Biology subjects

Hyman, A.

Publications and source records attributed to Hyman, A..

6 recordsLinked to original sources

bioRxiv2025

Structural insights into mitotic-centrosome assembly

Centrosomal material assembles rapidly in mitosis. In Drosophila, the coiled-coil protein Cnn forms a scaffold that recruits PCM clients; in C.elegans, SPD-5 plays an analogous role. Here we show that full-length Cnn and SPD-5 can both form spherical condensates in vitro, but that the interactions driving their assembly into scaffolds inside cells appear to diverge. We show that the Cnn PReM adopts a helical hairpin fold that autoinhibits CM2 binding but that phosphorylation appears to increase hairpin breathing to permit CM2 engagement and robust scaffold assembly. Phospho-blocking mutations prevent PReM-CM2 interactions and scaffold formation, whereas phospho-mimetic substitutions partially restore function. The human homologue CDK5RAP2 contains a CM2 domain that can partially substitute for fly CM2 in vivo and we identify a candidate CDK5RAP2 PReM region that forms macromolecular networks with human CM2 in vitro. By contrast, the putative PReM and CM2 regions of SPD-5 cannot substitute for their equivalent fly domains and they do not interact detectably, suggesting a distinct assembly mechanism in worms despite conserved PLK1-dependent control of PCM growth.

cell biology↗

bioRxiv2023

Ontogenetic Patterns in Juvenile Blue Crab density: Effects of Habitat and Turbidity in a Chesapeake Bay Tributary

Nursery habitats are characterized by favorable conditions for juveniles, such as higher food availability and lower predation risk, and dispropor-tionately contribute more individuals per unit area to adult segments of the population compared to other habitats. However, nursery habitat inference is complicated by changes in habitat preferences with ontogeny; individuals in early-life stages frequently inhabit different habitats than older juveniles or adults. In this mensurative field experiment, we modeled the density of two juvenile blue crab, Callinectes sapidus, size classes based on carapace width (CW) across multiple habitats at various locations within an estuarine seascape during the blue crab recruitment season. We examined four habi-tat types--unstructured sand, seagrass meadows, salt marsh edge (SME), and shallow detrital habitat (SDH). Results indicated that densities of small ju-venile blue crabs ([≤]15 mm CW) were highest in seagrass, whereas densities of larger juveniles (16-30 mm CW) were highest in SME. Densities of large juveniles in SME were also greater than those of small juveniles, suggest-ing possible secondary dispersal to SME by small juveniles after settlement and recruitment in seagrass. Turbidity was positively correlated with densi-ties of both size classes, although our model did not address whether this was due to top-down (refuge) or bottom-up (food availability) mechanisms. Ob-served patterns in size-specific habitat utilization may result from changing requirements of juvenile blue crabs with size, as animals minimize mortality-to-growth ratios. Taken together with previous work and patterns observed in SME, these findings emphasize the role of salt marsh habitat within juve-nile blue crab ontogeny and underscore the need to quantify and preserve the complete chain of habitats used by juveniles.

ecology↗

bioRxiv2023

Effects of structural complexity and water depth on the juvenile blue crab Callinectes sapidus in a simulated salt marsh mesocosm

The blue crab (Callinectes sapidus) is ecologically and economically important in Chesapeake Bay. Nursery habitats, which disproportionately contribute individuals to the adult segment of populations, are essential to blue crab population dynamics. Spartina alterniflora salt marshes are productive but fragmented intertidal nursery habitats which may serve as a refuge from predation for juvenile blue crabs. However, the effects of various characteristics of salt marshes on nursery metrics, such as survival, have not been quantified. Using mesocosm experiments, we examined the effects of shoot density and water depth on juvenile blue crab survival using adult blue crabs as predators. Survival increased significantly with shoot density, whereas water depth did not affect survival. Thus, in contrast to several previous studies, water depth did not influence survival of juvenile blue crabs, possibly due to different environmental conditions from prior studies. These findings indicate that salt marsh structural complexity enhances juvenile survival, and that the beneficial effect of shallow water on juvenile survival differs by environmental conditions.

ecology↗

bioRxiv2022

Different low-complexity regions of SFPQ play distinct roles in the formation of biomolecular condensates

Demixing of proteins and nucleic acids into condensed liquid phases is rapidly emerging as a ubiquitous mechanism governing the organisation of molecules within the cell. Long disordered low complexity regions (LCRs) are a common feature of proteins that form biomolecular condensates. RNA-binding proteins with prion-like composition have been highlighted as drivers of liquid demixing to form condensates such as nucleoli, paraspeckles and stress granules. Splicing factor proline- and glutamine-rich (SFPQ) is an RNA- and DNA-binding protein essential for DNA repair and paraspeckle formation. Here, we show that the shorter C-terminal LCR of SFPQ is the main region responsible for the condensation of SFPQ in vitro and in the cell. In contrast, we find that, unexpectedly, the longer N-terminal prion-like LCR of SFPQ attenuates condensation, suggesting a more regulatory role in preventing aberrant condensate formation in the cell. Our data add nuance to the emerging understanding of biomolecular condensate formation, by providing the first example of a common multifunctional nucleic acid-binding protein with an extensive prion-like region that serves to regulate rather than drive condensate formation. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=120 SRC="FIGDIR/small/518278v2_ufig1.gif" ALT="Figure 1"> View larger version (27K): org.highwire.dtl.DTLVardef@ed464dorg.highwire.dtl.DTLVardef@1a26fdcorg.highwire.dtl.DTLVardef@15debecorg.highwire.dtl.DTLVardef@12bd4ae_HPS_FORMAT_FIGEXP M_FIG C_FIG

molecular biology↗

bioRxiv2019

Soluble tubulin is locally enriched at mitotic centrosomes in C. elegans

During mitosis, the centrosome expands its capacity to nucleate microtubules. Understanding the mechanisms of centrosomal microtubule nucleation is, however, constrained by a lack of knowledge of the amount of soluble and polymer tubulin at mitotic centrosomes. Here we combined light microscopy and serial-section electron tomography to measure the amount of dimer and polymer at mitotic centrosomes in early C. elegans embryos. We show that a C. elegans one-cell stage centrosome at metaphase contains more than ten thousand microtubules with a total polymer concentration of 230 M. Centrosomes concentrate soluble /{beta} tubulin by about tenfold over the cytoplasm, reaching peak values of 470 M, giving a combined total monomer and polymer tubulin concentration at centrosomes of up to 660 M. These findings support in vitro data suggesting that microtubule nucleation in C. elegans centrosomes is driven in part by concentrating soluble tubulin.

cell biology↗

bioRxiv2018

PLK4 is a microtubule-associated protein that self assembles promoting de novo MTOC formation

Summary statementPLK4 binds to microtubules and self assembles into supramolecular assemblies that recruit tubulin and trigger de novo MTOC formation in Xenopus laevis extracts.\n\nAbstractThe centrosome is an important microtubule-organizing center (MTOCs) in animal cells and it consists of two barrel-shaped structures (centrioles), surrounded by the pericentriolar material (PCM), which nucleates microtubules. PCM components form condensates, supramolecular assemblies that concentrate microtubule nucleators. Centrosomes can form close to an existing structure (canonical duplication) or de novo. How centrosomes form de novo is not known. PLK4 is a master driver of centrosome biogenesis, which is critical to recruit several centriole components. Here, we investigate the beginning of centrosome biogenesis, taking advantage of Xenopus egg extracts, where we and others have shown that PLK4 can induce de novo MTOC formation (Eckerdt et al., 2011; Zitouni et al., 2016). Surprisingly, we observe that in vitro, PLK4 can self-assemble into supramolecular assemblies that recruit /{beta}-tubulin. In Xenopus extracts, PLK4 supramolecular assemblies additionally recruit the PLK4 substrate STIL and the microtubule nucleator, {gamma}-tubulin, and form acentriolar MTOCs de novo. The assembly of these robust microtubule asters is independent of dynein, similarly to centrosomes. We suggest a new mechanism of action for PLK4, where it forms a self-organizing catalytic scaffold that recruits centriole components, PCM factors and /{beta}-tubulin, leading to MTOC formation.

cell biology↗