Tubes of different sizes, shapes and cellular architectures compose most organs and glands. How these tubes are formed and what factors regulate their dimensions and their pattern of branching, are among the primary questions that must be addressed before we will understand how organs are made. These questions are also of great medical relevance, because defects in tubes are at the root of many disease states, such as polycystic kidney disease and atherosclerosis, and because the recruitment of capillary tubes to tumors by sprouting angiogenesis plays a pivotal role in cancer. The long-term goal of the lab is to develop an understanding at the molecular level of the basic cell biology of tube formation and branching morphogenesis (the process by which new tubes are induced to bud and branch from pre-existing ones).

We use a simple model tubular organ (the Drosophila tracheal system) to uncover the genetic and molecular basis of how tubes are made and shaped. Using the powerful tools available to a Drosophila geneticist, we are able to manipulate gene function in individual cells and to determine the effects of such manipulations on tube morphogenesis. A large-scale forward genetic screen has been carried out and mutations in roughly 70 genes have been identified that cause striking tracheal defects (manuscript in preparation).

Positional cloning of mutants including cystic lumens, impatent and asthmatic (see below) have recently been completed.



 Rotation projects 2015-16:

Tube formation projects:  Most organs and glands are composed of networks of branched and interconnected tubes.  Some of the smallest tubes are formed within single cells by a mysterious process called “cell hollowing.”  Examples of such tubes include the seamless endothelial tubes present in the mammalian vascular system as well as the terminal tubes of the Drosophila tracheal system. In a large-scale forward genetic screen carried out in Drosophila, a number of mutations that disrupt cell hollowing were identified.  By determining the molecular identity of the genes affected in these mutants we aim to build a molecular understanding of how cells convert themselves into tubes.

1) Functional characterization of cystic lumens.  Mutations in cystic lumens cause a striking defect in tube shape:  the lumens of mutant cells show areas of constriction and dilation.

2) Pilot screen for tip cell genes.  Sprouting of new tubes in the vascular system and of primary tracheal branches depends on selection of tip cells. We previously found that Notch and FGFR signaling are key in tip cell selection, but what genes act downstream of these pathways in tip cell behavior remains unknown.

Branching morphogenesis projects:  Formation of branched tubular organs often occurs by a process called “branching morphogenesis”.  Sprouting angiogenesis in the mammalian vascular system and primary branching of the Drosophila tracheal system both employ this mode of development – in which new tubes bud from the epithelium of pre-existing tubes – to form new branches in their tubular networks.  How cells rearrange within an epithelium during the formation of a new tube is not understood, although we have found that it is driven in part by a competition between cells for leading (“tip cell”) positions that divides the cells into leaders and followers.   Cells that have been sorted into the stalk of a new tube will continue to alter their arrangement in the epithelium, as they intercalate to form a longer and thinner tube.  To understand the cellular and molecular mechanisms which control these morphogenetic movements we will carry out a careful phenotypic and molecular analysis of mutants that disrupt these processes.

1) Live cell imaging of re-arrangement during primary branching.  Because branching morphogenesis is a dynamic process, attempting to understand the morphogenetic mechanisms at work by examination of fixed samples is problematic.  By taking advantage of the genetic tools available in Drosophila, it will be possible to generate twin spot clones within the tracheal system and watch as the differently marked cells (one daughter marked with green fluorescent protein, the other marked with cherry) move relative to each other within the epithelium during primary branching.  In addition, to determining how wild type control twin spots behave, we will be able to examine twin spots in which one daughter is homozygous for a mutant of interest while the other daughter is homozygous wild type.

2) Determine which components of the RTK signaling pathway are required for sprouting and testing an ontogenetic FGFR transgene to control pathway activation with precise spatial and temporal resolution