Biology subjects

Kursel, L. E.

Publications and source records attributed to Kursel, L. E..

6 recordsLinked to original sources

bioRxiv2024

Skp1 is a conserved structural component of the meiotic synaptonemal complex

SummaryDuring sexual reproduction, the parental chromosomes align along their length and exchange genetic information. These processes depend on a chromosomal interface called the synaptonemal complex. The structure of the synaptonemal complex is conserved across eukaryotes, but, surprisingly, the components that make it up are dramatically different in different organisms. Here we find that a protein well known for its role in regulating protein degradation has been moonlighting as a structural component of the synaptonemal complex in the nematode Pristionchus pacificus, and that it has likely carried out both of these functions for more than 100 million years. The synaptonemal complex (SC) is a meiotic interface that assembles between parental chromosomes and is essential for the formation of gametes. While the dimensions and ultrastructure of the SC are conserved across eukaryotes, its protein components are highly divergent. Recently, an unexpected component of the SC has been described in the nematode C. elegans: the Skp1-related proteins SKR-1/2, which are components of the Skp1, Cullin, F-box (SCF) ubiquitin ligase. Here, we find that the role of SKR-1 in the SC is conserved in nematodes. The P. pacificus Skp1 ortholog, Ppa-SKR-1, colocalizes with other SC proteins throughout meiotic prophase, where it occupies the middle of the SC. Like in C. elegans, the dimerization interface of Ppa-SKR-1 is required for its SC function. A dimerization mutant, Ppa-skr-1F105E, fails to assemble SC and is almost completely sterile. Interestingly, the evolutionary trajectory of SKR-1 contrasts with other SC proteins. Unlike most SC proteins, SKR-1 is highly conserved in nematodes. Our results suggest that the structural role of SKR-1 in the SC has been conserved since the common ancestor of C. elegans and P. pacificus, and that rapidly evolving SC proteins have maintained the ability to interact with SKR-1 for at least 100 million years.

genetics↗

bioRxiv2023

A suppressor screen in C. elegans identifies a multi-protein interaction interface that stabilizes the synaptonemal complex

Successful chromosome segregation into gametes depends on tightly-regulated interactions between the parental chromosomes. During meiosis, chromosomes are aligned end-to-end by an interface called the synaptonemal complex, which also regulates exchanges between them. However, despite the functional and ultrastructural conservation of this essential interface, how protein-protein interactions within the synaptonemal complex regulate chromosomal interactions remains poorly understood. Here we describe a novel interaction interface in the C. elegans synaptonemal complex, comprised of short segments of three proteins, SYP-1, SYP-3 and SYP-4. We identified the interface through a saturated suppressor screen of a mutant that destabilizes the synaptonemal complex. The specificity and tight distribution of suppressors point to a charge-based interface that promotes interactions between synaptonemal complex subunits and, in turn, allows intimate interactions between chromosomes. Our work highlights the power of genetic studies to illuminate the mechanisms that underly meiotic chromosome interactions. Significance StatementGamete production requires tightly regulated interactions between the parental chromosomes, which co-align and exchange information. These events are mediated by the synaptonemal complex - a thread-like structure that assembles between the parental chromosomes. The molecular interactions that underly synaptonemal complex assembly remain poorly understood due to rapid sequence divergence and challenges in biochemical reconstitution. Here we identify a novel three-component interface in the nematode synaptonemal complex. Destabilization and subsequent restoration of this interface link the integrity of the synaptonemal complex with chromosome alignment and regulation of exchanges. Beyond mechanistic understanding of chromosomal interactions, our work provides a blueprint for genetic probing of large cellular assemblies that are refractory to structural analysis and sheds light on the forces that shape their evolution.

genetics↗

bioRxiv2021

Unconventional conservation reveals structure-function relationships in the synaptonemal complex

Functional requirements constrain protein evolution, commonly manifesting in conserved primary amino acid sequence. Here, we extend this idea to secondary structural features by tracking their conservation in essential meiotic proteins with highly diverged sequences. The synaptonemal complex (SC) aligns parental chromosome pairs and regulates exchanges between them. In electron micrographs of meiocytes from all eukaryotic clades, the SC appears as a ~100 nm-wide ladder-like structure with regular striations. Despite the conserved ultrastructure and functions, the proteins that make up the SC are highly divergent in sequence. Here we found that, within the Caenorhabditis genus, SC proteins are significantly more diverged than other proteins. However, SC proteins have highly conserved protein length and coiled-coil domain structure. The same unconventional conservation signature holds true for SC proteins in Drosophila and mammals, suggesting it could be a universal feature of SC proteins. We used this evolutionary signature to identify a novel SC protein in the nematode Pristionchus pacificus, Ppa-SYP-1, which has no significant homology to any protein outside of Pristionchus. Our work suggests that the length and relative arrangement of coiled-coils play a key role in the structure and function of the SC. Furthermore, our analysis implies that expanding sequence analysis beyond measures of per-site identity or similarity can enhance our understanding of protein evolution and function. Short abstractFunctional requirements constrain protein evolution, commonly manifesting in a conserved amino acid sequence. Here, we extend this idea to secondary structural features by tracking their conservation in essential meiotic proteins with highly diverged sequences. The synaptonemal complex (SC) is a ~100 nm-wide ladder-like meiotic structure present in all eukaryotic clades, where it aligns parental chromosomes and regulates exchanges between them. Despite the conserved ultrastructure and functions of the SC, SC proteins are highly divergent within Caenorhabditis. However, SC proteins have highly conserved length and coiled-coil domain structure. We found the same unconventional conservation signature in Drosophila and mammals, and used it to identify a novel SC protein in Pristionchus pacificus, Ppa-SYP-1. Our work suggests that coiled-coils play wide-ranging roles in the structure and function of the SC, and more broadly, that expanding sequence analysis beyond measures of per-site similarity can enhance our understanding of protein evolution and function.

evolutionary biology↗

bioRxiv2020

Synaptonemal Complex dimerization regulates chromosome alignment and crossover patterning in meiosis

During sexual reproduction the parental homologous chromosomes find each other (pair) and align along their lengths by integrating local sequence homology with large-scale contiguity, thereby allowing for precise exchange of genetic information. The Synaptonemal Complex (SC) is a conserved zipper-like structure that assembles between the homologous chromosomes. This phase-separated interface brings chromosomes together and regulates exchanges between them. However, the molecular mechanisms by which the SC carries out these functions remain poorly understood. Here we isolated and characterized two mutations in the dimerization interface in the middle of the SC zipper in C. elegans. The mutations perturb both chromosome alignment and the regulation of genetic exchanges. Underlying the chromosome-scale phenotypes are distinct alterations to the way SC subunits interact with one another. We propose that the SC brings homologous chromosomes together through two biophysical activities: obligate dimerization that prevents assembly on unpaired chromosomes; and a tendency to phase-separate that extends pairing interactions along the entire length of the chromosomes.

cell biology↗

bioRxiv2019

Gametic specialization of centromeric histone paralogs in Drosophila virilis

In most eukaryotes, centromeric histone (CenH3) proteins mediate the highly conserved process of chromosome segregation as the foundational kinetochore assembly factor. However, in multicellular organisms, CenH3 proteins have to perform their essential functions in different chromatin environments. CenH3 proteins not only mediate mitosis and meiosis but also ensure epigenetic inheritance of centromere identity on sperm chromatin, which is highly compact and almost completely stripped of histones during spermiogenesis. We hypothesized that such disparate chromatin environments might impose different functional constraints on CenH3. If so, gene duplications could ameliorate the difficulty of encoding divergent and even potentially incompatible centromeric functions in the same gene. Here, we analyzed the cytological localization of two recently identified CenH3 paralogs, Cid1 and Cid5, in D. virilis using specific antibodies and epitope-tagged transgenic strains. We find that only ancestral Cid1 is present in somatic cells, whereas both Cid1 and Cid5 are expressed in testes and ovaries. However, Cid1 and Cid5 are alternately retained in male and female gametes; Cid1 is lost in male meiosis but retained throughout oogenesis, whereas Cid5 is lost during female meiosis but retained in mature sperm. Following fertilization, maternally deposited Cid1 rapidly replaces paternal Cid5 during the protamine-to-histone transition. Our studies reveal mutually exclusive gametic specialization of two divergent CenH3 paralogs. We suggest that centromeric histone duplication and divergence may allow essential genes involved in chromosome segregation to specialize and thereby resolve an intralocus conflict between maternal and paternal centromeric histone requirements in many animal species.

cell biology↗

bioRxiv2016

Recurrent gene duplication leads to diverse repertoires of centromeric histones in Drosophila species

Despite their essential role in the process of chromosome segregation in most eukaryotes, centromeric histones show remarkable evolutionary lability. Not only have they been lost in multiple insect lineages, but they have also undergone gene duplication in multiple plant lineages. Based on detailed study of a handful of model organisms including Drosophila melanogaster, centromeric histone duplication is considered to be rare in animals. Using a detailed phylogenomic study, we find that Cid, the centromeric histone gene, has undergone four independent gene duplications during Drosophila evolution. We find duplicate Cid genes in D. eugracilis (Cid2), in the montium species subgroup (Cid3, Cid4) and in the entire Drosophila subgenus (Cid5). We show that Cid3, Cid4, Cid5 all localize to centromeres in their respective species. Some Cid duplicates are primarily expressed in the male germline. With rare exceptions, Cid duplicates have been strictly retained after birth, suggesting that they perform non-redundant centromeric functions, independent from the ancestral Cid. Indeed, each duplicate encodes a distinct N-terminal tail, which may provide the basis for distinct protein-protein interactions. Finally, we show some Cid duplicates evolve under positive selection whereas others do not. Taken together, our results support the hypothesis that Drosophila Cid duplicates have subfunctionalized. Thus, these gene duplications provide an unprecedented opportunity to dissect the multiple roles of centromeric histones.\n\nAuthor SummaryCentromeres ensure faithful segregation of DNA throughout eukaryotic life, thus providing the foundation for genetic inheritance. Paradoxically, centromeric proteins evolve rapidly despite being essential in many organisms. We have previously proposed that this rapid evolution is due to genetic conflict in female meiosis in which centromere alleles of varying strength compete for inclusion in the ovum. According to this centromere drive model, essential centromeric proteins (like the centromeric histone, CenH3) must evolve rapidly to counteract driving centromeres, which are associated with reduced male fertility. A simpler way to allow for the rapid evolution of centromeric proteins without compromising their essential function would be via gene duplication. Duplication and specialization of centromeric proteins would allow one paralog to function as a drive suppressor in the male germline, while allowing the other to carry out its canonical centromeric role. Here, we present the finding of multiple CenH3 (Cid) duplications in Drosophila. We identified four instances of Cid duplication followed by duplicate gene retention in Drosophila. These Cid duplicates were born between 20 and 40 million years ago. This finding more than doubles the number of known CenH3 duplications in animal species and suggests that most Drosophila species encode two or more Cid paralogs, in contrast to current view that most animal species only encode a single CenH3 gene. We show that duplicate Cid genes encode proteins that have retained the ability to localize to centromeres. We present three lines of evidence, which suggest that the multiple Cid duplications have been retained due to subfunctionalization. Based on these findings, we propose the novel hypothesis that the multiple functions carried out by CenH3 proteins, i.e., meiosis, mitosis and gametic inheritance, may be inherently incompatible with one another when encoded in a single locus.

evolutionary biology↗