Biology subjects

Roberts-Galbraith, R. H.

Publications and source records attributed to Roberts-Galbraith, R. H..

8 recordsLinked to original sources

bioRxiv2026

Syntaxin-1 and syntaxin binding protein 1-1 are required for planarian behavior and brain regeneration

Background: Nervous system regeneration requires creation of new neurons and their integration into new and existing networks. How new neurons find their targets and reconnect in the environment of regenerating tissue remains a major gap in knowledge. The planarian Schmidtea mediterranea is well suited to the study of neural regeneration due to the remarkable ability of planarians to regenerate their entire body, including the nervous system. However, we have not yet been able to explore synaptogenesis in regeneration using planarians due to a lack of tools to study synapses. Here we investigate potential players in planarian synapse, focusing on the conserved syntaxin protein family, which functions in neurotransmitter vesicle fusion at the synapse. Results: We found that reduction of either syntaxin-1 (stx1) or syntaxin-binding protein 1-1 (stxbp1-1) decreased locomotion and impeded brain regeneration, specifically in synapse-rich regions. Conclusions: Our observations support STX-1 and STXBP1-1 as bona fide synapse components, providing a starting point for studies neuronal connectivity during homeostatic remodeling and regeneration.

neuroscience↗

bioRxiv2026

Neuropeptide Signaling Promotes Stem-Cell Driven Regeneration in Planarians

Neurons and neuroendocrine cells produce neuropeptides, which act as long-range signals to modulate organismal state and physiological function. In a few cases, neuropeptides have been thought to promote regeneration, but understanding this connection has been difficult due to the relatively poor regenerative capacity of most traditional model organisms. To test whether neuropeptides drive robust regeneration, we used the highly regenerative asexual planarian flatworm as a model. We began by investigating enzymes that cleave and process pre-propeptides to produce bioactive neuropeptides. We characterized 12 putative neuropeptide-processing enzymes and identified three enzymes, prohormone convertase 2 (pc2), carboxypeptidase E (CPE), and peptidylglycine alpha-hydroxylating monooxygenase (PHM-1) that regulate regeneration through their effects on stem cell differentiation and maintenance. We then investigated 51 of the 52 known neuropeptide-encoding genes in planarians, finding that 16 of these genes promote efficient regeneration and/or stem cell function. Our work indicates that diverse neuropeptides regulate endogenous pluripotent stem cells during homeostasis and in robust regeneration. Our data supports a key role for neuropeptide signaling in planarians to promote a pro-regenerative state, which could be valuable to mimic in regenerative therapies.

neuroscience↗

bioRxiv2025

A parenchymal niche regulates pluripotent stem cell function in planarians

Harnessing the extraordinary potential of stem cells requires exquisite control in vitro, in vivo, and in the context of potential therapies. Adult stem cells are commonly housed within a microenvironment, or "niche," that supplies signals to regulate stem cell function. It has been difficult to determine whether pluripotent stem cells have a similar endogenous niche due to the transient nature of the cell type in most animal species. We sought to establish the nature of a pluripotent stem cell niche using planarian flatworms, animals that maintain pluripotent stem cells throughout adulthood and use them for whole-body regeneration. We characterized the cellular microenvironment of planarian stem cells in detail, finding that each stem cell is surrounded by a diverse mixture of other stem cells and differentiated cells. We identified phagocytic cells marked by CTSL2 as the differentiated cell type most frequently found next to stem cells, in both homeostasis and regeneration. CTSL2+ cells, which we named abracada cells, wrap around stem cells, and then neighbor progenitors less often coincident with their specialization. We then tested whether abracada cells constitute a functional niche that regulates stem cells. We identified two innexin-encoding genes expressed in abracada cells that are critical for pluripotent stem cell function and planarian regeneration. Together, our results reveal for the first time a local, endogenous niche that actively regulates adult pluripotent stem cells.

cell biology↗

bioRxiv2025

Combinatorial mechanisms specify cellular location and neurotransmitter identity during regeneration of planarian neurons

During regenerative neurogenesis, neurons must be created in the right types and locations. Though regenerative neurogenesis is limited in humans, other animals use regenerative neurogenesis to faithfully restore form and function after brain injury. Planarians are flatworms with extraordinary capacity for brain regeneration. Planarians use pluripotent stem cells to create neurons after injury, rather than resident progenitors. In this context, genetic mechanisms that produce diverse neurons with correct local identity remain unknown. Here, we report the discovery of factors important for regenerative neurogenesis of dopaminergic neurons in the planarian central, peripheral, and pharyngeal nervous systems. Distinct genes promote dopaminergic neuronal identity and instruct neurons to inhabit regions of the nervous system. Our results demonstrate that planarian neuronal fate requires factors that simultaneously direct neurotransmitter choice and regional location. Our work suggests that combinatorial direction of cell type could inform and improve exogenous stem cell therapies aimed at precisely replacing neurons.

neuroscience↗

bioRxiv2023

Planarian LDB and SSDP proteins scaffold transcriptional complexes for regeneration and patterning

Sequence-specific transcription factors often function as components of large regulatory complexes. LIM-domain binding protein (LDB) and single-stranded DNA-binding protein (SSDP) function as core scaffolds of transcriptional complexes in animals and plants. Little is known about potential partners and functions for LDB/SSDP complexes in the context of tissue regeneration. In this work, we find that planarian LDB1 and SSDP2 promote tissue regeneration, with a particular function in mediolateral polarity reestablishment. We find that LDB1 and SSDP2 interact with one another and with characterized planarian LIM-HD proteins Arrowhead, Islet1, and Lhx1/5-1. SSDP2 and LDB1 also function with islet1 in polarity reestablishment and with lhx1/5-1 in serotonergic neuron maturation. Finally, we show new roles for LDB1 and SSDP2 in regulating gene expression in the planarian intestine and parenchyma; these functions may be LIM-HD-independent. Together, our work provides insight into LDB/SSDP complexes in a highly regenerative organism. Further, our work provides a strong starting point for identifying and characterizing potential binding partners of LDB1 and SSDP2 and for exploring roles for these proteins in diverse aspects of planarian physiology.

developmental biology↗

bioRxiv2022

Multiple polarity kinases inhibit phase separation of F-BAR protein Cdc15 and antagonize cytokinetic ring assembly in fission yeast

The F-BAR protein Cdc15 is essential for cytokinesis in Schizosaccharomyces pombe and it plays a key role in attaching the cytokinetic ring (CR) to the plasma membrane. Cdc15s abilities to bind to the membrane and oligomerize via its F-BAR domain are inhibited by phosphorylation of its intrinsically disordered region (IDR). Multiple cell polarity kinases regulate Cdc15 IDR phosphostate, and of these the DYRK kinase Pom1 phosphorylation sites on Cdc15 have been shown in vivo to prevent CR formation at cell tips. Here, we compared the ability of Pom1 to control of Cdc15 phosphostate and cortical localization to that of other Cdc15 kinases: Kin1, Pck1, and Shk1. We identified distinct but overlapping cohorts of Cdc15 phosphorylation sites targeted by each kinase, and the number of sites correlated with each kinases abilities to influence Cdc15 PM localization. Coarse-grained simulations predicted that cumulative IDR phosphorylation moves the IDRs of a dimer apart and toward the F-BAR tips. Further, simulations indicated that the overall negative charge of phosphorylation masks positively charged amino acids necessary for F-BAR oligomerization and membrane interaction. Finally, simulations suggested that dephosphorylated Cdc15 undergoes phase separation driven by IDR interactions. Indeed, dephosphorylated but not phosphorylated Cdc15 undergoes liquid-liquid phase separation to form droplets in vitro that recruit Cdc15 binding partners. In cells, Cdc15 phosphomutants also formed PM-bound condensates that recruit other CR components. Together, we propose that a threshold of Cdc15 phosphorylation by assorted kinases prevents Cdc15 condensation on the PM and antagonizes CR assembly.

cell biology↗

bioRxiv2022

Heterotrimeric G proteins regulate planarian regeneration and behavior

G protein-coupled receptors (GPCRs) play broad roles in development and stem cell biology, but few roles for GPCR signaling in complex tissue regeneration have been uncovered. Planarian flatworms robustly regenerate all tissues and provide a model with which to explore potential functions for GPCR signaling in somatic regeneration and pluripotent stem cell biology. As a first step toward exploring GPCR function in planarians, we investigated downstream signal transducers that work with GPCRs, called heterotrimeric G proteins. Here, we characterized the complete heterotrimeric G protein complement in Schmidtea mediterranea for the first time and found that seven heterotrimeric G protein subunits promote regeneration. We further characterized two subunits critical for regeneration, Gq1 and G{beta}1-4a, finding that they promote the late phase of anterior polarity re-establishment, likely through anterior pole-produced Follistatin. Incidentally, we also found that five heterotrimeric G proteins modulate planarian behavior. We further identified a putative serotonin receptor, gcr052, that we propose works with G{beta}x2 in planarian locomotion, demonstrating the utility of our strategy for identifying relevant GPCRs. Our work provides foundational insight into roles of heterotrimeric G proteins in planarian biology and serves as a useful springboard towards broadening our understanding of GPCR signaling in adult tissue regeneration.

developmental biology↗

bioRxiv2020

CBP/p300 orthologs CBP2 and CBP3 play distinct roles in planarian stem cell function

Chromatin modifications function as critical regulators of gene expression and cellular identity, especially in the regulation and maintenance of the pluripotent state. However, many studies of chromatin modification in stem cells--and pluripotent stem cells in particular--are performed in mammalian stem cell culture, an in vitro condition mimicking a very transient state during mammalian development. Thus, new models for study of pluripotent stem cells in vivo could be helpful for understanding the roles of chromatin modification, for confirming prior in vitro studies, and for exploring evolution of the pluripotent state. The freshwater flatworm, Schmidtea mediterranea, is an excellent model for studying adult pluripotent stem cells, particularly in the context of robust, whole-body regeneration. To identify chromatin modifying and remodeling enzymes critical for planarian regeneration and stem cell maintenance, we took a candidate approach and screened planarian homologs of 26 genes known to regulate chromatin biology in other organisms. Through our study, we identified six genes with novel functions in planarian homeostasis, regeneration, and behavior. We also identified in our list five planarian homologs of the mammalian CREB-Binding Protein (CBP) family of histone acetyltransferases, representing an expansion of this family in planarians. We find that two planarian CBP family members are required for planarian survival, with knockdown of Smed-CBP2 and Smed-CBP3 causing distinct defects in stem cell maintenance or function. Loss of CBP2 causes a quick, dramatic loss of stem cells, while knockdown of CBP3 more narrowly affects stem cells, preferentially decreasing markers of neural progenitors. We propose that the division of labor among a diversified CBP family in planarians presents an opportunity to dissect specific functions of a broadly important histone acetyltransferase family in stem cell biology.

developmental biology↗