Growth hormone receptor (Ghr) and hemoglobin alpha-chain pseudogene 3 (Hba-ps3) map proximal to the myelocytomatosis oncogene (Myc) on mouse chromosome 15

Three new allelic mouse mutations that cause skeletal overgrowth involve the natriuretic peptide receptor C gene (Npr3)

In 1979, a BALB/cJ mouse was identified with an exceptionally long body. This phenotype was found to be caused by a recessive mutation, designated longjohn (lgj), that mapped to the proximal region of chromosome 15. Several years later, a mouse with a similarly elongated body was identified in an outbred stock after chemical mutagenesis with ethylnitrosourea. This phenotype also was caused by a recessive mutation, designated strigosus (stri). The two mutations were found to be allelic. A third allele was identified in a DBA/2J mouse and was designated longjohn-2J (lgj(2J)). Analysis of skeletal preparations of stri/stri mice indicated that the endochondral ossification process was slightly delayed, resulting in an extended proliferation zone. A recent study reported that mice overexpressing brain natriuretic peptide, one of the members of the natriuretic peptide family, exhibit a skeletal-overgrowth syndrome with endochondral ossification defects. The Npr3 gene coding for type C receptor for natriuretic peptides (NPR-C), which is mainly involved in the clearance of the natriuretic peptides, mapped in the vicinity of our mouse mutations and thus was a candidate gene. The present study reports that all three mutations involve the Npr3 gene and provides evidence in vivo that there is a natriuretic-related bone pathway, underscoring the importance of natriuretic peptide clearance by natriuretic peptide type C receptor.

Dietary obesity linked to genetic loci on chromosomes 9 and 15 in a polygenic mouse model

Loci linked to sensitivity to dietary obesity were identified by Quantitative Trait Locus (QTL) analysis of two mapping populations derived from a cross between AKR/J and SWR/J mice. AKR/J mice are sensitive to dietary obesity when fed a high fat diet while SWR/J mice are resistant. Intercrosses between these strains segregate the phenotype of sensitivity to dietary obesity. Using an F2 mapping population of 931 male mice we found significant linkage with a QTL on chromosome 9 (Likelihood of the Odds [LOD] ratio of 4.85) and another QTL on chromosome 15 (LOD = 3.93). The presence of a QTL on chromosome 15 was confirmed in a separate mapping population of 375 male F1 x SWR/J mice (LOD = 3.82). These two loci are designated dietary obese 2 (Do2) and dietary obese 3 (Do3) for the chromosome 9 and 15 loci, respectively. Both of these chromosomal regions contain candidate genes which may contribute to variation in the phenotype. These loci also exert a significant control over individual adipose depot weights.

Chromosomal location and isoform analysis of mouse Fc epsilon RII/CD23

The gene for the mouse low affinity receptor for IgE (Fc epsilon RII, also known as CD23) was mapped on Chromosome (Chr) 8 proximal to Plat. This gene, symbolized Fcer2 (formerly Fce2) resides in a region of Chr 8 with linkage homology with human chromosomes 8 and 19. The mouse Fc epsilon RII was examined for the presence of alternate N-terminal forms such as seen in humans. An antisense RNA probe was prepared from the 5' end of the cDNA through the first 660 bp of the cDNA and was used to analyze message from Fc epsilon RII+ B cells and B cell hybridomas both before and after treatment with interleukin 4 (IL-4). Using RNase protection analysis, a major 640 bp band corresponding to the full length probe was seen, even after activation of the cells with LPS in the presence of IL-4, which is known to give high expression levels of the Fc epsilon RII. This result suggests that the mouse does not produce significant levels of an alternate IL-4 inducible Fc epsilon RII, as seen in man, and this may explain the more restricted cell lineage expression of the Fc epsilon RII in the mouse.

Gene order and genetic distance of 13 loci spanning murine chromosome 15

Thirteen genetic loci spanning murine chromosome 15 from 15A2 (Mlvi-2) to 15F2-3 (Gdc-1) have been mapped. The genetic distance extends to 55.4 cM. Among 151 animals, only 1 animal with a double cross-over was found. The linear order is unambiguous, with the exception of the distal end on 15F1-3. Our analysis favors the order cen-Ela-1/Hox-3-Wnt-1-Gdc-1-ter. This ordering makes necessary the introduction of three tightly spaced double recombination events around and within the Hox-3 locus. Alternatively, Hox-3 may be most distal, and several double recombinations at the telomere lead to map expansion. Despite the unequal distribution along chromosome 15 of G-versus R-bands, a comparison of distances determined by physical and genetic mapping does not indicate an overt difference in distance between both mapping techniques.

Molecular analysis of the aberrant replication banding pattern on chromosome 15 in murine T-cell lymphomas

Cytogenetic techniques revealed an altered early replication banding pattern on the distal part of chromosome 15 in some murine T-cell lymphomas. This pattern reverted back to normal replication in somatic cell hybrids that had become non-tumorigenic after fusion of leukemic cells with normal fibroblasts. The altered banding pattern was correlated with malignancy. To investigate the molecular basis of the aberrant pattern in more detail, centrifugal elutriation of cells containing bromodeoxyuridine labeled DNA was used to prepare newly replicated DNA from selected intervals of the S-phase from tumor cells, as well as from hybrid cells with the revertant phenotype. These different DNA fractions were probed for DNA sequences distributed over the distal half of chromosome 15. Only two out of ten chromosome 15 specific genes tested showed a clear change in replication timing between the two different cell lines tested. These two genes were the lymphocyte antigen-6, Ly-6, and the neighboring thyroglobulin gene, Tgn, which replicated at the beginning of S in the tumor cells and later in S in the non-tumorigenic hybrid cells.

Mapping anti-müllerian hormone (Amh) and related sequences in the mouse: identification of a new region of homology between MMU10 and HSA19p

A panel of 78 backcross progeny, BALB/cJ x (BALB/cJ x CAST/Ei)F1, was used to map the gene encoding anti-Müllerian hormone (Amh), also called Müllerian inhibiting substance, to mouse Chromosome 10 (MMU10). This analysis identified a new region of linkage homology between human Chromosome 19p (HSA 19p) and MMU10 and localized an apparent recombinational hot spot in (C57BL/6J x Mus spretus)F1 females [compared with (BALB/cJ x CAST/Ei)F1 males] to the interval between phenylalanine hydroxylase (Pah) and mast cell growth factor (Mgf). In addition, eight unlinked polymorphic sequences, provisionally designated Amh-related sequences (Amh-rs1 through Amh-rs8), were identified by Southern blot analysis using Amh probes. Amh-rs1, -rs2, -rs4, and -rs7 were mapped to MMU1, 13, 12, and 15, respectively, by recombinant inbred (RI) strain and intraspecific backcross analyses. The NXSM RI strain distribution patterns for the four unmapped loci are also presented.