Targeted disruption of Col11a2 produces a mild cartilage phenotype in transgenic mice: Comparison with the human disorder otospondylomegaepiphyseal dysplasia (OSMED)

Transgenic mice were prepared by homologous recombination with a Col11a2 ta rgeting gene in which an inverted neomycin-resistant gene was inserted betw een restriction sites in exons 27 and 28. The targeted allele was transcrib ed in shortened mRNAs, which could be detected by Northern blotting. Howeve r, translation of the full-length Col11a2 chain was unable to occur because of the presence of premature termination codons within the inverted neomyc in-resistant gene. Analysis of pepsin-resistant collagen chains from rib ca rtilage of homozygous mice demonstrated the lack of synthesis of intact alp ha2(XI) chains. However, pepsin-resistant collagen chains of either alpha1( XI) or alpha1(V) were still detected on sodium dodecyl sulfate polyacrylami de gel electrophoresis. Therefore, alpha2(XI) chains are not essential for the assembly of some molecular forms of triple-helical type V/XI collagen. The phenotype was milder than in the cho/cho mouse in which, as the result of mutation, translation of the full-length alpha1(XI) chain fails to occur and the mice die at birth (Li et al., 1995). Homozygous mice without expre ssion of an alpha2(XI) chain had a smaller body size, receding snouts, and deafness. Nasal bones in the homozygous transgenic mice were specifically s horter and dimpled on their external surfaces. Chondrocytes in growth plate s of all long bones were markedly disorganized and failed to align in colum ns. Analysis of growth plates from transgenic mice by in situ hybridization showed expression of alpha1(II) and alpha1(XI) but not of alpha1(I) or alp ha1(V) which, in contrast, were expressed in the developing bone and in the bone collar. Expression of alpha1(X) specifically in the hypertrophic cart ilage was observed in normal and transgenic mice. No obvious osteoarthritis was observed throughout the life of homozygous mice up to 1 year of age, a lthough minor morphologic anomalies in the articular cartilages were discer nible. The mild phenotype is consistent with similar mutations in the COL11 A2 gene seen in patients with nonocular Stickler syndrome and some patients with otospondylomegaepiphyseal dysplasia (OSMED), as well as in patients w ith a nonsyndromic form of deafness called DFNA13. (C) 2001 Wiley-Liss, Inc .