Search bioRxiv⌕ Search
Home/Archive/bioRxiv

bioRxiv · 10.1101/591974

Animal evolution coincides with a novel degree of freedom in exocytic transport processes

Kollmar, M.·Welz, T.·Straub, F.·Alzahofi, N.·Hatje, K.·Briggs, D. A.·Samol-Wolf, A.·Burkhardt, P.·Hume, A.·Kerkhoff, E.
View original source ↗Export metadata ↓

Abstract

Exocytic transport of transmembrane receptors and secreted ligands provides the basis for cellular communication in animals. The RAB8/RAB3/RAB27 trafficking regulators function in transport processes towards the cell membrane. The small G-proteins recruit a diversity of effectors that mediate transport along microtubule and actin tracks, as well as membrane tethering and fusion. SPIRE actin nucleators organise local actin networks at exocytic vesicle membranes. By complex formation with class-5 myosins, vesicle transport track generation and motor protein activation are coordinated. Our phylogenetic analysis traced the onset of SPIRE function back to the origin of the Holozoa. We have identified SPIRE in the closest unicellular relatives of animals, the choanoflagellates, and the more distantly related ichthyosporeans. The discovery of a SPIRE-like protein encoding a KIND and tandem-WH2 domains in the amoebozoan Physarum polycephalum suggests that the SPIRE-type actin nucleation mechanism originated even earlier. Choanoflagellate SPIRE interacts with RAB8, the sole choanoflagellate representative of the metazoan RAB8/RAB3/RAB27 family. Major interactions including MYO5, FMN-subgroup formins and vesicle membranes are conserved between the choanoflagellate and mammalian SPIRE proteins and the choanoflagellate Monosiga brevicollis SPIRE protein can rescue mouse SPIRE1/2 function in melanosome transport. Genome duplications generated two mammalian SPIRE genes (SPIRE1 and SPIRE2) and allowed for the separation of SPIRE protein function in terms of tissue expression and RAB GTPase binding. SPIRE1 is highest expressed in the nervous system and interacts with RAB27 and RAB8. SPIRE2 shows high expression in the digestive tract and specifically interacts with RAB8. We propose that at the dawn of the animal kingdom a new transport mechanism came into existence, which bridges microtubule tracks, detached vesicles and the cellular actin cytoskeleton by organising actin/myosin forces directly at exocytic vesicle membranes. The new degree of freedom in transport may reflect the increased demands of the sophisticated cellular communications in animals.

Explore related subjects

cell biologyPreprint

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

Kollmar, M., Welz, T., Straub, F., Alzahofi, N., Hatje, K., Briggs, D. A., Samol-Wolf, A., Burkhardt, P., Hume, A., Kerkhoff, E.. 2019-03-28. Animal evolution coincides with a novel degree of freedom in exocytic transport processes. https://doi.org/10.1101/591974

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related preprints

bioRxiv2026

Endothelial Cell Specific Thioredoxin 1-Dependent Signaling in Oxygen-1 Induced Retinopathy

Purpose: Retinopathy of prematurity (ROP) is a leading cause of childhood blindness, characterized byoxidative stress and dysregulated angiogenesis in preterm infants with immature antioxidant systems.This study aimed to investigate the specific role of endothelial cell-specific thioredoxin 1 (TXN1), a crucial oxidoreductase, in oxygen-induced retinopathy, hypothesizing that the absence of endothelial TXN1 directly impairs angiogenesis and exacerbates hyperoxia-induced injury. Methods: We generated tamoxifen-inducible, endothelial cell-specific Txn1 knockout mice (Txn1-iECKO) and utilized the oxygen-induced retinopathy (OIR) model, exposing litters to 85% oxygen from postnatal day 7 (P7) to P12. Retinal vascular morphology during vaso-obliteration and neovascularization phases, endothelial cell proliferation, and apoptotic cell death were assessed. Furthermore, human retinal microvascular endothelial cells (HRMECs) with TXN1 knockdown were subjected to hyperoxic conditions, followed by comprehensive gene expression profiling using RT2 Profiler PCR arrays and Ingenuity Pathway Analysis. Results: Deletion of endothelial Txn1 significantly enhanced vascular regression during the hyperoxic vaso-obliteration phase at P12 and markedly exacerbated pathological neovascularization at P17. Txn1-deficient retinas exhibited significantly impaired endothelial cell proliferation during the vaso-obliteration phase, while apoptotic cell death remained unchanged. Transcriptomic analysis of TXN1-deficient HRMECs under hyperoxia revealed an enhanced activation of NRF2-mediated oxidative stress response pathways. Conclusions: These findings identify endothelial TXN1 as an essential and oxygen-dependent regulator of vascular development in ischemic retinopathy, primarily influencing endothelial proliferation and redox signaling. This suggests TXN1's crucial protective role and highlights its therapeutic potential to mitigate ROP progression by modulating endothelial cell responses to oxidative stress.

cell biology↗
bioRxiv2026

A Dynamic Stem Cell State Links Environmental Cues to Skeletal and Regenerative Fates

Stem cells faithfully generate tissue architecture during development, yet how their identity and regenerative output are reshaped as anatomical niches mature and environmental signals change with aging and injury remains poorly understood. Rare skeletal stem cells (SSCs) across diverse skeletal sites are defined by combinations of cell-surface markers, precluding their genetic interrogation in vivo. Here, using spatially informed single cell transcriptomics, we identify Pannexin-3 (Panx3) to mark a dynamic functional state within bona fide SSCs and establish Panx3-CreERT2 mice for its longitudinal interrogation. Panx3 SSCs exhibit long-term clonal persistence, self-renewal and multipotency, whereas Panx3- SSCs can acquire this state. Successive SSC cohorts engage the Panx3 state during skeletal development, osteoanabolic stimulation expands pre-existing Panx3 SSC clones and injury induces it locally in previously unlabeled progenitors. Thus, anatomically distinct progenitors can converge on a common stem cell state in response to different environmental inputs. Three-dimensional reconstruction of chondrogenic niches further identifies signals that redirect Panx3-lineage cells towards stable cartilage, enabling durable regeneration in aged and osteoarthritic joints and with human SSCs. These findings establish anatomical origin, stem cell state and lineage fate as separable dimensions of stem cell identity and provide genetic access for interrogating and directing endogenous SSC function.

cell biology↗
bioRxiv2026

Proteome-wide profiling reveals compartment-specific RNA buffering of protein aggregation during stress

Cellular adaptation to stress requires extensive remodeling of RNA metabolism. The rewiring of the RNA-protein interaction landscape and the assembly of biomolecular condensates are central to this response, yet the global stress-induced reorganization of macromolecular RNA-protein assemblies remains incompletely characterized. Here, we apply R-DeeP, a density gradient approach coupled to quantitative mass spectrometry, to profile the RNA-dependent sedimentation behaviour of the Saccha-romyces cerevisiae proteome during heat and salt stress. We demonstrate that stress triggers a profound, stress-specific reorganization of the RNA interactome. Many proteins undergo pronounced, selective shifts into high-molecular weight fractions, indicative of aggregation. RNase treatment markedly exacerbates this aggregation, consistent with the model that RNA acts as a general chaperone that keeps proteins with intrinsically disordered regions soluble. Strikingly, our data demonstrate that this protection is compartmentalised. Nuclear proteins are partially shielded from stress-induced aggregation. This protection coincides with the nuclear accumulation of RNA caused by a block of RNA export during stress, and RNase treatment abolishes this protection. Nuclear RNA retention may therefore act as a buffer that actively increases the local chaperoning capacity of the nucleus. In contrast, cytoplasmic proteins, including translation factors and ribonucleoprotein granule components, exhibit increased aggregation under stress. Fluorescence microscopy confirmed that increased biochemical aggregation in density gradients reflects changes in assembly state in vivo. For many stress-induced aggregators, these changes are visible as spatial reorganisation in stressed cells, such as the formation of foci. Our findings suggest that cells use subcellular RNA distribution to tune the condensation and/or aggregation threshold of proteins in a compartment-specific manner.

cell biology↗