Impact of intra- and interstrain cross-fostering on mouse maternal care

The importance of maternal care in shaping an individual's phenotype in health and disease is becoming more and more apparent in both human and animal studies. However, in mouse studies using inbred strains or knockout mice to analyze the genetic influences on the development of normal and aberrant behavioral phenotypes, maternal behavior is very poorly characterized and often ignored. This study provides an extensive analysis of spontaneous maternal behavior of inbred mice in three conditions: (1) comparing two commonly used strains, (2) analyzing the impact of adopting pups from the same strain (intrastrain cross-fostering) and (3) analyzing the impact of adopting pups from a different strain (interstrain cross-fostering). For each condition, maternal behavior was analyzed continuously over 23-h periods on postnatal days 2, 4, 6 and 9. We report that (1) the maternal behavior of C57BL/6J and DBA/2J dams toward their biological offspring is highly similar, (2) intrastrain cross-fostering has minimal impact on maternal behavior of C57BL/6J and DBA/2J dams, (3) interstrain cross-fostering does not modify the strain differences in maternal care observed between AKR and C3H/He mothers and (4) the pup strain does influence the amount of maternal behavior shown by both mothers in interstrain cross-fostering. These latter findings demonstrate that both mother strain and pup strain are key determinants of maternal behavior.

The development of a highly informative mouse Simple Sequence Length Polymorphism (SSLP) marker set and construction of a mouse family tree using parsimony analysis

To identify highly informative markers for a large number of commonly employed murine crosses, we selected a subset of the extant mouse simple sequence length polymorphism (SSLP) marker set for further development. Primer pairs for 314 SSLP markers were designed and typed against 54 inbred mouse strains. We designed new PCR primer sequences for the markers selected for multiplexing using the fluorescent dyes FAM, VIC, NED, and ROX. The number of informative markers for C57BL/6J x DBA/2J is 217, with an average spacing of 6.8 centiMorgans (cM). For all other pairs of strains, the mean number of informative markers per cross is 197.0 (SD 37.8) with a mean distance between markers of 6.8 cM (SD 1.1). To confirm map positions of the 224 markers in our set that are polymorphic between Mus musculus and Mus spretus, we used The Jackson Laboratory (TJL) interspecific backcross mapping panel (TJL BSS); 168 (75%) of these markers had not been previously mapped in this cross by other investigators, adding new information to this community map resource. With this large data set, we sought to reconstruct a phylogenetic history of the laboratory mouse using Wagner parsimony analysis. Our results are largely congruent with the known history of inbred mouse strains.

Interstrain variation in murine aerobic capacity

PURPOSE

The contribution of genetic factors to aerobic capacity is unknown. The purpose of this study was to measure maximal aerobic performance among inbred strains of mice to provide basic heritability estimates.

METHODS

Eight female mice, 8 to 10 wk old, in 10 inbred strains (A/J, AKR/J, Balb/cJ, C(3)H/HeJ, C57Bl/6J, C57L/J, C(3)Heb/FeJ, CBA/J, DBA/2J, and SWR/J) were run on a treadmill until exhaustion. The protocol started at 22 m.min(-1) and increased in speed approximately 6 m.min(-1) every 4 min. After 4 min at 42.4 m.min(-1), the grade was increased 2% every 4 min thereafter until the mouse could not run off of the shock grid (150 V; 1.5 mA).

RESULTS

There were significant differences between inbred strains in maximal duration of exercise accomplished (P < 0.0001). The order of strain-specific exercise duration was Balb/cJ > SWR/J > CBA/J > C57L/J > C3H/HeJ > C3Heb/FeJ > C57Bl/6J > AKR/J > DBA/2J > A/J. Two measures of heritability in the broad sense, intraclass correlation (0.73), and the coefficient of genetic determination (0.58) were both significant.

CONCLUSION

These data indicate that there is a strong genetic contribution to aerobic capacity in mice.

Anomalous (preduodenal) portal vein: autosomal recessive mutation in AKR/J mice

BACKGROUND AND PURPOSE

Anomalous (preduodenal) portal vein was found in AKR/J mice. It is a rare congenital malformation in humans, and to the authors' knowledge, has never been reported in laboratory animals. Morphology, clinical signs of disease, and heritability of this anomaly were examined.

METHODS

Fifty-three strains of inbred mice (6,026 mice) in our mouse colony were examined for preduodenal portal vein and its association with clinical signs of disease (vomiting or abdominal pain) and other anomalies. Heritability also was tested by use of cross-backcross matings of AKR/J mice with clinically normal PT mice.

RESULTS

The portal vein was found at the ventral side of the duodenum in most (98%) AKR/J mice, whereas it ran at the dorsal side of the duodenum in 52 other inbred mouse strains in our mouse colony. Clinical signs of disease and other congenital anomalies were not detected in this strain of mice, although position has a high association with other congenital anomalies in humans. Heritability testing of this anomaly in AKR/J mice indicated single autosomal recessive inheritance.

CONCLUSIONS

Preduodenal portal vein found in AKR/J mice is a single autosomal recessive mutation, but is not associated with clinical signs of disease and other congenital malformations.

Genetic mapping of 262 loci derived from expressed sequences in a murine interspecific cross using single-strand conformational polymorphism analysis

We have demonstrated previously that noncoding sequences of genes are a robust source of polymorphisms between mouse species when tested using single-strand conformation polymorphism (SSCP) analysis, and that these polymorphisms are useful for genetic mapping. In this report we demonstrate that presumptive 3'-untranslated region sequence obtained from expressed sequence tags (ESTs) can be analyzed in a similar fashion, and we have used this approach to map 262 loci using an interspecific backcross. These results demonstrate SSCP analysis of genes or ESTs is a simple and efficient means for the genetic localization of transcribed sequences, and is furthermore an approach that is applicable to any system for which there is sufficient sequence polymorphism.

Lifespan and lesions in genetically heterogeneous (four-way cross) mice: a new model for aging research

Genetically heterogeneous animal models provide many advantages for research on aging but have been used infrequently. We present here lifespan and lesion data from a study of mice bred as a cross between (AKR/J x DBA/2J)F1 females and (C57BL/6J x SJL/J)F1 males. In such a four-way cross population, each mouse is genetically unique, but replicate populations of essentially similar genetic structure can be generated quickly, at low cost, and of arbitrary size from commercially available, genetically stable hybrid parents. We employed a protocol in which mice judged to be severely ill were euthanatized to obtain tissue in optimal condition for necropsy, and we were able to infer a likely cause of illness in 42 of 44 animals. Malignant lymphoma, including at least four histopathologically distinct subtypes, was the most common cause and was also a frequent incidental finding in mice dying of other causes. Neoplastic disease, benign or malignant, was the sole or a contributing cause of illness in 90% of the mice for which a cause could plausibly be assigned. A wide range of lethal and nonlethal degenerative lesions was also noted. The coefficient of variation for lifespan in these genetically heterogeneous mice was 26%, similar to that seen in analyses of recombinant inbred mouse lines. Baseline lifespan and pathology data on four-way cross mice is a useful prelude to the exploitation of this rodent model in tests of genetic and mechanistic hypotheses about aging.

Autoimmune diabetes-prone NOD mice express the Lyt2 alpha (Lyt2.1) and Lyt3 alpha (Lyt3.1) alleles of CD8

Predisposition to Type I insulin-dependent diabetes (IDD) has a strong underlying genetic basis involving class II major histocompatibility complex (MHC) genes as well as several non-MHC genetic systems. In the non-obese diabetic (NOD) mouse, a model for human IDD, genes associated with the appearance of immune cell infiltrates in the pancreatic islets (insulitis) and/or overt IDD have been mapped to chromosomes 1, 3, 6, 11, and 17. A recent report has suggested that CD8+ lymphocytes of the NOD mouse might be deficient in the expression of the CD8 beta molecule, a protein encoded by a gene on chromosome 6. The CD8 beta molecule is a T-cell surface marker, the lack of which could affect selection in the thymus, possibly permitting auto-reactive T-cell clones to populate the peripheral lymphoid tissues. For this reason, we examined the expression of the CD8 molecule by lymphocytes in the NOD mouse. Results indicate that the NOD mouse is not deficient in its transcription of detectable mRNA encoding either the CD8 alpha or beta subunits. However, the NOD mouse expresses the Lyt2 alpha and Lyt3 alpha alleles, suggesting that a portion of chromosome 6 centromeric to the diabetes-susceptibility genetic region is derived from an ancestry common to AKR and, like AKR, the CD8 alpha and CD8 beta 3.1 (but not CD8 beta 3.2) subunits are detected on the cell surface of T lymphocytes of the NOD mouse. Interestingly, though, the CD8 beta 3.1 molecule may not be expressed in the NOD mouse to the same extent as it is expressed in the AKR/J mouse, suggesting the possibility that the NOD mouse possesses a defect somewhere between transcription and cell surface expression of the CD8 beta molecule.

Molecular genetic characterization of the senescence-accelerated mouse (SAM) strains

Senescence-Accelerated Mouse (SAM) is a murine model of accelerated senescence, which consists of the senescence-prone P series and the senescence-resistant R series of strains. In order to characterize these SAM strains molecular genetically, we have performed a series of Southern hybridization experiments using oligonucleotide probes designed to recognize the endogenous mouse retrovirus sequences. The repertoires of endogenous retroviruses in different SAM strains indicated that each SAM strain is distinct. Comparisons of the SAM strains with the parental AKR/J strain revealed significant differences between them, suggesting the involvement of other strains in the course of the development of SAM. While some of the endogenous retroviruses were found in all of the SAM strains, others were found to be distributed uniquely, indicating their potential usefulness as genetic markers in the analysis of strain-specific phenotypes, and possibly of the phenomenon of accelerated senescence itself.

Genetics of dietary obesity in AKR/J x SWR/J mice: segregation of the trait and identification of a linked locus on chromosome 4

We describe a new multiple gene mouse model of differential sensitivity to dietary obesity that provides a tool for dissecting the genetic basis for body composition and obesity. AKR/J and SWR/J male mice, as well as male progeny of intercrosses between these strains, were fed a high-fat diet for 12 weeks beginning at 5 weeks of age. Body weight and energy intake were assessed weekly. At the conclusion of the dietary manipulation, an adiposity index was calculated by dividing the weight of seven dissected adipose depots by the carcass weight. AKR/J mice had approximately sixfold greater adiposity than SWR/J mice. Examination of the segregation of the adiposity trait in the progeny of crosses between these strains indicates that the trait is determined by a minimum of one to four genetic loci and that there is significant dominance of the AKR/J genotype. A preliminary analysis with markers linked to the known mouse obesity genes ob, db, tub, and fat showed no linkage with these loci. However, a quantitative trait locus was found that maps distal to the db gene on Chromosome (Chr) 4. This locus has been designated dietary obese 1 or Do1.

Assignment of a gene that determines erythrocytic guanosine-5'-triphosphate concentration (Gtpc) to mouse chromosome 9

Nine inbred mouse strains surveyed for erythrocytic guanosine-5'-triphosphate (GTP) concentration were found to segregate into two discrete groups. Strains having low GTP levels between 1.4 and 3.4 nmol/10(9) cells were C3H/HeJ, C3H/HeHa, A/J, and WB/ReJ. Strains having high GTP levels between 11.0 and 14.8 nmol/10(9) cells were AKR/J, DBA/2J, CBA/J, C57BL/6J, and C57L/J. Erythrocytic ATP levels did not vary significantly among these groups. Crosses between low and high GTP strains gave F1 progeny having intermediate levels of GTP, and the progeny of F1's backcrossed to parental strains segregated in a 1:1 ratio for GTP concentration. We designated the GTP concentration determining trait, Gtpc. Typing the C57BL/6J x C3H/HeJ (B x H) recombinant inbred strains for GTP levels revealed 0/12 strain distribution pattern differences for loci on both chromosomes 5 and 9. Backcross analysis did not provide evidence for linkage of Gtpc to W (dominant white spotting) on chromosome 5 with 15/45 recombinants. A test for linkage of Gtpc to transferrin (Trf) on chromosome 9 gave evidence of linkage with an observed recombination frequency of 14.6 +/- 5.5 and a 99% confidence interval of 3.9-33.9 cM.

Organization of the V gene segments in mouse T-cell antigen receptor alpha/delta locus

The mouse T-cell receptor (TCR) alpha/delta locus was mapped using 17 V alpha and 4 V beta subfamily-specific probes. Four complementary methods were used: (1) an estimate of the V gene repertoire by Southern blot analysis of genomic DNA with subfamily-specific probes; (2) an analysis of V gene segments deleted by TCR gene rearrangements from a panel of T-cell tumors and hybridomas; (3) an analysis of overlapping clusters of cosmid clones; and (4) an analysis of large DNA fragments separated by field-inversion gel electrophoresis. The alpha/delta locus spans about 1 Mb. The distance between the 3'-most V gene segment (V delta 1) and the delta constant gene (C delta) is no more than 150 kb. Sixty-six V gene segments have been mapped physically on cosmids. The members of individual V alpha gene segment subfamilies are dispersed throughout the locus. In contrast, the V delta gene segments V delta 1 to 5 are clustered at the 3' end of the V gene segment cluster. At least two DNA segment duplications, 45 to 80 kb in length, are present in the locus. These data provide information on the evolution of the alpha/delta locus and on organization features that might influence the expression of specific V gene segments in gamma delta cells.

Lymphomagenesis in AKR.Fv-1b congenic mice

In the AKR.Fv-1b congenic strain the Fv-1n allele of the AKR/J mice was substituted with the Fv-1b allele, thereby limiting viral replication and spread of the endogenous N-tropic murine leukemia virus. As a result of this genetic change AKR.Fv-1b mice develop a low spontaneous incidence (7%) of T-cell lymphomas and about 28% of Ly-1+ B-cell lymphomas are observed in old mice. Characteristic changes in thymus subpopulations of AKR/J mice (related to the formation of the dual tropic mink cell focus inducing (MCF) type virus in the thymus) were not observed in the thymus of AKR.Fv-1b mice. In contrast to the low susceptibility to spontaneous T-cell lymphoma development, these mice were highly sensitive to fractionated irradiation or to radiation leukemia virus (a mixture of N- and B-tropic viruses) induced T-cell lymphoma. Potential lymphoma cells (that would ultimately develop into Ly-1+ B-cell lymphomas) were demonstrated in bone marrow and spleens of 16-24-month-old mice. Analysis of the Ly-1+ IgM+ B-cell population in spleens of 18-month-old mice revealed a significant increase in this population (35% versus 2% in young spleens). The spontaneous Ly-1+ B-cell lymphoma incidence could be enhanced (up to 77%) by in vivo administration of anti-CD8 monoclonal antibody or IL-4 to 18-month-old mice. Virological analysis of T/B-cell lymphomas for class I MCF viruses indicated that Class I MCF development was tightly correlated with T-lymphoma development (except radiation induced tumors that showed no MCF provirus involvement). In contrast, Ly-1+ B-cell lymphoma development was independent of Class I MCF pathogenic virus involvement.

Autosomal dominant mouse cataract (Lop-10). Consistent differences of expression in heterozygotes

The clinical and histologic features are reported of an autosomal dominant mouse cataract that was first observed as a new mutation in a cross between BALB/cJ and AKR/J. In the homozygous state, the eyes were microphthalmic, and a dense white cataract was present when the eyes opened at day 12. Histologic changes were apparent from birth and as early as 18 days' gestation. Liquefaction started by day 4, and herniation of lens contents posteriorly was seen at day 11. Heterozygous mice had variable expression depending both on their genetic background and age. When the single gene was expressed fully, the cataract appeared as a fetal nuclear white opacity; partial expression gave a nuclear haze to snowflake nuclear opacities. Lop-10 appeared to be an excellent model for studying variable expression of a dominant gene.

Resistance to NK and metastatic potential of fibrosarcoma cells is associated with products encoded by the H-2D region

We have used the murine 3-methylcholanthrene induced T10 fibrosarcoma tumor cell system originating in (C3II/en x C57BL/6)F1 mice (H-2b x H-2k) to elucidate the possible correlation between metastatic potential, expression of individual H-2 antigens and susceptibility to NK cells. Transfection of the non metastatic and NK sensitive IC9 cells (Db+, Kk, Kb, Kk-) with the H-2Dk gene, altered the metastatic phenotype of the parental cells, yet had no effect on the susceptibility of these tumor cells to lysis by NK and did not elicit a specific CTL response in syngeneic hosts. Variants of the metastatic and NK resistant IE7 clone (Db+, Kk-, Kb-, Kk-), lacking H-2Dk, were selected by treatment with monoclonal anti H-2Dk antibodies and complement. These variants were sensitive to NK and poorly or non metastatic. Transfection of Dk negative variants with the H-2Dk gene, resulted in the isolation of several clones which expressed a wide range of metastatic phenotypes but maintained sensitivity to NK. In addition, by cloning the cDNA of the H-2Dk gene of the metastatic T10-IE7 variant cells and analyzing its nucleotide sequence, we found four single nucleotide changes. Two of them are not expected to alter the encoded amino acids, whereas the others should result in two amino acid substitutions in the alpha-2 domain of the class I H-2Kd protein product. These changes might account, at least partially, for the failure of the transfection of H-2Dk to restore resistance to NK.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of the AKR gene locus AKv-1 in susceptibility to chemical induction of thymic lymphomas

Various strains of mice demonstrate widely differing susceptibility to chemical induction of thymic lymphomas, in both timing and incidence. In AKR mice tumors appear very early and at high incidence after a single dose of N-methyl-N-nitrosourea, while in other strains they appear later and at lower incidences. In an attempt to determine the potential role of AKR ecotropic murine leukemia virus loci in this process, congenic mice of NFS/N background, into which the highly productive ecotropic murine leukemia virus loci AKv-1 or AKv-2 has been transferred, were challenged with N-methyl-N-nitrosourea. Although they had a lower incidence of thymic lymphomas than did the parental donor AKR, the NS.AKv-1 mice had a tumor incidence twice that of NFS/N or NS.AKv-2. However, no difference in timing was noted, and these three strains demonstrated tumor appearance much later than that of AKR/N. It is suggested that the presence of the AKv-1 loci, or a gene of the closely associated genomic region, increases the number of target cells that are susceptible to N-methyl-N-nitrosourea.

Genetic basis of resistance to trauma in inbred strains of mice

In this study the resistance to mechanical, thermal, and radiation trauma in four inbred strains of mice (AKR, BALB/c, CBA, and C57Bl/6) was compared with the degree of genetic resemblance, by analyzing the allozyme variabilities of these strains. It was shown that the highest degree of genetic resemblance was among CBA and AKR strains, which correlated with a similar degree of resistance to trauma. On the other hand, BALB/c and C57Bl/6 strains expressed significant differences, both genetically and with respect to the responses to trauma. The hypothesis is introduced that the genetic determination of the resistance to trauma is based on: a) a polygenic control of general physiological homeostasis, with the possibility that b) some specific genes or single loci may contribute more than others to such adaptations of the strains tested.

Comparison of sister chromatid exchanges in spleen and thymus lymphocytes from AKR, C57BL/6N x DBA/2J F1, and CBA mice following in vivo exposure to N-methyl-N-nitrosourea

The induction of sister chromatid exchange (SCE) by N-methyl-N-nitrosourea (MNU) was studied in spleen and thymus lymphocytes from AKR mice, which are highly susceptible to MNU-produced thymomas, CBA mice, which are much less sensitive to induction of thymomas by MNU, and C57BL/6N x DBA/2J F1 mice. MNU produced dose-related increases in SCE in concanavalin A (Con A)- and lipopolysaccharide-stimulated spleen lymphocytes and Con A-stimulated thymus lymphocytes from each mouse strain at 1 and 24 h posttreatment. MNU-induced SCE were generally higher in Con A-stimulated spleen lymphocytes compared to lipopolysaccharide-stimulated spleen lymphocytes and Con A-stimulated thymus lymphocytes from each mouse strain. On the whole, MNU-produced SCE were lower in AKR and CBA spleens than in C57BL/6N x DBA/2J F1 spleens. In addition, MNU-induced SCE levels in thymus lymphocytes from all three strains of mice were, for the most part, similar. These results indicate that if differences in MNU-induced genotoxicity in AKR, CBA, and C57BL/6N x DBA/2J F1 thymus lymphocytes exist, these differences cannot be ascertained by use of the in vivo/in vitro SCE assay.

Organization of the AKR Qa region: structure of a divergent class I sequence, Q5k

We established the organization of the AKR Qa region and determined the sequence of the Q4 and Q5 genes. Restriction mapping and genomic Southern blot analysis revealed that the AKR strain codes for only three H-2K homologous genes in this region. The AKR Q5 gene is not homologous to the Q5 gene of the C57BL strain, but is presumably allelic to the Q5 gene isolated from Balb/c. The organization and structure of the AKR Qa family is virtually identical to the Qa genes of the C3H mouse. The AKR Q5 gene, in contrast to other H-2K homologous Qa region genes, codes for a typical transmembrane region, and upon transfection into BHK cells, a 1.6 kb Q5 transcript is detected.

Hepatic mitochondrial coumarin 7-hydroxylase: comparison with the microsomal enzyme

The specific activity of cytochrome P450-linked coumarin 7-hydroxylase (COH) of hepatic mitoplasts from DBA/2N mice is up to 55% as great as the microsomal activity. According to Western blot and immunodiffusion analysis and inhibition studies with anti-P450Coh and metyrapone, the mitoplastic P450Coh had the same molecular weight and immunochemical and catalytic properties as the corresponding microsomal enzyme. The inducibility of the two proteins by pyrazole and their genetic regulation, as studied with DBA/2N and AKR/J mice, appears to be similar. However, the mitochondrial electron transfer system was not able to support the COH activity of reconstituted microsomal P450Coh although the enzyme was fully active with the microsomal NADPH-cytochrome P450 reductase. This indicates some differences between the two proteins with respect to their interaction with the electron transfer system. This was confirmed by the ability of anti-adrenodoxin reductase antibody to effectively inhibit the mitoplastic COH but not the COH reconstituted with purified microsomal P450Coh and NADPH-P450 reductase. We have previously found that P450Coh does not react with anti-P450b or anti-P450c antibodies, which recognize respective isoforms in rat liver mitoplasts. While P450Coh from microsomes and mitoplasts possess a number of properties in common, the mitoplast P450Coh represents a new subspecies of mitochondrial P450. Some characteristics of mitoplast P450Coh may be the result of post-translational modifications necessary for processing and translocation into the mitochondria.

Nucleotide sequence analysis of the C.AKR Lyt-2a gene: structural polymorphism in alleles encoding the Lyt-2.1 T-cell surface alloantigen

The Lyt-2a allele of the C.AKR strain of mice (genotype Lyt-2a, Lyt-3a) was cloned, and its complete nucleotide sequence as well as that of 2 kb of 5' flanking DNA was determined. The sequence was compared with the partial sequence of the Lyt-2a allele of DBA/2 (genotype Lyt-2a, Lyt-3b) and the nearly complete sequence of the B10.CAS2 Lyt-2b allele reported by Liaw and coworkers (1986). The coding regions of the two Lyt-2a alleles differ from each other by two nucleotide substitutions in the three exons over which they could be compared, resulting in two amino acid substitutions in the leader and transmembrane segments. The coding region of the C.AKR Lyt-2a allele differs from the Lyt-2b allele by two nucleotide substitutions in the extracellular V-like domain, one of which is silent and the second of which leads to substitution of valine for methionine at amino acid position 78 giving rise to the Lyt-2.1 allotypic specificity. The coding region of the DBA/2 Lyt-2a allele shares with C.AKR the allotypic substitution at position 78 and differs from Lyt-2b by three additional nucleotide substitutions in the coding regions, two of which lead to amino acid substitutions in the leader and transmembrane segments. It would therefore appear that the Lyt-2 alleles of the three strains analyzed are distinct, and the nomenclature Lyt-2a1 and Lyt-2a2 is suggested to distinguish the alleles of C.AKR and DBA/2, respectively. These alleles share a common difference from the Lyt-2b gene product at position 78, and since the amino acid substitutions which distinguish them from each other are in the leader and transmembrane segments, their mature Lyt-2 gene products appear antigenically identical.

Structure and expression of the Lyt-3a gene of C.AKR mice

The mouse Lyt-3a gene, which encodes the Lyt-3.1 T-cell surface alloantigen of the C.AKR strain, has been cloned, and the nucleotide sequence of its exons and more than 2 kb of 5' flanking sequence have been determined. The gene extends over approximately 16 kb of DNA and consists of six exons encoding leader, leader plus V-like domain, membrane-proximal, transmembrane, and cytoplasmic domains. The only difference between the coding region of the Lyt-3a gene and the cDNA sequences reported for Lyt-3b (Nakauchi et al. 1987. Panaccio et al. 1987) is at position 77 of the mature protein where Lyt-3a encodes serine and Lyt-3b encodes arginine. This substitution must therefore be the basis for the serological distinction between the Lyt-3.1 and Lyt-3.2 alloantigens. Potential TATA and CAAT sequences, two Sp1 protein binding sites, two extended repeats of the dinucleotide, CA, a number of short inverted repeats, and an inverted segment of the mouse B1 repetitive sequence are found 5' to the Lyt-3a gene. Two consensus poly-A addition signals and a complete copy of the mouse B1 sequence are found 3' to the gene. Both B1-related regions are flanked by short direct repeats suggesting that they arose by an insertional mechanism. Cotransfection of the Lyt-3a gene together with a cloned Lyt-2a gene resulted in expression of both Lyt-2 and Lyt-3.1 on the surface of Ltk- and BW5147 cells.(ABSTRACT TRUNCATED AT 250 WORDS)

N-methyl-N-nitrosourea-induced T-lymphomas of AKR/J mice contain somatically acquired ecotropic-like murine leukemia proviruses

We have studied somatically murine leukemia proviral integrations in primary N-methyl-N-nitrosourea (MNU)-induced thymic lymphomas of AKR/J mice. The majority of MNU-induced lymphomas contain newly acquired murine leukemia proviral sequences. In contrast to spontaneous AKR/J lymphomas which contain multiple integrations of mink cell focus-forming recombinant proviruses, MNU-induced lymphomas contain ecotropic-related proviruses. This conclusion was based on the demonstration that EcoRI- and PvuII-digested DNA from MNU-induced lymphomas contains new 3' proviral-cellular junction fragments that hybridize with the ecotropic-specific pAKV-4 and pAKV-5 hybridization probes. Also, EcoRI/PstI double digests of DNA from MNU-induced lymphomas revealed that the acquired proviruses do not contain an internal 3' EcoRI site characteristic of mink cell focus-forming recombinant viruses. The proviral integration patterns suggest that MNU-induced lymphomas are clonal or oligoclonal in nature. This conclusion is supported by comparison of proviral integration patterns in lymphomas obtained from thymus and spleen of individual mice, and by analyses of T-cell receptor beta-chain gene rearrangements. The frequent occurrence of ecotropic-related proviral sequences in MNU-induced lymphomas suggests that these newly acquired proviruses may play a role in tumor development.

Induction of anti-MuLV cytotoxic T lymphocytes in the AKR.H-2b and AKR.H-2b:Fv-1b mouse strains

Following secondary in vitro sensitization with AKR/Gross virus-induced tumors, AKR.H-2b:Fv-1b mice develop cytotoxic T lymphocytes (CTL) specific for AKR/Gross viral antigens. It has recently been determined that the responder status of AKR.H-2b:Fv-1b to AKR/Gross virus declines with age. The nonresponsiveness observed in AKR.H-2b:Fv-1b is similar to that observed in AKR.H-2b mice which (regardless of age) does not develop anti-AKR/Gross virus CTL. It was of interest to determine the ability of these congenic mouse strains to respond to other murine leukemia viruses (MuLV). This was accomplished by immunizing AKR.H-2b and young or moderately aged AKR.H-2b:Fv-1b with Friend-Moloney-Rauscher (FMR) virus-induced tumors, and assessing the ability of anti-FMR CTL to develop following secondary in vitro stimulation. It was observed that both AKR.H-2b and AKR.H-2b:Fv-1b developed specific anti-FMR virus CTL. Similarly, following tumor challenge AKR.H-2b mice were unable to prevent the outgrowth of a syngeneic AKR/Gross virus-induced tumor, but were able to reject a syngeneic FMR virus-induced tumor.

T cell receptor beta-chain genes in BW5147 and other AKR tumors. Deletion order of murine V beta gene segments and possible 5' regulatory regions

The AKR thymoma BW5147 has rearranged both of its TCR beta-chain loci, using the same J beta region (J beta 2.5) in each, but with different V beta gene segments. Although the two rearrangements are expressed approximately equally in cytoplasmic RNA, the principle of allelic exclusion is maintained because only one rearrangement is in-frame and capable of encoding a functional protein. In hybridomas made with BW5147 as the fusion partner, this protein may combine with the alpha-chain protein derived from the normal cell to form new Ag/MHC specificities. An analysis of the sequences upstream from the BW5147 rearrangements and additional V regions suggests that two conserved sequences, 10 and nine nucleotides in length and located adjacent to each other 70 to 100 nucleotides 5' of the initiation codon, may be important in the expression of TCR beta-chain genes. Although B and T cells derive from common stem cells, no sequences are observed in T cells that are homologous to the octamer located 5' of all Ig genes. This implies that at least some of the sequences that regulate transcription are not shared in the two major types of lymphocytes. A survey of BW5147 and six other AKR thymomas using probes for 10 of the 18 known V region families indicates a distribution of V beta rearrangements in the tumors consistent with that found in thymocytes. Four of these tumors have apparent VDJ rearrangements on both chromosomes, with the deletion of other V beta gene segments. These data suggest that the primary mechanism of VDJ beta rearrangement is by looping out and excision of the intervening DNA and that most of the V regions are located 5' to the C region. These data were also used to develop a deletion order of the V beta gene segments in the TCR beta-chain locus.

Thymic lymphoma induction by the AKT8 murine retrovirus

The directly transforming murine retrovirus, AKT8, was isolated from a spontaneous AKR thymoma and carries the cell-derived viral oncogene, akt. We have now shown that this virus produces thymic lymphomas after inoculation of susceptible mouse strains. The presence of the AKT8 genome in the DNA of the virus-induced tumors was demonstrated by Southern blotting using an akt-specific probe. These results establish the in vivo pathogenicity of the AKT8 virus and its akt oncogene, and imply a potential role for the cellular akt proto-oncogene in tumor development.

Alpha/beta T-cell antigen receptor gene and protein expression occurs at early stages of thymocyte differentiation

Alterations in gene expression that orchestrate eukaryotic cellular differentiation often require appropriate interactions between differentiating cells and a specialized microenvironment. During T-lymphocyte differentiation, immature thymocytes undergo a stringent intrathymic selection process that requires intimate contact with thymic stromal elements. Since this selection process generates T cells that are self-tolerant and recognize nominal antigen only within the context of self-major histocompatibility antigen complex molecules, it is possible that thymocyte/stromal cell interactions are mediated, in part, by antigen-specific receptors expressed on differentiating thymocytes. However, the developmental stage at which alpha/beta antigen-specific receptors are expressed during T-cell maturation has been a matter of debate. To address this issue, we have studied alpha/beta T-cell antigen receptor gene and protein expression on normal thymocyte subsets of AKR/J mice, as well as on a panel of AKR/J primary thymic lymphomas characterized for CD4 (L3T4) and CD8 (Lyt-2) differentiation antigen expression. The data unequivocally demonstrate that alpha/beta heterodimers are expressed not only on phenotypically mature thymocytes but also on the majority of CD4+8+ double-positive cells that comprise the predominant nonmature thymocyte subset. Furthermore, a fraction of thymocytes in the CD4-8- double-negative compartment, known to contain progenitor cells, also expresses readily detectable cell-surface alpha/beta receptors. Therefore, during the process of intrathymic selection, interactions between nonmature thymocytes and stromal cells via the antigen-receptor complex may play a pivotal role in T-cell differentiation and should be considered in formulating schemes for functional T-cell selection.

DNA sequence analysis of the C3H H-2Kk and H-2Dk loci. Evolutionary relationships to H-2 genes from four other mouse strains

We generated nucleotide sequences for H-2Kk and H-2Dk from the C3H mouse, as well as for a genomic clone of H-2Db, in order to conduct an evolutionary analysis of the H-2 genes from three haplotypes, k, d, and b. H-2Kk from both the C3H and AKR strains, H-2Kd, H-2Kb, H-2Dk, H-2Ld, H-2Dd, H-2Db, and H-2Dp DNA sequences were aligned, and the alignments used to construct phylogenetic trees inferring the evolutionary relationships among the nine genes by two independent methods. Both approaches yielded trees with similar topologies. In addition, the sequence alignments revealed patterns of nucleotide substitutions which implicate both point mutation and recombination in the divergence of the H-2 genes. Future considerations for evolutionary analysis of class I genes are discussed.

Mouse thiopurine methyltransferase pharmacogenetics: biochemical studies and recombinant inbred strains

Thiopurine methyltransferase (TPMT) catalyzes the S-methylation of 6-mercaptopurine and other heterocyclic and aromatic thiol compounds. In humans, TPMT activity is controlled by a common genetic polymorphism. C57BL/6J (B6) and AKR/J (AK) inbred mice have low hepatic and renal TPMT activities, whereas DBA/2J (D2) mice have high enzyme activities. Low TPMT activity is inherited in these mice as an autosomal recessive trait. The properties of TPMT in liver homogenates from B6, AK and D2 mice were compared in order to study the biochemical basis for inherited differences in TPMT activity among these strains. Biochemical and physical properties of hepatic TPMT were very similar in all three strains. Apparent Michaelis (Km) constants for 6-mercaptopurine were 0.98, 0.75 and 1.1 mM for B6, AK and D2 mice, respectively. Apparent Km values for S-adenosyl-L-methionine, the methyl donor for the reaction, were 2.2, 1.5 and 3.0 microM for B6, AK and D2 mice. IC50 values for inhibition by 3,4-dimethoxy-5-hydroxybenzoic acid were 0.83, 1.0 and 1.2 microM, whereas IC50 values for inhibition by S-adenosyl-L-homocysteine were 5.4, 6.6 and 5.8 microM for B6, AK and D2 mice, respectively. Half-life and slope values for thermal inactivation of hepatic TPMT were similar among B6, AK and D2 mice. No differences among strains in Rf values of the enzyme activity after electrophoresis were detected. Ion exchange chromatography with an NaCl gradient showed a major peak of TPMT activity that eluted with 51 to 56 mM NaCl for all three strains.(ABSTRACT TRUNCATED AT 250 WORDS)

Nucleotide sequence and functional analysis of the LTRs of endogenous ecotropic MuLV proviruses of AKR and BALB/c mice

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Molecular cloning of the akt oncogene and its human homologues AKT1 and AKT2: amplification of AKT1 in a primary human gastric adenocarcinoma

A previous report described the isolation of a directly transforming retrovirus, AKT8, from a spontaneous thymoma of an AKR mouse. The AKT8 provirus has now been molecularly cloned from a transformed, nonproducer cell line. The virus genome contains both viral and nonviral, cell-related sequences; the nonviral sequence has been designated v-akt, the presumed viral oncogene of the AKT8 virus. This gene lacks homology to the 16 other oncogenes tested. The cloned provirus has undergone a partial deletion, during cell passage in vitro, that prevents direct demonstration of the transforming ability of this molecular clone. Two human homologues of the v-akt oncogene, AKT1 and AKT2, were cloned. A survey of 225 human tumors for changes involving AKT1 led to the discovery of a 20-fold amplification of this gene in one of the five gastric adenocarcinomas tested. The results demonstrate that AKT8 has the characteristic structure of a directly transforming retrovirus and that it contains a gene derived from highly conserved cellular sequences that may be involved in the pathogenesis of some human malignancies.

Thymic epithelium controls thymocyte expression of preleukemic phenotype and leukemogenic retroviruses

Congenitally athymic AKR-streaker (nustr/nustr) mice were grafted separately with syngeneic or allogeneic, irradiated (1200 R) thymic reticuloepithelial (TRE) elements (stroma) or nonirradiated whole thymus grafts (control group) from N-tropic murine leukemia virus (MuLV) infection-susceptible (Fv-1n/n) or N-tropic-MuLV-infection-resistant (Fv-1b/n) murine strains. From 3 to 13 mo after grafting, the mononuclear cells repopulating the thymus grafts were stained with fluorescent monoclonal antibodies to thymocyte differentiation antigens, peanut agglutinin, and an antibody to MuLV antigens and were then analyzed by flow cytometry. Irradiated TRE of the Fv-1n/n genotype, whether from high or low leukemia-incidence strains, contained lymphoid cells of host (nustr/nustr) origin with alterations in thymocyte differentiation and MuLV antigen expression consistent with preleukemic changes. In contrast, transplanted TRE of the low leukemia-incidence Fv-1b/n genotype restricted preleukemic changes in thymocyte differentiation and MuLV antigen expression by lymphoid cells derived from the nustr/nustr host. Thus, nustr/nustr lymphocytes must infect susceptible TRE (Fv-1n/n) with N-tropic-MuLV before preleukemic changes occur in the mustr/nustr lymphocytes that later migrate to the thymus. Therefore, it was the radiation-resistant cells in the thymus that amplified or suppressed expression of AKR MCF retroviruses and the preleukemic phenotype, not the thymic lymphocytes. Thy-1.1+ splenocytes of ungrafted nustr/nustr mice were comparable in percentage to nustr/+ but were deficient in the Lyt-1+2- subpopulation and unresponsive to mitogens or alloantigens in vitro. Analysis of splenocyte cell surface markers, mitogen, MLC, and CML responses of Fv-1n/n-thymus-grafted nustr/nustr mice showed restoration of Lyt-1+2- cells to levels comparable to nustr/+ and reconstitution of in vitro proliferative and cytotoxic responses.

Nucleotide conservation of endogenous ecotropic murine leukemia proviruses in inbred mice: implications for viral origin and dispersal

Nucleotide sequence analysis of the ecotropic murine leukemia proviruses of AKR, BALB/c, and C57BL/6 mice indicated that these viral genomes differ from each other in less than 0.5% of their sequenced nucleotides, whereas they differ from the laboratory Moloney, Friend, or RadLV viruses or a partial ecotropic provirus found in wild mice by 8-22% of their sequenced nucleotides. The limited variation of endogenous ecotropic proviruses found in these common mouse strains indicates that few cycles of virus replication separated the introduction of the ecotropic endogenous retroviruses into the germlines of the progenitors of these now divergent mouse strains, and is consistent with the hypothesis that these common inbred strains were derived from a pool of very few mice, at least one of which was infected with an ecotropic murine leukemia virus. Ecotropic germline proviruses now found in common inbred mice most likely derive from germline reintegrations of the viral progeny of that initial single infection.

Expression of mink cell focus-forming murine leukemia virus-related transcripts in AKR mice

We used a synthetic 16-base-pair mink cell focus-forming (MCF) env-specific oligomer as radiolabeled probe to study MCF murine leukemia virus (MuLV)-related transcripts in brain, kidney, liver, spleen, and thymus tissues of AKR mice ranging from 5 weeks to 6 months (mo) of age. Tissue-specific expression of poly (A) + RNAs was seen: 6.0-kilobase (kb) transcripts were detected in the liver and kidney; 7.2- and 1.8-kb RNA species were present in the thymus. In addition, all the tissues tested contained 3.0-kb messages. The transcription of these MCF-related mRNAs was independent of the presence of ecotropic and xenotropic MuLVs. In general, expression of the MCF env-related transcripts appeared to peak at 2 mo of age; these messages were barely detectable in brain, kidney, liver, and spleen tissues after 2 mo and in thymus tissue after 4 mo of age. All of the subgenomic MCF env-related mRNAs (6.0, 7.2, 1.8, and 3.0 kb) appeared to contain the 190-base-pair cellular DNA insert, characteristic of the long terminal repeats associated with endogenous MCF env-related proviruses (A. S. Khan and M. A. Martin, Proc. Natl. Acad. Sci. USA 80:2699-2703, 1983). No genomic-size (8.4-kb) transcripts corresponding to endogenous MCF-related proviruses were detected. An 8.4-kb MCF env-related mRNA was first seen at 3 mo of age, exclusively in thymus tissue. This species most likely represents the first appearance of a recombinant MCF-related MuLV genome. The transcripts which were detected in thymus tissue might be involved in the generation of leukemogenic MCF viruses.

A mutant lymphoma cell line with a defective Thy-1 glycoprotein gene

We characterized a mutant T-cell lymphoma line selected for the inability to express the Thy-1 glycoprotein. This cell line is a member of the D complementation class of Thy-1- somatic cell mutants, and it lacks detectable cell-surface Thy-1.1 glycoprotein and detectable cytoplasmic Thy-1 mRNA. Southern blot analysis using a number of probes isolated from the cloned Thy-1.2 gene demonstrated that, in the mutant, one copy of the Thy-1 gene is absent from the genome and the other has undergone rearrangement. This rearrangement results from a deletion of the 5' portion of the gene removing the first two alternate exons and promoters and a portion of the second intron. The deletion breakpoint within the mutant Thy-1 gene was localized to within 400 nucleotides by Southern blot analysis. The breakpoint is near two classes of mouse repetitive elements-a mouse B1-family repetitive element and a simple repetitive sequence-suggesting a mechanism of rearrangement leading to the mutation. Southern blot analysis demonstrated that two closely linked molecular markers on chromosome 9 are unaltered, demonstrating that the deletion in this mutant cell line is subchromosomal.

Analysis of the D-region products of H-2q using monoclonal antibodies reveals the expression of a new class I-like molecule

To analyze how many D-region-encoded molecules could be detected in H-2q, we produced a panel of nine monoclonal antibodies from AKR (KkDk) anti-AKR.M (KkDq) immunizations. All of the Dq region antibodies cross-reacted on Dd and/or Ld, and all except one cross-reacted on Db, confirming the previously observed serologic and amino acid sequence homology between the D-region products of H-2d, H-2b, and H-2q. All of these monoclonal antibodies precipitated 46,000 dalton molecules from both cell-surface-labeled and biosynthetically labeled B10.AKM spleen cells, indicating that all were reactive with class I-like molecules. Sequential immunoprecipitation analysis with one of these antibodies, 66-3-5, reveals the presence of a previously unidentified class I-like molecule. Tryptic peptide map analysis reveals that this molecule may be the product of a newly described H-2Dq-region gene.

[Detection of DNA sequences sensitive to glucocorticoids in the thymus of AKR mice and their inactivation in thymoma]

A high increase in transcriptionally active DNA fraction (TA DNA) has been detected in the thymus of young AKR mice and in thymoma. Hybridization of TA DNA with [32P] cDNA synthesized on poly A+-mRNA of cortisol-induced animals has shown that TA DNA of young AKR mice contains 40 times as much cortisol-activated repeated sequences (RS) as that of thymoma. The decrease of cortisol-activated (RS) in AKR thymoma TA DNA was found to be the result of their transition into transcriptionally inactive (TI) DNA. It is concluded that chromatin conformation changes take place in cortisol-activated RS DNA region of AKR mouse thymus before transformation. Unstable conformation of RS DNA in the thymoma can possibly promote their transition into TI DNA.

Genetic study of lymphoma induction by Friend murine leukemia virus in crosses involving AKR mice

The AKR mouse strain is uniquely susceptible to thymic lymphoma. Friend murine leukemia virus (F-MuLV) induced thymic lymphoma in this strain after a median latency of 3-4 months, whereas in several other mouse strains F-MuLV caused erythroblastosis. In the investigation of genetic determinants of the AKR predisposition to thymic lymphoma, series of congenic mouse strains and progeny of crosses involving AKR mice were inoculated with F-MuLV; these mice were followed for the development of lymphoma. The results suggested that AKR genes on chromosomes 7 and 15, other than inherited ecotropic virus, are involved in the predisposition to rapid onset of thymic lymphoma after inoculation with F-MuLV.

Organization and evolution of D region class I genes in the mouse major histocompatibility complex

Chromosome walking has been used to study the organization of the class I genes in the D and Qa regions of the MHC of the BALB/c mouse and in the D region of the AKR mouse. Five and eight class I genes are found in the D and Qa regions of the BALB/c mouse, respectively, while the AKR mouse contains only a single class I D region gene that has been identified by transfection as the Dk gene. Restriction map homologies and crosshybridization experiments suggest that the multiple class I genes in the D region of the BALB/c mouse have been generated by unequal crossing-over involving class I genes from the Qa region. The expanded D region of BALB/c and other H-2d haplotype mouse strains appears to be metastable, since evidence for gene contraction in the Dd region has been found in two mutant strains. Thus the D region and also the Qa region class I genes are in a dynamic state, evolving by gene expansion and contraction.

Dextran sulfate-induced peritoneal lysophospholipase activity varies among mouse strains

Lysophospholipase (LPL) activity resulting from the intraperitoneal injection of dextran sulfate (DS) was studied in different mouse strains. AKR/J and BALB/cByJ mouse strains showed decreased LPL levels when a low molecular weight DS was injected but increased LPL activity when high molecular weight DS was injected intraperitoneally. C57BL/6 mice had increased LPL activity with low molecular weight DS but decreased LPL activity with high molecular weight DS. All three mouse strains showed increased peritoneal-cell changes when injected with DS of a molecular weight of 79,000.

Anergy for delayed-type hypersensitivity in preleukemic AKR mice

A singular anergy for delayed-type hypersensitivity (DTH) in preleukemic AKR mice was discovered. This total anergy for DTH against allogeneic cells, which developed in the AKR mice by 4 to 5 months of age, was not due to an artifact of route of sensitization or of other assay parameters and was not found in other strains sharing H-2 or other genetic background. The mice had an intact capacity to be stimulated in mixed lymphocyte culture to produce cytotoxic effector cells. Although the relationship to lymphoma was not directly addressed in these experiments, the genetic and temporal characteristics of this anergy suggest a biologically important relationship to the preleukemic state.

AKR/J gene(s) unlinked to H-2 determines dominant inheritance of lymphocyte hyporesponsiveness to acetylcholine receptor

Mice with the H-2b major histocompatibility complex haplotype are high immune responders to nicotinic acetylcholine receptors (AChR), whereas mice with the H-2k haplotype are generally low responders. F1 progeny of C57BL/6 (H-2b) mice crossed with mice of most H-2k strains are high responders to AChR in standard conditions of testing helper T cell proliferation in vitro (4 X 10(5) lymph node cells/microwell, 1 wk after primary challenge in vivo). In contrast, the F1 progeny of AKR/J (H-2k) crossed with high responder (H-2b) strains (B6, A.BY, or C3H.SW) were all hyporesponsive to AChR when lymphocytes were tested at 4 X 10(5) cells/well. However, at a density of 1 X 10(6) or greater/well, a high level of antigen-specific responsiveness was demonstrable in the F1 hybrid lymphocytes. A shift from low to high responsiveness to AChR at high cell densities was observed also in the H-2b strain AKR.B6. Other strains previously demonstrated to be low responders to AChR did not become responsive to AChR when lymphocyte numbers were increased to 1.4 X 10(6)/well. The N2 generation yielded by backcrossing (AKR X B6)F1 mice to AKR/J were all low responders, whereas N2 progeny derived by backcrossing F1 to B6 were high or low responders in a ratio of approximately 1:1 (independent of their H-2 phenotype). Results consistent with this observation were obtained in (AKR X B6) F2 mice. These data suggest that at least one AKR/J gene outside of the H-2 complex exerts a hyporesponsive influence on the I-A-dependent helper T cell response to AChR in H-2b mice.

Further studies on the asymmetry of chromosome 15 duplication in trisomic leukemias of heterozygous origin: preferential status of the AKR chromosome

Four combinations of translocation heterozygotes with cytogenetically distinct chromosomes 15 were used to investigate whether the T-cell leukemia-associated preferential duplication of the AKR-derived chromosome 15 (AKR-15) is determined by factors within this chromosome, or is due to genes within the AKR genotype, but outside chromosome 15. Two of the four combinations were also used to determine whether the AKR-15 duplication preference could be cancelled by MCF-viremia in permissive F1 hybrids. Chemically and virally induced 15-trisomic leukemias showed the same AKR-15 duplication preference, which was due to some autonomous property of AKR-15 itself. It was maintained in (C57BL 6;15 X C57BL) F1 leukemias, where 6;15 is the only AKR-derived chromosome propagated on the C57BL/background. In the (C57BL 6;15 X AKR) F1 hybrid cross where both chromosomes 15 are of AKR origin, duplication occurred at random. To approach the second question, MCF viremia was induced by neonatal virus inoculation into permissive (AKR 6;15 X B6Fv-In) F1 hosts. The preferential duplication status of the AKR-derived 6;15 remained unchanged.

Genetic control of apomorphine-induced climbing behavior in two inbred mouse strains

Over a wide dose range (1-32 mg/kg), apomorphine-induced climbing behavior was significantly greater in the AKR/J than in the DBA/2J inbred mouse strain. A similar difference was found when apomorphine-induced stereotypy was examined. A cross-fostering study demonstrated that the strain difference in apomorphine-induced climbing behavior did not result from differences in post-natal rearing environment. After apomorphine administration, brain levels of the drug were similar in the two strains indicating that the difference in behavioral response to apomorphine in the two strains was not due to differences in metabolism or distribution of the drug. The climbing response to apomorphine was examined in the F1 cross of the two strains (AKD2F1/J) and in 10 AKXD recombinant inbred strains. Results suggested that the trait was partially dominant and not X-linked; furthermore, a few and possibly one locus was responsible for the differences in apomorphine-induced climbing behavior observed in the AKR/J and DBA/2J mice.

New regulatory factors for melanogenesis: developmental changes in neonatal mice of various genotypes

The biosynthesis of melanin occurs through sequential steps known as the Mason-Raper pathway. The initial steps are the conversion of tyrosine to dihydroxyphenylalanine (dopa) and of dopa to dopaquinone by the enzyme tyrosinase (EC 1.10.3.1). Until recently it was assumed that once these first two conversions were completed, the subsequent reactions occurred spontaneously. However, studies with mouse melanoma cells in culture revealed that subsequent steps in the pathway are also regulated. In this report, we demonstrate that these steps are also regulated in skins of fetal and newborn mice. The specific activities of the regulatory factors change during the first week after birth and differ in mice of different genotypes. The findings provide new insights into genetic and developmental regulation of the pigmentary system in mammals.

Genes affecting mink cell focus-inducing (MCF) murine leukemia virus infection and spontaneous lymphoma in AKR F1 hybrids

An assessment of the importance of mink cell focus-inducing (MCF)-type recombinant murine leukemia viruses in spontaneous thymic lymphomagenesis and of the genetic factors affecting its occurrence was carried out with F1 hybrids between AKR and various other inbred strains. There was generally close agreement between the frequency of detection of MCF virus, of thymocyte antigenic amplification in the preleukemic period, and of spontaneous lymphoma. Also, hybrid combinations with moderate to high spontaneous lymphoma were uniformly susceptible to lymphoma induction by neonatal inoculation of MCF 247 virus, while lower leukemic hybrids were at least partially resistant to the induced disease. At least four resistance genes can be identified as affecting the disease in the various hybrids: Fv-1, Rmcf, an unidentified gene carried by the C57 series of mice and SJL, and an unidentified minor gene carried by several other strains.

Thymic epithelial genotype influences the production of recombinant leukemogenic retroviruses in mice

By using T1 oligonucleotide fingerprinting and mapping techniques, we analyzed the genomic structure of retroviruses produced by thymocytes and splenocytes of reciprocal bone marrow-and thymus-grafted chimeras. We found that the genetic factor(s) derived from NZB mice that suppresses the development of thymic leukemia in (AKR X NZB)F1 mice also prevents the formation of recombinant leukemogenic viruses and the expression of preleukemic changes in the (AKR X NZB)F1 thymocytes. The NZB mouse gene or genes appeared to exert this suppressive effect by acting on the thymic reticuloepithelial cells and not on the thymic lymphocytes of (AKR X NZB)F1 hybrids. Prospective studies with thymic epithelial grafts from young mice showed that the AKR thymic epithelium could mediate the formation and expression of leukemogenic recombinant viruses and preleukemic changes in thymocytes that lead to the development of thymic leukemia, whereas the (AKR X NZB)F1 thymic epithelium was deficient in this regard. Our results also confirmed a previous observation that during in vivo generation of recombinant leukemogenic viruses, the acquisition of polytropic virus-related sequences in the 3' portion of the p15E gene and the U3 region and in the 5' part of the gp70 gene can occur independently.

A mouse gene on chromosome 5 that restricts infectivity of mink cell focus-forming recombinant murine leukemia viruses

DBA/1, DBA/2, CBA/N, and CBA/Ca mice carry a gene which specifically restricts infectivity of mink cell focus-forming (MCF) murine leukemia viruses. The gene, designated Rmcfr, is dominant or semidominant and maps to chromosome 5; it is closely linked to the morphologic marker gene Hm. The Rmcf gene may be of much use as a means of determining the role of MCF viruses in various forms of leukemogenesis.