and age changes.
Panel A (C) shows the cross sections of the anterior (posterior) TVPs form Figs 2–4. Panel B and D show the growth curve of the TVP. (Anterior part) The growth curve of the anterior TVP in C57BL6J mice is different from that in BALB/cA (panel B). (Posterior part) The posterior TVPs showed almost the same growth curve in the two strains between E12.5 and P10 (panel D). Scale bar = 100 μm.
Fig 6.
Morphological association between the muscle and bone in the C57BL6J, BALB/cA, and ICR mice.
There are morphological correlations between the anterior TVP and the SP at E15 and P0 (R = 0.719, p = 0.008; panel A). However, there are not correlations between the TVP angle and the SP at P10 (R = 0.357, p = 0.254; panel B).
Fig 7.
Impact of bone deformation on muscle shape.
CT images show the top of the condylar head (panels A and D). Panels B and E show the frontal sections. Panels C and F show high magnification view of panels B and E. At 70 days after discectomy, deformation of the mandibular condyle is evident in the temporomandibular joints (panels A, D, and G). The shape of the temporalis muscle (T) has changed after discectomy (panels B, C, E, and F). The muscle on the discectomy side is not only in contact with the condylar head but is also in contact with the condylar neck (panels F and H; oval). The muscle on the non-surgery side is separated from the condylar neck (panels C and H; oval). Scale bar: 500 μm (panels A-F).