In our previous study, fatty acid-binding protein 5 (FABP5) was expressed in septoclasts with long processes which are considered to resorb uncalcified matrix of the growth plate (GP) cartilage, and no apparent abnormalities were detected in the histo-architecture of the GP of FABP5-deficient (FABP5−/−) mice. Those finding lead us to hypothesize that another FABP can compensate the deletion of FABP5 in septoclasts of its gene-mutant mice. Based on the hypothesis, the present study examined the expression levels of several other FABPs in septoclasts and their morphology in FABP5−/− mouse tibiae. Processes of FABP5−/− septoclasts tend to be shorter than wild septoclasts. FABP4-positive septoclasts in FABP5−/− mice were more numerous than those cells in wild mice.Peroxisome proliferator-activated receptor (PPAR) γ was expressed in FABP4-positive septoclasts of FABP5−/− mice as well as mice administered with GW1929, a PPARγ agonist, suggesting that the occurrence of PPARγ induces an increase of FABP4-positive septoclasts. The present finding suggests that the functional exertion of FABP5 in septoclasts is supplemented by FABP4 in normal and FABP5−/− mice, and that the expression of FABP4 is up-regulated in accompany with PPARγ in FABP5−/− for maintenance of resorptive activity in the GP.

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The mammalian secondary palate develops through complex processes including palatal shelf growth, elevation, and fusion. Palatal shelf elevation is a process accompanied by large-scale morphological changes over a short period. The elevation pattern changes along the anterior-posterior axis; the anterior region elevates by the "flip-up" model, and the middle and posterior regions reorient through the "flow" model. However, the mechanisms of both models are unclear because of the rapid progression of the elevation in utero. To observe palatal elevation in real time in detail, we aimed to establish a live imaging method using explants of the anterior region of the palatal shelf in mouse embryos before the beginning of elevation.Changes in the degree of shelf orientation were measured, which showed that the palatal shelf continuously changed shape toward the lingual side. The changes in the angle between the lingual and buccal bases of the palatal shelf were different; the morphological change at the lingual side resulted in a more acute angle, and the change at the buccal side resulted in a more obtuse angle. The morphological changes of the lingual and buccal sides occurred nearly simultaneously, suggesting that the anterior region of the palatal shelf in vitro elevated according to the "flip-up" model. This live imaging method enables the continuous observation of palatal shelf elevation and provides new insights into palatogenesis.

We previously reported that septoclasts, which are uncalcified growth plate (GP) cartilage matrix-resorbing cells, are derived from pericytes surrounding capillary endothelial cells. Resorption of the GP is assumed to be regulated synchronously by septoclasts, pericytes, and endothelial cells. To reveal the contribution of the extracellular matrix (ECM) to the regulatory mechanisms of septoclastic cartilage resorption, we investigated the spatial correlation between the cells and the ECM in the GP matrix and basement membrane (BM) and investigated the expression of integrins-ECM receptors-in the cells. Septoclasts attached to the transverse septa containing collagen-II/-X at the tip of their processes and to the longitudinal septa containing collagen-II/-X at the spine-like processes extending from their bodies and processes.Collagen-IV and laminin α4 in the BM were sparsely detected between septoclasts and capillary endothelial cells at the chondro-osseous junction (COJ) and were absent in the outer surface of pericytes at the metaphysis. Integrin α1/α2, integrin α1, and integrin α2/α6 were detected in the cell membranes of septoclasts, pericytes, and endothelial cells, respectively. These results suggest that the adhesion between septoclasts and the cartilage ECM forming the scaffolds for cartilage resorption and migration is provided by integrin α2-collagen-II/-X interaction and that the adhesions between the BM and pericytes or endothelial cells are mediated by integrin α1-collagen-IV and integrin α2/α6-laminin interaction, respectively.