Cell birth and death in the developing Drosophila retina

Tanya Wolff, Purdue University

Abstract

The establishment of pattern is critical to an epithelium's function, yet an understanding of the complex network of factors that contribute to building patterns is still in its infancy. Through the cooperation of many factors, order is imposed on an initially unpatterned system. To this end, this work provides a basic description of two patterning events in the Drosophila eye, cell death and the initial organization of the ommatidial precursors, or unit eyes of the compound eye. The Drosophila eye is particularly well suited to studies on pattern formation. The cellular lattice is a highly precise, 750-fold reiteration of 19 cell units. The eye assembles by a non-clonal mechanism in which fates are specified by the particular set of contacts a cell makes with its neighbors. Work presented here shows that ommatidial organization begins in the morphogenetic furrow of third instar eye discs as cells organize into discrete units. Observations of patterning events in the furrow, neuronal antigen expression and mitotic labelling studies indicate that pattern formation proceeds from the center of a row to its periphery. Mitotic labelling studies suggest cells are regulated at the G1/S transition of the cell cycle and that the signal to divide is conveyed via contacts with specific subsets of cells. The removal of surplus cells from the developing eye organizes the retinal lattice. Quantitative and histological methods demonstrate two phases of cell death. The first, which occurs between 35-55 hrs of development, removes 2-3 cells per ommatidium. The second removes a perimeter population of clusters, smoothing the eye's edge. Two mutants in which the first phase of cell death does not occur normally have been identified and characterized. The presence of a normal late phase of death suggests two distinct mechanisms for cell death operate in the eye. Actin and tubulin distribution throughout development is correlated with cell shape change and suggests the cytoskeleton is an important player in the generation of cellular architecture. These studies provide fundamental descriptions of pattern formation and cell death that can serve as a framework for the identification of genes and programs regulating patterning processes.

Degree

Ph.D.

Advisors

Ready, Purdue University.

Subject Area

Cellular biology

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