In this study, we investigated the process of supernumerary upper incisor formation in the Pax6 mutant rat, rSey 2 /rSey 2 , which exhibits a facial cleft between the medial nasal and maxillary processes. Histological investigation and epithelial labeling studies of wild type rat embryos indicated that the upper incisor develops by fusion of two primary dental placodes (PDPs) in the medial nasal process with a contribution from the epithelium of the maxillary process. In the rSey 2 /rSey 2 embryo, both PDPs are formed but they stay apart, then subsequently these PDPs independently develop into upper incisor tooth buds. In order to examine if the failure of the two placodes to fuse is due to the cleft between the maxillary and medial nasal processes, maxillary and medial nasal process fusion was inhibited with a barrier in wild type embryos. This resulted in the maintenance of the two distinct PDPs. These results demonstrate that fusion of the facial processes reduces the number of odontogenic placodes and is required to assemble all components at one site for rat upper incisor formation. The results also provide further insight into the mechanism of supernumerary incisor formation in human cleft lip conditions. Developmental Dynamics 235:2134 -2143, 2006.

<b><i>Introduction:</i></b> Minimal change disease (MCD) and primary focal segmental glomerulosclerosis (FSGS) are representative podocyte diseases. The clinical cause of MCD and FSGS has not been clearly elucidated yet. However, it is important to distinguish MCD and FSGS because their prognoses and responses to treatment are quite different. <b><i>Objective:</i></b> This study aimed to examine whether parietal epithelial cell (PEC) marker and repeat biopsy are useful for diagnosing primary FSGS. <b><i>Methods:</i></b> Clinicopathological features of 17 patients with the nephrotic syndrome, who underwent kidney biopsy ≥2 times from 1975 to 2017, and had MCD or FSGS were analyzed using PAX8. We defined patients with PAX8+ cells as PAX8+ and the remainder as PAX8– patients. Three cases of sample insufficiency and 1 non-steroid-resistant or frequently relapsing case indicated for repeat biopsy were excluded. <b><i>Results:</i></b> Among the 13 patients studied, 4 were PAX8+ and 9 were PAX8– (median age: 41 and 46 years, ­respectively, at first biopsy). PAX8+ and PAX8– patients showed no significant differences in clinical data and histological diagnosis except for a significant difference in histological diagnosis at the second biopsy. The number of PAX8+ patients increased to 6. Unlike the first biopsy results, FSGS was present in 5 of 6 (83.3%) PAX8+ patients; MCD occurred in all 7 (100%) PAX8– patients. Three of 6 (50.0%) PAX8+ patients undergoing repeat biopsy were steroid resistant; no (0%) PAX8– patient was steroid resistant. All cases of final FSGS diagnosis were PAX8+ at the first or second biopsy. Only 1 PAX8+ MCD patient was steroid resistant. All PAX8– MCD patients were frequently relapsing. <b><i>Conclusions:</i></b> More PAX8+ patients were diagnosed with FSGS than PAX8– patients. Clinical presentation of MCD in PAX8– patients was frequently relapsing. PEC marker staining in patients with the nephrotic syndrome, e.g., MCD, may help to diagnose FSGS.

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