Experiment
The effects of host genotype were analyzed on the development of neu-induced mammary tumors in this study by crossing transgenic mice expressing the neu oncogene under control of the MMTV promotor with recombinant congenic CcS/Dem strains. Linkage analysis of the neu-transgene carrying F2 hybrids between the most susceptible, CcS10/Dem, and the most resistant, CcS19/Dem, recombinant congenic strains revealed 3 main effects QTL, two interacting loci, and suggestive loci.
For linkage tests of mammary tumor susceptibility a (CsS19 x BALB/c)F1 x (CcS10 x C.FVB-tg (MMTV-Erbb2)NK1Mul)F1 cross was created to segregate STS/A derived donor chromosomal regions carried by CcS19 and CcS10 mice in the presence of the neu transgene. 369 female progeny were generated, of which 166 ((CsS19 x BALB/c)F1 x (CcS10 x C.FVB-Tg(MMTV-Erbb2)NK1Mul))F1)-Tg(MMTV-Erbb2)NK1Mul/0 F2 mice were neu positive and tested. The STS-derived chromosomal regions were the only ones segregating in the cross, comprising app 23% of the genome.
The donor chromosomal regions were scanned for genetic loci and gene-gene interactions controlling tumor latency, tumor number or metastasis to the lung. Tumor latency time was used to calculate relative risks between geneotypes (or genotype combinations) and the 95% confidence intervals for each locus.
Three significant, main effects, mammary tumor susceptibility loci were detected:
Mts1, mammary tumor susceptibility 1, was detected on Chromosome 4, peaking with marker D4Mit126 (142.15 Mb), corrected p value=0.0004. The Mts1 maximal region mapped from D4Mit71 (66.71 cM) to the telomere (88.63 cM). Based on tumor latency, mice heterozygous for the STS/A and the BALB/c allele at this locus showed approximately 15 times higher risk of developing mammary tumors than mice homozygous for BALB/c alleles at the same locus. Runx3 was identified as a potential candidate gene. [Table 1, 4].
Mts1 (D4Mit126) also showed a suggestive main effect on tumor multiplicity, p=0.14. Mice homozygous for the BALB/c allele at Mts1 developed fewer mammmary tumors than heterozygotes. [Table 3.]
A suggestive interaction was also detected between Mts1 (D1Mit126) and Mts5 (D8Mit17) effecting mammary tumor number, p=0.03. [Table 3.]
The data also suggested a possible second locus on Chromosome 4 linked to D4Mit11 (122.91 Mb), 18 cM centromeric to Mts1. The maximal region for this locus ranged from D4Mit15 (43.16 cM to D4Mit70 (67.01 cM). STS/A homozygous and heterozygous mice at this locus showed 9 and 6 times the increased risk, respectively, compared to homozygous BALB/c mice.
[p=0.02, Table 1]. Present data could not rule out the possibility that this locus represented the same locus as Mts1, the locus was provisionally named Mts1b. Khdrbs1 is a potential candidate gene. [Table 1, 4].
Mts2, mammary tumor susceptibility 2, mapped to Chromosome 10 linked with marker D10Mit28 (9.13 Mb), corrected p value = 0.02. The maximal region for this locus ranged from the acromere (0.0 cM) to D10Mit3 (16.53 cM). Mice that were heterozygous at the Mts2 locus had approximately 3 times lower risk compared to BALB/c homozygotes at the same locus.
Esr1 was identified as a potential candidate gene.
Mts3, mammary tumor susceptibility 3, mapped to Chromosome 19 linked with marker D19Mit6 (61.13 Mb), corrected p value =0.05. The maximal region for this locus mapped from D19Mit35 (51.41 cM) to the telomere (55.66 cM). Based on tumor latency, mice heterozygous for the STS/A and the BALB/c allele at this locus showed approximately 5 times higher risk of developing mammary tumors than mice homozygous for BALB/c alleles at the same locus. [Table 1].
Two additional loci were detected in a significant pair-wise marker-marker interaction effecting mammary tumor latency.
The effect of one locus depends on the genotype of the interacting locus [Table 2 and Table 4]; neither of the two loci alone displayed any significant effects.
Mts4, mammary tumor susceptibility 4, mapped to Chromosme 6, linked with marker D6Mit122 (59.07 Mb). The maximal region for Mts4 ranged from D6Mit118 (25.4 cM) to D6Mit320 (32.45 cM).
Mts5, mammary tumor susceptibility 5, mapped to Chromosome 8, linked with marker D8Mit17 (13.40 Mb). The maximal region for Mts5 mapped from the acromere (0.0 cM) to D8Mit64 (19.01 cM). Markers Ikbkb, Adam9 and Fgfr1 are potential candidate genes for this QTL.
A suggestive locus effecting tumor number was detected on Chromosome 1 linked with marker D1Mit291 (88.97 cM) ranging between D1Mit403 (81.63 cM) and the telomere (98.51 cM).
Another was detected on Chromosome 8 linked with D8Mit36 (70.47 cM) ranging between D8Mit117 (61.34 cM) and D8Mit42 (74.46 cM) also effecting tumor number. Foxc2 and Gse1 are potential candidate genes.
Another suggestive locus effecting tumor metastsis was detected on Chromosome 17 linked with marker D17Mit72 (49.75 cM). The maximal region ranged between D17Mit38 (45.64) and the telomere (60.67 cM).
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