During organogenesis axial patterning is essential for growth and development. The fruit fly, Drosophila, provides an ideal model for genetic analysis of dorsoventral (DV) patterning and growth of the eye primordium. DV patterning is the first axis formed in eye. Our goal is to identify key genes involved in early eye patterning. In early eye imaginal disc, the DV patterning is established by initiation of expression of a dorsal selector gene, pannier (pnr), which controls the expression of wingless (wg) signaling gene and Iroquois family transcription factors. The dorsal genes antagonize the function of ventral genes including Lobe (L), Serrate (Ser) and fringe (fng). The interaction of these two groups of genes leads to preferential activation of Notch signaling at the DV border to induce growth and differentiation. One of the major questions that need to be addressed is the molecular genetic basis for such regulatory interactions. In the ventral domain, a Notch ligand Serrate (Ser) and a novel protein Lobe (L) play key roles. L is expressed in both dorsal and ventral domains but is only required for ventral eye growth as a component of Notch signaling pathway. L is required for ventral eye development, growth, and survival. To understand the molecular genetic basis of L functions in cell survival, specification and growth, we will use molecular genetics approaches commonly employed in Drosophila model system to analyze (i) the function of L and Homothorax (Hth), a negative regulator of eye development, in the control of eye growth (ii) the L function in retinal cell fate determination and differentiation, and (iii) function of L and Cullin-4, an E3 ubiquitin ligase, in the control of ventral eye cell survival. These studies will help to elucidate the genetic circuitry involved in L mediated Notch pathway regulation of cell survival, growth, and patterning. Most of the genes studied here are highly conserved as they are present in higher mammals including humans, and genetic control of DV patterning is an important event during mammalian eye development. This study will help in revealing mechanisms of genetic interactions involved in early eye development. Thus, our study will also contribute to the understanding of mammalian eye development and etiology of early childhood retinal diseases.
Axial patterning, a fundamental process of organogenesis in multi-cellular organisms, involves transition of a mono-layered epithelium to a three- dimensional organ. A well established model of the Drosophila melanogaster (fruit fly) will be employed to study dorso-ventral (DV) (axial) patterning and growth in the developing eye. DV patterning, the first lineage restriction event occurring in the eye, results in the formation of dorsal and ventral domains of the eye. The border between the dorsal and ventral domains of the eye is the site of Notch (N) signaling pathway which regulates cell proliferation and differentiation of the eye. We will try to understand the genetic mechanism of DV patterning and growth during early eye imaginal disc development in Drosophila. The DV boundary is established by interactions of dorsal selector genes and ventral genes. The dorsal factors include a GATA-family transcription factor Pannier (Pnr), the secreted morphogen Wingless (Wg), and Iroquois (Iro-C) family homeobox proteins. In the ventral domain, a Notch ligand Serrate (Ser) and a novel protein Lobe (L) play key roles. L is expressed in both dorsal and ventral domains but is only required for ventral eye growth as a component of Notch signaling pathway. The Drosophila eye begins from a ventral equivalent state on which dorsal fate is established. One of the important questions is how the initial ventral fate of the eye is established and maintained. Our earlier studies have demonstrated that L is required for ventral eye development, growth, and survival. To understand the molecular genetic basis of L functions in cell survival, specification and growth, we will use molecular genetics approaches commonly employed in Drosophila model system to analyze (i) the function of L and Homothorax (Hth), a negative regulator of eye development, in the control of eye growth (ii) the L function in retinal cell fate determination and differentiation, and (iii) function of L and Cullin-4, an E3 ubiquitin ligase, in the control of ventral eye cell survival. These studies will help to elucidate the genetic circuitry involved in L mediated Notch pathway regulation of cell survival, growth, and patterning. Since the genetic machinery is highly conserved it will be interesting to extrapolate the information to higher vertebrates. These studies will contribute towards understanding the genetic mechanism of early developmental events during organogenesis. The genetic machinery involved in axial patterning is highly conserved across the species. In humans and other vertebrates, DV polarity of the retina directs the retinal axon projections to the brain. These studies will shed light on the role of early developmental events that may affect the retinal axon projection to the brain. It will also help to understand the molecular basis of developmental defects caused by mutations in the human homolog of Drosophila.
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