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Abstract. Type XI collagen is a structural component of the cartilage extracellular matrix and plays an important role in skeletal morphogenesis. As a step toward defining the molecular mechanisms responsible for the regulation of type XI collagen expression, we characterized the promoter region of the mouse a2(XI) collagen gene (Collla2). We also generated transgenic mice harboring various fragments of the promoter and the first intron of Collla2 linked to the Escherichia coli 13-galactosidase gene to identify the c/s-acting elements responsible for tissue-and site-specific expression during development. Cloning and sequence analysis of the 5' flanking region of Collla2 showed that the putative 3' end of the retinoid X receptor 13 gene was located 742 bp upstream of the Collla2 start site. This suggested that the promoter region of Collla2 was localized within this 742-bp sequence, which contained multiple consensus regulatory elements. Examination of the transgenic mice revealed that the longest DNA construct (containing the entire promoter and first intron sequences) directed lacZ expression in the notochord as well as in the primordial cartilage throughout the body, with the pattern of expression mimicking that of endogenous Collla2 transcripts. On the other hand, deletion of the upstream ~290 bp resulted in the elimination of lacZ expression in the primordial cartilage of the carpals, tarsals, and vertebral bodies, whereas lacZ expression in the notochord and in the other primordial cartilage elsewhere was not affected. Deletion of the first intron sequence also resulted in the loss of lacZ expression in the primordial cartilage of the carpals, tarsals, and vertebral bodies, as well as in the notochord. These results demonstrate that the upstream 742-bp and first intron segments of the mouse Collla2 gene contain the necessary information to confer high level tissue-specific expression in mouse embryos. In addition, our observations suggest the presence of site-specific cis-acting elements that control Colllla2 gene expression in different cartilaginous components of the skeleton.T H~ collagen superfamily consists of various collagens, which play an important role as structural components in the connective tissue. Among them, types II, IX, and XI collagens are predominantly found in hyaline cartilage, where they form heterotypic fibrils that confer tensile strength and provide a scaffolding for matrix proteoglycans (Kielty et al., 1993). The type XI collagen molecule is thought to coassemble with type II collagen molecules to form fibrils, whereas type IX collagen is associated with the surface of the fibrils (Mendler et al., 1989;Vaughan et al., 1988). The type XI collagen molecule is composed of three distinct subunits: al(XI), c~2(XI), and c~3(XI) (Morris and B~ichinger, 1987). The c~3(XI) chain is believed to be a posttranslational variation product of the cd(II) collagen gene (Furuto and Miller, 1983), whereas

Covalent modifications of histone tails play important roles in gene transcription and silencing. We recently identified an ERG ( ets -related gene)-associated protein with a SET (suppressor of variegation, enhancer of zest and trithorax) domain (ESET) that was found to have the activity of a histone H3-specific methyltransferase. In the present study, we investigated the interaction of ESET with other chromatin remodelling factors. We show that ESET histone methyltransferase associates with histone deacetylase 1 (HDAC1) and HDAC2, and that ESET also interacts with the transcription co-repressors mSin3A and mSin3B. Deletion analysis of ESET reveals that an N-terminal region containing a tudor domain is responsible for interaction with mSin3A/B and association with HDAC1/2, and that truncation of ESET enhances its binding to mSin3. When bound to a promoter, ESET represses the transcription of a downstream luciferase reporter gene. This repression by ESET is independent of its histone methyltransferase activity, but correlates with its binding to the mSin3 co-repressors. In addition, the repression can be partially reversed by treatment with the HDAC inhibitor trichostatin A. Taken together, these data suggest that ESET histone methyltransferase can form a large, multi-protein complex(es) with mSin3A/B co-repressors and HDAC1/2 that participates in multiple pathways of transcriptional repression.

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Neurotization of the MCN by surgically connecting ICNs is a safe, reliable, and effective procedure for reconstruction of the brachial plexus in patients suffering from birth-related palsy.