Cranial neural tube defects (NTDs) occur in mice carrying mutant alleles of many different genes, whereas isolated spinal NTDs (spina bifida) occur in fewer models, despite being common human birth defects. Spina bifida occurs at high frequency in the Axial defects (Axd) mouse mutant but the causative gene is not known. In the current study, the Axd mutation was mapped by linkage analysis. Within the critical genomic region, sequencing did not reveal a coding mutation whereas expression analysis demonstrated significant up-regulation of grainyhead-like 2 (Grhl2) in Axd mutant embryos. Expression of other candidate genes did not differ between genotypes. In order to test the hypothesis that over-expression of Grhl2 causes Axd NTDs, we performed a genetic cross to reduce Grhl2 function in Axd heterozygotes. Grhl2 loss of function mutant mice were generated and displayed both cranial and spinal NTDs. Compound heterozygotes carrying both loss (Grhl2 null) and putative gain of function (Axd) alleles exhibited normalization of spinal neural tube closure compared with Axd/+ littermates, which exhibit delayed closure. Grhl2 is expressed in the surface ectoderm and hindgut endoderm in the spinal region, overlapping with grainyhead-like 3 (Grhl3). Axd mutants display delayed eyelid closure, as reported in Grhl3 null embryos. Moreover, Axd mutant embryos exhibited increased ventral curvature of the spinal region and reduced proliferation in the hindgut, reminiscent of curly tail embryos, which carry a hypomorphic allele of Grhl3. Overall, our data suggest that defects in Axd mutant embryos result from over-expression of Grhl2.

No abstract

No abstract

The usefulness of adult human perichondrium for the restoration of articular cartilage defects depends on the potential to form hyalin cartilage. In order to evaluate the capacity of adult human perichondrium to form hyalin cartilage in vitro, perichondrium of the rib of eight adult human beings was cultured in vitro. After removal of residual cartilage, perichondrial explants were cultured for 7 or 10 days. The explants were histologically examined using specific stains to prove the presence of glycosaminoglycans (GAGs) normal for hyalin cartilage. Clear differentiation of perichondrial cells towards chondrocytes was noted. The chondrocytes synthesized new matrix substances normally present in hyalin cartilage. This investigation supports the usefulness of adult human rib perichondrium for the restoration of cartilage defects. Due to the enormous potential of the rib perichondrium to form hyalin cartilage in vitro, even defects in joints with a rather thick cartilage layer might be restored using this biological material.