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Proliferation, progenitor cell specification and neurogenesis in the Drosophila eye
Normal development requires the carefully orchestrated coordination of proliferation, cell fate specification, and cellular differentiation. My lab is interested in understanding how these processes are integrated during formation of a complex sensory organ, specifically the eye. We use the genetically amenable Drosophila model system and focus on three critical aspects of eye development: (1) the coordination of cell proliferation and retina primordium induction; (2) the control of organ type specification and the induction of an eye-specific neurogenetic program; (3) the development of morphological and functional characteristics of photoreceptor neurons.
The Retinal Pigmented Epithelium and the Microphthalmia-associated transcription factor The overall objective of this research is to understand how the Retinal Pigmented Epithelium (RPE) is specified and how does it contribute to retinal morphogenesis. The current focus is on the study of the Microphthalmia (Mitf) transcription factor, a major player in the formation of an RPE in mouse. We work in close collaboration with the laboratory of Dr. E. Steingrimsson (University of Iceland) coordinating our efforts by studying the Mitf gene in both mouse and fly. Our goal is to identify the conserved genetic components of the mouse and fly Mitf pathways. During mouse eye development, neural retina (NR) and Retinal Pigmented Epithelium (RPE) originate from different portions of the optic vesicle: the distal part forms the NR while the proximal part develops into the RPE. As the optic vesicle collapses into an optic cup, distal and proximal portions of the epithelium are brought into close proximity forming a bilayered structure. This organization facilitates interactions between the two cell layers and, during eye development, the RPE is thought to produce secreted factors that lead to proper patterning and maintenance of the vertebrate retina (Jablonski et al., 2000; Sheedlo and Turner, 1998; Raymond and Jackson, 1995; Sheedlo et al., 1992; Gaur et al., 1992). The Mitf transcription factor is expressed during critical stages of vertebrate eye development. Mitf expression is initially detected in the entire budding optic vesicle (including both presumptive NR and RPE regions) (Bora et al., 1998; Nguyen and Arnheiter, 2000), but is soon down-regulated within the retinal primordium and the expression of particular Mitf isoforms becomes restricted to RPE cells. In mouse embryos homozygous mutant for Mitf loss-of-function alleles, formation of the optic vesicle and cup occurs at the expected stage, however the partitioning of this tissue into neural retina and pigmented epithelium is disturbed leading to a transformation of regions of the RPE into stratified neural retina (Packer, 1967). The Drosophila eye, although structurally very different from the mouse eye, also develops from a bilayered epithelial structure. The progenitor epithelium that gives rise to the adult fly eye and associated head cuticle, called eye imaginal disc, consists of a flattened sac with a basal columnar cell layer (from which the retina develops) and an apical cuboidal cell layer. Until recently this cell layer was not thought to be directly involved in retinal morphogenesis and it does not, in fact, contribute directly to any part of the adult eye (these cells give rise to head cuticle). However, two groups have shown that interactions between the two layers are, in fact, essential to proper retinal development (Cho et al., 2000; Gibson and Schubiger, 2000). The Microphthalmia transcription factor is conserved in Drosophila (dMitf) and is expressed in a variety of tissues including the eye imaginal disc. We have initiated gain-of-function and loss-of-function analyses of Mitf in Drosophila and are currently investigating its role in proliferation, apoptosis and cell fate specification. Through genetic screens, we plan to identify components of the Mitf genetic pathway and we are screening for proteins that directly interact with both fly and mouse Mitf using the yeast 2-hybrid method. A functional dissection of fly and mouse Mitf protein and its many evolutionarily conserved domains is also in progress.
Selected Publications:
S. S. Ranade, D. Yang-Zhou, S. W. Kong, E. McDonald, T. Cook and F. Pignoni (2008) Analysis of the Otd-dependent transcriptome supports the evolutionary conservation of CRX/OTX/OTD functions in flies and vertebrates. Dev. Biol., 315:521-534.
T. Zhang, S. Ranade, C. Q. Cai, C. Clouser and F. Pignoni (2006) Direct control of neurogenesis by selector factors in the fly eye: regulation of atonal by Ey and So. Development 133:4881-9.
K. L. Kenyon, D. Yang-Zhou, C. Q. Cai, S. Tran B. Hu, C. Clouser, G. Decene, S. Ranade and F. Pignoni (2005) Partner specificity is essential for proper function of the SIX type homeodomain proteins Sine oculis and Optix during fly eye development. Dev. Biol., 286:158-68.
K. L. Kenyon, D. J. Li, C. Clouser, S. Tran and F. Pignoni (2005) The fly SIX-type homeodomain proteins Sine Oculis and Optix partner with different cofactors during eye development. Dev. Dyn., 234:497-504.
T. Zhang, S. Tran, C. Clouser and F. Pignoni (2005) Nicastrin controls aspects of photoreceptor specification and differentiation in the Drosophila eye. Dev. Dyn., 234:590-601.
J. H. Hallsson, B. S. Haflidadóttir, C. Stivers, W. Odenwald, H. Arnheiter, F. Pignoni (corresponding author) and E. Steingrímsson (2004) The bHLH-Zip transcription factor Mitf is conserved in Drosophila and functions in eye development. Genetics, 167:233-241.
K. L. Kenyon, S. S. Ranade, J. Curtiss, M. Mlodzik and F. Pignoni (2003) Coordinating proliferation and tissue specification to promote regional identity in the Drosophila head. Developmental Cell 5: 403-414.
F. Pignoni, B. Hu, K.H. Zavitz, J. Xiao, P.A. Garrity and S.L. Zipursky (1997) The eye-specification proteins So and Eya form a complex and regulate multiple steps in Drosophila eye development. Cell 91:881-891. |
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