Influence of a nonfragile FHIT transgene on murine tumor susceptibility.

FHIT, at a constitutively active chromosome fragile site, is often a target of chromosomal aberrations and deletion in a large fraction of human tumors. Inactivation of murine Fhit allelessignificantly increases susceptibility of mice to spontaneous and carcinogen-induced tumorigenesis. In this study, transgenic mice, carrying a human FHIT cDNA under control of the endogenous promoter, were produced to determine the effect of Fhit expression, from a nonfragile cDNA transgene outside the fragile region, on carcinogen-induced tumor susceptibility of wildtype and Fhit heterozygous mice. Mice received sufficient oral doses of N-nitrosomethybenzylamine (NMBA) to cause forestomach tumors in >80% of nontransgenic control mice. Although the level of expression of the FHIT transgene in the recombinant mouse strains was much lower than the level of endogenous Fhit expression, the tumor burden in NMBA-treated male transgenic mice was significantly reduced, while female transgenic mice were not protected. To determine if the difference in protection could be due to differences in epigenetic changes at the transgene loci in male versus female mice, we examined expression, hypermethylation and induced re-expression of FHIT transgenes in male and female mice or cells derived from them. The transgene was methylated in male and female mice and in cell lines established from male and female transgenic kidneys, the FHIT locus was both hypermethylated and deacetylated. It is likely that the FHIT transgene is more tightly silenced in female transgenic mice, leading to a lack of protection from tumor induction.

Skeletal dysplasia and male infertility locus on mouse chromosome 9.

In mice and humans, growth insufficiency and male infertility are common disorders that are genetically and phenotypically complex. We describe a spontaneously arising mouse mutant, chagun, that is affected by both dwarfism and male infertility. Dwarfism disproportionately affects long bones and is characterized by a defect in the proliferative zone of chondrocytes in the growth plate. Gonads of mutant males are small, with apparent germ cell loss and no evidence of mature sperm. The locus responsible for chagun is recessive and maps to distal chromosome 9, in a region homologous to human chromosome 3. This location is consistent with chagun defining a novel locus. Identification of the mutant gene will uncover the basis for another type of skeletal dysplasia and male infertility.

Molecular cloning of Ian4: a BCR/ABL-induced gene that encodes an outer membrane mitochondrial protein with GTP-binding activity.

Using the representation difference analysis technique, we have identified a novel gene, Ian4, which is preferentially expressed in hematopoietic precursor 32D cells transfected with wild-type versus mutant forms of the Bcr/Abl oncogene. Ian4 expression was undetectable in 32D cells transfected with v-src, oncogenic Ha-ras or v-Abl. Murine Ian4 maps to chromosome 6, 25 cM from the centromere. The Ian4 mRNA contains two open reading frames (ORFs) separated by 5 nt. The first ORF has the potential to encode for a polypeptide of 67 amino acids without apparent homology to known proteins. The second ORF encodes a protein of 301 amino acids with a GTP/ATP-binding site in the N-terminus and a hydrophobic domain in the extreme C-terminus. The IAN-4 protein resides in the mitochondrial outer membrane and the last 20 amino acids are necessary for this localization. The IAN-4 protein has GTP-binding activity and shares sequence homology with a novel family of putative GTP-binding proteins: the immuno-associated nucleotide (IAN) family.

Genomic organization, promoter analysis, and chromosomal mapping of the mouse gene encoding Cdk9.

Cdk9, previously known as PITALRE, belongs to the Cdc2 family of protein kinases. We report the isolation and characterization of the complete gene coding for the murine Cdk9 protein. The gene contains seven exons spanning over 6 kb of genomic DNA, and the exon/intron boundaries conformed to the GT/AG rule. The Cdk9 gene mapped on mouse chromosome 2, which is consistent with the known region of synteny with human chromosome 9q34.1. The length of the individual exons ranged from 82 to 850 bp, and introns ranged from 452 to 1,465 bp. The further 5' flanking region of the gene showed features of a housekeeping promoter, such as the lack of a canonical TATA box and the presence of a CCAAT box as well as several GC boxes, which are potential binding sites for numerous transcription factors. Additionally, we performed a basic analysis of the transcriptional activity of the promoter and found that the 364 bp of Cdk9 5' flanking region were able to elicit high transcriptional levels of a luciferase reporter gene in NIH3T3 cells. This study provides the molecular basis for understanding the transcriptional control of the Cdk9 gene, and could serve to facilitate the molecular genetic investigation of Cdk9 function during mouse embryonal development.

Muir-Torre-like syndrome in Fhit-deficient mice.

To investigate the role of the Fhit gene in carcinogen induction of neoplasia, we have inactivated one Fhit allele in mouse embryonic stem cells and produced (129/SvJ x C57BL/6J) F(1) mice with a Fhit allele inactivated (+/-). Fhit +/+ and +/- mice were treated intragastrically with nitrosomethylbenzylamine and observed for 10 wk posttreatment. A total of 25% of the +/+ mice developed adenoma or papilloma of the forestomach, whereas 100% of the +/- mice developed multiple tumors that were a mixture of adenomas, squamous papillomas, invasive carcinomas of the forestomach, as well as tumors of sebaceous glands. The visceral and sebaceous tumors, which lacked Fhit protein, were similar to those characteristic of Muir-Torre familial cancer syndrome.

Hepatitis B virus transgenic mouse model of chronic liver disease.

A model for hepatitis B virus-associated chronic liver disease has been made using cloned hepatitis B virus DNA as a transgene in a severe combined immunodeficient host. These mice consistently support virus gene expression and replication. After adoptive transfer of unprimed, syngeneic splenocytes, these mice cleared virus from liver and serum, and developed chronic liver disease. This model will permit identification of the host and virus contributions to chronic liver disease in the absence of tolerance.

Complete cDNA cloning, genomic organization, chromosomal assignment, functional characterization of the promoter, and expression of the murine Bamacan gene.

Bamacan is a chondroitin sulfate proteoglycan that abounds in basement membranes. To gain insights into the bamacan gene regulation and transcriptional control, we examined the genomic organization and identified the promoter region of the mouse bamacan gene. Secondary structure analysis of the protein reveals a sequential organization of three globular regions interconnected by two alpha-helix coiled-coils. The N- and the C-terminal ends carry a P-loop and a DA box motif that can act cooperatively to bind ATP. These features as well as the high sequence homology with members of the SMC (structural maintenance of chromosome) protein family led us to conclude that bamacan is a member of this protein family. The gene comprises 31 exons and is driven by a promoter that is highly enriched in GC sequences and lacks TATA and CAAT boxes. The promoter is highly functional in transient cell transfection assays, and step-wise 5' deletions identify a strong enhancer element between -659 and -481 base pairs that includes Jun/Fos proto-oncogene-binding elements. Using backcrossing experiments we mapped the Bam gene to distal chromosome 19, a locus syntenic to human chromosome 10q25. Bamacan is differentially expressed in mouse tissues with the highest levels in testes and brain. Notably, bamacan mRNA levels are low in normal cells and markedly reduced during quiescence but are highly increased when cells resume growth upon serum stimulation. In contrast, in all transformed cells tested, bamacan is constitutively overexpressed, and its levels do not change with cell cycle progression. These results suggest that bamacan is involved in the control of cell growth and transformation.

Characterization of a novel receptor that maps near the natural killer gene complex: demonstration of carbohydrate binding and expression in hematopoietic cells.

A novel type II integral membrane protein has been identified in the course of screening for genes overexpressed in a mouse model of chronic myelogenous leukemia blast crisis. This new protein, designated NKCL, consists of a 210-amino acid polypeptide with a short, NH2-terminal cytoplasmic tail of 17 amino acids preceding a transmembrane domain and a COOH-terminal extracellular region. The COOH-terminal 132 amino acids bear typical features of the C-type animal lectin carbohydrate-recognition domain. The Nkcl gene is unique in that it maps just proximal to the region of the genome that encodes group V members of the C-type animal lectin family near the natural killer gene complex on mouse chromosome 6, but its protein product also has features of several group II C-type animal lectins. Most notably, it has a complete Ca2+-binding site 2, which forms part of the sugar-binding site in other members of the family, and binds mannose in a Ca2+-dependent manner. Moreover, its expression is not restricted to natural killer cells, as reported for the majority of group V lectins. Nkcl is expressed in pluripotent myeloid precursors, precursor and mature macrophages, and neutrophils.

The murine Fhit locus: isolation, characterization, and expression in normal and tumor cells.

The murine Fhit locus maps near the centromere nu proximal Ptprg locus on mouse chromosome 14. The cDNA sequence and structure are similar to those of the human gene, with exons 5-9 encoding the protein. The predominant mRNA in the tissues and cell lines tested was an alternatively spliced form missing exon 3. Most murine cell lines tested, including lines established from normal mouse embryos and tumors, expressed very low or undetectable levels of Fhit mRNA. Most normal mouse tissues expressed wild-type Fhit mRNA, whereas approximately 40% of murine lung carcinomas expressed wild-type and aberrant Fhit RT-PCR products that lacked various exons. Several tumorigenic mouse cell lines exhibited homozygous deletions of Fhit exons. We conclude that the murine Fhit gene, like its human counterpart, is a target of alterations involved in murine carcinogenesis.

The Tight skin mouse: demonstration of mutant fibrillin-1 production and assembly into abnormal microfibrils.

Mice carrying the Tight skin (Tsk) mutation harbor a genomic duplication within the fibrillin-1 (Fbn 1) gene that results in a larger than normal in-frame Fbn 1 transcript. In this study, the consequences of the Tsk mutation for fibrillin-containing microfibrils have been examined. Dermal fibroblasts from Tsk/+ mice synthesized and secreted both normal fibrillin (approximately 330 kD) and the mutant oversized Tsk fibrillin-1 (approximately 450 kD) in comparable amounts, and Tsk fibrillin-1 was stably incorporated into cell layers. Immunohistochemical and ultrastructural analyses of normal and Tsk/+ mouse skin highlighted differences in the gross organization and distribution of microfibrillar arrays. Rotary shadowing of high Mr preparations from Tsk/+ skin demonstrated the presence of abundant beaded microfibrils. Some of these had normal morphology and periodicity, but others were distinguished by diffuse interbeads, longer periodicity, and tendency to aggregate. The presence of a structurally abnormal population of microfibrils in Tsk/+ skin was unequivocally demonstrated after calcium chelation and in denaturating conditions. Scanning transmission electron microscopy highlighted the presence of more mass in Tsk/+ skin microfibrils than in normal mice skin microfibrils. These data indicate that Tsk fibrillin-1 polymerizes and becomes incorporated into a discrete population of beaded microfibrils with altered molecular organization.

A tandem duplication within the fibrillin 1 gene is associated with the mouse tight skin mutation.

Mice carrying the Tight skin (Tsk) mutation have thickened skin and visceral fibrosis resulting from an accumulation of extracellular matrix molecules. These and other connective tissue abnormalities have made Tskl + mice models for scleroderma, hereditary emphysema, and myocardial hypertrophy. Previously we localized Tsk to mouse chromosome 2 in a region syntenic with human chromosome 15. The microfibrillar glycoprotein gene, fibrillin 1 (FBN1), on human chromosome 15q, provided a candidate for the Tsk mutation. We now demonstrate that the Tsk chromosome harbors a 30- to 40-kb genomic duplication within the Fbn1 gene that results in a larger than normal in-frame Fbn1 transcript. These findings provide hypotheses to explain some of the phenotypic characteristics of Tskl + mice and the lethality of Tsk/Tsk embryos.

Genomic structure and chromosomal mapping of the mouse VE-cadherin gene (Cdh5).

Vascular endothelial cadherin (VE-cadherin) is located strictly at endothelial junctions and appears to be a major adhesive component of cell to cell contacts. Genomic clones spanning 36 kb and encompassing the mouse VE-cadherin gene have been isolated and characterized. The gene is composed of 12 exons that exhibit conventional vertebrate splicing. The first exon is entirely untranslated, and both exons 2 and 12 contain untranslated regions. A single major transcriptional start site was identified and located 75 bases upstream of the translation initiation codon in the cDNA sequence. The proximal 5'-flanking domain lacks consensus TATA and CAAT boxes at the usual positions. Exon-intron boundaries are similar to those of other cadherin genes, with some exceptions that may have a functional significance in VE-cadherin behavior. The VE-cadherin gene (locus Cdh5) maps to mouse chromosome 8, where it colocalizes with E-cadherin (locus Cdh1), P-cadherin (locus Cdh3), and M-cadherin (locus Cdh14) genes, suggesting that it might be part of a larger cluster of cadherin sequences.

Molecular basis of the pleiotropic phenotype of mice carrying the hypervariable yellow (Ahvy) mutation at the agouti locus.

The murine agouti locus regulates a switch in pigment synthesis between eumelanin (black/brown pigment) and phaeomelanin (yellow/red pigment) by hair bulb melanocytes. We recently described a spontaneous mutation, hypervariable yellow (Ahvy) and demonstrated that Ahvy is responsible for the largest range of phenotypes yet identified at the agouti locus, producing mice that are obese with yellow coats to mice that are of normal weight with black coats. Here, we show that agouti expression is altered both temporally and spatially in Ahvy mutants. Agouti expression levels are positively correlated with the degree of yellow pigmentation in individual Ahvy mice, consistent with results from other dominant yellow agouti mutations. Sequencing of 5' RACE and genomic PCR products revealed that Ahvy resulted from the integration of an intracisternal A particle (IAP) in an antisense orientation within the 5' untranslated agouti exon 1C. This retrovirus-like element is responsible for deregulating agouti expression in Ahvy mice; agouti expression is correlated with the methylation state of CpG residues in the IAP long terminal repeat as well as in host genomic DNA. In addition, the data suggest that the variable phenotype of Ahvy offspring is influenced in part by the phenotype of their Ahvy female parent.

Physical and genetic localization of the gene encoding the AP-2 transcription factor to mouse chromosome 13.

Transcription factors are a major determinant of developmental fate. The chromosomal localization of the genes encoding these proteins provides important information that can link them to known genetic abnormalities. Here, we report the mapping of the mouse gene for transcription factor AP-2, a protein that has been implicated in human oncogenesis. Using FISH, we have mapped the gene encoding the transcription factor AP-2, Tcfap2, to mouse Chromosome 13A5-B1. We have also extended this analysis by placing Tcfap2 on the mouse genetic map, and we discuss the candidate mouse mutations that map in the vicinity of this transcription factor.