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Distribution of crossing over on mouse synaptonemal complexes using immunofluorescent localization of MLH1 protein
L K Anderson1, A Reeves, L M Webb
1Department of Biology, Colorado State University, Fort Collins, Colorado 80523, USA. lorrie@lamar.colostate.edu
Abstract:
We have used immunofluorescent localization to examine the distribution of MLH1 (MutL homolog) foci on synaptonemal complexes (SCs) from juvenile male mice. MLH1 is a mismatch repair protein necessary for meiotic recombination in mice, and MLH1 foci have been proposed to mark crossover sites. We present evidence that the number and distribution of MLH1 foci on SCs closely correspond to the number and distribution of chiasmata on diplotene-metaphase I chromosomes. MLH1 foci were typically excluded from SC in centromeric heterochromatin. For SCs with one MLH1 focus, most foci were located near the middle of long SCs, but near the distal end of short SCs. For SCs with two MLH1 foci, the distribution of foci was bimodal regardless of SC length, with most foci located near the proximal and distal ends. The distribution of MLH1 foci indicated interference between foci. We observed a consistent relative distance (percent of SC length in euchromatin) between two foci on SCs of different lengths, suggesting that positive interference between MLH1 foci is a function of relative SC length. The extended length of pachytene SCs, as compared to more condensed diplotene-metaphase I bivalents, makes mapping crossover events and interference distances using MLH1 foci more accurate than using chiasmata.
Insights
MLH1 foci accurately map meiotic recombination crossovers on mouse synaptonemal complexes (SCs). Their distribution reveals interference patterns, offering a more precise method than chiasmata analysis for studying recombination.
Area of Science:
- Genetics
- Cell Biology
- Molecular Biology
Background:
- Meiotic recombination is crucial for accurate chromosome segregation.
- MLH1 (MutL homolog) is a key mismatch repair protein involved in meiotic recombination.
- MLH1 foci on synaptonemal complexes (SCs) are proposed to mark crossover sites.
Purpose of the Study:
- To investigate the distribution of MLH1 foci on SCs in juvenile male mice.
- To determine if MLH1 foci correlate with crossover sites and chiasmata.
- To analyze interference patterns between MLH1 foci.
Main Methods:
- Immunofluorescent localization of MLH1 foci on SCs from juvenile male mice.
- Analysis of MLH1 foci distribution relative to SC length and chromosomal regions.
- Comparison of MLH1 foci distribution with chiasmata on diplotene-metaphase I chromosomes.
Main Results:
- MLH1 foci distribution closely corresponds to chiasmata number and distribution.
- MLH1 foci were excluded from centromeric heterochromatin.
- Foci distribution indicated positive interference, dependent on relative SC length.
- Pachytene SCs allowed more accurate mapping of crossovers and interference than diplotene-metaphase I bivalents.
Conclusions:
- MLH1 foci serve as reliable markers for meiotic crossover sites in mice.
- The distribution patterns of MLH1 foci provide insights into recombination interference mechanisms.
- Mapping MLH1 foci on extended pachytene SCs offers a more precise method for studying recombination events and interference than traditional chiasmata analysis.