(A–E) Analysis of Wt and Rab23-/- skulls by µ-CT (A–C) and alizarin red, alcian blue staining (D–E) at E18.5. Rab23-/- skulls show fusion in the parieto-temporal suture (B-a, black arrow), coronal suture (B-a, green arrow and B-b, µ-CT slice, green arrow), frontonasal suture (C-a, arrow) and lambdoid suture (E-a, arrow). Wt sutures were open at this embryonic stage (A–a, A–b) (n = 10 for each age and genotype). fb: frontal bone, pb: parietal bone. Scale bar: 1 mm. (F) The prevalence of suture fusion in Rab23-/- mouse at E18.5 shown in percentage. Only parieto-temporal suture showed bi-lateral suture fusion in all the samples. (n = 10 for sagittal and interfrontal suture, n = 40 for lambdoid suture and n = 20 for other sutures). (G) Skeletal Analysis of the limbs in Rab23-/- mouse show pre-axial polydactyly of the fore limb (FL, 1a, 2a) and pre axial polysyndactyly of the hind limb (HL, 1a, 2a) at E18.5 (n = 10 for each age and genotype. Scale bar: 1.5 mm. (H–K) E18.5 mouse calvaria indicating fb: frontal bone, pb: parietal bone, ipb: interparietal bone and ls: lambdoid suture (H). Analysis of Wt and Rab23-/- calvaria by µ-CT at E18.5 shows Rab23-/- lambdoid sutures form bony protrusions from parietal bones project towards the interparietal bones (J, arrow), or ectopic bony islands in the mid-sutural mesenchyme (K, arrow) (n = 6 for each age and genotype). Scale bar: 500 µm. (L) Measurements of the lambdoid suture shows Rab23-/- lambdoid sutures are narrower as compare to the Wt samples at E18.5 (n = 6 for each age and genotype). Data represented as mean ± SD, paired Student’s t-test was used. Statistical significance was defined as a p-value < 0.05 (*). (M) In vitro calvaria culture system. This system was used to culture Wt and Rab23-/- calvaria containing patent lambdoid sutures at E17.5 and E18.5. (N, O) Represents E18.5 Wt and patent lambdoid suture containing Rab23-/- calvaria culture in vitro for 3 days in presence of alizarin red. Rab23-/- lambdoid suture shows fusion at day 3 (N, alizarin red bone staining, O, µ-CT images), whereas Wt controls remain open (n = 10 for each genotype). Scale bar: 500 µm. (P) Rab23 expression in the whole calvarial tissue at E16.5 is shown by digoxigenin labeled whole mount in situ hybridization (P–a) and shown at E15.5 sutural tissue sections by RNAscope (P–b). Co-expression of RAB23 (green) and osteoblast marker RUNX2 (red) in the calvarial sutural section at E17.5 is shown by immunohistochemical staining (P–c), nuclear staining (blue). RAB23 protein expression in the sutures at E15.5 is shown by western blotting (P–d). fb: frontal bone, pb: parietal bone, ipb: interparietal bone, fs: frontal suture, ss: sagittal suture, ls: lambdoid suture. Scale bar: 500 µm (a), 100 µm (b, c).