Biology subjects

Petersen, C. P.

Publications and source records attributed to Petersen, C. P..

8 recordsLinked to original sources

bioRxiv2026

DDR and TMEM132 genes control progenitor targeting and regenerative assembly of the planarian eye

How progenitors can faithfully self-assemble to build new organs in adulthood is a central unsolved problem in regeneration biology. The planarian eye is a model for uncovering principles of de novo organogenesis during regeneration. In this process, pluripotent adult stem cells specify into ovo+ migratory progenitors which target to the eye field due to Wnt and FGFRL signals produced from bodywall muscle, then differentiate into photoreceptor neurons (PRNs) and pigmented optic cup (OC) cells, followed by organization of these two cell types in an opposing pattern that completes eye organ maturation. We used scRNA-seq to characterize eye progenitor transcriptomes during regeneration, followed by FISH validation, and RNAi screening to identify regulators of eye regeneration. This uncovered a function for the discoidin domain receptor ddr-1 in preventing the premature terminal differentiation of migratory eye progenitors. DDRs encode collagen receptors, and bodywall muscle is the major source of collagen in planarians, suggesting eye progenitors likely interface with muscle ECM for their proper deployment in regeneration. We further identified a novel eye morphogenesis phenotype from knockdown of tmem132-1, causing failed heterotypic adhesion between eye cell types. TMEM132 factors are conserved cell-surface receptors that mediate adhesion and regulate migration, and human TMEM132 mutations are associated with several neurobehavioral diseases. Therefore, planarian tmem132-1 likely directly regulates the capture and assembly of migratory progenitors into mature eyes during regeneration. Together, these results define new steps in the eye regeneration pathway and suggest ancient roles for DDR and TMEM132 in progenitor migration and coordinated organ assembly.

developmental biology↗

bioRxiv2024

Injury-induced Neuregulin-ErbB signaling from muscle mobilizes stem cells for whole-body regeneration in Acoels

The activation of progenitor cells near wound sites is a common feature of regeneration across species, but the conserved signaling mechanisms responsible for this step in whole-body regeneration are still incompletely understood. The acoel Hofstenia miamia undergoes whole-body regeneration using Piwi+ pluripotent adult stem cells (neoblasts) that accumulate at amputation sites early in the regeneration process. The EGFR signaling pathway has broad roles in controlling proliferation, migration, differentiation, and cell survival across metazoans. Using a candidate RNAi screening approach, we identify the Hofstenia EGFR erbB4-2 and Neuregulin nrg-1 genes as essential for blastema formation. Structure prediction of NRG-1 and ERBB4-2 proteins supports the likelihood of these factors interacting directly. After amputation injuries, nrg-1 expression is induced in body-wall muscle cells at the wound site by 6 hours and localizes to the tip of the outgrowing blastema over the next several days, while erbB4-2 is broadly expressed, including in muscle and neoblasts. Under nrg-1(RNAi) and erbB4-2(RNAi) conditions that impair blastema formation, animals still undergo the earliest responses to injury to activate expression of the Early Growth Response transcription factor egr, indicating a crucial role for EGFR signaling downstream of initial wound activation. nrg-1(RNAi) and erbB4-2(RNAi) animals possess Piwi+ and H3P+ mitotic neoblasts which hyperproliferate normally after amputation, but these cells fail to accumulate at the wound site. Therefore, muscle provides a source for Neuregulin-ErbB signaling necessary for the mobilization of proliferative progenitors to enable blastema outgrowth for whole-body regeneration in Hofstenia. These results indicate a shared functional requirement for muscle signaling to enable regeneration between planarians and acoels across 550 million years of evolution.

developmental biology↗

bioRxiv2024

map3k1 suppresses terminal differentiation of migratory eye progenitors in planarian regeneration

Proper stem cell targeting and differentiation is necessary for regeneration to succeed. In organisms capable of whole body regeneration, considerable progress has been made identifying wound signals initiating this process, but the mechanisms that control the differentiation of progenitors into mature organs are not fully understood. Using the planarian as a model system, we identify a novel function for map3k1, a MAP3K family member possessing both kinase and ubiquitin ligase domains, to negatively regulate terminal differentiation of stem cells during eye regeneration. Inhibition of map3k1 caused the formation of multiple ectopic eyes within the head, but without controlling overall head, brain, or body patterning. By contrast, other known regulators of planarian eye patterning like WntA and notum also regulate head regionalization, suggesting map3k1 acts distinctly. Eye resection and regeneration experiments suggest that unlike Wnt signaling perturbation, map3k1 inhibition did not shift the target destination of eye formation in the animal. Instead, map3k1(RNAi) ectopic eyes emerge in the regions normally occupied by migratory eye progenitors, and the onset of ectopic eyes after map3k1 inhibition coincides with a reduction to eye progenitor numbers. Furthermore, RNAi dosing experiments indicate that progenitors closer to their normal target are relatively more sensitive to the effects of map3k1, implicating this factors in controlling the site of terminal differentiation. Eye phenotypes were also observed after inhibition of map2k4, map2k7, jnk, and p38, identifying a putative pathway through which map3k1 prevents differentiation. Together, these results suggest that map3k1 regulates a novel control point in the eye regeneration pathway which suppresses the terminal differentiation of progenitors during their migration to target destinations. Author SummaryDuring adult regeneration, progenitors must migrate and differentiate at the proper locations in order to successfully restore lost or damaged organs and tissues, yet the mechanisms underlying these abilities are not fully understood. The planarian eye is a model to study this problem, because this organ is regenerated using migratory progenitors that travel long distances through the body in an undifferentiated state prior to terminal differentiation upon their arrival at target destinations. We determined that a pathway involving the MAP kinase kinase kinase map3k1 holds planarian eye progenitors in an undifferentiated state during their transit. Inhibition of map3k1 caused a dramatic body transformation in which migratory progenitors differentiate inappropriately early, and in the wrong locations, into mature eyes. By analyzing this phenotype and measuring the change to eye progenitor abundance after map3k1 inhibition, we found that map3k1 prevents ectopic differentiation of eye cells rather than mediating body-wide patterning through the Wnt pathway. Our study argues that whole-body regeneration mechanisms involve separate steps to control patterning and progenitor differentiation.

developmental biology↗

bioRxiv2022

Planarian dorsoventral Netrins organize a muscle midline signaling center and regulate blastema formation

Integration of positional information across body axes is likely critical for whole-body regeneration to define the territories of missing tissue in three dimensions with fidelity. The body-wall musculature in planarians expresses patterning factors regulating the anteroposterior, dorsoventral, and mediolateral axes, but how this information coordinates is not fully understood. We identify a previously described factor specifically expressed in dorsal midline muscle as a BMP/Activin decoy receptor bambi-2. Analysis of scRNAseq indicates bambi-2+ cells coexpress midline-specifying transcription factor pitx and longitudinal muscle-specifying factor myoD, and production of bambi-2+ cells requires these factors. In laterally amputated animals regenerating an entirely new midline, bambi-2+ cells are initially formed at the wound site, then dynamically spread, and ultimately reset to restore bilateral symmetry. We further identify a system of dorsoventral Netrin and Netrin receptor signals expressed from body-wall muscle that control midline identity and blastema morphology. Ventral and laterally expressed netrins -1, -4, and -5 signal via dorsally-enriched netrin repulsion receptors unc5-C, unc5-E, and dcc-2, which together limit mediolateral spread of bambi-2+ dorsal midline muscle and influence the architecture of the muscle system. Our results suggest a model in which ventral determinants dictate mediolateral information important for blastema morphology.

developmental biology↗

bioRxiv2022

High throughput expression-based phenotyping and RNAi screening reveals novel regulators of planarian stem cells

The complexity of cell types and states revealed by single-cell RNAseq atlases presents a challenge for the systematic analysis of fate determinants using traditional screening methodologies. Differentiation in the planarian Schmidtea mediterranea exemplifies this problem, as these animals continuously produce over 100 differentiated cell types for homeostasis and regeneration using neoblast adult pluripotent stem cells. The signaling factors enabling neoblast self-renewal and selective differentiation of these many fates are still incompletely understood. We developed a method using high-throughput expression profiling by qPCR and whole-animal RNAseq to simultaneously assess numerous cell fate markers as the phenotypic readout in large-scale RNAi screens. Applying this method, we performed an RNAi screen of 400 kinases, receptors, and other regulatory molecules to reveal specific functions for 30 previously unknown factors in neoblast biology. 17 genes were required for neoblast maintenance, including factors likely involved in cell-cycle regulation, nutrient sensing, and chromatin modification. Multidimensional expression information additionally revealed several specific regulators of other neoblast activities, including a mink1 kinase regulating global neoblast differentiation, the energy responsive kinase adenylate kinase-2 regulating intestine specification within the neoblast population, an RNA acetyl transferase nat10 regulating epidermal differentiation, and a pak1 kinase restricting neoblast localization to prevent tissue outgrowths. These results identify several new regulators of neoblast activities and demonstrate the applicability of expression-based screening for systematic analysis of stem cell phenotypes in whole animals.

developmental biology↗

bioRxiv2021

Src acts with WNT/FGFRL signaling to pattern the planarian anteroposterior axis

Tissue identity determination is critical for regeneration, and the planarian anteroposterior (AP) axis uses positional control genes expressed from bodywall muscle to determine body regionalization. Canonical Wnt signaling establishes anterior versus posterior pole identities through notum and wnt1 signaling, and two Wnt/FGFRL signaling pathways control head and trunk domains, but their downstream signaling mechanisms are not fully understood. Here we identify a planarian Src homolog that restricts head and trunk identities to anterior positions. src-1(RNAi) animals formed enlarged brains and ectopic eyes and also duplicated trunk tissue, similar to a combination of Wnt/FGFRL RNAi phenotypes. src-1 was required for establishing territories of positional control gene expression, indicating it acts at an upstream step in patterning the AP axis. Double RNAi experiments and eye regeneration assays suggest src-1 can act in parallel to at least some Wnt and FGFRL factors. Co-inhibition of src-1 with other posterior-promoting factors led to dramatic patterning changes and a reprogramming of Wnt/FGFRLs into controlling new positional outputs. These results identify src-1 as a factor that promotes robustness of the AP positional system that instructs appropriate regeneration. HighlightsO_LISrc-1 suppresses head and trunk identity C_LIO_LISrc-1 can regulate positional control gene domains C_LIO_LISrc-1 likely acts independently of notum/Wnt and FGFRL signals C_LIO_LISrc-1 inhibition broadly sensitizes animals to AP pattern disruption C_LI

developmental biology↗

bioRxiv2018

Positional information specifies the site of organ regeneration and not tissue maintenance in planarians

Most animals undergo homeostatic tissue maintenance, yet those capable of robust regeneration in adulthood use mechanisms significantly overlapping with homeostasis. Here we show in planarians that modulations to body-wide patterning systems shift the target site for eye regeneration while still enabling homeostasis of eyes outside this region. The uncoupling of homeostasis and regeneration, which can occur during normal positional rescaling after axis truncation, is not due to altered injury signaling or stem cell activity, nor specific to eye tissue. Rather, pre-existing tissues, which are misaligned with patterning factor expression domains, compete with properly located organs for incorporation of migratory progenitors. These observations suggest that patterning factors determine sites of organ regeneration but do not solely determine the location of tissue homeostasis. These properties provide candidate explanations for how regeneration integrates pre-existing tissues and how regenerative abilities could be lost in evolution or development without eliminating long-term tissue maintenance and repair.\n\nOne Sentence SummaryHomeostatic tissue maintenance can occur independent of precise positional information in planarians.

developmental biology↗

bioRxiv2017

A core signaling mechanism at the origin of animal nociception

All animals must detect noxious stimuli to initiate protective behavior, but the evolutionary origin of nociceptive systems is not well understood. Here, we show that a remarkably conserved signaling mechanism mediates the detection of noxious stimuli in animals as diverse as flatworms and humans. Planarian flatworms are amongst the simplest bilateral animals with a centralized nervous system, and capable of directed behavior. We demonstrate that noxious heat and irritant chemicals elicit robust escape behaviors in the planarian Schmidtea mediterranea, and that the conserved ion channel TRPA1 is required for these responses. TRPA1 mutant fruit flies (Drosophila) are also defective in the avoidance of noxious heat 1-3. Unexpectedly, we find that either the planarian or the human TRPA1 can restore noxious heat avoidance to TRPA1 mutant Drosophila, even though neither is directly activated by heat. Instead, our data suggest that TRPA1 activation is mediated by H2O2/Reactive Oxygen Species, early markers of tissue damage rapidly produced as a result of heat exposure. Together, our data reveal a core function for TRPA1 in noxious heat transduction, demonstrate its conservation from planarians to humans, and imply that human nociceptive systems may share a common ancestry with those of most extant animals, tracing back their origin to a progenitor that lived more than 500 million years ago.

neuroscience↗