EvodevoPub Date : 2021-05-10DOI: 10.1186/s13227-021-00176-z
Allan Martín Carrillo-Baltodano, Océane Seudre, Kero Guynes, José María Martín-Durán
{"title":"Early embryogenesis and organogenesis in the annelid Owenia fusiformis.","authors":"Allan Martín Carrillo-Baltodano, Océane Seudre, Kero Guynes, José María Martín-Durán","doi":"10.1186/s13227-021-00176-z","DOIUrl":"10.1186/s13227-021-00176-z","url":null,"abstract":"<p><strong>Background: </strong>Annelids are a diverse group of segmented worms within Spiralia, whose embryos exhibit spiral cleavage and a variety of larval forms. While most modern embryological studies focus on species with unequal spiral cleavage nested in Pleistoannelida (Sedentaria + Errantia), a few recent studies looked into Owenia fusiformis, a member of the sister group to all remaining annelids and thus a key lineage to understand annelid and spiralian evolution and development. However, the timing of early cleavage and detailed morphogenetic events leading to the formation of the idiosyncratic mitraria larva of O. fusiformis remain largely unexplored.</p><p><strong>Results: </strong>Owenia fusiformis undergoes equal spiral cleavage where the first quartet of animal micromeres are slightly larger than the vegetal macromeres. Cleavage results in a coeloblastula approximately 5 h post-fertilization (hpf) at 19 °C. Gastrulation occurs via invagination and completes 4 h later, with putative mesodermal precursors and the chaetoblasts appearing 10 hpf at the dorso-posterior side. Soon after, at 11 hpf, the apical tuft emerges, followed by the first neurons (as revealed by the expression of elav1 and synaptotagmin-1) in the apical organ and the prototroch by 13 hpf. Muscles connecting the chaetal sac to various larval tissues develop around 18 hpf and by the time the mitraria is fully formed at 22 hpf, there are FMRFamide<sup>+</sup> neurons in the apical organ and prototroch, the latter forming a prototrochal ring. As the mitraria feeds, it grows in size and the prototroch expands through active proliferation. The larva becomes competent after ~ 3 weeks post-fertilization at 15 °C, when a conspicuous juvenile rudiment has formed ventrally.</p><p><strong>Conclusions: </strong>Owenia fusiformis embryogenesis is similar to that of other equal spiral cleaving annelids, supporting that equal cleavage is associated with the formation of a coeloblastula, gastrulation via invagination, and a feeding trochophore-like larva in Annelida. The nervous system of the mitraria larva forms earlier and is more elaborated than previously recognized and develops from anterior to posterior, which is likely an ancestral condition to Annelida. Altogether, our study identifies the major developmental events during O. fusiformis ontogeny, defining a conceptual framework for future investigations.</p>","PeriodicalId":49076,"journal":{"name":"Evodevo","volume":"12 1","pages":"5"},"PeriodicalIF":4.1,"publicationDate":"2021-05-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1186/s13227-021-00176-z","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"38898791","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
EvodevoPub Date : 2021-03-25DOI: 10.1186/s13227-021-00172-3
Tyler A Square, Shivani Sundaram, Emma J Mackey, Craig T Miller
{"title":"Distinct tooth regeneration systems deploy a conserved battery of genes.","authors":"Tyler A Square, Shivani Sundaram, Emma J Mackey, Craig T Miller","doi":"10.1186/s13227-021-00172-3","DOIUrl":"10.1186/s13227-021-00172-3","url":null,"abstract":"<p><strong>Background: </strong>Vertebrate teeth exhibit a wide range of regenerative systems. Many species, including most mammals, reptiles, and amphibians, form replacement teeth at a histologically distinct location called the successional dental lamina, while other species do not employ such a system. Notably, a 'lamina-less' tooth replacement condition is found in a paraphyletic array of ray-finned fishes, such as stickleback, trout, cod, medaka, and bichir. Furthermore, the position, renewal potential, and latency times appear to vary drastically across different vertebrate tooth regeneration systems. The progenitor cells underlying tooth regeneration thus present highly divergent arrangements and potentials. Given the spectrum of regeneration systems present in vertebrates, it is unclear if morphologically divergent tooth regeneration systems deploy an overlapping battery of genes in their naïve dental tissues.</p><p><strong>Results: </strong>In the present work, we aimed to determine whether or not tooth progenitor epithelia could be composed of a conserved cell type between vertebrate dentitions with divergent regeneration systems. To address this question, we compared the pharyngeal tooth regeneration processes in two ray-finned fishes: zebrafish (Danio rerio) and threespine stickleback (Gasterosteus aculeatus). These two teleost species diverged approximately 250 million years ago and demonstrate some stark differences in dental morphology and regeneration. Here, we find that the naïve successional dental lamina in zebrafish expresses a battery of nine genes (bmpr1aa, bmp6, cd34, gli1, igfbp5a, lgr4, lgr6, nfatc1, and pitx2), while active Wnt signaling and Lef1 expression occur during early morphogenesis stages of tooth development. We also find that, despite the absence of a histologically distinct successional dental lamina in stickleback tooth fields, the same battery of nine genes (Bmpr1a, Bmp6, CD34, Gli1, Igfbp5a, Lgr4, Lgr6, Nfatc1, and Pitx2) are expressed in the basalmost endodermal cell layer, which is the region most closely associated with replacement tooth germs. Like zebrafish, stickleback replacement tooth germs additionally express Lef1 and exhibit active Wnt signaling. Thus, two fish systems that either have an organized successional dental lamina (zebrafish) or lack a morphologically distinct successional dental lamina (sticklebacks) deploy similar genetic programs during tooth regeneration.</p><p><strong>Conclusions: </strong>We propose that the expression domains described here delineate a highly conserved \"successional dental epithelium\" (SDE). Furthermore, a set of orthologous genes is known to mark hair follicle epithelial stem cells in mice, suggesting that regenerative systems in other epithelial appendages may utilize a related epithelial progenitor cell type, despite the highly derived nature of the resulting functional organs.</p>","PeriodicalId":49076,"journal":{"name":"Evodevo","volume":"12 1","pages":"4"},"PeriodicalIF":4.1,"publicationDate":"2021-03-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7995769/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"25516971","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
EvodevoPub Date : 2021-03-16DOI: 10.1186/s13227-021-00174-1
Jeffrey R Thompson, Periklis Paganos, Giovanna Benvenuto, Maria Ina Arnone, Paola Oliveri
{"title":"Post-metamorphic skeletal growth in the sea urchin Paracentrotus lividus and implications for body plan evolution.","authors":"Jeffrey R Thompson, Periklis Paganos, Giovanna Benvenuto, Maria Ina Arnone, Paola Oliveri","doi":"10.1186/s13227-021-00174-1","DOIUrl":"https://doi.org/10.1186/s13227-021-00174-1","url":null,"abstract":"<p><strong>Background: </strong>Understanding the molecular and cellular processes that underpin animal development are crucial for understanding the diversity of body plans found on the planet today. Because of their abundance in the fossil record, and tractability as a model system in the lab, skeletons provide an ideal experimental model to understand the origins of animal diversity. We herein use molecular and cellular markers to understand the growth and development of the juvenile sea urchin (echinoid) skeleton.</p><p><strong>Results: </strong>We developed a detailed staging scheme based off of the first ~ 4 weeks of post-metamorphic life of the regular echinoid Paracentrotus lividus. We paired this scheme with immunohistochemical staining for neuronal, muscular, and skeletal tissues, and fluorescent assays of skeletal growth and cell proliferation to understand the molecular and cellular mechanisms underlying skeletal growth and development of the sea urchin body plan.</p><p><strong>Conclusions: </strong>Our experiments highlight the role of skeletogenic proteins in accretionary skeletal growth and cell proliferation in the addition of new metameric tissues. Furthermore, this work provides a framework for understanding the developmental evolution of sea urchin body plans on macroevolutionary timescales.</p>","PeriodicalId":49076,"journal":{"name":"Evodevo","volume":"12 1","pages":"3"},"PeriodicalIF":4.1,"publicationDate":"2021-03-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1186/s13227-021-00174-1","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"25484584","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
EvodevoPub Date : 2021-03-02DOI: 10.1186/s13227-021-00173-2
Alice Laciny
{"title":"Among the shapeshifters: parasite-induced morphologies in ants (Hymenoptera, Formicidae) and their relevance within the EcoEvoDevo framework.","authors":"Alice Laciny","doi":"10.1186/s13227-021-00173-2","DOIUrl":"https://doi.org/10.1186/s13227-021-00173-2","url":null,"abstract":"<p><p>As social insects, ants represent extremely interaction-rich biological systems shaped by tightly integrated social structures and constant mutual exchange with a multitude of internal and external environmental factors. Due to this high level of ecological interconnection, ant colonies can harbour a diverse array of parasites and pathogens, many of which are known to interfere with the delicate processes of ontogeny and caste differentiation and induce phenotypic changes in their hosts. Despite their often striking nature, parasite-induced changes to host development and morphology have hitherto been largely overlooked in the context of ecological evolutionary developmental biology (EcoEvoDevo). Parasitogenic morphologies in ants can, however, serve as \"natural experiments\" that may shed light on mechanisms and pathways relevant to host development, plasticity or robustness under environmental perturbations, colony-level effects and caste evolution. By assessing case studies of parasites causing morphological changes in their ant hosts, from the eighteenth century to current research, this review article presents a first overview of relevant host and parasite taxa. Hypotheses about the underlying developmental and evolutionary mechanisms, and open questions for further research are discussed. This will contribute towards highlighting the importance of parasites of social insects for both biological theory and empirical research and facilitate future interdisciplinary work at the interface of myrmecology, parasitology, and the EcoEvoDevo framework.</p>","PeriodicalId":49076,"journal":{"name":"Evodevo","volume":"12 1","pages":"2"},"PeriodicalIF":4.1,"publicationDate":"2021-03-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1186/s13227-021-00173-2","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"25422973","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
EvodevoPub Date : 2021-01-07DOI: 10.1186/s13227-020-00171-w
Joachim M Surm, Yehu Moran
{"title":"Insights into how development and life-history dynamics shape the evolution of venom.","authors":"Joachim M Surm, Yehu Moran","doi":"10.1186/s13227-020-00171-w","DOIUrl":"10.1186/s13227-020-00171-w","url":null,"abstract":"<p><p>Venomous animals are a striking example of the convergent evolution of a complex trait. These animals have independently evolved an apparatus that synthesizes, stores, and secretes a mixture of toxic compounds to the target animal through the infliction of a wound. Among these distantly related animals, some can modulate and compartmentalize functionally distinct venoms related to predation and defense. A process to separate distinct venoms can occur within and across complex life cycles as well as more streamlined ontogenies, depending on their life-history requirements. Moreover, the morphological and cellular complexity of the venom apparatus likely facilitates the functional diversity of venom deployed within a given life stage. Intersexual variation of venoms has also evolved further contributing to the massive diversity of toxic compounds characterized in these animals. These changes in the biochemical phenotype of venom can directly affect the fitness of these animals, having important implications in their diet, behavior, and mating biology. In this review, we explore the current literature that is unraveling the temporal dynamics of the venom system that are required by these animals to meet their ecological functions. These recent findings have important consequences in understanding the evolution and development of a convergent complex trait and its organismal and ecological implications.</p>","PeriodicalId":49076,"journal":{"name":"Evodevo","volume":"12 1","pages":"1"},"PeriodicalIF":4.1,"publicationDate":"2021-01-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7791878/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"38793552","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
EvodevoPub Date : 2020-12-15DOI: 10.1186/s13227-020-00170-x
Eva Terzibasi Tozzini, Alessandro Cellerino
{"title":"Nothobranchius annual killifishes.","authors":"Eva Terzibasi Tozzini, Alessandro Cellerino","doi":"10.1186/s13227-020-00170-x","DOIUrl":"https://doi.org/10.1186/s13227-020-00170-x","url":null,"abstract":"<p><p>Annual fishes of the genus Nothobranchius inhabit ephemeral habitats in Eastern and Southeastern Africa. Their life cycle is characterized by very rapid maturation, a posthatch lifespan of a few weeks to months and embryonic diapause to survive the dry season. The species N. furzeri holds the record of the fastest-maturing vertebrate and of the vertebrate with the shortest captive lifespan and is emerging as model organism in biomedical research, evolutionary biology, and developmental biology. Extensive characterization of age-related phenotypes in the laboratory and of ecology, distribution, and demography in the wild are available. Species/populations from habitats differing in precipitation intensity show parallel evolution of lifespan and age-related traits that conform to the classical theories on aging. Genome sequencing and the establishment of CRISPR/Cas9 techniques made this species particularly attractive to investigate the effects genetic and non-genetic intervention on lifespan and aging-related phenotypes. At the same time, annual fishes are a very interesting subject for comparative approaches, including genomics, transcriptomics, and proteomics. The N. furzeri community is highly diverse and rapidly expanding and organizes a biannual meeting.</p>","PeriodicalId":49076,"journal":{"name":"Evodevo","volume":"11 1","pages":"25"},"PeriodicalIF":4.1,"publicationDate":"2020-12-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1186/s13227-020-00170-x","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"38713867","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
EvodevoPub Date : 2020-12-04DOI: 10.1186/s13227-020-00169-4
Reiko Kuroda, Masanori Abe
{"title":"The pond snail Lymnaea stagnalis.","authors":"Reiko Kuroda, Masanori Abe","doi":"10.1186/s13227-020-00169-4","DOIUrl":"https://doi.org/10.1186/s13227-020-00169-4","url":null,"abstract":"<p><p>The freshwater snail Lymnaea stagnalis has a long research history, but only relatively recently has it emerged as an attractive model organism to study molecular mechanisms in the areas of developmental biology and translational medicine such as learning/memory and neurodegenerative diseases. The species has the advantage of being a hermaphrodite and can both cross- and self-mate, which greatly facilitates genetic approaches. The establishment of body-handedness, or chiromorphogenesis, is a major topic of study, since chirality is evident in the shell coiling. Chirality is maternally inherited, and only recently a gene-editing approach identified the actin-related gene Lsdia1 as the key handedness determinant. This short article reviews the natural habitat, life cycle, major research questions and interests, and experimental approaches.</p>","PeriodicalId":49076,"journal":{"name":"Evodevo","volume":"11 1","pages":"24"},"PeriodicalIF":4.1,"publicationDate":"2020-12-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1186/s13227-020-00169-4","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"38689526","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
EvodevoPub Date : 2020-11-16DOI: 10.1101/2020.11.16.385708
J. McDonald, Pegah Nabili, Lily Thorsen, S. Jeon, A. Shingleton
{"title":"Sex-specific plasticity and the nutritional geometry of insulin-signaling gene expression in Drosophila melanogaster","authors":"J. McDonald, Pegah Nabili, Lily Thorsen, S. Jeon, A. Shingleton","doi":"10.1101/2020.11.16.385708","DOIUrl":"https://doi.org/10.1101/2020.11.16.385708","url":null,"abstract":"Background Sexual-size dimorphism (SSD) is replete among animals, but while the selective pressures that drive the evolution of SSD have been well studied, the developmental mechanisms upon which these pressures act are poorly understood. Ours and others’ research has shown that SSD in D. melanogaster reflects elevated levels of nutritional plasticity in females versus males, such that SSD increases with dietary intake and body size, a phenomenon called sex-specific plasticity (SSP). Additional data indicate that while body size in both sexes responds to variation in protein level, only female body size is sensitive to variation in carbohydrate level. Here, we explore whether these difference in sensitivity at the morphological level are reflected by differences in how the insulin/IGF-signaling (IIS) and TOR-signaling pathways respond to changes in carbohydrates and proteins in females versus males, using a nutritional geometry approach. Results The IIS-regulated transcripts of 4E-BP and InR most strongly correlated with body size in females and males, respectively, but neither responded to carbohydrate level and so could not explain the sex-specific response to body size to dietary carbohydrate. Transcripts regulated by TOR-signaling did, however, respond to dietary carbohydrate in a sex-specific manner. In females, expression of dILP5 positively correlated with body size, while expression of dILP2,3 and 8, was elevated on diets with a low concentration of both carbohydrate and protein. In contrast, we detected lower levels of dILP2 and 5 protein in the brains of females fed on low concentration diets. We could not detect any effect of diet on dILP expression in males. Conclusion Although females and males show sex-specific transcriptional responses to changes in protein and carbohydrate, the patterns of expression do not support a simple model of the regulation of body-size SSP by either insulin- or TOR-signaling. The data also indicate a complex relationship between carbohydrate and protein level, dILP expression and dILP peptide levels in the brain. In general, diet quality and sex both affect the transcriptional response to changes in diet quantity, and so should be considered in future studies that explore the effect of nutrition on body size.","PeriodicalId":49076,"journal":{"name":"Evodevo","volume":" ","pages":""},"PeriodicalIF":4.1,"publicationDate":"2020-11-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49525163","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
EvodevoPub Date : 2020-11-10DOI: 10.1186/s13227-020-00168-5
Celeste R Banfill, Alex C C Wilson, Hsiao-Ling Lu
{"title":"Further evidence that mechanisms of host/symbiont integration are dissimilar in the maternal versus embryonic Acyrthosiphon pisum bacteriome.","authors":"Celeste R Banfill, Alex C C Wilson, Hsiao-Ling Lu","doi":"10.1186/s13227-020-00168-5","DOIUrl":"https://doi.org/10.1186/s13227-020-00168-5","url":null,"abstract":"<p><strong>Background: </strong>Host/symbiont integration is a signature of evolutionarily ancient, obligate endosymbioses. However, little is known about the cellular and developmental mechanisms of host/symbiont integration at the molecular level. Many insects possess obligate bacterial endosymbionts that provide essential nutrients. To advance understanding of the developmental and metabolic integration of hosts and endosymbionts, we track the localization of a non-essential amino acid transporter, ApNEAAT1, across asexual embryogenesis in the aphid, Acyrthosiphon pisum. Previous work in adult bacteriomes revealed that ApNEAAT1 functions to exchange non-essential amino acids at the A. pisum/Buchnera aphidicola symbiotic interface. Driven by amino acid concentration gradients, ApNEAAT1 moves proline, serine, and alanine from A. pisum to Buchnera and cysteine from Buchnera to A. pisum. Here, we test the hypothesis that ApNEAAT1 is localized to the symbiotic interface during asexual embryogenesis.</p><p><strong>Results: </strong>During A. pisum asexual embryogenesis, ApNEAAT1 does not localize to the symbiotic interface. We observed ApNEAAT1 localization to the maternal follicular epithelium, the germline, and, in late-stage embryos, to anterior neural structures and insect immune cells (hemocytes). We predict that ApNEAAT1 provisions non-essential amino acids to developing oocytes and embryos, as well as to the brain and related neural structures. Additionally, ApNEAAT1 may perform roles related to host immunity.</p><p><strong>Conclusions: </strong>Our work provides further evidence that the embryonic and adult bacteriomes of asexual A. pisum are not equivalent. Future research is needed to elucidate the developmental time point at which the bacteriome reaches maturity.</p>","PeriodicalId":49076,"journal":{"name":"Evodevo","volume":"11 1","pages":"23"},"PeriodicalIF":4.1,"publicationDate":"2020-11-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1186/s13227-020-00168-5","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"38351067","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
EvodevoPub Date : 2020-10-17eCollection Date: 2020-01-01DOI: 10.1186/s13227-020-00167-6
Nicholas D Holland, Ildiko M L Somorjai
{"title":"Serial blockface SEM suggests that stem cells may participate in adult notochord growth in an invertebrate chordate, the Bahamas lancelet.","authors":"Nicholas D Holland, Ildiko M L Somorjai","doi":"10.1186/s13227-020-00167-6","DOIUrl":"https://doi.org/10.1186/s13227-020-00167-6","url":null,"abstract":"<p><strong>Background: </strong>The cellular basis of adult growth in cephalochordates (lancelets or amphioxus) has received little attention. Lancelets and their constituent organs grow slowly but continuously during adult life. Here, we consider whether this slow organ growth involves tissue-specific stem cells. Specifically, we focus on the cell populations in the notochord of an adult lancelet and use serial blockface scanning electron microscopy (SBSEM) to reconstruct the three-dimensional fine structure of all the cells in a tissue volume considerably larger than normally imaged with this technique.</p><p><strong>Results: </strong>In the notochordal region studied, we identified 10 cells with stem cell-like morphology at the posterior tip of the organ, 160 progenitor (Müller) cells arranged along its surface, and 385 highly differentiated lamellar cells constituting its core. Each cell type could clearly be distinguished on the basis of cytoplasmic density and overall cell shape. Moreover, because of the large sample size, transitions between cell types were obvious.</p><p><strong>Conclusions: </strong>For the notochord of adult lancelets, a reasonable interpretation of our data indicates growth of the organ is based on stem cells that self-renew and also give rise to progenitor cells that, in turn, differentiate into lamellar cells. Our discussion compares the cellular basis of adult notochord growth among chordates in general. In the vertebrates, several studies implied that proliferating cells (chordoblasts) in the cortex of the organ might be stem cells. However, we think it is more likely that such cells actually constitute a progenitor population downstream from and maintained by inconspicuous stem cells. We venture to suggest that careful searches should find stem cells in the adult notochords of many vertebrates, although possibly not in the notochordal vestiges (nucleus pulposus regions) of mammals, where the presence of endogenous proliferating cells remains controversial.</p>","PeriodicalId":49076,"journal":{"name":"Evodevo","volume":" ","pages":"22"},"PeriodicalIF":4.1,"publicationDate":"2020-10-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1186/s13227-020-00167-6","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"38515449","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}