Structural model of the amino propeptide of collagen XI alpha1 chain with similarity to the LNS domains.

Fibrillar collagens are the principal structural molecules of connective tissues. The assembly of collagen fibrils is regulated by quantitatively minor fibrillar collagens, types V and XI. A unique amino-terminal propeptide domain of these collagens has been attributed this regulatory role. The structure of the amino terminal propeptide has yet to be determined. Low sequence similarity necessitated a secondary structure-based method to carry out homology modeling based upon the determined structure of LNS family members, named for a common structure in the laminin LG5 domain, the neurexin 1B domain and the sex hormone binding globulin. Distribution of amino acids within the model suggested glycosaminoglycan interaction and calcium binding. These activities were tested experimentally. Sequence analyses of existing genes for collagens indicate that 16 known collagen alpha chains may contain an LNS domain. A similar approach may prove useful for structure/function studies of similar domains in other collagens with similar domains. This will provide mechanistic details of the organization and assembly of the extracellular matrix and the underlying basis of structural integrity in connective tissues. The absolute requirement for collagen XI in skeletal growth is indicated by collagen XI deficiencies such as chondrodystrophies found in the cho/cho mouse and in humans with Stickler syndrome.

Suppression of MeCP2beta expression inhibits neurite extension in PC12 cells.

Regulation of gene expression is critical to the proper development of neuronal cells. The methyl-CpG binding protein 2 (MeCP2) operates as a transcriptional repressor by facilitating histone deacetylation and DNA methylation-dependent transcriptional silencing. This study examined the importance of MeCP2 in the regulation of neurite formation in PC12 cells. Expression of MeCP2 increased in a time-dependent manner after induction of neuronal differentiation. Expression was assessed at both the transcriptional and translation levels, and reached a maximum at 24 h post-induction. In addition, a marked inhibition of neurite extension and proper localization of a marker for synapse formation, synapsin I, were observed when MeCP2 expression was decreased by the addition of an antisense morpholino oligomer directed to the translational initiation site for MeCP2beta. The removal of the antisense oligomer allowed neurite extension to progress. However, the addition of antisense oligomer to previously differentiated PC12 cells did not affect established neurite processes. Taken collectively, our results indicate a role for MeCP2beta early in the events of neurite formation and that the relative levels of MeCP2alpha and MeCP2beta may be different in early differentiating neurons than is found in the adult brain. In addition, unique functions may exist for the two isoforms of MeCP2. Our results indicate that the inhibition of neurite elaboration caused by a reduction in MeCP2 may be reversible.