Distribution of crossing over on mouse synaptonemal complexes using immunofluorescent localization of MLH1 protein

Genetics. 1999 Apr;151(4):1569-79.


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.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Adaptor Proteins, Signal Transducing
  • Animals
  • Base Pair Mismatch
  • Binding Sites
  • Carrier Proteins
  • Crossing Over, Genetic*
  • DNA Repair
  • Male
  • Mice
  • Mice, Inbred C57BL
  • Microscopy, Fluorescence
  • MutL Protein Homolog 1
  • Neoplasm Proteins / metabolism*
  • Nuclear Proteins
  • Recombination, Genetic
  • Spermatocytes / metabolism
  • Spermatocytes / ultrastructure
  • Synaptonemal Complex / genetics*


  • Adaptor Proteins, Signal Transducing
  • Carrier Proteins
  • Mlh1 protein, mouse
  • Neoplasm Proteins
  • Nuclear Proteins
  • MutL Protein Homolog 1