Peroxisomes and the endoplasmic reticulum (ER) cooperate in cellular lipid metabolism. They form membrane contacts through interaction of the peroxisomal membrane protein ACBD5 (acyl-coenzyme A–binding domain protein 5) and the ER-resident protein VAPB (vesicle-associated membrane protein–associated protein B). ACBD5 binds to the major sperm protein domain of VAPB via its FFAT-like (two phenylalanines [FF] in an acidic tract) motif. However, molecular mechanisms, which regulate formation of these membrane contact sites, are unknown. Here, we reveal that peroxisome–ER associations via the ACBD5-VAPB tether are regulated by phosphorylation. We show that ACBD5-VAPB binding is phosphatase-sensitive and identify phosphorylation sites in the flanking regions and core of the FFAT-like motif, which alter interaction with VAPB—and thus peroxisome–ER contact sites—differently. Moreover, we demonstrate that GSK3β (glycogen synthase kinase-3 β) regulates this interaction. Our findings reveal for the first time a molecular mechanism for the regulation of peroxisome–ER contacts in mammalian cells and expand the current model of FFAT motifs and VAP interaction.

Stem cells (SCs) receive inductive cues from the surrounding microenvironment and cells. Limited molecular evidence has connected tissue-specific mesenchymal stem cells (MSCs) with mesenchymal transit amplifying cells (MTACs). Using mouse incisor as the model, we discover a population of MSCs neibouring to the MTACs and epithelial SCs. With Notch signaling as the key regulator, we disclose molecular proof and lineage tracing evidence showing the distinct MSCs contribute to incisor MTACs and the other mesenchymal cell lineages. MTACs can feedback and regulate the homeostasis and activation of CL-MSCs through Delta-like 1 homolog (Dlk1), which balances MSCs-MTACs number and the lineage differentiation. Dlk1 ’s function on SCs priming and self-renewal depends on its biological forms and its gene expression is under dynamic epigenetic control. Our findings can be validated in clinical samples and applied to accelerate tooth wound healing, providing an intriguing insight of how to direct SCs towards tissue regeneration.

Tooth eruption is a continuous biological process with dynamic changes at cellular and tissue levels, particularly within the periodontal ligament (PDL). Occlusion completion is a significant physiological landmark of dentition establishment. However, the importance of the involvement of molecular networks engaging in occlusion establishment on the final PDL maturation is still largely unknown. In this study, using rat and mouse molar teeth and a human PDL cell line for RNAseq and proteomic analysis, we systematically screened the key molecular links in regulating PDL maturation before and after occlusion establishment. We discovered Notch, a key molecular pathway in regulating stem cell fate and differentiation, is a major player in the event. Intercepting the Notch pathway by deleting its key canonical transcriptional factor, RBP-Jkappa, using a conditional knockout strategy in the mice delayed PDL maturation. We also identified that Lamin A, a cell nuclear lamina member, is a unique marker of PDL maturation, and its expression is under the control of Notch signaling. Our study therefore provides a deep insight of how PDL maturation is regulated at the molecular level, and we expect the outcomes to be applied for a better understanding of the molecular regulation networks in physiological conditions such as tooth eruption and movement and also for periodontal diseases.

Peroxisomes and the endoplasmic reticulum (ER) cooperate in cellular lipid metabolism. They form membrane contacts through interaction of the peroxisomal membrane protein ACBD5 [acyl-coenzyme A-binding domain protein 5] and the ER-resident protein VAPB [vesicle-associated membrane protein-associated protein B]. ACBD5 binds to the major sperm protein domain of VAPB via its FFAT-like [two phenylalanines (FF) in an acidic tract] motif. However, molecular mechanisms, which regulate formation of these membrane contact sites, are unknown. Here, we reveal that peroxisome-ER associations via the ACBD5-VAPB tether are regulated by phosphorylation. We show that ACBD5-VAPB binding is phosphatase-sensitive and identify phosphorylation sites in the flanking regions and core of the FFAT-like motif, which alter interaction with VAPB and thus, peroxisome-ER contact sites differently. Moreover, we demonstrate that GSK3β [glycogen synthase kinase-3 beta] regulates this interaction. Our findings reveal for the first time a molecular mechanism for the regulation of peroxisome-ER contacts in mammalian cells and expand the current model of FFAT motifs and VAP interaction.SUMMARYKors et al. reveal that peroxisome-ER associations via the ACBD5-VAPB tether are regulated by phosphorylation and GSK3β in mammalian cells. Phosphorylation sites in the FFAT-like motif of ACBD5 affect the binding to VAPB and thus, peroxisome-ER contact sites, differently.