HNF1 is a transcriptional activator of many hepatic genes including albumin, alpha1-antitrypsin, and alpha- and beta-fibrinogen. It is related to the homeobox gene family and is predominantly expressed in liver and kidney. Mice lacking HNF1 fail to thrive and die around weaning after a progressive wasting syndrome with a marked liver enlargement. The transcription rate of genes like albumin and alpha1-antitrypsin is reduced, while the gene coding for phenylalanine hydroxylase is totally silent, giving rise to phenylketonuria. Mutant mice also suffer from severe Fanconi syndrome caused by renal proximal tubular dysfunction. The resulting massive urinary glucose loss leads to energy and water wasting. HNF1-deficient mice may provide a model for human renal Fanconi syndrome.

The distal region of mouse chromosome 7 contains a cluster of imprinted genes that includes 1t19 and Igf2 (insulin-like growth factor 2). H19 is expressed as an untranslated RNA found at high levels in endodermal and mesodermal embryonic tissues. This gene is imprinted and exclusively expressed from the allele of maternal origin. The Igf2 gene shows a similar pattern of expression but is expressed from the paternal allele. We have generated a targeted deletion of the 1-119 transcription unit by insertion of a neo replacement cassette. The homozygous mutant animals are viable and fertile and display an overgrowth phenotype of 8% compared with wild-type littermates. This is associated with the disruption of Igf2 imprinting and the consequent biallelic expression of this gene. A striking feature of the recombinant H19 allele is the occurrence of a parental imprint set on the neo replacement cassette. Therefore imprinting of the 1-119 locus is independent of the H19 gene itself. Taken together with the results of a larger H19 mutation described previously, this indicates that an imprinting control element is located within the region 10 kb upstream of H19.[Key Words: H19; homologous recombination; Igf2; genomic imprinting] Received January 16, 1997; revised version accepted April 24, 1997.In mammals, normal embryonic development is achieved only in the presence of the maternal and paternal genome (McGrath and Solter 1984;Surani et al. 1984). Extensive research using mice carrying translocations has shown that certain chromosomal regions must carry genes for which the maternal and paternal copy are not functionally identical (Cattanach and Kirk 1985;Beechey and Cattanach 1996). This observation has led to the notion of an imprint set on certain genes during gametogenesis. This results in differential expression of the two parental alleles of these genes, which can occur at certain developmental stages and in certain tissues. Imprinting can therefore be defined by two steps: marking of certain genes at the time the two genomes are separated and recognition of this marking at specific times during embryogenesis. The mechanism by which imprinting is established is as yet unknown, although methylation of CpGs is a possible candidate (Li et al. 1993;Razin and Cedar 1994). Whether this methylation is a cause or only a consequence of imprinting remains unclear (Sasaki et al. 1995).To date, 17 genes have been shown to be imprinted in mouse and in man (for review, see Barlow i995; John and Surani 1996). In the distal region of mouse chromosome 7, a cluster of such genes covering -600 kb has been 3Corresponding author. E-MAIL dandolo@cochin.inserm.fr; FAX 33-1-44-41-24-62.described. These genes are HI 9, Mash2, and p5 7 Kjp~ (Bartolomei et al. 1991;Guillemot et al. 1995;Hatada and Mukai 1995), which are expressed from the chromosome of maternal origin, and Igf2 (insulin-like growth factor 2), and Ins2 (insulin 2), expressed from the chromosome of paternal origin (DeChiara et al. 1991;Giddings et al. 1994;Deltour et al. 1995) (...

CUG-BP1/CELF1 is a multifunctional RNA-binding protein involved in the regulation of alternative splicing and translation. To elucidate its role in mammalian development, we produced mice in which the Cugbp1 gene was inactivated by homologous recombination. These Cugbp1 ؊/؊ mice were viable, although a significant portion of them did not survive after the first few days of life. They displayed growth retardation, and most Cugbp1 ؊/؊ males and females exhibited impaired fertility. Male infertility was more thoroughly investigated. Histological examination of testes from Cugbp1 ؊/؊ males showed an arrest of spermatogenesis that occurred at step 7 of spermiogenesis, before spermatid elongation begins, and an increased apoptosis. A quantitative reverse transcriptase PCR analysis showed a decrease of all the germ cell markers tested but not of Sertoli and Leydig markers, suggesting a general decrease in germ cell number. In wild-type testes, CUG-BP1 is expressed in germ cells from spermatogonia to round spermatids and also in Sertoli and Leydig cells. These findings demonstrate that CUG-BP1 is required for completion of spermatogenesis.Following transcription, a eukaryotic pre-mRNA undergoes nuclear maturation. The mature mRNA is then exported to the cytoplasm, where its stability and translation are finely regulated. It is increasingly clear that a strong link exists between the nuclear and the cytoplasmic events that affect a pre-mRNA and the resulting mRNA. This is illustrated by the observation that a number of RNA-binding proteins, such as those belonging to the CELF or BRUNOL family, control both the splicing of pre-mRNA and the cytoplasmic fate of mature mRNA.The vertebrate CELF family consists of six members, and the name (CUG-BP1 and ETR-3 Like Factors) was derived from the two founding members, CUG-BP1/CELF1 and ETR-3/CUG-BP2/CELF2 (19). The same family was also named BRUNOL (Bruno-like) due to the sequence similarity that its members share with Drosophila melanogaster Bruno (15). The biochemical functions of these proteins are numerous. In mammals, CELF1 to CELF6 were shown to regulate the alternative splicing of some pre-mRNA by stimulating either inclusion or skipping of nonconstitutive exons (for a review, see reference 1). Furthermore, in the cytoplasm, by binding to the 5Ј regions of the cognate mRNAs, CUG-BP1/CELF1 stimulates the translation of the cdk inhibitor p21 and determines the translation initiation codon of the transcription factor C/EBP␤ (41, 42). CUG-BP2/CELF2 controls the stability and the translation of cyclooxygenase-2 mRNA by binding to the 3Ј untranslated region (3ЈUTR) (26). In Xenopus embryos, EDEN-BP (embryo deadenylation element-binding protein,

To investigate the in vivo function of Fas ligand (FasL), we produced a mouse strain with a FasL gene flanked by loxP sequences. Mice with homozygous floxed FasL gene showed no obvious abnormalities. However, germline deletion of the FasL gene, obtained after mating with mice expressing ubiquitous Cre recombinase, resulted in an unexpectedly severe phenotype. FasL−/− mice exhibited an extreme splenomegaly and lymphadenopathy associated with lymphocytic infiltration into multiple organs and autoimmune disease. This severe phenotype led to the premature death at 4 mo of age of >50% of the homozygous mice. It stands in sharp contrast with the milder disease observed in gld (generalized lymphoproliferative disease) mice, indicating that the FasL allele of these mice encodes a protein still able to bind, albeit at a very low level, the Fas receptor.

The initiation of X-chromosome inactivation in female mammals is controlled by a key locus, the X-inactivation centre (Xic). The Xist gene, which maps to the candidate region for Xic and is expressed exclusively from the inactive X chromosome, is thought to be an essential component of the Xic. To test whether sequences spanning several hundred kilobases and including Xist from the Xic region are capable of initiating inactivation, we have created a series of transgenic mice using a 460 kb yeast artificial chromosome (YAC). Analysis in these mice of the expression of Xist, of a LacZ reporter gene and of two genes in the region that are normally silent on the inactive X chromosome, suggests that essential sequences for Xist expression and X-inactivation may be absent in these transgenic animals.