Molecular Hemotology Overview

A Cooperative Center of Excellence in Hematology

      Hematology has pioneered the application of new scientific methods to the study of disease processes. With the emergence of protein chemistry came the discovery of the basis of sickle cell anemia as a single amino acid substitution in the beta-chain of hemoglobin. With the advent of molecular biology and recombinant DNA methods the thalassemia syndromes became the first inherited human disorders for which the genetic basis was fully determined (Orkin and Kazazian 1984). As improved techniques for gene transfer were developed, consideration of potential somatic gene therapy approaches to hematologic disorders arose (Williams and Orkin 1986).

      From a vantage point many years hence, the 1990s may be viewed as the first decade of molecular developmental biology. Basic principles of patterning of embryos and cell specification were defined in invertebrates, only to be rediscovered in various guises in vertebrates. The commonality of gene function has led to an extraordinary unification of modern biology and the appreciation of conserved pathways from yeast to humans. As gene discovery programs provide many new genes to investigators to place within a biological context, we have entered an era of "functional genomics", in which the challenge will be to understand the function of newly recognized genes--what they do, how they act, how they go awry in disease, and how they can be harnessed to combat disease.

      Besides a time of great excitement in developmental biology and gene discovery, the 1990s have seen the coming to fruition of new techniques for genetic manipulation in the mouse (Capecchi 1989) and the emergence of a promising, complementary vertebrate system, the zebrafish (Mullins et al. 1994). Transgenic, gene knockout, and conditional gene targeting strategies in the mouse have provided for the first time the capacity to test gene function and requirement in vivo in an animal whose basic biology is very similar to that of man. Mouse models of human disorders can now be engineered in a systematic manner for careful analysis of pathophysiology and treatment. Although genetic manipulation has not been so readily achieved in zebrafish, the ability to perform large-screen genetic screens for nearly any conceivable phenotype, coupled with rapid improvements in zebrafish genomics, has opened up new opportunities to link gene function and development.

      Although the molecular bases of many inherited and acquired hematologic disorders are now well defined, we do not have a complete understanding of the mechanisms by which hematopoietic cells develop. An appreciation of this fundamental problem will provide important insights into diverse issues pertinent to blood cell development, including mechanisms by which cell fates are determined during embryogenesis, by which a choice between self-renewal (proliferation) and differentiation is made by hematopoietic stem cells, by which specific lineages are chosen during progenitor development, and by which aberrant gene expression due to chromosomal events leads to leukemia. Increased understanding of these areas should create new opportunities in on-going efforts to express foreign sequences following gene transfer into hematopoietic stem cells for either experimental or therapeutic purposes. New knowledge regarding the origin, gene expression, and development of hematopoietic stem cells may eventually permit in vitro generation and expansion of these cells for therapeutic approaches in which bone marrow transplantation of hematopoietic stem cells might be envisioned.

      As we hope to illustrate below in this application, efforts in our Center of Excellence in Molecular Hematology at Children's Hospital during the past 4 years have contributed significantly to the advancement of molecular developmental hematopoiesis. Particularly through the activity of mouse embryonic stem (ES) and zebrafish CORES considerable new research has been supported and enhanced, far beyond what could have been envisioned at the inception of the Center. In addition, by the parallel emphasis on two vertebrate genetic systems we have realized synergy in the molecular analysis of blood cell development. In the proposal presented here, we aim to capitalize on this success and widen the impact of Center both locally and beyond.