Leptotene/Zygotene Chromosome Movement Via the SUN/KASH Protein Bridge in Caenorhabditis elegans

The Caenorhabditis elegans inner nuclear envelope protein matefin/SUN-1 plays a conserved, pivotal role in the process of genome haploidization. CHK-2–dependent phosphorylation of SUN-1 regulates homologous chromosome pairing and interhomolog recombination in Caenorhabditis elegans. Using time-lapse microscopy, we characterized the movement of matefin/SUN-1::GFP aggregates (the equivalent of chromosomal attachment plaques) and showed that the dynamics of matefin/SUN-1 aggregates remained unchanged throughout leptonene/zygotene, despite the progression of pairing. Movement of SUN-1 aggregates correlated with chromatin polarization. We also analyzed the requirements for the formation of movement-competent matefin/SUN-1 aggregates in the context of chromosome structure and found that chromosome axes were required to produce wild-type numbers of attachment plaques. Abrogation of synapsis led to a deceleration of SUN-1 aggregate movement. Analysis of matefin/SUN-1 in a double-strand break deficient mutant revealed that repair intermediates influenced matefin/SUN-1 aggregate dynamics. Investigation of movement in meiotic regulator mutants substantiated that proper orchestration of the meiotic program and effective repair of DNA double-strand breaks were necessary for the wild-type behavior of matefin/SUN-1 aggregates

corona Is Required for Higher-Order Assembly of Transverse Filaments into Full-Length Synaptonemal Complex in Drosophila Oocytes

The synaptonemal complex (SC) is an intricate structure that forms between homologous chromosomes early during the meiotic prophase, where it mediates homolog pairing interactions and promotes the formation of genetic exchanges. In Drosophila melanogaster, C(3)G protein forms the transverse filaments (TFs) of the SC. The N termini of C(3)G homodimers localize to the Central Element (CE) of the SC, while the C-termini of C(3)G connect the TFs to the chromosomes via associations with the axial elements/lateral elements (AEs/LEs) of the SC. Here, we show that the Drosophila protein Corona (CONA) co-localizes with C(3)G in a mutually dependent fashion and is required for the polymerization of C(3)G into mature thread-like structures, in the context both of paired homologous chromosomes and of C(3)G polycomplexes that lack AEs/LEs. Although AEs assemble in cona oocytes, they exhibit defects that are characteristic of c(3)G mutant oocytes, including failure of AE alignment and synapsis. These results demonstrate that CONA, which does not contain a coiled coil domain, is required for the stable ‘zippering’ of TFs to form the central region of the Drosophila SC. We speculate that CONA's role in SC formation may be similar to that of the mammalian CE proteins SYCE2 and TEX12. However, the observation that AE alignment and pairing occurs in Tex12 and Syce2 mutant meiocytes but not in cona oocytes suggests that the SC plays a more critical role in the stable association of homologs in Drosophila than it does in mammalian cells

A Novel Mouse Synaptonemal Complex Protein Is Essential for Loading of Central Element Proteins, Recombination, and Fertility

The synaptonemal complex (SC) is a proteinaceous, meiosis-specific structure that is highly conserved in evolution. During meiosis, the SC mediates synapsis of homologous chromosomes. It is essential for proper recombination and segregation of homologous chromosomes, and therefore for genome haploidization. Mutations in human SC genes can cause infertility. In order to gain a better understanding of the process of SC assembly in a model system that would be relevant for humans, we are investigating meiosis in mice. Here, we report on a newly identified component of the murine SC, which we named SYCE3. SYCE3 is strongly conserved among mammals and localizes to the central element (CE) of the SC. By generating a Syce3 knockout mouse, we found that SYCE3 is required for fertility in both sexes. Loss of SYCE3 blocks synapsis initiation and results in meiotic arrest. In the absence of SYCE3, initiation of meiotic recombination appears to be normal, but its progression is severely impaired resulting in complete absence of MLH1 foci, which are presumed markers of crossovers in wild-type meiocytes. In the process of SC assembly, SYCE3 is required downstream of transverse filament protein SYCP1, but upstream of the other previously described CE–specific proteins. We conclude that SYCE3 enables chromosome loading of the other CE–specific proteins, which in turn would promote synapsis between homologous chromosomes

Correction: Investigating the Role of RIO Protein Kinases in Caenorhabditis elegans.

[This corrects the article DOI: 10.1371/journal.pone.0117444.]

<i>riok-1</i> is required for normal germ cell proliferation.

<p>(A) Overview of the adult <i>C. elegans</i> hermaphrodite gonad. One of the two gonad U-shaped tubular gonad is shown. The single somatic distal tip cell (DTC) maintains a population of self-renewing germline stem cells. Germ cells enter into the meiotic prophase I in the transition zone and then progress to the pachytene stage. During these stages, germ cells are only partially enclosed in a membrane and share a common cytoplasmic core. As germ cells exit pachytene, they move through the “loop” region and enter diplotene and begin to fully cellularise. A signal from sperm directs the most proximal oocytes to undergo maturation and fertilisation occurs are the oocyte moves through the spermatheca into the uterus. (B-C) Dissected gonads were stained with anti-pH3 staining to detect proliferating germ cells and DAPI to visualise DNA. Asterisks indicate the distal end of the gonad. Scale bar = 15μm. (D-E) <i>riok-1(RNAi)</i> gonads had a reduced number of pH3 stained cells in the mitotic zone (D) Wild-type worms with <i>riok-1</i> knocked down at 20°C and 25°C <i>(n = 50)</i> (E)) <i>rrf-1;pCB19(RNAi)</i> and <i>rrf-1</i>:<i>riok-1(RNAi)</i> worms at 20°C and 25°C <i>(n = 50)</i>. Error bars represent SEM; _**** = P values &lt;0.0001.</p

The putative promoters of <i>riok-2</i> and -<i>3</i> drive GFP in distinct tissues.

<p>(<b>A)</b><i>riok-2</i> transgenic worms displayed weak GFP expression in the metacorpus and posterior bulb of the pharynx. Scale bar = 25μm (B) <i>riok-3</i> transgenic worms revealed weak GFP expression, in some head and was strongly expressed in a tail neuron which may be the PVQ, PHAL or PQR neuron. Scale bar = 25μm.</p

<i>riok-1(RNAi)</i> sterility is associated with an oogenesis defect.

<p>(A) Total average brood size for wild-type worms knocked down for r<i>iok-1</i>, <i>riok-2</i> or <i>riok-3</i> at 20°C, 23°C and 25°C. <i>riok-1(RNAi)</i> worms have a significant reduction in brood size at 20°C and are sterile at 23°C and 25°C. Error bars represent the SEM; <i>n</i> ≥<i>6</i>. _**** = P values &lt;0.0001. _*** = P values 0.0003 for <i>riok-3</i> at 25°C (B) Average number of progeny produced in 17 hours from crossing <i>fog-2(q71)</i> male and female worms. Crosses were; control, ♀ <i>fog-2(q71)</i> x <i>♂ fog-2(q71)</i>; ♀ <i>fog-2(q71)</i> x <i>♂riok-1(RNAi)</i>; ♀ <i>fog-2(q71)riok-1(RNAi)</i> x <i>♂ fog-2(q71)</i>. Thirteen individual crosses per treatment were conducted at 25°C with 10 males mated per L4 female. _**** = P &lt;0.0001. (C) Knockdown of <i>riok-1</i> in <i>rrf-1</i> worms resulted in significantly reduced progeny. Total brood size for <i>rrf-1</i> worms grown on <i>riok-1</i> and pCB19 (negative control) RNAi at 25°C. Error bars represent SEM. <i>n = 23</i>, _**** = P &lt;0.0001.</p