The overall goal of our lab is to understand the molecular mechanisms that link cell growth, cell division, and cell fate patterning during development. Animal growth results from the precise coordination of these different processes, as well as from complex interactions between neighboring cells within individual organs and tissues. Although the molecular pathways that control cell proliferation, cellular biosynthesis, and cell fate specification are known, what remains unclear is how they intersect and are influenced by each other during the development of tissues and organs. To this end we are carrying out studies in vivo to determine the mechanisms that link growth to pattern formation, using the Drosophila wing as a model system.
|The role of Wingless in growth regulation of the developing wing|
(Wg), a member of the conserved Wnt gene family of pattern regulators,
is a major organizer of cell fates in the developing wing and is also
believed to control wing growth. Through the use of genetics and
molecular biology, we aim to identify the growth regulatory
targets and mechanisms used by Wingless to control cellular growth,
cell cycle progression, and cell survival in vivo.
The Drosophila wing imaginal disc. Wingless staining is shown in red, nuclear staining in green. The disc is oriented as described in the upper right hand corner: A, anterior; P, posterior; D, dorsal; V, ventral.
Image taken from Johnston, L.A. and Sanders, A.L. 2003. Wingless promotes cell survival but constrains growth during Drosophila wing development. Nature Cell Biology, 5 (9): 827-833 (Abstract, PDF).
The zone of non-proliferating cells (ZNC) at the dorsal/ventral boundary of the wing disc and the genes involved in its setup and maintenance.
Johnston, L. A. and Edgar, B. A. 1998. Wingless and Notch regulate cell-cycle arrest in the developing Drosophila wing. Nature 394, 82-84. (Abstract, PDF)
|Intrinsic control of organ size|
What is the genetic program intrinsic to organs that regulates their size? Our observations suggest that organs such as the wing "sense" anomalous growth rates and compensate by altering overall growth. We are using a series of genetic and molecular assays to understand how this occurs. Our experiments address how developing organs like wings monitor their mass, how cells sense growth rate differences between themselves, which growth parameters (cell cycle, cellular growth, cell survival) respond to growth alterations, and determine how these features interact to control wing size and shape. We are carrying out experiments that will identify the direct cell cycle, cell survival, and cellular growth targets regulated in situations of aberrant growth, as well as the critical intercellular signals and signal transduction targets important for overall organ size regulation.
The size difference between two male Drosophila: one wildtype, one carrying a mutation in Drosophila myc (dmyc).
Image taken from Johnston, L. A., Prober, D. A., Edgar, B. A., Eisenman, R. N., and Gallant, P. 1999. Drosophila myc regulates cellular growth during development. Cell 98, 779-790. (Abstract, PDF)
|Genetic approach to study cell competition|
competition occurs when slow-growing cells reside within a population
of faster growing ones, with the result that the cells with a growth
disadvantage are targeted for death. To study this phenomenon, we are
using a genetic approach to generate three types of cell clones with
differing growth rates within the same organ, to uncover and follow the
mechanisms used by the organ to deal with cell competition.
A clonal assay of cell competition that utilizes three clone types. Mitotic recombination produces a GFP-expressing "Gal4" clone (green) and its "Sibling", marked by a cell surface marker (red). An independant recombination event produces a B-galactosidase-marked "Neutral" clone (blue).
de la Cova, C., Abril, M., Bellosta, P., Gallant, P., and Johnston, L. A. Drosophila Myc regulates organ size by inducing cell competition. Cell, 117: 107-116. (Abstract, PDF)