Analysis of asymmetric cell division in Drosophila

All living organisms, including humans, develop from a single cell. Many different types of cells have to be created during this process. To generate this huge variety, some cells are able to divide asymmetrically into two different daughter cells. They do this by segregating certain proteins into one of the two daughter cells during mitosis, which then trigger a particular cell fate in this cell but not in its sister. The experiments described here aim at understanding how proteins can be asymmetrically segregated during mitosis. We propose to use the fruitfly Drosophila melanogaster as a model system to understand asymmetric cell divisions. In Drosophila, a protein called Numb is known to segregate asymmetrically in cells of the developing nervous system. We know that Numb localization requires the so-called Par-protein complex that localizes on one side of the cell during mitosis and directs Numb to the opposite side. We have recently shown that the Par-proteins do this by phosphorylating and inhibiting another protein called Lgl on one side of a cell. Our model is that Lgl is needed for localization of certain proteins to the cell cortex. Since it is inhibited on one side, these proteins will be excluded from this side of the cortex and accumulate on the opposite side. The proposed experiments are aimed at understanding how Lgl directs other proteins to the cell cortex. For this, we will identify Lgl binding proteins using immunoprecipitation and mass-spectroscopy and characterize them using the cell-biological and genetic tools available in Drosophila. We will also develop tools that allow us to analyze where in a cell Lgl binds its individual binding partners. In addition, we will develop methods that allow us to locally inactivate Lgl and other proteins in only a particular region of a cell to understand where in the cell these proteins function. These experiments will help us to understand how determinants like Numb are asymmetrically segregated in mitosis. Since Numb is conserved in humans and recent experiments have shown that a mouse homolog is important for regulating the pool of stem cells in the vertebrate brain, we believe that these experiments are of potential medical relevance particularly in the field of stem cell therapy.

All living organisms, including humans, develop from a single cell. Many different types of cells have to be created during this process. To generate this huge variety, some cells are able to divide asymmetrically into two different daughter cells. They do this by segregating certain proteins into one of the two daughter cells during mitosis, which then trigger a particular cell fate in this cell but not in its sister. The experiments described here aim at understanding how proteins can be asymmetrically segregated during mitosis. We propose to use the fruitfly Drosophila melanogaster as a model system to understand asymmetric cell divisions. In Drosophila, a protein called Numb is known to segregate asymmetrically in cells of the developing nervous system. We know that Numb localization requires the so-called Par-protein complex that localizes on one side of the cell during mitosis and directs Numb to the opposite side. We have recently shown that the Par-proteins do this by phosphorylating and inhibiting another protein called Lgl on one side of a cell. Our model is that Lgl is needed for localization of certain proteins to the cell cortex. Since it is inhibited on one side, these proteins will be excluded from this side of the cortex and accumulate on the opposite side. The proposed experiments are aimed at understanding how Lgl directs other proteins to the cell cortex. For this, we will identify Lgl binding proteins using immunoprecipitation and mass-spectroscopy and characterize them using the cell-biological and genetic tools available in Drosophila. We will also develop tools that allow us to analyze where in a cell Lgl binds its individual binding partners. In addition, we will develop methods that allow us to locally inactivate Lgl and other proteins in only a particular region of a cell to understand where in the cell these proteins function. These experiments will help us to understand how determinants like Numb are asymmetrically segregated in mitosis. Since Numb is conserved in humans and recent experiments have shown that a mouse homolog is important for regulating the pool of stem cells in the vertebrate brain, we believe that these experiments are of potential medical relevance particularly in the field of stem cell therapy.