Computer analysis of cell division in Drosophila imaginal discs: Model revision and extension to simulate leg disc growth

Abstract

Extension of a computer model designed by the author to simulate clone growth in the Drosophila head disc allows modelling of growth in the leg disc. A fault of the earlier model, namely break-up of clones caused by cells being pushed away from their neighbours is rectified by reducing the amount of separation allowed between recently divided daughter cells. A geometrical method is used to convert sectorial clones in the leg disc to the parallel sided clones seen in the adult leg. It is suggested here that clone growth in leg and head discs occurs in similar ways, based on the random division of cells in a two dimensional plane, the radial growth in the leg disc being due to lack of external constraints like those present in the head disc, for example the larval brain to head disc linkage. Several parameters of growth, including differential mitotic activity over the growing disc, and relative orientations of individual cell divisions are investigated, and the relevance of these data to experiments on real discs is discussed. In particular, the accuracy of information about cell division orientations gleaned from twin spot studies is questioned.