Somatic regulation of female germ cell regeneration and development in planarians

Female germ cells develop into oocytes, with the capacity for totipotency. In most animals, these remarkable cells are specified during development and cannot be regenerated. By contrast, planarians, known for their regenerative prowess, can regenerate germ cells. To uncover mechanisms required for female germ cell development and regeneration, we generated gonad-specific transcriptomes and identified genes whose expression defines progressive stages of female germ cell development. Strikingly, early female germ cells share molecular signatures with the pluripotent stem cells driving planarian regeneration. We uncovered spatial heterogeneity within somatic ovarian cells and found that a regionally enriched FoxL homolog is required for oocyte differentiation, but not specification, suggestive of functionally distinct somatic compartments. Unexpectedly, a neurotransmitter-biosynthetic enzyme, AADC, is also expressed in somatic gonadal cells, and plays opposing roles in female and male germ cell development. Thus, somatic gonadal cells deploy conserved factors to regulate germ cell development and regeneration in planarians.

PI3K Plays an Essential Role in Planarian Regeneration and Tissue Maintenance

Phosphatidylinositol 3-kinase (PI3K) signaling plays a central role in various biological processes, and its abnormality leads to a broad spectrum of human diseases, such as cancer, fibrosis, and immunological disorders. However, the mechanisms by which PI3K signaling regulates the behavior of stem cells during regeneration are poorly understood. Planarian flatworms possess abundant adult stem cells (called neoblasts) allowing them to develop remarkable regenerative capabilities, thus the animals represent an ideal model for studying stem cells and regenerative medicine in vivo. In this study, the spatiotemporal expression pattern of Djpi3k, a PI3K ortholog in the planarian Dugesia japonica, was investigated and suggests its potential role in wound response and tissue regeneration. A loss-of-function study was conducted using small molecules and RNA interference technique, providing evidence that PI3K signaling is required for blastema regrowth and cilia maintenance during planarian regeneration and homeostasis. Interestingly, the mitotic and apoptotic responses to amputation are substantially abated in PI3K inhibitor-treated regenerating animals, while knockdown of Djpi3k alleviates the mitotic response and postpones the peak of apoptotic cell death, which may contribute to the varying degrees of regenerative defects induced by the pharmacological and genetic approaches. These observations reveal novel roles for PI3K signaling in the regulation of the cellular responses to amputation during planarian regeneration and provide insights for investigating the disease-related genes in the regeneration-competent organism in vivo.

m6A-mediated Cell-cell Communication Controls Planarian Regeneration

Regeneration is the regrowth of damaged tissues or organs, a vital mechanism responding to damages from primitive organisms to higher mammals. Planarian possesses active whole-body regenerative capability owning to its vast reservoir of adult stem cells, neoblasts, thus provides an ideal model to delineate the underlying mechanisms for regeneration. N6-methyladenosine (m6A) regulates stem cell renewal and differentiation. However, how m6A controls regeneration at whole-organism level remains largely unknown. Here, we demonstrate that the depletion of m6A methyltransferase regulatory subunit wtap abolishes planarian regeneration, through regulating cell-cell communication and cell cycle. scRNA-Seq analysis unveils that the wtap knockdown induces a unique type of neural progenitor-like cells (NP-like cells), characterized by specific expression of the cell-cell communication ligand grn. Intriguingly, the depletion of m6A-modified transcripts grn/cdk9 (or cdk7) axis rescues the defective regeneration of planarian without wtap. Overall, our study reveals an indispensable role of m6A-dependent cell-cell communication essential for whole-organism regeneration.

Protein Core Fucosylation Regulates Planarian Head Regeneration via Neoblast Proliferation

Protein glycosylation is an important posttranslational modification that plays a crucial role in cellular function. However, its biological roles in tissue regeneration remain interesting and primarily ambiguous. In this study, we profiled protein glycosylation during head regeneration in planarian Dugesia japonica using a lectin microarray. We found that 6 kinds of lectins showed increased signals and 16 kinds showed decreased signals. Interestingly, we found that protein core fucosylation, manifested by Lens culinaris agglutinin (LCA) staining, was significantly upregulated during planarian head regeneration. Lectin histochemistry indicated that the LCA signal was intensified within the wound and blastemal areas. Furthermore, we found that treatment with a fucosylation inhibitor, 2F-peracetyl-fucose, significantly retarded planarian head regeneration, while supplement with L-fucose could improve DjFut8 expression and stimulate planarian head regeneration. In addition, 53 glycoproteins that bound to LCA were selectively isolated by LCA-magnetic particle conjugates and identified by LC-MS/MS, including the neoblast markers DjpiwiA, DjpiwiB, DjvlgA, and DjvlgB. Overall, our study provides direct evidence for the involvement of protein core fucosylation in planarian regeneration.