PAM1, a Putative RNA-Binding Protein Critical for Nuclear Dynamics in Meiosis

During prophase I of meiosis, chromosomes engage in complex interactions and exhibit very dynamic patterns of behavior, which are essential for their proper segregation to daughter cells. In early prophase I, telomeres of all chromosomes attach to the nuclear envelope and cluster, forming a telomere bouquet. It is generally believed that telomere clustering facilitates pairing of homologous chromosomes by bringing their ends together. However, the exact function of the bouquet remains elusive. To study chromosome dynamics in meiotic prophase, we use a bouquet defective mutant in maize, pam1 (plural abnormalities of meiosis 1).   The mutant exhibits lack of telomere clustering, even though the telomeres attach to the nuclear envelope.  It also displays reduced pairing of homologous chromosomes. We found that pam1 shows significantly decreased chromosome motility in early meiotic prophase. In addition, clustering of nuclear pores, which coincides with the bouquet formation, is abnormal in the pam1 mutant. We have cloned the Pam1 gene and found that it encodes a putative RNA binding protein. Overall, our data suggest that Pam1 affects chromosome behavior but also controls the overall nuclear dynamics during the prophase of meiosis through a novel mechanism.