Blood neutrophils (polymorphonuclear granulocytes) are an important component of native defenses against bacterial and fungal infections. The neutrophil nucleus is multilobed, believed to be a structural modification permitting the cells to migrate rapidly out of the bloodstream and towards the site of infection. Cellular mechanisms responsible for nuclear Iobulation are essentially unknown. The long-term objective of this project is to define these cellular mechanisms and to view them in the larger context of the relationships between interphase nuclear architecture and function. Collaborative studies by this laboratory have established that the nuclear envelope protein lamin B receptor (LBR) is essential for neutrophil nuclear Iobulation. Genetic deficiencies of LBR expression result in the human Pelger-Huet anomaly and mouse ichthyosis mutation, both frequently fatal in the homozygous state and characterized by hypolobulated neutrophils. Based upon present knowledge about the properties of the nuclear envelope and LBR, the specific aims of this project are: a) to determine LBR expression levels during granulopoiesis; b) to examine the levels of other nuclear envelope proteins which may influence the action of LBR; c) to examine the effects of chromatin protein modifications on nuclear shape; d) to explore the possible role of cytoskeletal elements in nuclear Iobulation. This project should help to establish whether factors other than LBR expression level (such as histone modifications and cytoskeletal integrity) are important in the mechanism of granulocyte nuclear Iobulation. Experiments designed to achieve the specific aims will involve the use of long-term cultures (LTC) and colony assays of murine bone marrow from wildtype and ichthyosis mice. Granulocytic colonies will be examined by immunostaining and in situ hybridization techniques. Drugs that affect histone modifications and cytoskeletal integrity will be employed to perturb nuclear Iobulation during granulopoiesis. Pseudo- or Acquired Pelger-Huet anomaly, with hypolobulated neutrophil nuclei, is also occasionally observed in infections, toxic drug reactions and Myelodysplastic Syndrome (a diverse group of disorders with high propensity to transform to leukemia), suggesting that other factors besides LBR are involved in the determination of neutrophil nuclear shape.