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Chromosome movements and licensing of synapsis must be tightly regulated during early meiosis to ensure accurate chromosome segregation and avoid aneuploidy, although how these steps are coordinated is not fully understood. Here we show that GRAS-1, the worm homolog of mammalian GRASP/Tamalin and CYTIP, coordinates early meiotic events with cytoskeletal forces outside the nucleus. GRAS-1 localizes close to the nuclear envelope (NE) in early prophase I and interacts with NE and cytoskeleton proteins. Delayed homologous chromosome pairing, synaptonemal complex (SC) assembly, and DNA double-strand break repair progression are partially rescued by the expression of human CYTIP in gras-1 mutants, supporting functional conservation. However, Tamalin, Cytip double knockout mice do not exhibit obvious fertility or meiotic defects, suggesting evolutionary differences between mammals. gras-1 mutants show accelerated chromosome movement during early prophase I, implicating GRAS-1 in regulating chromosome dynamics. GRAS-1-mediated regulation of chromosome movement is DHC-1-dependent, placing it acting within the LINC-controlled pathway, and depends on GRAS-1 phosphorylation at a C-terminal S/T cluster. We propose that GRAS-1 serves as a scaffold for a multi-protein complex coordinating the early steps of homology search and licensing of SC assembly by regulating the pace of chromosome movement in early prophase I.

The decapod crustacean exoskeleton is a multi-layered structure composed of chitin-protein fibers embedded with calcium salts. Decapod claws display tooth-like denticles, which come into direct contact with predators and prey. They are subjected to more regular and intense mechanical stress than other parts of the exoskeleton and therefore must be especially resistant to wear and abrasion. Here, we characterized denticle properties in five decapod species. Dactyls from three brachyuran crabs (Cancer borealis, Callinectes sapidus, and Chionoecetes opilio) and two anomuran crabs (Paralomis birsteini and Paralithodes camtschaticus) were sectioned normal to the contact surface of the denticle, revealing the interior of the denticle and the bulk endocuticle in which it is embedded. Microhardness, micro- and ultrastructure, and elemental composition were assessed along a transect running the width of the cuticle using microindentation hardness testing, optical and scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDS), respectively. In all species tested, hardness was dramatically higher-up to ten times-in the denticle than in the bulk endocuticle. Likewise, in all species there was an increase in packing density of mineralized chitin-protein fibers, a decrease in width of the pore canals that run through the cuticle, and a decrease in phosphorous content from endocuticle to denticle. The changes in hardness across the cuticle, and the relationship between hardness, calcium, and magnesium content, however, varied among species. Although mechanical resistance of the denticles was exceptionally high in all species, the basis for resistance appears to differ among species. STATEMENT OF SIGNIFICANCE: Understanding the diverse mechanisms by which animals attain exceptionally high mechanical resistance may enable development of novel, biologically inspired materials. Decapod crustacean claws, and particularly the tooth-like denticles that these claws display, are of interest in this regard, as they must be especially resistant to wear. We assessed mechanical, elemental, and structural properties of the claw cuticle in five decapod species. Without exception, microhardness was dramatically higher in the denticle than in the bulk endocuticle. Multivariant statistical analyses, however, showed that the relationships among microhardness, elemental content, and structural variables differed among species. Such patterns likely result from strong evolutionary pressure on feeding and defensive structures and a trade-off between mechanical properties and energetic cost of exoskeleton formation.