Vertebrate Limb Development 2

Abnormalities in normal heart formation are the most common birth defect, occurring in 1 in 120 live births. If uncorrected, these defects can have serious debilitating effects on quality of life and in severe cases lead to premature death. Other less life-threatening birth defects also dramatically decrease quality of life in affected individuals. Among these, limb defects are the most common. We are interested in studying the causes of two human syndromes that lead to serious abnormalities in normal heart and limb formation. Patients with Holt-Oram Syndrome (HOS) have severely malformed hearts and limbs and those with Ulnar-Mammary Syndrome (UMS) are afflicted with abnormal limb and mammary gland development.|In each syndrome the corruption of the genetic information in a single gene is sufficient to cause all of the associated abnormalities. Armed with this knowledge of the exact genetic cause of each syndrome we propose to investigate the underlying biology of these diseases. Using the mouse and chicken, we are generating syndrome models that provide a powerful method to understand how loss of normal gene function leads to the disruption of heart and limb formation. In both animal models, the development of the heart and limbs occurs in a similar manner to our own and each animal model has experimental advantages we can exploit. Understanding the genesis of these syndromes will provide information vital in order to devise more effective diagnostic and corrective treatments in human patients.

Limb defects are the second most common congenital abnormality present in human live births and diseases affecting the musculoskeletal system are a significant clinical problem, particularly in the older population. The goal of our work is to understand how the limbs form normally during embryogenesis and the genesis of limb abnormalities and diseases that affect the musculoskeletal system in humans. ||Limbs are formed from specific regions of the flank of the embryo. At early stages of embryonic development, the forelimb and hindlimb buds are morphologically uniform and indistinguishable from one another. During subsequent steps of development however, dramatic changes take place. Each bud develops to form a network of interconnected limb elements e.g. bones, muscles, and tendons-with morphologies characteristic of either the forelimb or hindlimb. We are using vertebrate animal models to understand the mechanisms that control the initiation of limb bud formation and the subsequent construction of the individual limb elements during embryonic development. A longer-term aim is to apply these findings to develop to potential therapeutic approaches that could contribute to maintenance and possible regeneration of these structures in later life.||We use the developing limb as a model system using predominantly mouse and chick model organisms but also zebrafish and frog (and in future, as part of collaboration, we also plan to include Bat). In general our strategy is to interrogate gene function using a combination of coordinated gene misexpression and gene deletion experiments, often in more than one model system. In the mouse, we take advantage of gene conditional alleles and a repertoire of Cre deleter transgenics that we have developed ourselves or have collected. We often include transgene reporters to aid in phenotyping. In the chick, we are using genetic techniques to misexpress genes (either retroviral vectors or electroporation or direct application of recombinant proteins or substances) in combination with more classical embryological approaches. A new and important aspect of current and future work is to develop the use of in vitro techniques as an alternative, complementary approach to our in vivo models. Currently this involves the generation and characterisation of cell lines derived from transgenic reporter mouse lines we have produced and collected.