Cyclin O controls entry into the cell-cycle variant required for multiciliated cell differentiation

mTOR controls ependymal cell differentiation by targeting the alternative cell cycle and centrosomal proteins

Ependymal cells are multiciliated glial cells lining the ventricles of the mammalian brain. Their differentiation from progenitor cells involves cell enlargement and progresses through centriole amplification phases and ciliogenesis. These phases are accompanied by the sharp up-regulation of mTOR Complex 1 activity (mTORC1), a master regulator of macromolecule biosynthesis and cell growth, whose function in ependymal cell differentiation is unknown. We demonstrate that mTORC1 inhibition by rapamycin preserves the progenitor pool by reinforcing quiescence and preventing alternative cell cycle progression for centriole amplification. Overexpressing E2F4 and MCIDAS circumvents mTORC1-regulated processes, enabling centriole amplification despite rapamycin, and enhancing mTORC1 activity through positive feedback. Acute rapamycin treatment in multicentriolar cells during the late phases of differentiation causes centriole regrouping, indicating a direct role of mTORC1 in centriole dynamics. By phosphoproteomic and phosphomutant analysis, we reveal that the mTORC1-mediated phosphorylation of GAS2L1, a centrosomal protein that links actin and microtubule cytoskeletons, participates in centriole disengagement. This multilayered and sequential control of ependymal development by mTORC1, from the progenitor pool to centriolar function, has implications for pathophysiological conditions like aging and hydrocephalus-prone genetic diseases.

Mucosal Immunity: Lessons from the Lower Respiratory and Small Intestinal Epithelia

Mucosal epithelia represent a diverse group of tissues that function as a barrier against the external environment and exert a wide variety of tissue-specific secondary functions. This review focuses on the lower respiratory tract and small intestinal epithelia, which serve as two distinct sites within the body with respect to their physiological functions. This review provides an overview of their physiology, including both physiological and mechanical defense systems, and their immune responses, which allow both tissues to tolerate commensal organisms while mounting a response against potential pathogens. By highlighting the commonalities and differences across the two tissue types, opportunities to learn from these tissues emerge, which can inform the development of novel therapeutic strategies that harness the unique properties of mucosal epithelia.

Mucociliary cell type compositions - bridging the gap between genes and emergent tissue functions

When multiple cell types are brought together to form a tissue-specific collective, the combination of cell functions and cell-cell interactions leads to novel behaviors and properties beyond the simple addition of individual features, often referred to as emergent tissue functions. During evolution, functional adaptations in organs are significantly influenced by changes in cell type compositions, and in diseases, aberrations in cell type compositions result in impaired organ functions. Investigating the mechanisms that regulate cell type compositions could elucidate an important organizational meta-level that bridges gene functions and cellular features de facto facilitating the emergence of collective cell behaviors and novel tissue functions. Due to their unique evolutionary positioning and diverse functions, mucociliary epithelia could provide an optimal system to unravel principle mechanisms of adaptations in cell type compositions that facilitate the evolution of new or optimization of existing tissue functions, and could reveal novel entry points to counteract human diseases. An integrative investigation of signaling, transcriptional, epigenetic and morphogenetic mechanisms across a broad range of mucociliary tissues with different specialized cells and cell type compositions can help us to connect gene functions and contributions to self-organized behaviors in cell collectives determining emergent tissue functions. Taking such route moving forward has the potential to unravel novel principles in mucociliary self-organization and to reveal broadly applicable principles underlying the generation and modification of emergent tissue functions across species and organ systems.