New advances in Drosophila provide opportunities to study gene functions

Since the discovery that animal development is under genetic control, one of the major challenges for developmental biologists has been to decipher the functions of specific genes in patterning. The most successful and widely accepted approach to address these challenges in the past 15–20 years has been to characterize the defects associated with specific gene mutations after either random mutagenesis or targeted gene knock outs. Studies in Drosophila melanogaster and Caenorhabditis elegans have validated the use of systematic genetic approaches to dissect developmental pathways. In particular, the seminal screens for both maternal and zygotic mutations affecting embryonic pattern in Drosophila have led to a comprehensive model encompassing a finite set of mechanisms underlying the establishment of the embryonic axes and subsequent segmentation of the embryo (1, 2). In theory, however, one needs to reflect on whether the knowledge gained through one methodology can provide a thorough understanding of development. Perhaps many critical developmental steps have been missed because the genetic screens that were conducted do not take into account gene pleiotropy or redundancy. In other words, is it possible that the genetic approach has unraveled only part of the logic of development? A paper in this issue of Proceedings (3) illustrates that many of the genes that have not yet been analyzed in Drosophila encode potentially important developmental functions. This analysis underscores the need to address their biological functions because they may identify new genetic networks involved in patterning. The genetic approach used to dissect developmental pathways relies on the identification of mutations that affect specific processes. Because this approach relies on single mutational events, it only detects genes, which, when mutated, result in readily obvious mutant phenotypes. This may not be the case, however, if the gene is pleiotropic or if multiple gene activities act in a redundant …