Meiotin-1, a Meiosis-enriched Protein Present in Normal Leptotene Chromosomes and Lacking in Precociously Condensed Leptotene Chromosomes

During mitotic prophase, chromosomes progressively compact to their metaphase length. In contrast, meiotic chromosomes condense moderately until late in prophase I, then they condense more dramatically (coil) to their fully condensed state. Meiotin-1 is a meiosis-enriched, chromosomal protein. We propose that it delays coiling until after reciprocal genetic exchange. We have used immunoblotting and immunocytochemistry with normal lily cells undergoing meiosis to demonstrate that meiotin-1 is present during the early portions of prophase I, but diminishes at the time when meiotic chromosomes begin to coil. Additionally, we have examined lily meiotic nuclei undergoing the reversible phenomenon of precocious leptotene chromosome condensation (precocious coiling). The leptotene chromosomes that are precociously condensed lack meiotin-1 immunostaining. Furthermore nuclei returning to the normal state of moderate prophase I condensation acquire meiotin-1.