Analysis of cranio-facial deformities caused by abnormal endochondral ossification

软骨发育不全和软骨发育不良都是先天性畸形，分别由FGFR 3和PTH/PTHrP受体的组成性活性形式引起。我们试图阐明FGFR 3和PTHrP中的哪一个在软骨细胞分化中显示出主导功能。此外，PTHrP在内部区域具有核仁靶向信号。而不介导与PTH的共同受体。因此，我们研究了PTHrP和FGFR 3在软骨发育中的生物学作用。（1）FGFR 3/PTHrP基因缺失突变的18日龄胎儿表现为四肢短缩，与PTHrP^<-/->胎儿的畸形一致。FGFR 3 ^<-/->/PTHrP^<-/->复合突变胎儿显示出骨骺软骨细胞数量减少和软骨发育不良的形式，这是PTHrP^<-/->胎儿的特征性特征。因此，PTHrP似乎主要对FGFR 3起作用，或位于PTHrP对软骨细胞增殖的下游。FGFR 3 ^<-/->/PTHrP^<-/->胎鼠软骨细胞凋亡率明显低于PTHrP ^<-/->胎鼠。此外，FGFR 3 ^<-/->和复合胎显示在肥大区VEGF表达显著降低，而PTHrP缺陷胎在匹配区域显示丰富的VEGF mRNA。因此，FGFR 3似乎在增殖软骨细胞上PTHrP信号传导的上游起作用，以及独立地作用于肥大软骨细胞。（2）PTHrP的大部分生物学活性是通过与PTH的共同受体结合而介导的。然而，PTHrP在内部区域显示核仁靶向信号。用PTHrP cDNA的截短形式转染的软骨细胞系显示该肽在核仁中通过从AUG密码子开始的翻译和从CUG密码子开始的翻译介导。

Achondroplasia and chondrodysplaisa, both of which are congenital deformities, are caused by constitutively-active forms of FGFR3 and PTH/PTHrP receptor, respectively. We have attempted to clarify which of FGFR3 and PTHrP show predominant function on chondrocyte differentiation. Furthermore, PTHrP has a nucleolar targeting signal in the internal region., without mediating the common receptor with PTH. Thus, we examined the biological action of PTHrPand FGFR3 in cartilage development.(1)The 18-day-old fetus with null mutation of FGFR3/PTHrP genes revealed shorted limbs, consistent with the abnormalities of the PTHrP^<-/-> fetuses. The FGFR3^<-/->/PTHrP^<-/-> compound mutant fetuses showed reduced numbers of epiphyseal chondrocytes and a form of chondrodysplasia, which are characteristic features of the PTHrP^<-/-> fetus. Therefore, PTHrP appeared to function predominantly to FGFR3, or to lie down-stream of PTHrP on chondrocyte proliferation. However, the numbers of apoptotic chondrocytes were significantly reduced in FGFR3^<-/->/PTHrP^<-/-> fetuses, compared with that of PTHrP^<-/-> fetus. In addition, the FGFR3^<-/-> and the compound fetuses revealed the markedly reduced expression of VEGF in the hypertrophic zone, whereas the PTHrP deficient fetus displayed the abundant mRNA of VEGF in the matched region. Thus, FGFR3 appears to act functionally in the upstream to PTHrP signaling on proliferating chondrocytes, as well as to act independently on hypertrophic chondrocytes.(2)The majority of the biological activity of PTHrP is mediated through the binding to the common receptor with PTH. However, PTHrP shows a nucleolar targeting signal in the internal region. Chondrocytic cell line transfected with truncated forms of PTHrP cDNA showed this peptide in the nucleoli mediated by translation initiating from AUG-codon and alternatively initiating from CUG codons.