My lab is interested in developmentally regulated programmed cell death or apoptosis. As we are now coming to appreciate, the transformation of a group of multipotent cells into a viable organism involves a web of cell-cell interactions and responses that lead to complex patterning. One significant mechanism for patterning is provided by programmed cell death (PCD) or apoptosis. PCD is vital for sculpting tissues and deleting unnecessary cells and structures, e.g., removal of the interdigital cells during mammalian limb formation and pruning of the nervous system. Proper regulation of PCD is also critical in the prevention of disease in adult animals: excessive PCD is found in a number of neurodegenerative diseases while a loss of PCD is critical to the progression of cancer.

Cell Death in Drosophila Eye Development

Scanning electron micrograph of an adult Drosophila eye. Notice the near perfect rows of ommatidia or unit eyes.

We are working to understand the process that directs some cells into death to establish the beautifully patterned adult Drosophila eye. Each fly retina is composed of approximately 750 identical unit eyes, or ommatidia. The beautiful, almost crystalline, appearance of the adult eye requires selective cell death of a subset of support cells that make up the interommatidial lattice. As a final step in patterning, the unpatterned interommatidial cells are organized into an interweaving hexagonal lattice of nine secondary and tertiary pigment cells (2°/3°s) that pattern the ommatidial array. Emergence of this lattice represents a balance between recruitment of 2°/3°s and elimination of unneeded interommatidial cells through selective PCD. Approximately one-third of interommatidial cells are removed by death (see below).

Flourescent images of Drosophila retina late in pupal development. The yellow hexagon outlines one ommatitidial core and its surrounding interommatidial lattice of 2°/3° pigment cells. Wild type is on the left and a klumpfuss mutant is on the right. The cells in red are cells that should have undergone programmed cell death (PCD).

What do we know about how this death is regulated? Signaling receptors like Notch (N) and the Drosophila EGF Receptor (dEGFR) appear to act as death and life signals, respectively, and the conserved downstream apoptotic machinery, e.g., caspases, BCL-2-like proteins, etc. are also present. However, these do not give a complete picture of the highly regulated death in the pupal retina. The goal of my lab is to further elucidate the signaling pathways and networks that are required to create the precise pattern of PCD in the fly eye and then apply this knowledge to the greater issue of PCD regulation during development and oncogenesis.

Klumpfuss and PCD

The klumpfuss locus encodes the Drosophila ortholog of Wilms Tumor Suppressor-1 (WT-1), a tumor suppressor gene identified by its loss of activity in pediatric kidney tumors called Wilms tumors. Additionally, mutations in the WT-1 locus have been linked to acute leukemia and DSRCT (Desmoplastic Small Round Cell Tumor) as well as devastating developmental defects such as Denys-Drasch and Frazier Syndromes. WT-1 and klumpfuss are unique members of the EGR family of nuclear factors, characterized by four (vs. the typical three) C2H2 zinc fingers that appear to modulate WT-1s function as both an activator and repressor of transcription.
In the Drosophila eye, klumpfuss is both necessary and sufficient to drive programmed cell death in the lattice, i.e., mutations in klumpfuss result in a partial block of cell death in the interommatidial lattice while overexpression kills lattice cells. Our genetic and biochemical data places klumpfuss in the thick of the known programmed cell death regulators and pathways and make klumpfuss an ideal tool for identifying new players in developmental PCD. Additionally, the role of klumpfuss in PCD will likely elucidate some of the mechanisms of WT-1 function during both development and cancer in vertebrates.

Techniques in our studies include: classical and molecular genetics, immunohistochemistry, cell biology, and morphology of developing tissue, microarray analysis, biochemistry, and molecular biology.