MEIOTIC PROPHASE CHROMOSOME BEHAVIOR IN MAIZE

¹ Dept. Molecular and Cell Biology, 341 LSA, University of California,Berkeley, CA 94720-3200 USA

² Dept. Biol. Sci., Biology Unit 1, Florida State University, Tallahasee, FL 32306-4370 USA

We are investigating the chromosomal rearrangements that occur during pairing and synapsis of homologous chromosomes of maize. Using a polyacrylamide gel embedding technique in combination with fluorescence in situ hybridization (FISH), we are conducting a three dimensional (3-D) analysis of meiotic telomere and centromere behavior. Images are collected using a computerized epifluorescence microscope and the data stacks are processed by 3-D deconvolution. To analyze the kinetics of whole chromosome pairing we are using an oat-based chromosome addition line in which a single maize homologous chromosome pair has been introduced. By selectively staining the maize chromosomes with maize FISH probes , we demonstrate that telomeres undergo a dramatic rearrangement from a random distribution at leptotene to a clustered distribution on the nuclear envelope at zygotene, and that homologous chromosomes do not approach each other until telomere clustering is initiated. Using in vitro anther culture, we demonstrate that telomere attachment to the nuclear envelope is blocked by colchicine, however, this occurs at low concentrations of the drug that do not disrupt cytoplasmic microtubules. We are using immunocytochemistry in 3D to describe the redistribution of enzymes involved in meiotic recombination during initiation of pairing. At the end of leptotene just as the telomeres are beginning to cluster, rad51 foci begin to appear on the chromatin. The foci are at a maximum in midzygotene (400-600/nucleus), but as pairing proceeds their number decreases until in pachytene only a few (10-20) persist.