Biology subjects

Hollis, J. A.

Publications and source records attributed to Hollis, J. A..

5 recordsLinked to original sources

bioRxiv2026

The SPARK complex forms the molecular basis of vertebrate fertilization

Fertilization requires gamete recognition and membrane fusion, yet the molecular basis of this process in vertebrates remains unknown. Here we identify SPARK (sperm protein assembly and receptor-binding key), a conserved multi-protein complex that integrates all known sperm fertilization factors, including TMEM81-IZUMO1-SPACA6 and DCST1/2, together with two newly identified components, TMDD1 and FAM187A. SPARK subunits are mutually dependent for stability in mature sperm, and disruption of any single component causes male sterility in zebrafish and mice. Incubating zebrafish sperm with soluble egg receptor Bouncer partially rescues fertilization of Bouncer-deficient eggs in a SPARK-dependent manner, consistent with egg receptor binding priming the complex for fusion. Thus, we propose SPARK as a con-served molecular machine that couples gamete recognition to membrane fusion.

developmental biology↗

bioRxiv2026

Remote homology and functional genetics unmask deeply preserved Scm3/HJURP orthologs in metazoans

AbstractIn most animals and fungi, centromere identity and function depend on the Scm3/HJURP chaperone, which deposits CENPA at centromeres. However, Scm3/HJURP orthologs appeared to be missing in insects, nematodes, many vertebrates, and other metazoans, suggesting radical chaperone replacement in these lineages. Here, we combine remote homology detection, AlphaFold-based structural modeling, and functional genetics in zebrafish and Caenorhabditis elegans to identify previously unknown Scm3/HJURP orthologs that localize to centromeres and whose loss causes catastrophic mitotic failure. We further show that Drosophila CAL1, long considered a functional analog, is instead a highly diverged Scm3/HJURP ortholog. Despite rapid primary-sequence divergence, predicted and known structures reveal a broadly conserved CENPA-H4-binding scm3 fold across fungi, vertebrates, nematodes, insects, and most metazoans. Our work demonstrates how rapid divergence can obscure the broad conservation of essential centromere machinery and provides a generalizable strategy for unmasking missing orthologs. TeaserAnimals encode a rapidly evolving, essential cell cycle gene previously thought to be absent.

evolutionary biology↗

bioRxiv2023

Evolutionary origin and structural ligand mimicry by the inserted domain of alpha-integrin proteins

Heterodimeric integrin proteins transmit signals through conformational changes upon ligand binding between their alpha () and beta ({beta}) subunits. Early in chordate evolution, some subunits acquired an "inserted" (I) domain, which expanded their ligand binding capacity but simultaneously obstructed the ancestral ligand-binding pocket. While this would seemingly impede conventional ligand-mediated integrin activation, it was proposed that the I domain itself could serve both as a ligand replacement and an activation trigger. Here, we provide compelling evidence in support of this longstanding hypothesis using high-resolution cryo-electron microscopy structures of two distinct integrin complexes: the ligand-free and E-cadherin-bound states of the E{beta}7 integrin with the I domain, as well as the 4{beta}7 integrin lacking the I domain in both a ligand-free state and bound to MadCAM-1. We trace the evolutionary origin of the I domain to an ancestral collagen-collagen interaction domain. Our analyses illuminate how the I domain intrinsically mimics an extrinsic ligand, enabling integrins to undergo the canonical allosteric cascade of conformational activation and dramatically expanding the range of cellular communication mechanisms in vertebrates.

molecular biology↗

bioRxiv2021

Acentrosomal spindle assembly and stability in C. elegans oocytes requires a kinesin-12 non-motor microtubule interaction domain

During the meiotic divisions in oocytes, microtubules are sorted and organized by motor proteins to generate a bipolar spindle in the absence of centrosomes [1]. In most organisms, kinesin-5 family members crosslink and slide microtubules to generate outward force that promotes acentrosomal spindle bipolarity [2-7]. However, the mechanistic basis for how other kinesin families act on acentrosomal spindles has not been explored. We investigated this question in C. elegans oocytes, where kinesin-5 is not required to generate outward force [8]. Instead, the kinesin-12 family motor KLP-18 performs this function [9-12]. KLP-18 acts with adaptor protein MESP-1 (meiotic spindle 1) to sort microtubule minus ends to the periphery of a microtubule array, where they coalesce into spindle poles [12]. If either of these proteins is depleted, outward sorting of microtubules is lost and minus ends converge to form a monoaster. Here we use a combination of in vitro biochemical assays and in vivo mutant analysis to provide insight into the mechanism by which these proteins collaborate to promote acentrosomal spindle assembly. We identify a microtubule binding site on the C-terminal stalk of KLP-18 and demonstrate that a direct interaction between the KLP-18 stalk and MESP-1 activates non-motor microtubule binding. We also provide evidence that this C-terminal domain is required for KLP-18 activity during spindle assembly and show that KLP-18 is continuously required to maintain spindle bipolarity. This study thus provides new insight into the construction and maintenance of the oocyte acentrosomal spindle as well as into kinesin-12 mechanism and regulation.

cell biology↗

bioRxiv2020

Excess crossovers impede faithful meiotic chromosome segregation in C. elegans

During meiosis, at least one crossover must form between each pair of homologous chromosomes to ensure their proper partitioning. However, most organisms limit the number of crossovers by a phenomenon called crossover interference; why this occurs is not well understood. Here we investigate the functional consequences of extra crossovers in Caenorhabditis elegans. Using a fusion chromosome that exhibits a high frequency of supernumerary crossovers, we find that essential chromosomal structures are mispatterned, subjecting chromosomes to improper spindle forces and leading to congression and segregation defects. Moreover, we uncover mechanisms that counteract these errors; anaphase I chromosome bridges were often able to resolve in a LEM-3 nuclease dependent manner, and tethers between homologs that persisted were frequently resolved during Meiosis II by a second mechanism. This study thus provides evidence that excess crossovers impact chromosome patterning and segregation, and also sheds light on how these errors are corrected.

cell biology↗