Shugoshin is essential for meiotic prophase checkpoints inC. elegans

Abstract

21 22The conserved factor Shugoshin is dispensable in C. elegans for the two-step loss of sister 23 chromatid cohesion that directs the proper segregation of meiotic chromosomes. We show that 24 the C. elegans ortholog of Shugoshin, SGO-1, is required for checkpoint activity in meiotic 25prophase. This role in checkpoint function is similar to that of the meiotic chromosomal protein, 26 HTP-3. Null sgo-1 mutants exhibit additional phenotypes similar to that of a partial loss of 27 function allele of HTP-3: premature synaptonemal complex disassembly, the activation of 28 alternate DNA repair pathways and an inability to recruit a conserved effector of the DNA 29 damage pathway, HUS-1. SGO-1 localizes to pre-meiotic nuclei, when HTP-3 is present but not 30 yet loaded onto chromosome axes, suggesting an early role in regulating meiotic chromosome 31 metabolism. We propose that SGO-1 acts during pre-meiotic replication to ensure fully 32 functional meiotic chromosome architecture, rendering these chromosomes competent for 33 checkpoint activity and normal progression of meiotic recombination. Given that most research 34

The conserved AAA-ATPase PCH-2 distributes its regulation of meiotic prophase events by remodeling multiple meiotic HORMADs inC. elegans

“…htp-3(vc75) is a missense mutation that replaces histidine 96 with a tyrosine in the HORMA domain (H96Y) (Figure 2A). HTP-3 H96Y properly localizes to meiotic chromosomes [42] and does not affect pairing, synapsis and crossover recombination [42,43]. However, we and others previously showed that this mutation in htp-3 abolished meiotic checkpoint responses in C. elegans [42,43].…”

“…HTP-3 H96Y properly localizes to meiotic chromosomes [42] and does not affect pairing, synapsis and crossover recombination [42,43]. However, we and others previously showed that this mutation in htp-3 abolished meiotic checkpoint responses in C. elegans [42,43]. Because of this phenotype, we analyzed HTP-3's relationship with PCH-2 in regulating pairing, synapsis, recombination, and meiotic progression.…”

“…We previously showed that htp-3 H96Y mutants abolishes both the DNA damage response and the synapsis checkpoint [43], similar to null mutations in htp-3 and him-3 [55]. A null mutation in htp-1 only affects the synapsis checkpoint [55].…”

“…Altogether, our analysis of pairing, synapsis and crossover recombination indicate that PCH-2 and HTP-3 act together to regulate pairing and synapsis but independently to regulate DNA repair and crossover formation. Since htp-3 H96Y single mutants also show defects in the DNA damage response [43] while pch-2 mutants do not [48], this separation of function is not necessarily surprising. However, more importantly these data strongly support a model in which PCH-2 acts through HTP-3's HORMA domain to control the rate of pairing and synapsis but not the process of meiotic recombination.…”

“…him-3 R93Y mutants showed wildtype levels of apoptosis while htp-1 G97T mutants exhibited germline apoptosis similar to that of syp-1 single mutants (Figure S6, p value < 0.0001 by student t-test), likely as a consequence of the asynapsis and defects in recombination we observe (Figure 5). Both syp-1;him-3 R93Y and syp-1;htp-1 G97T double mutants showed similar levels of germline apoptosis as syp-1 single mutants (Figure S6), indicating that both him-3 R93Y or htp-1 G97T mutants are competent for meiotic checkpoint activation, unlike htp-3 H96Y mutants [43].…”