The chromosomal distribution of phosphorylated histone H3 differs between plants and animals at meiosis

Plant (Secale cereale, Triticum aestivum) and animal (Eyprepocnemis plorans ) meiocytes were analyzed by indirect immunostaining with an antibody recog nizing histone H3 phosphorylated at serine 10, to study the relationship be tween H3 phosphorylation and chromosome condensation at meiosis. To investi gate whether the dynamics of histone H3 phosphorylation differs between chr omosomes with a different mode of segregation, we included in this study mi totic cells and also meiotic cells of individuals forming bivalents plus th ree different types of univalents (A chromosomes, B chromosomes and X chrom osome). During the first meiotic division, the H3 phosphorylation of the en tire chromosomes initiates at the transition from leptotene to zygotene in rye and wheat, whereas in E. plorans it does so at diplotene. In all specie s analyzed H3 phosphorylation terminates toward interkinesis. The immunosig nals at first meiotic division are identical in bivalents and univalents of A and B chromosomes, irrespective of their equational or reductional segre gation at anaphase I. The grasshopper X chromosome, which always segregates reductionally, also shows the same pattern. Remarkable differences were fo und at second meiotic division between plant and animal material. In E. plo rans H3 phosphorylation occurred all along the chromosomes, whereas in plan ts only the pericentromeric regions showed strong immunosignals from propha se II until telophase II. In addition, no immunolabeling was detectable on single chromatids resulting from equational segregation of plant A or B chr omosome univalents during the preceding anaphase I. Simultaneous immunostai ning with anti-tubulin and anti-phosphorylated H3 antibodies demonstrated t hat the kinetochores of all chromosomes interact with microtubules, even in the absence of detectable phosphorylated H3 immunosignals. The different p attern of H3 phosphorylation in plant and animal meiocytes suggests that th is evolutionarily conserved post-translational chromatin modification might be involved in different roles in both types of organisms. The possibility that in plants H3 phosphorylation is related to sister chromatid cohesion is discussed.