Mutations in extracellular matrix molecules

Involvement of ITIH5, a candidate gene for congenital uterovaginal aplasia (Mayer-Rokitansky-Küster-Hauser syndrome), in female genital tract development

The ITI (inter-trypsine inhibitor) gene family includes five genes (ITIH1 to ITIH5) that encode proteins involved in the dynamics of the extracellular matrix (ECM). ITIH5 was found inactivated by partial deletion in a case of congenital uterovaginal aplasia, a human rare disease also called Mayer-Rokitansky-Küster-Hauser (MRKH) syndrome. The aim of the present study was to analyze the expression of ITIH5 in the uterus in adult life and during embryogenesis in order to establish the involvement of this gene in both normal and pathological conditions of uterus development. This was achieved in mice by reverse transcription-quantitative PCR, whole-mount hybridization, and Western blot analysis. Itih5 expression was much stronger in female genital tract primordia (Müllerian ducts) and derivatives than elsewhere in the body. This gene was strongly expressed during pregnancy and development of the female genital tract, indicating that the encoded protein probably had an important function in the uterus during these periods. Two different specific isoforms of the protein were detected in Müllerian derivatives during embryogenesis and in adults. Although ITIH genes are expected to be predominantly expressed in the liver, ITIH5 is mainly expressed in the uterus during development and adult life. This tends to indicate an additional and specific role of this gene in the female reproductive tract, and furthermore reinforces ITIH5 as a putative candidate gene for MRKH syndrome.

Coordinate integrin and c-Met signaling regulate Wnt gene expression during epithelial morphogenesis

Integrin receptors for the extracellular matrix and receptor tyrosine kinase growth factor receptors represent two of the major families of receptors that transduce into cells information about the surrounding environment. Wnt proteins are a major family of signaling molecules that regulate morphogenetic events. There is presently little understanding of how the expression of Wnt genes themselves is regulated. In this study, we demonstrate that alpha3beta1 integrin, a major laminin receptor involved in the development of the kidney, and c-Met, the receptor for hepatocyte growth factor, signal coordinately to regulate the expression of Wnt7b in the mouse. Wnt signals in turn appear to regulate epithelial cell survival in the papilla of the developing kidney, allowing for the elongation of epithelial tubules to form a mature papilla. Together, these results demonstrate how signals from integrins and growth factor receptors can be integrated to regulate the expression of an important family of signaling molecules so as to regulate morphogenetic events.

Adhesion complexes implicated in intestinal epithelial cell-matrix interactions

This article review summarizes data on cell-substratum adhesion complexes involved in the regulation of cellular functions in the intestine. We first focus on the molecular composition of the two main adhesion structures-the beta1 integrin-adhesion complex and the hemidesmosome-found in vivo and in two human intestinal cell lines. We also report the key findings on the cellular behavior and response to the extracellular matrix that involve integrins, the main transmembrane anchors of these complexes. How the dynamics of cell/extracellular matrix interactions contribute to cell migration, proliferation, differentiation, and tumorigenicity is discussed in the light of the data provided by the human intestinal cells.

Characterization of Osf1, an osteoblast-specific transcription factor binding to a critical cis-acting element in the mouse Osteocalcin promoters

To elucidate the mechanisms of osteoblast-specific gene expression we are studying the regulation of osteocalcin, the most osteoblast-specific gene. Previous studies of OG2, one of the two mouse osteocalcin genes, identified two osteoblast-specific cis-acting elements, OSE1 and OSE2, the latter being the binding site of Cbfa1, the only osteoblast-specific transcription factor known to date. Here we show that OSE1 is a cis-acting element as important as OSE2 for the osteoblast-specific expression of OG2 in cell culture and transgenic mice. We also show that OSE1 is present in the promoter of several osteoblast-specific genes including Cbfa1 itself. These biological features demonstrate the importance of OSE1 and led us to further characterize this site and the factor binding to it, provisionally termed Osf1. We first defined the core OSE1 sequence, 5'-TTACATCA-3', which is necessary and sufficient for Osf1 binding to DNA. This sequence has no strong homology to any known transcription factor-binding sites. As a first step in identifying Osf1, we performed an analytical purification of this protein using nuclear extracts from two different osteoblastic cell lines. We purified Osf1 to homogeneity through a five-step procedure including a renaturation experiment and found that its apparent molecular mass is 40 kDa. In conclusion, this study indicates the existence of multiple osteoblast-specific cis-acting elements of equal importance in controlling OG2 promoter activity and provides the first biochemical characterization of Osf1, a novel osteoblast-specific transcription factor.

Inherited disorders of the extracellular matrix

Primary and secondary defects in extracellular matrix proteins emphasize the role of these proteins in neuromuscular disorders; mutations have been found in the genes for the laminin-alpha 2 chain, for all three alpha chains of collagen VI and for integrin alpha 2. Secondary alterations in protein expression occur in association with these primary defects, and in other disorders they implicate the extracellular matrix. Animal models are helping to elucidate the function of some of these proteins, to develop therapeutic strategies and to suggest candidate proteins for other neuromuscular disorders.