Genetic and functional analysis of PARP, a DNA strand break-binding enzyme.

Poly(ADP-ribose) polymerase (PARP) is a nuclear enzyme activated by binding to a single- or double-strand break of DNA and is one of the death substrates for caspase-3 in apoptosis. The nuclear function of PARP is well studied and recent PARP-knockout studies indicate that PARP takes part in chromosomal stability. To analyze the effect of PARP overexpression, or loss of function, we have cloned PARP cDNA and the gene from Drosophila melanogaster and studied its function in developmental stages. Organization of exons corresponds to the functional domains of PARP. An alternatively spliced form of PARP lacking exon 5, which encodes the auto-modification domain, is found in Drosophila. Expression of the PARP gene is at high levels in embryos at 0-6h after egg laying and gradually decreased. In situ mRNA hybridization indicates localization of PARP mRNA in cells along the central nervous system at a late stage of embryogenesis. Overexpression of the gene in the developing eye primordia of D. melanogaster is an excellent experimental model to analyze the cell cycle and programmed cell death. We introduced PARP expression vector overexpresses PARP in the eye discs of Drosophila, and established the PARP transgenic flies by P element-mediated germ line transformation. These flies showed mild roughening of the normally smooth ommatidial lattice involving tissue polarity disruption characterized by missrotation and incorrect chirality of ommatidia. Possible mechanisms of involvement of PARP in the development are discussed.