Analysis of factors decreasing testis weight in MRL mice.
MRL/MpJ (MRL) mouse testes have several unique characteristics, including the appearance of oocytes, the occurrence of metaphase-specific apoptosis of meiotic spermatocytes, and the presence of heat-shock-resistant spermatocytes. In the present study we used chromosomal mapping to determine the genomic background associated with small testis size in MRL mice. We prepared and analyzed C57BL/6-based congenic mice carrying MRL mouse loci. Quantitative trait loci (QTL) analysis revealed susceptibility loci for small testis size at 100 cM on chromosome (Chr) 1 and at around 80 cM on Chr 2. Analysis with B6.MRLc1 and B6.MRLc2 congenic mice and double-congenic mice confirmed the QTL data and showed that low testis weight in MRL mice was caused by germ cell apoptosis. Through histological examinations we found that B6.MRLc1 and B6.MRLc2 mice showed stage-specific apoptosis in their testes, the former at metaphase stage XII and the later at pachytene stage IV. Metaphase-specific apoptosis of spermatocytes occurs due to mutation of the exonuclease 1 (Exo1) gene located at 100 cM on Chr 1. Thus, the mutation of the Exo1 gene is also responsible for low testis weight caused by metaphase-specific apoptosis. In conclusion, testis weight is reduced in MRL mice due to apoptosis of germ cells caused by mutations in loci on Chrs 1 and 2.
Office for Faculty Development and Teaching Enriched Veterinary Medicine, Graduate School of Veterinary Medicine, Hokkaido University, Sapporo, 060-0818, Japan.
Saori
S
Otsuka
Yuka
Y
Namiki
Osamu
O
Ichii
Yoshiharu
Y
Hashimoto
Nobuya
N
Sasaki
Daiji
D
Endoh
Yasuhiro
Y
Kon
D000818:Animals; D017209:Apoptosis; D002874:Chromosome Mapping; D003433:Crosses, Genetic; D005260:Female; D008040:Genetic Linkage; D005838:Genotype; D008297:Male; D051379:Mice; D020297:Mice, Congenic; D008810:Mice, Inbred C57BL; D019463:Mice, Inbred MRL lpr / Q000235:genetics*; D009929:Organ Size / Q000235:genetics; D040641:Quantitative Trait Loci / Q000235:genetics; D012671:Seminiferous Tubules / Q000166:cytology / Q000648:ultrastructure; D013094:Spermatozoa / Q000166:cytology / Q000648:ultrastructure; D013737:Testis / Q000033:anatomy & histology*