Localization of mouse Rad51 and Lim15 proteins on meiotic chromosomes at late stages of prophase 1.
BACKGROUND
In meiosis, eukaryotic chromosomes show a series of morphological changes, during which chromosomes synapse and recombine. To understand the mechanisms of the morphological changes and recombination of chromosomes, we examined stage-specific localization of the Rad51 and Lim15 proteins on the chromosomes in meiotic prophase 1. These proteins are homologous with the RecA protein and have general properties of searching and pairing of homologous DNA sequences. We used mouse chromosomes whose small sizes allow us to identify the locations of these proteins on the entire structures of the chromosomes.


RESULTS
In the leptotene and zygotene stages, the Rad51 protein was present on chromatin loops of mouse testis chromosomes then the protein left the loops. In the pachytene stage, the Rad51 protein was present almost exclusively along the core of the synaptonemal complexes (SC). When the stage proceeded to diplotene, the protein was present in the synaptic regions of chromosomes, in particular, in the chiasma regions. The protein was not present on separated homologous SC cores. On the other hand, the Lim15 protein that was found on chromatin loops in early prophase 1, was present almost exclusively at both ends of the SC cores throughout the late stages of prophase 1.


CONCLUSIONS
The Rad51 and Lim15 proteins are present in chromatin loops when chromosomes form SC. The proteins may promote pairing of homologous DNA sequences that would lead formation of SC. The Rad51 protein in the SC cores may be involved in chiasma formation in late stages. The Lim15 protein, instead, may be involved in recombination in the telomeric region or in cohesion of sister chromatids for segregation.
Ikeya
T
T
Department of Cell Genetics, National Institute of Genetics, Mishima, Shizuoka, Japan.
Shinohara
A
A
Sato
S
S
Tabata
S
S
Ogawa
T
T
D000251:Adenosine Triphosphatases; D000818:Animals; D018797:Cell Cycle Proteins; D002467:Cell Nucleus / Q000648:ultrastructure; D002875:Chromosomes / Q000648:ultrastructure*; D004268:DNA-Binding Proteins / Q000032:analysis*; D004706:Endodeoxyribonucleases; D005455:Fluorescent Antibody Technique; D007124:Immunoenzyme Techniques; D008297:Male; D008540:Meiosis; D051379:Mice; D009687:Nuclear Proteins; D028044:Phosphate-Binding Proteins; D011418:Prophase; D051135:Rad51 Recombinase; D013090:Spermatocytes / Q000166:cytology; D013573:Synaptonemal Complex; D013737:Testis / Q000166:cytology
D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; C513032:Dmc1 protein, mouse; D009687:Nuclear Proteins; D028044:Phosphate-Binding Proteins; D051135:Rad51 Recombinase; C495154:Rad51 protein, mouse; D004706:Endodeoxyribonucleases; C019329:deoxyribonuclease II; D000251:Adenosine Triphosphatases