Increasing Diversity in Developmental Biology.

The demographic profile of the scientific and biomedical workforce in the United States does not reflect the population at large (https://ncses.nsf.gov/pubs/nsf21321/data-tables; www.census.gov), raising concerns that there will be too few trained researchers in the future, the scope of research interests will not be broad enough, gaps in equity and social justice will continue to increase, and the safeguards to the integrity of the scientific enterprise could be jeopardized. To diversify the pool of scientists, the Society for Developmental Biology (SDB) developed the Choose Development! Program-a two-summer immersion for undergraduate students belonging to underrepresented (UR) populations in STEM to join the research laboratory of an established SDB member. This research-intensive experience was augmented by a multi-tier mentoring plan for each student, society-wide recognition, professional development activities and networking at national meetings. The strengths of the Choose Development! Program were leveraged to expand inclusion and outreach at the Society's leadership level, the Board of Directors (BOD), which then led to significant changes that impacted the SDB community. The cumulative outcomes of the Choose Development! Program provides evidence that community-based, long-term advocacy, and mentoring of young UR scientists is successful in retaining UR students in scientific career paths and making a scientific society more inclusive.

Scientific societies fostering inclusivity through speaker diversity in annual meeting programming: a call to action.

Scientific societies aiming to foster inclusion of scientists from underrepresented (UR) backgrounds among their membership often delegate primary responsibility for this goal to a diversity-focused committee. The National Science Foundation has funded the creation of the Alliance to Catalyze Change for Equity in STEM Success (ACCESS), a meta-organization bringing together representatives from several such STEM society committees to serve as a hub for a growing community of practice. Our goal is to coordinate efforts to advance inclusive practices by sharing experiences and making synergistic discoveries about what works. ACCESS has analyzed the approaches by which member societies have sought to ensure inclusivity through selection of annual meeting speakers. Here we discuss how inclusive speaker selection fosters better scientific environments for all and identify challenges and promising practices for societies striving to maximize inclusivity of speakers in their scientific programming.

Long-term tracking demonstrates effectiveness of a partnership-led training program to advance the careers of biomedical researchers from underrepresented groups.

The demographic profile of the biomedical workforce in the U.S. does not reflect the population at large, raising concerns that there will be insufficient trained researchers in the future, and the scope of research interests will not be sufficiently broad. To diversify and expand the pool of researchers trained to conduct research on cancer and cancer health disparities, a series of training activities to recruit and train primarily Hispanic students at both the undergraduate and graduate level were developed. The strengths of both a Hispanic Serving Institution and an NIH-designated Comprehensive Cancer Center were leveraged to develop appropriate research training and professional development activities. The career progression of the participants and degree completion rates was tracked, along with persistent interest in biomedical research in general and cancer and cancer health disparities research in particular for these underrepresented individuals. Finally, this report demonstrates that these training activities increased general knowledge about cancer among participants.

Sternopygus macrurus electric organ transcriptome and cell size exhibit insensitivity to short-term electrical inactivity.

Electrical activity is an important regulator of cellular function and gene expression in electrically excitable cell types. In the weakly electric teleost fish Sternopygus macrurus, electrocytes, i.e., the current-producing cells of the electric organ, derive from a striated muscle lineage. Mature electrocytes are larger than muscle fibers, do not contain sarcomeres, and are driven continuously at frequencies higher than those exerted on muscle cells. Previous work showed that the removal of electrical activity by spinal cord transection (ST) for two and five weeks led to an upregulation of some sarcomeric proteins and a decrease in electrocyte size. To test whether changes in gene transcription preceded these phenotypic changes, we determined the sensitivity of electrocyte gene expression to electrical inactivity periods of two and five days after ST. Whole tissue gene expression profiles using deep RNA sequencing showed minimal alterations in the levels of myogenic transcription factor and sarcomeric transcripts after either ST period. Moreover, while analysis of differentially expressed genes showed a transient upregulation of genes associated with proteolytic mechanisms at two days and an increase in mRNA levels of cytoskeletal genes at five days after electrical silencing, electrocyte size was not affected. Electrical inactivity also resulted in the downregulation of genes that were classified into enriched clusters associated with functions of axon migration and synapse structure. Overall, these data demonstrate that unlike tissues in the myogenic lineage in other vertebrate species, regulation of gene transcription and cell size in the muscle-like electrocytes of S. macrurus is highly insensitive to short-term electrical inactivity. Moreover, together with data obtained from control and long-term ST studies, the present data suggest that neural input might influence post-transcriptional processes to affect the mature electrocyte phenotype.

Properties of skeletal muscle in the teleost Sternopygus macrurus are unaffected by short-term electrical inactivity.

Skeletal muscle is distinguished from other tissues on the basis of its shape, biochemistry, and physiological function. Based on mammalian studies, fiber size, fiber types, and gene expression profiles are regulated, in part, by the electrical activity exerted by the nervous system. To address whether similar adaptations to changes in electrical activity in skeletal muscle occur in teleosts, we studied these phenotypic properties of ventral muscle in the electric fish Sternopygus macrurus following 2 and 5 days of electrical inactivation by spinal transection. Our data show that morphological and biochemical properties of skeletal muscle remained largely unchanged after these treatments. Specifically, the distribution of type I and type II muscle fibers and the cross-sectional areas of these fiber types observed in control fish remained unaltered after each spinal transection survival period. This response to electrical inactivation was generally reflected at the transcript level in real-time PCR and RNA-seq data by showing little effect on the transcript levels of genes associated with muscle fiber type differentiation and plasticity, the sarcomere complex, and pathways implicated in the regulation of muscle fiber size. Data from this first study characterizing the acute influence of neural activity on muscle mass and sarcomere gene expression in a teleost are discussed in the context of comparative studies in mammalian model systems and vertebrate species from different lineages.

The myogenic electric organ of Sternopygus macrurus: a non-contractile tissue with a skeletal muscle transcriptome.

In most electric fish species, the electric organ (EO) derives from striated muscle cells that suppress many muscle properties. In the gymnotiform Sternopygus macrurus, mature electrocytes, the current-producing cells of the EO, do not contain sarcomeres, yet they continue to make some cytoskeletal and sarcomeric proteins and the muscle transcription factors (MTFs) that induce their expression. In order to more comprehensively examine the transcriptional regulation of genes associated with the formation and maintenance of the contractile sarcomere complex, results from expression analysis using qRT-PCR were informed by deep RNA sequencing of transcriptomes and miRNA compositions of muscle and EO tissues from adult S. macrurus. Our data show that: (1) components associated with the homeostasis of the sarcomere and sarcomere-sarcolemma linkage were transcribed in EO at levels similar to those in muscle; (2) MTF families associated with activation of the skeletal muscle program were not differentially expressed between these tissues; and (3) a set of microRNAs that are implicated in regulation of the muscle phenotype are enriched in EO. These data support the development of a unique and highly specialized non-contractile electrogenic cell that emerges from a striated phenotype and further differentiates with little modification in its transcript composition. This comprehensive analysis of parallel mRNA and miRNA profiles is not only a foundation for functional studies aimed at identifying mechanisms underlying the transcription-independent myogenic program in S. macrurus EO, but also has important implications to many vertebrate cell types that independently activate or suppress specific features of the skeletal muscle program.

Unique patterns of transcript and miRNA expression in the South American strong voltage electric eel (Electrophorus electricus).

BACKGROUND: With its unique ability to produce high-voltage electric discharges in excess of 600 volts, the South American strong voltage electric eel (Electrophorus electricus) has played an important role in the history of science. Remarkably little is understood about the molecular nature of its electric organs. RESULTS: We present an in-depth analysis of the genome of E. electricus, including the transcriptomes of eight mature tissues: brain, spinal cord, kidney, heart, skeletal muscle, Sachs' electric organ, main electric organ, and Hunter's electric organ. A gene set enrichment analysis based on gene ontology reveals enriched functions in all three electric organs related to transmembrane transport, androgen binding, and signaling. This study also represents the first analysis of miRNA in electric fish. It identified a number of miRNAs displaying electric organ-specific expression patterns, including one novel miRNA highly over-expressed in all three electric organs of E. electricus. All three electric organ tissues also express three conserved miRNAs that have been reported to inhibit muscle development in mammals, suggesting that miRNA-dependent regulation of gene expression might play an important role in specifying an electric organ identity from its muscle precursor. These miRNA data were supported using another complete miRNA profile from muscle and electric organ tissues of a second gymnotiform species. CONCLUSIONS: Our work on the E. electricus genome and eight tissue-specific gene expression profiles will greatly facilitate future research on determining the coding and regulatory sequences that specify the function, development, and evolution of electric organs. Moreover, these data and future studies will be informed by the first comprehensive analysis of miRNA expression in an electric fish presented here.

Nonhuman genetics. Genomic basis for the convergent evolution of electric organs.

Little is known about the genetic basis of convergent traits that originate repeatedly over broad taxonomic scales. The myogenic electric organ has evolved six times in fishes to produce electric fields used in communication, navigation, predation, or defense. We have examined the genomic basis of the convergent anatomical and physiological origins of these organs by assembling the genome of the electric eel (Electrophorus electricus) and sequencing electric organ and skeletal muscle transcriptomes from three lineages that have independently evolved electric organs. Our results indicate that, despite millions of years of evolution and large differences in the morphology of electric organ cells, independent lineages have leveraged similar transcription factors and developmental and cellular pathways in the evolution of electric organs.

Mechanisms of muscle gene regulation in the electric organ of Sternopygus macrurus.

Animals perform a remarkable diversity of movements through the coordinated mechanical contraction of skeletal muscle. This capacity for a wide range of movements is due to the presence of muscle cells with a very plastic phenotype that display many different biochemical, physiological and morphological properties. What factors influence the maintenance and plasticity of differentiated muscle fibers is a fundamental question in muscle biology. We have exploited the remarkable potential of skeletal muscle cells of the gymnotiform electric fish Sternopygus macrurus to trans-differentiate into electrocytes, the non-contractile electrogenic cells of the electric organ (EO), to investigate the mechanisms that regulate the skeletal muscle phenotype. In S. macrurus, mature electrocytes possess a phenotype that is intermediate between muscle and non-muscle cells. How some genes coding for muscle-specific proteins are downregulated while others are maintained, and novel genes are upregulated, is an intriguing problem in the control of skeletal muscle and EO phenotype. To date, the intracellular and extracellular factors that generate and maintain distinct patterns of gene expression in muscle and EO have not been defined. Expression studies in S. macrurus have started to shed light on the role that transcriptional and post-transcriptional events play in regulating specific muscle protein systems and the muscle phenotype of the EO. In addition, these findings also represent an important step toward identifying mechanisms that affect the maintenance and plasticity of the muscle cell phenotype for the evolution of highly specialized non-contractile tissues.

Electric fish: new insights into conserved processes of adult tissue regeneration.

Biology is replete with examples of regeneration, the process that allows animals to replace or repair cells, tissues and organs. As on land, vertebrates in aquatic environments experience the occurrence of injury with varying frequency and to different degrees. Studies demonstrate that ray-finned fishes possess a very high capacity to regenerate different tissues and organs when they are adults. Among fishes that exhibit robust regenerative capacities are the neotropical electric fishes of South America (Teleostei: Gymnotiformes). Specifically, adult gymnotiform electric fishes can regenerate injured brain and spinal cord tissues and restore amputated body parts repeatedly. We have begun to identify some aspects of the cellular and molecular mechanisms of tail regeneration in the weakly electric fish Sternopygus macrurus (long-tailed knifefish) with a focus on regeneration of skeletal muscle and the muscle-derived electric organ. Application of in vivo microinjection techniques and generation of myogenic stem cell markers are beginning to overcome some of the challenges owing to the limitations of working with non-genetic animal models with extensive regenerative capacity. This review highlights some aspects of tail regeneration in S. macrurus and discusses the advantages of using gymnotiform electric fishes to investigate the cellular and molecular mechanisms that produce new cells during regeneration in adult vertebrates.

Activation of Pax7-positive cells in a non-contractile tissue contributes to regeneration of myogenic tissues in the electric fish S. macrurus.

The ability to regenerate tissues is shared across many metazoan taxa, yet the type and extent to which multiple cellular mechanisms come into play can differ across species. For example, urodele amphibians can completely regenerate all lost tissues, including skeletal muscles after limb amputation. This remarkable ability of urodeles to restore entire limbs has been largely linked to a dedifferentiation-dependent mechanism of regeneration. However, whether cell dedifferentiation is the fundamental factor that triggers a robust regeneration capacity, and whether the loss or inhibition of this process explains the limited regeneration potential in other vertebrates is not known. Here, we studied the cellular mechanisms underlying the repetitive regeneration of myogenic tissues in the electric fish S. macrurus. Our in vivo microinjection studies of high molecular weight cell lineage tracers into single identified adult myogenic cells (muscle or noncontractile muscle-derived electrocytes) revealed no fragmentation or cellularization proximal to the amputation plane. In contrast, ultrastructural and immunolabeling studies verified the presence of myogenic stem cells that express the satellite cell marker Pax7 in mature muscle fibers and electrocytes of S. macrurus. These data provide the first example of Pax-7 positive muscle stem cells localized within a non-contractile electrogenic tissue. Moreover, upon amputation, Pax-7 positive cells underwent a robust replication and were detected exclusively in regions that give rise to myogenic cells and dorsal spinal cord components revealing a regeneration process in S. macrurus that is dependent on the activation of myogenic stem cells for the renewal of both skeletal muscle and the muscle-derived electric organ. These data are consistent with the emergent concept in vertebrate regeneration that different tissues provide a distinct progenitor cell population to the regeneration blastema, and these progenitor cells subsequently restore the original tissue.

S. macrurus myogenic regulatory factors (MRFs) induce mammalian skeletal muscle differentiation; evidence for functional conservation of MRFs.

The current-producing cells of the electric organ, i.e., electrocytes, in Sternopygus macrurus derive from skeletal muscle fibers. Mature electrocytes are not contractile, but they do retain some muscle proteins, are multinucleated, and receive cholinergic innervation. Electrocytes express the myogenic regulatory factors (MRFs) MyoD, myogenin, Myf5 and MRF4 despite their incomplete muscle phenotype. Although S. macrurus MRFs share functional domains which are highly conserved and their expression is confined to the myogenic lineage, their capability to induce the muscle phenotype has not been determined. To test the functional conservation of S. macrurus MRFs to transcriptionally activate skeletal muscle gene expression and induce the myogenic program, we transiently over-expressed S. macrurus MyoD (SmMyoD) and myogenin (SmMyoG) in mouse C3H/10T1/2 and NIH3T3 embryonic cells. RT-PCR and immunolabeling studies showed that SmMyoD and SmMyoG can efficiently convert these two cell lines into multinucleated myotubes which expressed differentiated muscle markers. The levels of myogenic induction by SmMyoD and SmMyoG were comparable to those obtained with mouse MRF homologs. Furthermore, SmMyoD and SmMyoG proteins were able to induce mouse MyoD and myogenin in C3H/10T1/2 cells. We conclude that S. macrurus MRFs are functionally conserved as they can transcriptionally activate skeletal muscle gene expression and induce the myogenic program in mammalian non-muscle cells. Hence, these data suggest that the partial muscle phenotype of electrocytes is not likely due to differences in the MRF-dependent transcriptional program between skeletal muscle and electric organ.

Inhibition of mammalian muscle differentiation by regeneration blastema extract of Sternopygus macrurus.

Tissue regeneration through stem cell activation and/or cell dedifferentiation is widely distributed across the animal kingdom. By comparison, regeneration in mammals is poor and this may reflect a limited dedifferentiation potential of mature cells. Because mammalian myotubes can dedifferentiate in the presence of newt blastema extract, the present study tested the dedifferentiation induction capability of the blastema from the teleost Sternopygus macrurus (SmBE). Our in vitro data showed that SmBE did not induce cell cycle reentry of myonuclei in myotubes. Instead, SmBE caused myotubes to detach and time-lapse imaging analyses characterized the cellular events before their detachment. Furthermore, SmBE enhanced myoblast proliferation and reversibly inhibited their differentiation. These data suggest the presence of protein factors in SmBE that regulate mammalian muscle physiology and differentiation, but do not support the conservation of a dedifferentiation induction capability by the blastema of S. macrurus.

Expression of myogenic regulatory factors in the muscle-derived electric organ of Sternopygus macrurus.

In most groups of electric fish, the current-producing cells of electric organs (EOs) derive from striated muscle fibers but retain some phenotypic characteristics of their precursor muscle cells. Given the role of the MyoD family of myogenic regulatory factors (MRFs) in the transcriptional activation of the muscle program in vertebrates, we examined their expression in the electrocytes of the gymnotiform Sternopygus macrurus. We estimated the number of MRF genes in the S. macrurus genome and our Southern blot analyses revealed a single MyoD, myogenin, myf5 and MRF4 gene. Quantitative RT-PCR showed that muscle and EO transcribe all MRF genes. With the exception of MyoD, the endogenous levels of myogenin, myf5 and MRF4 transcripts in electrocytes were greater than those detected in muscle fibers. These data indicate that MRF expression levels are not sufficient to predict the level to which the muscle program is manifested. Qualitative expression analysis of MRF co-regulators MEF2C, Id1 and Id2 also revealed these genes not to be unique to either muscle or EO, and detected similar expression patterns in the two tissues. Therefore, the partial muscle program of the EO is not associated with a partial expression of MRFs or with apparent distinct levels of some MRF co-factors. In addition, electrical inactivation by spinal cord transection (ST) resulted in the up-regulation of some muscle proteins in electrocytes without an accompanying increase in MRF transcript levels or notable changes in the co-factors MEF2C, Id1 and Id2. These findings suggest that the neural regulation of the skeletal muscle program via MRFs in S. macrurus might differ from that of their mammalian counterparts. Together, these data further our understanding of the molecular processes involved in the plasticity of the vertebrate skeletal muscle program that brings about the muscle-like phenotype of the non-contractile electrogenic cells in S. macrurus.

Evidence of post-transcriptional regulation in the maintenance of a partial muscle phenotype by electrogenic cells of S. macrurus.

Electrocytes, the current-producing cells of electric organs (EOs) in electric fish, are unique in that they derive from striated muscle and they possess biochemical characteristics of both muscle and non-muscle cells. In the freshwater teleost Sternopygus macrurus, electrocytes are multinucleated cells that do not contract yet retain expression of some proteins common to skeletal muscle cells. Given the role that transcriptional regulation plays in the activation of the myogenic program in vertebrates, we examined the expression patterns of several genes associated with multiple functions of skeletal muscle in mature electrocytes of S. macrurus. Our expression analyses detected transcripts for alpha-actin, alpha-acetylcholine (ACh) receptor (alpha-AChR), desmin, muscle creatine kinase (MCK), myosin heavy chain (MHC) isoforms, titin, tropomyosin, and troponin-T genes in the EO. However, immunolabeling studies revealed that electrocytes do not contain MCK, MHCs, or tropomyosin or troponin-T proteins. These results underscore the contribution of gene regulatory mechanisms in the maintenance of the muscle-like phenotype of EO that may be transcriptional-independent. We also report the classification and frequency of distinct transcripts from a random selection of 420 clones from an EO cDNA library. This is the first characterization of expressed genes in an EO, and it is an important step toward identifying mechanisms that affect different muscle protein systems for the evolution of highly specialized noncontractile tissues. Evidence of post-transcriptional regulation in the maintenance of a partial muscle phenotype by electrogenic cells of S. macrurus.

Distribution of Kv1-like potassium channels in the electromotor and electrosensory systems of the weakly electric fish Apteronotus leptorhynchus.

The electromotor and electrosensory systems of the weakly electric fish Apteronotus leptorhynchus are model systems for studying mechanisms of high-frequency motor pattern generation and sensory processing. Voltage-dependent ionic currents, including low-threshold potassium currents, influence excitability of neurons in these circuits and thereby regulate motor output and sensory filtering. Although Kv1-like potassium channels are likely to carry low-threshold potassium currents in electromotor and electrosensory neurons, the distribution of Kv1 alpha subunits in A. leptorhynchus is unknown. In this study, we used immunohistochemistry with six different antibodies raised against specific mammalian Kv1 alpha subunits (Kv1.1-Kv1.6) to characterize the distribution of Kv1-like channels in electromotor and electrosensory structures. Each Kv1 antibody labeled a distinct subset of neurons, fibers, and/or dendrites in electromotor and electrosensory nuclei. Kv1-like immunoreactivity in the electrosensory lateral line lobe (ELL) and pacemaker nucleus are particularly relevant in light of previous studies suggesting that potassium currents carried by Kv1 channels regulate neuronal excitability in these regions. Immunoreactivity of pyramidal cells in the ELL with several Kv1 antibodies is consistent with Kv1 channels carrying low-threshold outward currents that regulate spike waveform in these cells (Fernandez et al., J Neurosci 2005;25:363-371). Similarly, Kv1-like immunoreactivity in the pacemaker nucleus is consistent with a role of Kv1 channels in spontaneous high-frequency firing in pacemaker neurons. Robust Kv1-like immunoreactivity in several other structures, including the dorsal torus semicircularis, tuberous electroreceptors, and the electric organ, indicates that Kv1 channels are broadly expressed and are likely to contribute significantly to generating the electric organ discharge and processing electrosensory inputs.

Reinnervation of the rat levator ani muscle after neonatal denervation.

After axonal injury on postnatal day 14 (P14), but not P21, motoneurons in the spinal nucleus of the bulbocavernosus (SNB) do not display their normal response to circulating testosterone levels. This could result from a permanent disruption of communication between motoneurons and their testosterone-sensitive target muscles. We assessed the extent of reinnervation of one of these target muscles, the levator ani (LA) muscle, 5 months after the pudendal nerve was cut either on P14 or P21. The number of motoneurons innervating the LA in control and nerve cut animals was determined using retrograde labeling procedures. Functional recovery of the LA muscle was determined via the testing of its in situ contractile properties. Compared to control muscles, reinnervated LA muscles were smaller, had fewer muscle fibers, generated a lower maximum tetanic tension, and were more fatigable. In spite of the fact that fewer motoneurons reinnervated the LA muscle after nerve cut on P14 than on P21, there were no differences in the weight or contractile properties of the LA muscle between these two groups. These data suggest that motoneurons that survived injury on P14 innervated more muscle fibers than normal and exhibited a similar ability to functionally reinnervate the target muscle as those motoneurons that survived injury on P21.

Transcription of MyoD and myogenin in the non-contractile electrogenic cells of the weakly electric fish, Sternopygus macrurus.

The MyoD family of basic helix-loop-helix (bHLH) myogenic regulatory factors (MRFs) are transcriptional activators of skeletal muscle gene expression and are pivotal in inducing the full myogenic program. The expression of these factors after muscle differentiation is complete and the mechanism by which they modulate (or maintain) the muscle phenotype is less well understood. The myogenically derived electric organ (EO) of the electric fish Sternopygus macrurus is an excellent model to address this question. The electrocytes, i.e., the electrogenic cells of the EO, are not contractile but they do retain some muscle proteins. In order to examine the molecular regulatory pathways that control the muscle-to-electrocyte cell conversion, we have cloned the MyoD and myogenin cDNAs from S. macrurus. Clustal-based alignments showed that the functional domains observed in mammalian MyoD and myogenin are highly conserved in these MRF homologs. Expression analyses revealed that mature electrocytes, which retain the muscle proteins dystrophin, desmin, acetylcholine receptors (AChRs), alpha-actin, and alpha-actinin, also transcribe the MyoD and myogenin genes. RT-PCR studies confirmed that expression of these MRFs is confined to the myogenic lineage. Surprisingly, the levels of MyoD and myogenin transcripts in skeletal muscle and EO could not be used to predict the level to which a cell manifests the muscle program. We conclude that expression of multiple MRFs is not sufficient to induce non-contractile cells to fully express the skeletal muscle program. These data also suggest that the MRF transcriptional program in S. macrurus may be distinct from MRF-dependent myogenesis in other vertebrate systems.

Skeletal muscle transformation into electric organ in S. macrurus depends on innervation.

The cells of the electric organ, called electrocytes, of the weakly electric fish Sternopygus macrurus derive from the fusion of mature fast muscle fibers that subsequently disassemble and downregulate their sarcomeric components. Previously, we showed a reversal of the differentiated state of electrocytes to that of their muscle fiber precursors when neural input is eliminated. The dependence of the mature electrocyte phenotype on neural input led us to test the hypothesis that innervation is also critical during formation of electrocytes. We used immunohistochemical analyses to examine the regeneration of skeletal muscle and electric organ in the presence or absence of innervation. We found that blastema formation is a nerve-dependent process because regeneration was minimal when tail amputation and denervation were performed at the same time. Denervation at the onset of myogenesis resulted in the differentiation of both fast and slow muscle fibers. These were fewer in number, but in a spatial distribution similar to controls. However, in the absence of innervation, fast muscle fibers did not progress beyond the formation of closely apposed clusters, suggesting that innervation is required for their fusion and subsequent transdifferentiation into electrocytes. This study contributes further to our knowledge of the influence of innervation on cell differentiation in the myogenic lineage.