Planarian stem cells sense the identity of the missing pharynx to launch its targeted regeneration

In order to regenerate tissues successfully, stem cells must detect injuries and restore missing cell types through largely unknown mechanisms. Planarian flatworms have an extensive stem cell population responsible for regenerating any organ after amputation. Here, we compare planarian stem cell responses to different injuries by either amputation of a single organ, the pharynx, or removal of tissues from other organs by decapitation. We find that planarian stem cells adopt distinct behaviors depending on what tissue is missing to target progenitor and tissue production towards missing tissues. Loss of non-pharyngeal tissues only increases non-pharyngeal progenitors, while pharynx removal selectively triggers division and expansion of pharynx progenitors. By pharmacologically inhibiting either mitosis or activation of the MAP kinase ERK, we identify a narrow window of time during which stem cell division and ERK signaling produces pharynx progenitors necessary for regeneration. These results indicate that planarian stem cells can tailor their output to match the regenerative needs of the animal.

The Diversity of Muscles and Their Regenerative Potential across Animals

Cells with contractile functions are present in almost all metazoans, and so are the related processes of muscle homeostasis and regeneration. Regeneration itself is a complex process unevenly spread across metazoans that ranges from full-body regeneration to partial reconstruction of damaged organs or body tissues, including muscles. The cellular and molecular mechanisms involved in regenerative processes can be homologous, co-opted, and/or evolved independently. By comparing the mechanisms of muscle homeostasis and regeneration throughout the diversity of animal body-plans and life cycles, it is possible to identify conserved and divergent cellular and molecular mechanisms underlying muscle plasticity. In this review we aim at providing an overview of muscle regeneration studies in metazoans, highlighting the major regenerative strategies and molecular pathways involved. By gathering these findings, we wish to advocate a comparative and evolutionary approach to prompt a wider use of “non-canonical” animal models for molecular and even pharmacological studies in the field of muscle regeneration.

Cell proliferation dynamics in regeneration of the operculum head appendage in the annelid Pomatoceros lamarckii

Regeneration of lost or damaged appendages is a widespread and ecologically important ability in the animal kingdom, and also of great significance to developing regenerative medicine. The operculum of serpulid polychaetes is one among the many diverse appendages found in the lophotrochozoan superphylum, a clade hitherto understudied with respect to the mechanisms of appendage regeneration. In this study, we establish the normal time course of opercular regeneration in the serpulid Pomatoceros lamarckii and describe cell proliferation patterns in the regenerating opercular filament. The P. lamarckii operculum regenerates through a rapid and consistent series of morphogenetic events. Based on 5-bromo-2'-deoxyuridine (BrdU) labeling and anti-phosphohistone H3 immunohistochemistry, opercular regeneration appears to be a mixture of an early morphallactic stage, and a later phase characterized by widespread proliferative activity within the opercular filament. Tracking residual pigmentation suggests that the distal part of the stump gives rise to the most distal structures of the operculum via morphallactic remodeling, whereas more proximal structures are derived from the proximal stump. Our work underscores the diversity of regenerative strategies employed by animals and introduces P. lamarckii as an emerging model of appendage regeneration.