Identification of Two Additional Genomic Loci Responsible for experimentally induced testicular teratoma 2 and 3 (ett2 and ett3).

Experimental testicular teratomas (ETTs) can be induced in 129/Sv mouse by E12.5 fetal testes transplant into adult testes. Previously, we conducted linkage analysis to explore candidate genes possibly involved in ETT development using F2 intercross fetuses derived from F1[LTXBJ × 129/Sv- + /Ter (+ /+)] hybrids. By linkage analysis on Chr 18 and Chr 19, we identified the genomic locus for experimental testicular teratoma 1 (ett1) on Chr 18. In the present study, we conducted additional mapping and linkage analysis on teratoma susceptibility and genome composition on Chr 1-17. The results revealed two new candidate loci, experimental testicular teratoma 2 (ett2) and experimental testicular teratoma 3 (ett3), on Chr 3 and 7. Interestingly, the rates of ETT generation were increased in the case of ett2 and ett3 regions replaced with LTXBJ strain. To determine whether a polymorphic gene was present, we performed exome analysis of 129/Sv- + /Ter (+ /+) and LTXBJ. This revealed the presence of SNPs in all three loci, ett1 to ett3. ett1 contains polymorphic Mc4r; ett2 contains polymorphic Polr3c, Cd160, and Pdzk1; and ett3 contains polymorphic Prmt3. We found additional loci responsible for ETT formation, namely, ett2 and ett3, and identified candidate genes in these regions by exome analysis.

Identification of genomic locus responsible for experimentally induced testicular teratoma 1 (ett1) on mouse Chr 18.

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 (129/Sv-Ter (+/+)) fetal testes possessed the ability to develop the experimental testicular teratomas (ETTs), indistinguishable from the STTs at a morphological level. In this study, linkage analysis was performed for exploration of possible candidate genes involving in ETT development using F2 intercross fetuses derived from [LTXBJ × 129/Sv-Ter (+/+)] F1 hybrids. 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 1.1 Mb region between the SSLP markers D18Mit81 and D18Mit184 on chromosome 18 in the 129/Sv-Ter (+/+) genetic background. Since this locus is different from the previously known loci (including Ter, pgct1, and Tgct1) for STT development, we named this novel gene "experimental testicular teratoma 1 (ett1)". To resolve the location of ett1 independently from other susceptibility loci, ett1 loci was introduced in a congenic strain in which the distal segment of chromosome 18 in LTXBJ strain mice had been replaced by a 1.99 Mbp genomic segment of the 129/Sv-Ter (+/+) mice. Congenic males homozygous for the ett1 loci were confirmed to have the ability to form ETTs, indicating that this locus contain the gene responsible for ETTs. We listed candidate genes included in this region, and discussed about their possible involvement in induction of ETTs.

A spontaneous smc1b mutation causes cohesin protein dysfunction and sterility in mice.

In this paper, we describe a novel spontaneous mutation of the Smc1b gene coding a cohesin component, which causes female and male sterility. We have discovered an ICR male mouse with a novel autosomal recessive gene that causes small gonads and sterility in both sexes. Mutant female and male mice homozygous for the novel sterility gene had normal body weights and showed normal mating behavior, but did not produce any offspring. Histological examination showed that Sertoli cells and spermatogonia were present in the testicular seminiferous tubules in 8-week-old mutant male mice, but no spermatids or spermatozoa were observed. Mutant females showed a markedly reduced number of oocytes with age. The novel sterility gene mapped between D15Mit105 (47.9 cM) and D15Mit171 (54.5 cM) on chromosome 15. Sequences of three candidate sterility genes, Dmc1, Mei1 and Smc1b, which are closely linked to these microsatellite markers, were compared between normal and mutant mice. The Dmc1 and Mei1 genes showed the same sequences in both normal and mutant mice, but the Smc1b gene had a deletion of 16 nucleotides in exon 5, in the mutant mice. We concluded that this deletion led to a frame-shift, which generated a stop codon at position 761 (amino acid 247) of the Smc1b cDNA in mutant mice.

Mouse Offspring Derived from Fetal Ovaries or Reaggregates Which were Cultured and Transplanted into Adult Females.

Primordial germ cells (PGCs) and gonia could be promising novel targets and vehicles for manipulation of the mammalian germ line. To make such manipulation a practical possibility, PGCs or gonia must be allowed to produce gametes and offspring after they were isolated from embryos and manipulated in culture. As the first step to develop such research strategy, we obtained offspring from mouse oogonia which were isolated from embryonic ovaries and cultured as dispersed cells before transplantation into female mice as reaggregates.

The ter mutation first causes primordial germ cell deficiency in ter/ter mouse embryos at 8 days of gestation.

The ter (teratoma) mutation causes primordial germ cell (PGC) deficiency in ter/ter embryos at 9.5-12.5 days of post-coitum (dpc) in mouse strains 129/Sv-ter and LTXBJ-ter. To study the effects of the ter mutation on the PGC development more precisely, we examined the PGC number and distribution in 7.5-12.5 dpc embryo of ter congenic C57BL/6J-ter strain using their complete serial sections. The ter genotypes of embryos were identified by the polymerase chain reaction (PCR) polymorphisms of the microsatellite DNA of the Grl-1 locus mapped near the ter locus. Results showed that: (i) the PGC number in ter/ter embryos was similar to those of + /ter and + / + embryos at 7.5 dpc, and did not increase at 8.0-12.5 dpc, although those of normal littermates did usually; (ii) the PGC migration to genital ridges was never affected in all embryos; and (iii) the ter genotype difference in the PGC numbers was not recognized between + /ter and + / + embryos. We concluded that the ter mutation does not affect the PGC appearance around 7.5 dpc, but first causes PGC deficiency around 8.0 dpc at the beginning of their migration and proliferation, suggesting that the normal function of the ter gene may be essential for the proliferation or survival mechanisms of PGC.

The ter mutation responsible for germ cell deficiency but not testicular nor ovarian teratocarcinogenesis in ter / ter congenic mice.

The ter (teratoma) gene causes germ cell deficiency and a high incidence of congenital testicular teratomas derived from primordial germ cells in 129/Sv-ter strain mice. Ovarian teratomas in LTXBJ mice originate from ovarian parthenotes. In order to study the function of the ter gene in germ cell development and teratocarcinogenesis, we examined the influence of a foreign genetic background on the ter action by introducing the ter gene of 129/Sv-ter strain mice into C57BL/6J, LTXBJ and C3H/HeJ genetic backgrounds by the backcross method and by thus establishing B6-ter, LTXBJ-ter and C3H-ter ter congenic strains, respectively. Histological analysis showed that germ cell deficiency occurred in both sexes of the ter mutants, through the fetal stages to adulthood, but that congenital testicular teratocarcinogenesis did not occur after the fifth backcross generation. The ter/ter gonads were smaller than normal (+/+ or +/ter). Experimental testicular teratomas never developed from intratesticular grafts of B6-ter genital ridges. LTXBJ-ter/ter females had no ovarian teratomas. It is concluded that the ter gene is solely responsible for germ cell deficiency, but not testicular teratocarcinogenesis, in ter congenic strains having background genes other than 129/Sv-ter and that the ter gene is not involved in ovarian teratocarcinogenesis.