Cytological Monitoring of Meiotic Crossovers in Spermatocytes and Oocytes
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Crossing-over between homologous chromosomes is essential for accurate chromosome segregation at anaphase-I of meiosis. Defective crossing-over is associated with infertility, pregnancy miscarriage, and congenital disease. This chapter presents optimized protocols for the analysis of meiotic crossovers at the cytological level in spermatocytes and oocytes from mouse. The first approach employs immunocytology to detect MLH1, a DNA mismatch-repair protein that specifically marks crossover sites in the pachytene stage of meiotic prophase-I. These immunocytological methods have general utility for the analysis of other recombination steps, such as initiation and DNA strand exchange. The second approach visualizes chiasmata, the points of physical exchange between homologous chromosomes that are present during the diakinesis and metaphase-I stages. Both approaches are readily adaptable to the analysis of crossing over in other vertebrate species.
Key wordsMeiosis Homologous recombination Crossover Chiasma Chromosome spread Spermatocytes Oocytes Aneuploidy MLH1
M.I. was supported by a Japan Society for the Promotion of Science postdoctoral fellowship for research abroad. S.S. was supported by an A.P. Giannini Foundation postdoctoral fellowship. N.H. is an investigator of the Howard Hughes Medical Institute.
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