Biology subjects

Deis, R.

Publications and source records attributed to Deis, R..

5 recordsLinked to original sources

bioRxiv2026

Lysosome-Related Organelles Orchestrate Guanine Crystal Formation in Pigment Cells

Iridosomes, the guanine crystal-forming organelles of pigment-producing iridophores, are among the most versatile, visually striking yet mechanistically uncharacterized organelles in vertebrate biology. Lysosome-related organelles (LROs) support cell type-specific functions by adapting endolysosomal pathways for specialized roles. Here, we show that iridosomes represent a previously unrecognized subtype of LROs. Using transcriptomic profiling of zebrafish iridophores, CRISPR-Cas9-mediated gene disruption, and cryogenic transmission electron microscopy, we define the molecular program underlying iridosome biogenesis. Iridosomes have evolved unique adaptations for crystal growth while retaining core features of other LROs. Key regulators, including RAB32a, AP3M2, and HPS5, are essential for crystal formation, with gene knockouts causing reduced crystal number, altered morphology, and distinct maturation defects. We further identify hallmark LRO features in iridosomes, including intraluminal vesicles and pH-regulated developmental transitions. Cross-species transcriptomic analysis confirms that iridosomes share an LRO signature across vertebrates, including teleost fish and reptiles, suggesting ancient evolutionary origins. These findings establish iridosomes as crystalline LROs and as a model for investigating how cells construct structurally specialized organelles through coordinated trafficking, acid-base regulation, and crystallization, with implications for LRO evolution and human disease.

developmental biology↗

bioRxiv2024

Controlled pH Alteration Enables Guanine Accumulation and Drives Crystallization within Iridosomes

Many animals exhibit remarkable colors produced by the constructive interference of light reflected from arrays of intracellular guanine crystals. These systems are utilized for various purposes, including vision, camouflage, communication, and thermal regulation. Each guanine crystal forms within a membrane-bound organelle called an iridosome, where precise control over crystal formation occurs. While the presence of guanine crystals in iridosomes is well-documented, the mechanisms facilitating the accumulation of water-insoluble guanine and driving its crystallization remain unclear. Here, we employ advanced imaging and spectroscopy techniques to characterize the maturation of iridosomes in zebrafish iridophores during development. Using cryo-electron microscopy, we found that amorphous guanine accumulates in early-stage iridosomes. Synchrotron-based soft X-ray microscopy studies revealed that, unlike mature crystals, the accumulated guanine is initially in its protonated state. Live imaging with a pH sensor demonstrated that early-stage iridosomes are acidic and that their pH gradually approaches neutrality during maturation. Additionally, the application of a V-ATPase inhibitor reduced the acidity of iridosomes and significantly decreased crystal formation, suggesting the involvement of V-ATPase in regulating the organelle pH. Our findings reveal new insights into the molecular mechanisms facilitating guanine accumulation and crystallization within iridosomes, emphasizing the pivotal role of pH alternations in the precise formation of biogenic crystals.

cell biology↗

bioRxiv2022

Biogenic plate-like guanine crystals form via templated nucleation of thin crystal leaflets on amyloid scaffolds

Controlling the morphology of crystalline materials is challenging, as crystals have a strong tendency towards thermodynamically stable structures. Yet, organisms form crystals with distinct morphologies, such as the plate-like guanine crystals produced by many terrestrial and aquatic species for light manipulation. Regulation of crystal morphogenesis was hypothesized to entail physical growth restriction by the surrounding membrane, combined with fine-tuned interactions between organic molecules and the growing crystal. Using cryo electron tomography of developing zebrafish larvae, we found that guanine crystals form via templated nucleation of thin leaflets on preassembled scaffolds made of 20-nm-thick amyloid fibers. These leaflets then merge and coalesce into a single plate-like crystal. Our findings provide new insights into how organisms control the morphology and, thereby, the optical properties of crystals.

biophysics↗

bioRxiv2022

Microtubules control Buc Phase separation and Balbiani body condensation in zebrafish oocyte polarity

Vertebrate oocyte polarity has been observed for two centuries and is essential for embryonic axis formation and germline specification, yet its underlying mechanisms remain unknown. In oocyte polarization, critical RNA-protein (RNP) granules delivered to the oocytes vegetal pole, are stored by the Balbiani body (Bb), a membraneless organelle conserved across species from insects to humans. However, the mechanisms of Bb formation are still unclear. Here, we elucidate mechanisms of Bb formation in zebrafish through developmental biomolecular condensation. Using super-resolution microscopy, live imaging, biochemical, and genetic analyses in-vivo, we demonstrate that Bb formation is driven by molecular condensation through phase-separation of the essential intrinsically disordered protein Bucky ball (Buc). Live imaging, molecular analyses, and FRAP experiments in-vivo reveal Buc-dependent changes in the Bb condensates dynamics and apparent material properties, transitioning from liquid-like condensates to a solid-like stable compartment. Furthermore, we identify a multi-step regulation by microtubules that controls Bb condensation: first through dynein-mediated trafficking of early condensing Buc granules, then by scaffolding condensed granules, likely through molecular crowding, and finally by caging the mature Bb to prevent overgrowth and maintain shape. These regulatory steps ensure the formation of a single intact Bb, which is considered essential for oocyte polarization and embryonic development. Our work offers insight into the long-standing question of the origins of embryonic polarity in non-mammalian vertebrates, support a paradigm of cellular control over molecular condensation by microtubules, and highlight biomolecular condensation as a key process in female reproduction.

developmental biology↗

bioRxiv2021

Ciliary control of meiotic chromosomal pairing mechanics and germ cell morphogenesis

The hallmark of meiosis is chromosomal pairing and synapsis via synaptonemal complexes, but chromosomal pairing also depends on cytoplasmic counterparts that tether and rotate telomeres on the nuclear envelope. Telomeres slide on perinuclear microtubules, shuffling chromosomes and mechanically driving their homology searches. Pull of telomeres towards the centrosome drives formation of the "zygotene chromosomal bouquet". These telomere dynamics are essential for pairing and fertility, and the bouquet, discovered in 1900, is universally conserved. Nevertheless, how cytoplasmic counterparts of bouquet formation are mechanically regulated has remained enigmatic. Here, we report the "zygotene cilium" - a previously unrecognized cilium, in oocytes. We show in zebrafish that this cilium specifically connects to the bouquet centrosome, constituting a cable system of the cytoplasmic bouquet machinery. Furthermore, zygotene cilia extend throughout the germline cyst, a conserved germ cell organization. Using multiple ciliary mutants and laser-induced excision, we demonstrate that the zygotene cilium is essential for chromosomal bouquet and synaptonemal complex formation, germ cell morphogenesis, ovarian development and fertility. Mechanistically, we provide evidence that the cilium functions at least partly via anchoring the bouquet centrosome in order to counterbalance telomere rotation and pulling. We also show that the zygotene cilium is conserved in both male and female meiosis in zebrafish, as well as in mammals. Our work uncovers the novel concept of a cilium as a critical player in meiosis and sheds new light on reproduction phenotypes in ciliopathies. We propose a cellular paradigm that cilia can control chromosomal dynamics.

cell biology↗