J:216992

Spontaneous testicular teratomas (STTs) composed by various kinds of tissues are derived from primordial germ cells (PGCs) in the fetal testes of the mouse. In contrast, intra-testicular grafts of the mouse strain 129T1/Sv-Dnd⁺/Dnd⁺ fetal testes possessed the ability to develop the experimental testicular teratomas (ETTs), indistinguishable from the STTs at a morphological level.

Linkage analysis was performed for exploration of possible candidate genes involved in ETT development using F2 intercross fetuses derived from (LTXBJ/Sv x 129T1/Sv-Dnd⁺/Dnd⁺) F1 hybrids. In this study, 114 of 125 fetal samples exhibiting ETT phenotype and 197 of 235 fetal samples exhibiting no ETT phenotype were randomly selected for use in linkage analysis (n = 311). Linkage analysis with selected simple sequence length polymorphisms along chromosomes 18 and 19, which have been expected to contain ETT-susceptibility loci, demonstrated that a novel recessive candidate gene responsible for ETT development is located in a 1.1 Mb region between the SSLP markers D18Mit81 and D18Mit184 on chromosome 18 in the 129T1/Sv-Dnd⁺/Dnd⁺ genetic background. The authors chose to designate this locus Ett1 (experimentally induced testicular teratoma 1). Allelic segregation at Ett1 was predominantly skewed toward homozygous 129T1/Sv-Dnd⁺/Dnd⁺ strain alleles with strongest association at D18Mit81 (66.5 Mbp) (Chi^2 = 41.0; P = 0.13 x 10^-8).

The Ett1 locus exists in a region spanning 1.1 Mbp (66.3 - 67.4 Mbp), which includes peak markers D18Mit81 and D18Mit184. To resolve the location of Ett1 independently from other ETT susceptibility loci, a large segment of Chr 18 from the 129T1/Sv-Dnd⁺/Dnd⁺ strain was transferred onto the LTXBJ/Sv strain background through 13 consecutive backcross generations to generate the unique strain LT.129T1-(D18Mit81-D18Mit9). After 13 backcross generations, congenic mice were mated to generate F1 intercross offspring. Intercross proceeded more than seven cycles. During the crossing, genotyping was performed with PCR using D18Mit81 and D18Mit184 primer sets. When fetal testis from N4 mice was transplanted to N1 adult testis, Ett1 locus-dependent ETT formation was observed, demonstrating that the LT-Ett1 congenic strain LT.129T1-(D18Mit81-D18Mit9) possesses an inducing gene of ETT.