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Chromosome dynamics in meiotic prophase

Early stages of meiotic prophase I are a period of dramatic reorganization of chromosomes in the nucleus, which includes their spatial repositioning. Until now, this process in plants could only be studied in fixed cells because isolated plant prophase I meiocytes cannot be cultured in vitro. We developed a system to observe meiosis in intact live anthers, which, in contrast to isolated meiocytes, can be cultured over a period of several days. Meiocytes are imaged using multiphoton excitation microscopy, which allows observing cells located several tissue layers deep from the surface. Using this approach, we discovered that maize chromosomes show very dynamic and complex patterns of motility during the prophase of meiosis.

Chromosome movement in maize during the pachytene stage of meiotic prophase

To elucidate the mechanisms controlling prophase I chromosome motility, we are searching for mutants defective in chromosome movements. We found that the plural abnormalities of meiosis 1 (pam1) mutant in maize exhibits a dramatic reduction in the speed and amplitude of chromosome movements. The pam1 mutant was previously identified as defective in the formation of telomere bouquet. In pam1, telomeres attach to the nuclear envelope but fail to cluster. This defect is followed by several downstream meiotic defects, such as homologous chromosome pairing defects in zygotene, and presence of unresolved interlocks (chromosome entanglements) in pachytene, as well as an overall delay of meiosis progression. We cloned the Pam1 gene and found that it encodes an RNA-binding protein. We are now working to uncover the mechanism by which this protein controls chromosome dynamics.

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