PgmNr W4017: PP1α phosphatase GSP-2 regulates meiotic chromosome segregation during spermatogenesis in C. elegans.

Authors:
Yi-Hsiu Lin 1 ; Jui-Ching Wu 1,2


Institutes
1) Department of Clinical Laboratory Sciences and Medical Biotechnology, National Taiwan University, Taipei, Taiwan; 2) Department of Laboratory Medicine, National Taiwan University Hospital, Taipei, Taiwan.


Keyword: Gametogenesis, Fertilization, Egg-embryo transition

Abstract:

During spermatogenesis, it is crucial to properly partition duplicated chromosomes into four haploid cells with two consecutive divisions. It is unclear if the two chromosome segregation events are regulated by the same mechanism. Previously it is shown that two male-specific PP1 phosphatases are specifically required for chromosome segregation in meiosis II, suggesting the two chromosome segregation events, which separate homologs and sisters respectively, are regulated by different mechanisms. Here we investigate the roles of GSP-1 and GSP-2, the C. elegans homologs of the ubiquitously expressed PP1β and PP1α, in male meiotic divisions. Interestingly, despite high sequence identity, gsp-1 and gsp-2 mutant male worms show very different effects in spermatogenesis. Although gsp-1 mutant hermaphrodites are sterile, males lacking gsp-1 are completely fertile and show normal progression of sperm meiotic divisions in our analyses, indicating GSP-1 primarily functions in oocyte production. Contrarily, male worms lacking gsp-2 show high penetrance of male infertility. Examination of mature sperm revealed high percentage of sperm with abnormal nuclei and variable sizes produced by gsp-2 mutant males. By immunofluorescence staining, gsp-2 mutant male gonads exhibited a variety of abnormal chromosome morphology at division zones, indicating chromosome segregation defects during male meiosis. To further investigate the defects, we examined the progression of male meiotic chromosome segregation in live gsp-2 mutant males. In the absence of GSP-2, the chromosomes fail to be organized at the center of the cell, causing a delay of anaphase I onset. Furthermore, during anaphase I, the chromosomes are either separated rapidly without typical dumbbell-shape arrangement, or at a reduced speed with lagging chromosomes. During the second division, onset of anaphase II is also delayed and chromosome bridges were detected during separation. These results suggest GSP-2 is required for proper orientation of chromosomes during both meiotic divisions. In addition to defects in chromosome separation, we found paired chromosomes are often disengaged into multiple chromosomal bodies in gsp-2 mutant spermatocytes during meiosis I, indicating premature cohesion removal during first meiotic division. We reasoned GSP-2 might be required for protecting sister chromatid cohesin by restricting the localization of Aurora B kinase AIR-2 as described in oocytes. Consistent with this, we found AIR-2 is spread to the sister chromatids in the absence of GSP-2. These results suggest GSP-2 antagonizes AIR-2 function to regulate timely cohesin removal during male meiosis as in female meiosis. Taken together, we conclude that GSP-2 PP1 phosphatase is required for both chromosome orientation as well as stepwise chromosomal cohesion removal during male meiotic divisions.



Wormbase Genetic Index
1. gsp-1
2. gsp-2
3. air-2