As the human genome project approaches completion, the challenge for mammalian geneticists is to develop approaches for the systematic determination of mammalian gene function. Mouse mutagenesis will be a key element of studies of gene function. Phenotype-driven approaches using the chemical mutagen ethylnitrosourea (ENU) represent a potentially efficient route for the generation of large numbers of mutant mice that can be screened for novel phenotypes. The advantage of this approach is that, in assessing gene function, no a priori assumptions are made about the genes involved in any pathway. Phenotype-driven mutagenesis is thus an effective method for the identification of novel genes and pathways. We have undertaken a genome-wide, phenotype-driven screen for dominant mutations in the mouse. We generated and screened over 26,000 mice, and recovered some 500 new mouse mutants. Our work, along with the programme reported in the accompanying paper, has led to a substantial increase in the mouse mutant resource and represents a first step towards systematic studies of gene function in mammalian genetics.

Vertebrate organs show consistent left-right (L-R) asymmetry in placement and patterning. To identify genes involved in this process we performed an ENU-based genetic screen. Of 135 lines analyzed 11 showed clear single gene defects affecting L-R patterning, including 3 new alleles of known L-R genes and mutants in novel L-R loci. We identified six lines (termed "gasping") that, in addition to abnormal L-R patterning and associated cardiovascular defects, had complex phenotypes including pulmonary agenesis, exencephaly, polydactyly, ocular and craniofacial malformations. These complex abnormalities are present in certain human disease syndromes (e.g., HYLS, SRPS, VACTERL). Gasping embryos also show defects in ciliogenesis, suggesting a role for cilia in these human congenital malformation syndromes. Our results indicate that genes controlling ciliogenesis and left-right asymmetry have, in addition to their known roles in cardiac patterning, major and unexpected roles in pulmonary, craniofacial, ocular and limb development with implications for human congenital malformation syndromes. Developmental Dynamics 238:581-594, 2009.

Objective: The Gnas transcription unit located within an imprinting region encodes several proteins, including the G-protein a-subunit, Gsa, its isoform XLas and their variant truncated neural forms GsaN1 and XLN1. Gsa and GsaN1 are expressed predominantly from the maternally derived allele in some tissues, whereas XLas and XLN1 are expressed exclusively from the paternally derived allele. The relative contribution of full-length Gsa and XLas, and truncated forms GsaN1 and XLN1 to phenotype is unknown. The edematous-small point mutation (Oed-Sml) in exon 6 of Gnas lies downstream of GsaN1 and XLN1, but affects full-length Gsa and XLas, allowing us to address the role of full-length Gsa and XLas. The aim of this study was therefore to determine the metabolic phenotypes of Oed and Sml mice, and to correlate phenotypes with affected transcripts. Methods: Mice were fed standard or high-fat diets and weighed regularly. Fat mass was determined by DEXA analysis. Indirect calorimetry was used to measure metabolic rate. Glucose was measured in tolerance tests and biochemical parameters in fasted plasma samples. Histological analysis of fat and liver was carried out post mortem. Results: Oed mice are obese on either diet and have a reduced metabolic rate. Sml mice are lean and are resistant to a high-fat diet and have an increased metabolic rate. Conclusion: Adult Oed and Sml mice have opposite metabolic phenotypes. On maternal inheritance, the obese Oed phenotype can be attributed to non-functional full-length Gsa. In contrast, on paternal inheritance, Sml mice were small and resistant to the development of obesity on a high-fat diet, effects that can be attributed to mutant XLas. Thus, the neural isoforms, GsaN1 and XLN1, do not appear to play a role in these metabolic phenotypes.