Affiliation: Skirball Institute of Biomolecular Medicine, NYU School of Medicine
Keywords: s. extracellular matrix; t. cell junctions and adhesion
The shape of organs can be critical to their function; for example, changes in the curvature of the human cornea result in visual disorders such as myopia, hypermetropia, astigmatism or keratoconus. A simpler model system like Drosophila may provide insights into the development of curved refractive structures such as the cornea. Each ommatidium of the Drosophila eye contains a biconvex corneal lens that focuses light on the underlying photoreceptor cells. The central part of the corneal lens is thought to be secreted by the underlying cone and primary pigment cells, while the peripheral portion is attached to the secondary and tertiary pigment cells. Here we show that loss of the zinc-finger containing transcription factor Blimp-1 specifically from the secondary and tertiary pigment cells causes flattening of the external corneal lens surface, dramatically reducing its refractive power. One possible mechanism for this effect of Blimp-1 would be a change in the pattern of attachments of the corneal lens to the peripheral pigment cells. The fly corneal lens is a cuticular structure containing the polysaccharide chitin, and the morphology of other chitinous structures such as denticles and tracheal tubes has been shown to depend on the localization of specific zona pellucida (ZP) domain containing proteins, which attach the apical extracellular matrix to the plasma membrane. In a transcriptomic study of the effects of Blimp-1 knockdown in the mid-pupal retina, we observed changes in the expression levels of several genes encoding ZP domain proteins; dusky-like (dyl), CG10005 and cypher (cyr) were downregulated, while neyo, piopio and quasimodo were upregulated. We find that loss of dyl or cyr also causes flattening of the outer surface of the corneal lens. These observations suggest that Blimp-1 may influence corneal lens architecture in part by ensuring the appropriate distribution of the ZP proteins that attach its periphery to the secondary and tertiary pigment cells.