Functional Annotation Of The Piebald Deletion Region Of Mouse Chromosome 14

Abstract

We currently know a great deal about the mouse genome, including sequence, genomic location and expression patterns for many genes. However, the function of individual genes is unknown in many cases. Understanding gene function is critical to assess a gene’s relationship to human health and disease. Forward genetic screens are a classic strategy to evaluate animals for phenotypes of interest and link a gene to a biological function. The piebald deletion complex is a set of overlapping chromosomal deficiencies on distal mouse chromosome 14 created during the specific locus test. We have surveyed the functional genetic content of the piebald deletion region in an essential gene mutagenesis screen of 952 genomes to recover seven lethal mutants. The screen uses the deletion resource and the spotted coat color of the piebald mouse to identify developmentally critical genes within an ~19Mb interval of the distal region of mouse chromosome 14. The ENU-induced mutations were mapped to defined genetic intervals using the piebald deletion panel. Lethal mutations identified included a loss-of-function allele of Phr1 resulting in respiratory distress at birth and a locus required for establishment of the left-right embryonic axis. We further characterized the ENU-induced mutation disrupting left-right patterning as an allele of Progesterone induced blocking factor 1 (Pibf1) by positional cloning and the characterization of a second allele. We show that the phenotype of Pibf1-deficient embryos is consistent with disrupted Hedgehog signaling. We also find that PIBF1 localizes to the ciliary axoneme and that loss of Pibf1 disrupts the formation of both cilia and microvilli suggesting a role in the organization of the cytoskeleton. Thus, our studies identify Pibf1 as a gene important for cytoskeletal organization, ciliogenesis and signal transduction. A functional map of the piebald region integrates experimental genetic data from the deletion panel, mutagenesis screen, and the targeted disruption of specific genes. A comparison of several genomic intervals targeted in regional mutagenesis screens suggests that the piebald region is characterized by a low gene density and high essential gene density with a distinct genomic content and organization that supports complex regulatory interactions and promotes evolutionary stability.