Protein phosphatase 1 beta is required far the maintenance of muscle attachments

Type 1 serine/threonine protein phosphatases (PP1) are important regulators of many cellular and developmental processes, including glycogen metabolis m, muscle contraction, and the cell cycle [1-5], Drosophila and humans both have multiple genes encoding PP1 isoforms [3,6,7]; each has one beta and s everal alpha isoform genes (alpha(1), alpha(2), alpha(3) in flies, alpha an d gamma in humans; mammalian PP1 beta is also known as PP1 delta), The alph a/beta subtype differences are highly conserved between flies and mammals [ 6], Though all these proteins are >85% identical to each other and have ind istinguishable activities in vitro, we show here that the Drosophila beta i soform has a distinct biological role, We show that PP1 beta 9C corresponds to flapwing (flw), previously identified mutants of which are viable but f lightless because of defects in indirect flight muscles (IFMs) [8], We have isolated a new, semi-lethal flw allele that shows a range of defects, espe cially in muscles, which break away from their attachment sites and degener ate.