Limits...
A yeast two-hybrid screen for SYP-3 interactors identifies SYP-4, a component required for synaptonemal complex assembly and chiasma formation in Caenorhabditis elegans meiosis.

Smolikov S, Schild-Prüfert K, Colaiácovo MP - PLoS Genet. (2009)

Bottom Line: SYP-4 is essential for the localization of SYP-1, SYP-2, and SYP-3 CR proteins onto chromosomes, thereby playing a crucial role in the stabilization of pairing interactions between homologous chromosomes.The lack of chiasmata observed in syp-4 mutants supports the elevated levels of chromosome nondisjunction manifested in high embryonic lethality.Altogether our findings place SYP-4 as a central player in SC formation and broaden our understanding of the structure of the SC and its assembly.

View Article: PubMed Central - PubMed

Affiliation: Department of Genetics, Harvard Medical School, Boston, Massachusetts, United States of America.

ABSTRACT
The proper assembly of the synaptonemal complex (SC) between homologs is critical to ensure accurate meiotic chromosome segregation. The SC is a meiotic tripartite structure present from yeast to humans, comprised of proteins assembled along the axes of the chromosomes and central region (CR) proteins that bridge the two chromosome axes. Here we identify SYP-4 as a novel structural component of the SC in Caenorhabditis elegans. SYP-4 interacts in a yeast two-hybrid assay with SYP-3, one of components of the CR of the SC, and is localized at the interface between homologs during meiosis. SYP-4 is essential for the localization of SYP-1, SYP-2, and SYP-3 CR proteins onto chromosomes, thereby playing a crucial role in the stabilization of pairing interactions between homologous chromosomes. In the absence of SYP-4, the levels of recombination intermediates, as indicated by RAD-51 foci, are elevated in mid-prophase nuclei, and crossover recombination events are significantly reduced. The lack of chiasmata observed in syp-4 mutants supports the elevated levels of chromosome nondisjunction manifested in high embryonic lethality. Altogether our findings place SYP-4 as a central player in SC formation and broaden our understanding of the structure of the SC and its assembly.

Show MeSH

Related in: MedlinePlus

SYP-4 is required for the stabilization of homologous pairing interactions.(A) Diagram of a C. elegans germline indicating the position of the zones scored in the time-course analysis of homologous pairing. The color codes indicate the genotypes examined in (C). (B) High magnification images of pachytene nuclei from wild type and syp-4 mutants stained with DAPI and hybridized with FISH probes recognizing either the PC end or the non-PC end of chromosome I (green and red, respectively). FISH signals are frequently unpaired in syp-4 mutants. Bars, 2 µm. (C) Graphs depicting the percentage of nuclei carrying paired homologous chromosomes (y-axis) within each zone along the germline (x-axis). The regions being recognized by each of the FISH probes are indicated above the graphs.
© Copyright Policy
Related In: Results  -  Collection


getmorefigures.php?uid=PMC2742731&req=5

pgen-1000669-g005: SYP-4 is required for the stabilization of homologous pairing interactions.(A) Diagram of a C. elegans germline indicating the position of the zones scored in the time-course analysis of homologous pairing. The color codes indicate the genotypes examined in (C). (B) High magnification images of pachytene nuclei from wild type and syp-4 mutants stained with DAPI and hybridized with FISH probes recognizing either the PC end or the non-PC end of chromosome I (green and red, respectively). FISH signals are frequently unpaired in syp-4 mutants. Bars, 2 µm. (C) Graphs depicting the percentage of nuclei carrying paired homologous chromosomes (y-axis) within each zone along the germline (x-axis). The regions being recognized by each of the FISH probes are indicated above the graphs.

Mentions: In C. elegans, synapsis is crucial for the stabilization of chromosome paring interactions [2],[13],[14]. Since our immunolocalization studies place SYP-4 as a central region protein, we used fluorescence in situ hybridization (FISH) to monitor its role in chromosome pairing throughout prophase. We divided gonads from wild type and syp-4(tm2713) mutants into 7 zones and analyzed the percentage of nuclei carrying paired chromosomes in each one of these zones (Figure 5A). Specifically, we monitored pairing at opposite ends (the pairing center (PC) and non-PC ends) of chromosomes I and X. Levels of homologous pairing progressively increased in wild type nuclei as they entered meiosis in zones 2 to 3. In early pachytene (zone 4), chromosomes I and X were observed pairing with their homologous partners in approximately 100% of the nuclei examined and this level was maintained throughout late pachytene (zone 7) (Figure 5C). In contrast, although an increase in homologous pairing levels was detected in syp-4(tm2713) mutants initiating at the same time as in wild type, pairing levels failed to reach 100% and decreased as prophase progressed (Figure 5C, and Table S2, p<0.0001 for all loci in zones 6 and 7). This inability to stabilize pairing interactions was more pronounced for chromosome I than for the X chromosome, as exemplified by the observation of homologous pairing at the PC end of chromosome I in only 74% of the nuclei examined in zone 4, compared to 94% at the PC end of the X chromosome in the same zone (Figure 5C, p<0.0001). These differences probably reflect the yet unexplained propensity of the X chromosomes to pair more efficiently compared to the autosomes when SC formation is impaired, as seen in other mutants in C. elegans [35]–[37]. In addition, significantly higher levels of pairing were observed in the PC regions compared to the non-PC regions (Figure 5C). Specifically, pairing levels were 25% and 56% higher at the PC end compared to the non-PC end of chromosomes I and X, respectively (for Chromosome I, zone 3, p = 0.0061; for the X chromosome, zone 4, p<0.0001). The higher levels of pairing observed at the PC ends most likely stem from the fact that the initiation of homologous pairing events occurs at the PCs in a SYP-independent manner [2],[13],[14],[38]. Taken together, our observations indicate that unlike axis-associated proteins, SYP-4 is dispensable for the initiation of paring interactions, but as meiosis progresses it is crucial for the stabilization of pairing interactions. Our studies, therefore, further support a role for SYP-4 as a central region component of the SC.


A yeast two-hybrid screen for SYP-3 interactors identifies SYP-4, a component required for synaptonemal complex assembly and chiasma formation in Caenorhabditis elegans meiosis.

Smolikov S, Schild-Prüfert K, Colaiácovo MP - PLoS Genet. (2009)

SYP-4 is required for the stabilization of homologous pairing interactions.(A) Diagram of a C. elegans germline indicating the position of the zones scored in the time-course analysis of homologous pairing. The color codes indicate the genotypes examined in (C). (B) High magnification images of pachytene nuclei from wild type and syp-4 mutants stained with DAPI and hybridized with FISH probes recognizing either the PC end or the non-PC end of chromosome I (green and red, respectively). FISH signals are frequently unpaired in syp-4 mutants. Bars, 2 µm. (C) Graphs depicting the percentage of nuclei carrying paired homologous chromosomes (y-axis) within each zone along the germline (x-axis). The regions being recognized by each of the FISH probes are indicated above the graphs.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2742731&req=5

pgen-1000669-g005: SYP-4 is required for the stabilization of homologous pairing interactions.(A) Diagram of a C. elegans germline indicating the position of the zones scored in the time-course analysis of homologous pairing. The color codes indicate the genotypes examined in (C). (B) High magnification images of pachytene nuclei from wild type and syp-4 mutants stained with DAPI and hybridized with FISH probes recognizing either the PC end or the non-PC end of chromosome I (green and red, respectively). FISH signals are frequently unpaired in syp-4 mutants. Bars, 2 µm. (C) Graphs depicting the percentage of nuclei carrying paired homologous chromosomes (y-axis) within each zone along the germline (x-axis). The regions being recognized by each of the FISH probes are indicated above the graphs.
Mentions: In C. elegans, synapsis is crucial for the stabilization of chromosome paring interactions [2],[13],[14]. Since our immunolocalization studies place SYP-4 as a central region protein, we used fluorescence in situ hybridization (FISH) to monitor its role in chromosome pairing throughout prophase. We divided gonads from wild type and syp-4(tm2713) mutants into 7 zones and analyzed the percentage of nuclei carrying paired chromosomes in each one of these zones (Figure 5A). Specifically, we monitored pairing at opposite ends (the pairing center (PC) and non-PC ends) of chromosomes I and X. Levels of homologous pairing progressively increased in wild type nuclei as they entered meiosis in zones 2 to 3. In early pachytene (zone 4), chromosomes I and X were observed pairing with their homologous partners in approximately 100% of the nuclei examined and this level was maintained throughout late pachytene (zone 7) (Figure 5C). In contrast, although an increase in homologous pairing levels was detected in syp-4(tm2713) mutants initiating at the same time as in wild type, pairing levels failed to reach 100% and decreased as prophase progressed (Figure 5C, and Table S2, p<0.0001 for all loci in zones 6 and 7). This inability to stabilize pairing interactions was more pronounced for chromosome I than for the X chromosome, as exemplified by the observation of homologous pairing at the PC end of chromosome I in only 74% of the nuclei examined in zone 4, compared to 94% at the PC end of the X chromosome in the same zone (Figure 5C, p<0.0001). These differences probably reflect the yet unexplained propensity of the X chromosomes to pair more efficiently compared to the autosomes when SC formation is impaired, as seen in other mutants in C. elegans [35]–[37]. In addition, significantly higher levels of pairing were observed in the PC regions compared to the non-PC regions (Figure 5C). Specifically, pairing levels were 25% and 56% higher at the PC end compared to the non-PC end of chromosomes I and X, respectively (for Chromosome I, zone 3, p = 0.0061; for the X chromosome, zone 4, p<0.0001). The higher levels of pairing observed at the PC ends most likely stem from the fact that the initiation of homologous pairing events occurs at the PCs in a SYP-independent manner [2],[13],[14],[38]. Taken together, our observations indicate that unlike axis-associated proteins, SYP-4 is dispensable for the initiation of paring interactions, but as meiosis progresses it is crucial for the stabilization of pairing interactions. Our studies, therefore, further support a role for SYP-4 as a central region component of the SC.

Bottom Line: SYP-4 is essential for the localization of SYP-1, SYP-2, and SYP-3 CR proteins onto chromosomes, thereby playing a crucial role in the stabilization of pairing interactions between homologous chromosomes.The lack of chiasmata observed in syp-4 mutants supports the elevated levels of chromosome nondisjunction manifested in high embryonic lethality.Altogether our findings place SYP-4 as a central player in SC formation and broaden our understanding of the structure of the SC and its assembly.

View Article: PubMed Central - PubMed

Affiliation: Department of Genetics, Harvard Medical School, Boston, Massachusetts, United States of America.

ABSTRACT
The proper assembly of the synaptonemal complex (SC) between homologs is critical to ensure accurate meiotic chromosome segregation. The SC is a meiotic tripartite structure present from yeast to humans, comprised of proteins assembled along the axes of the chromosomes and central region (CR) proteins that bridge the two chromosome axes. Here we identify SYP-4 as a novel structural component of the SC in Caenorhabditis elegans. SYP-4 interacts in a yeast two-hybrid assay with SYP-3, one of components of the CR of the SC, and is localized at the interface between homologs during meiosis. SYP-4 is essential for the localization of SYP-1, SYP-2, and SYP-3 CR proteins onto chromosomes, thereby playing a crucial role in the stabilization of pairing interactions between homologous chromosomes. In the absence of SYP-4, the levels of recombination intermediates, as indicated by RAD-51 foci, are elevated in mid-prophase nuclei, and crossover recombination events are significantly reduced. The lack of chiasmata observed in syp-4 mutants supports the elevated levels of chromosome nondisjunction manifested in high embryonic lethality. Altogether our findings place SYP-4 as a central player in SC formation and broaden our understanding of the structure of the SC and its assembly.

Show MeSH
Related in: MedlinePlus