The brain is the most complex organ in all higher animals.  Understanding the construction principles that underlie its complex architecture is one of the most challenging problems in modern neurobiology.  Recent advances in the molecular genetic analysis of several model systems have resulted in the identification of developmental control genes that are involved in generating the embryonic brain.  However, it is still largely unclear how these genes, and the embryonic process that they control, relate to the architectural organization of the adult brain.

Several studies in vertebrates have addressed the role played by cell lineage and clonal restriction in shaping anatomically and functionally distinct brain regions.  However, it has been difficult to analyse this comprehensively in the vertebrate brain due to the billions of neurons involved.  A model system that is ideal to analyse the role of neuronal cell lineage in adult brain organization is Drosophila, an organism for which powerful classical neurogenetic and molecular neurogenetic techniques are available.  Importantly, in the last few years, significant and timely advances have been made in the analysis of brain development and in the use of clonal analysis in Drosophila, which now set the stage for a lineage-based analysis of the adult brain.

The goal of the research outlined here is to explore the construction principles of the adult brain in Drosophila through a lineage-based molecular genetic dissection.  Our central working hypothesis is that architecture of the highly complex mature brain can be de-composed into approximately 90 modular subunits each of which corresponds to the clonal progeny of one identified brain neuroblast.   We further postulate that the morphological differentiation of these clonal units involves the action of developmental control genes, which function not only in the embryo but also during postembryonic development and in the adult brain.  To investigate this, we propose to carry out two integrated and complementary research projects.  The first is a comprehensive lineage-based neuroanatomical analysis of the overall architecture of the adult brain at the morphological level.  The second is a focused molecular analysis of the role of specific developmental control genes in determining the anatomical features of individual clonal units in the adult brain.  Both projects are mutually synergistic; morphological information is central for molecular studies of gene action; information on gene function is essential for understanding the origin of brain morphology.

            Our experimental design is based on the powerful analysis methods offered by MARCM and GAL4/UAS technologies. In investigations at the morphological level, we will use randomly induced wildtype MARCM clones together with high resolution confocal microscopy and digital 3D modeling to generate precise neuroanatomical maps of all of the neuroblast clones in the adult brain.  These standardized digital 3D models will incorporate all of the major morphological features of each neuroblast clone.  Once completed, they should allow virtual dissection and reconstruction of the cell lineages that make up the adult brain, and also represent a useful standardized repository for gene expression patterns of the mature brain.  In investigations at the molecular genetic level, we will combine immunocytochemistry, confocal microscopy and digital 3D modeling to map the expression patterns in the adult brain cortex of a set of developmental control genes that characterize embryonic brain neuroblasts.  For genes that are regionally expressed in the adult brain, we will use gene-specific GAL4 and UAS-RNAi lines to examine the effects of gene knockdown on morphology, and in positive cases, we will generate GAL4-restricted MARCM lines for clonal mutant analysis of loss-of-function phenotypes in adult brain morphology.