Maintenance Of Adult Homeostasis Research Articles

The instructive extracellular matrix of the lung: basic composition and alterations in chronic lung disease.

The pulmonary extracellular matrix (ECM) determines the tissue architecture of the lung, and provides mechanical stability and elastic recoil, which are essential for physiological lung function. Biochemical and biomechanical signals initiated by the ECM direct cellular function and differentiation, and thus play a decisive role in lung development, tissue remodelling processes and maintenance of adult homeostasis. Recent proteomic studies have demonstrated that at least 150 different ECM proteins, glycosaminoglycans and modifying enzymes are expressed in the lung, and these assemble into intricate composite biomaterials. These highly insoluble assemblies of interacting ECM proteins and their glycan modifications can act as a solid phase-binding interface for hundreds of secreted proteins, which creates an information-rich signalling template for cell function and differentiation. Dynamic changes within the ECM that occur upon injury or with ageing are associated with several chronic lung diseases. In this review, we summarise the available data about the structure and function of the pulmonary ECM, and highlight changes that occur in idiopathic pulmonary fibrosis (IPF), pulmonary arterial hypertension (PAH), chronic obstructive pulmonary disease (COPD), asthma and lung cancer. We discuss potential mechanisms of ECM remodelling and modification, which we believe are relevant for future diagnosis and treatment of chronic lung disease.

The mouse genome displays highly dynamic populations of KRAB-zinc finger protein genes and related genetic units.

KRAB-containing poly-zinc finger proteins (KZFPs) constitute the largest family of transcription factors encoded by mammalian genomes, and growing evidence indicates that they fulfill functions critical to both embryonic development and maintenance of adult homeostasis. KZFP genes underwent broad and independent waves of expansion in many higher vertebrates lineages, yet comprehensive studies of members harbored by a given species are scarce. Here we present a thorough analysis of KZFP genes and related units in the murine genome. We first identified about twice as many elements than previously annotated as either KZFP genes or pseudogenes, notably by assigning to this family an entity formerly considered as a large group of Satellite repeats. We then could delineate an organization in clusters distributed throughout the genome, with signs of recombination, translocation, duplication and seeding of new sites by retrotransposition of KZFP genes and related genetic units (KZFP/rGUs). Moreover, we harvested evidence indicating that closely related paralogs had evolved through both drifting and shifting of sequences encoding for zinc finger arrays. Finally, we could demonstrate that the KAP1-SETDB1 repressor complex tames the expression of KZFP/rGUs within clusters, yet that the primary targets of this regulation are not the KZFP/rGUs themselves but enhancers contained in neighboring endogenous retroelements and that, underneath, KZFPs conserve highly individualized patterns of expression.

Use of mouse models to validate and therapeutically target transforming growth factor beta as an important player in breast cancer progression

Transforming growth factor betas (TGF-βs) play key roles in embryogenesis, maintenance of adult homeostasis and response to injury. In epithelial carcinogenesis the TGF-β play complex roles, functioning as tumor suppressors early in the process, but as pro-oncogenic factors in late-stage metastatic disease, when TGF-β ligands are frequently overexpressed. To probe this complexity in vivo, and determine whether TGF-β might be a viable therapeutic target, we developed a transgenic mouse overexpressing a soluble TGF-β antagonist. This antagonist ('SR2F') consisted of the extracellular domain of the type II TGF-β receptor fused to the Fc domain of human IgG1. The SR2F was secreted into the circulation and distributed to all organs except the brain. To determine the effect of this TGF-β antagonist on breast carcinogenesis, the mouse mammary tumor virus (MMTV)-SR2F and wild-type control mice were crossed with the MMTV-neu transgenic mouse model of metastatic breast cancer. The neu/SR2F bigenic mice showed a significant threefold decrease in the incidence of lung metastases compared with mice expressing neu alone. A similar suppression of metastasis was seen in using a tail vein injection model of metastatic melanoma. Importantly, the SR2F did not accelerate primary tumorigenesis, despite the fact that TGF-β has been shown to function as a tumor suppressor in the MMTV-neu model [1]. Furthermore, none of the pathology that is usually associated with TGF-β loss, such as autoimmune disease and increased spontaneous tumorigenesis, was observed on prolonged exposure to SR2F. The mechanistic basis for the unexpected selectivity of the SR2F in antagonizing the pro-metastatic effects of TGF-β while sparing effects on tumor suppression and normal homeostasis is currently not clear, but it does not seem to be a dosage effect. Overall, our data suggest that high molecular weight TGF-β antagonists might have promise in the clinic for prevention of metastasis. This study demonstrates the utility of a transgenic approach for testing expensive protein-based therapeutics in long-term realistic models of cancer progression.

The knockout mouse: six years old and growing stronger.

Site-specific alteration of the mouse genome has become a routine procedure. The past six years have witnessed the generation and characterization of several hundred novel animals, each harboring an independent mutation in one of the 50 to 100,000 estimated murine genes (1). Genes previ­ ously predicted to be involved in normal development or in the maintenance of adult homeostasis have been targeted for mutation, as have murine homologues of genes implicated in human disease, including some affecting the respiratory system. The phenotypes resulting from these mutations have ranged from the predictable to the surprising-witness the unexpected respiratory defects in animals lacking a func­ tional endothelin-l gene (2), or the relatively benign pulmo­ nary pathology associated with a number of mutant alleles of the CFTR gene (reviewed in 3). The phenotypic charac­ terization of these animals has helped to define biological functions of individual genes and to identify networks of genetic interactions. Rather than attempt to summarize a vast accumulation of data thus far generated, this Perspective will address some of the limitations inherent in this technology, emphasizing how an understanding of these limitations is contributing to a more thorough genetic description of a mammalian organism and its development. The protocol for mutagenesis is by now straightforward: cloned DNA, first mutated in vitro, is introduced into a popu­ lation of pluripotent embryonic stem (ES) cells grown in cul­ ture; those cells in which recombination has replaced the tar­ get, endogenous gene with its mutant homologue are isolated and transplanted into a blastocyst stage mouse embryo; this embryo is implanted and allowed to develop to term, and the resulting chimera (containing cells from the blastocyst as well as ES cells) is then bred to propagate the mutant se­ quences (4, 5). If the mutant allele is a recessive lethal, it can be maintained in the heterozygous state, and a simple genetic cross is used to generate homozygosity. The majority of the currently available mutant animals carry loss-of-func­ tion, or null, alleles of the gene of interest. Not only are such mutations technically the simplest to construct, but the phenotype of the ensuing knockout mouse establishes a baseline requirement for the target gene. Initial expectations of this approach are that the time and place of gene action will be defined, that development may