CD133/Prom1 marks proximal mouse oviduct epithelial progenitors and adult epithelial cells with a low generative capacity

The epithelium lining the oviduct or fallopian tube consists of multiciliated and secretory cells, which support fertilization and preimplantation development, however, its homeostasis remains poorly understood. CD133/Prom1 expression has been used as a marker to identify adult stem cell populations in various organs and often associated with cancer cells that have stem-like properties. Using an antibody targeted to CD133 and a Cre recombinase-based lineage tracing strategy, we found that CD133/Prom1 expression is not associated with a stem/progenitor population in the oviduct but marked predominantly multiciliated cells with a low generative capacity. Additionally, we have shown that CD133 is disparately localised along the oviduct during neonatal development, and that Prom1 expressing secretory cells in the ampulla rapidly transitioned to multiciliated cells and progressively migrated to the ridge of epithelial folds.

A WNT4- and DKK3-driven canonical to noncanonical Wnt signaling switch controls multiciliogenesis

Multiciliated cells contain hundreds of cilia whose directional movement powers the mucociliary clearance of the airways, a vital host defense mechanism. Multiciliated cell specification requires canonical Wnt signaling, which then must be turned off. Next, ciliogenesis and polarized ciliary orientation are regulated by noncanonical Wnt/planar cell polarity (Wnt/PCP) signaling. The mechanistic relationship between the Wnt pathways is unknown. We show that DKK3, a secreted canonical Wnt regulator and WNT4, a noncanonical Wnt ligand act together to facilitate a canonical to noncanonical Wnt signaling switch during multiciliated cell formation. In primary human airway epithelial cells, DKK3 and WNT4 CRISPR knockout blocks, whereas ectopic expression promotes, multiciliated cell formation by inhibiting canonical Wnt signaling. Wnt4 and Dkk3 single-knockout mice also display defective ciliated cells. DKK3 and WNT4 are co-secreted from basal stem cells and act directly on multiciliated cells via KREMEN1 and FZD6, respectively. We provide a novel mechanism that links specification to cilium biogenesis and polarization for proper multiciliated cell formation.

Esrrγa regulates nephron and ciliary development by controlling prostaglandin synthesis

Cilia are essential for the ontogeny and function of many tissues, including the kidney. Here, we report that transcription factor ERRγ ortholog estrogen related receptor gamma a (Esrrγa) is essential for renal cell fate choice and ciliogenesis in zebrafish. esrrγa deficiency altered proximodistal nephron patterning, decreased the multiciliated cell populace and disrupted ciliogenesis in the nephron, Kupffer's vesicle and otic vesicle. These phenotypes were consistent with interruptions in prostaglandin signaling, and we found that ciliogenesis was rescued by PGE2 or the cyclooxygenase enzyme Ptgs1. Genetic interaction revealed that peroxisome proliferator-activated receptor gamma, coactivator 1 alpha (Ppargc1a), which acts upstream of Ptgs1-mediated prostaglandin synthesis, has a synergistic relationship with Esrrγa in the ciliogenic pathway. These ciliopathic phenotypes were also observed in mice lacking renal epithelial cell (REC) ERRγ, where significantly shorter cilia formed on proximal and distal tubule cells. Decreased cilia length preceded cyst formation in REC-ERRγ knockout mice, suggesting that ciliary changes occur early during pathogenesis. These data position Esrrγa as a novel link between ciliogenesis and nephrogenesis through regulation of prostaglandin signaling and cooperation with Ppargc1a.

Notch signaling mediates olfactory multiciliated cell specification

Epithelial multiciliated cells (MCCs) use motile cilia to direct external fluid flow, the disruption of which is associated with human diseases in a broad array of organs such as those in the respiratory, reproductive, and renal systems. While many of the signaling pathways that regulate MCC formation in these organ systems have been identified, similar characterization of MCC differentiation in the developing olfactory system has been lacking. Here, using live cell tracking, targeted cell ablation, and temporally-specific inhibition of the Notch signaling pathway, we identify the earliest time window of zebrafish olfactory MCC (OMCC) differentiation and demonstrate these cells' derivation from peridermal cells. We also describe regionally segregated Notch signaling across time points of rapid OMCC differentiation and show that Notch signaling downregulation yields an increase in OMCCs, suggesting that OMCC fate is normally repressed in a region-specific manner during olfactory development. Finally, we describe Notch signaling's regulation of the differentiation/ciliogenesis-associated genes foxj1a and foxj1b. Taken together, these findings provide new insights into the origins and developmental programming of OMCCs in vivo.

A role for Cep70 in centriole amplification in multiciliated cells

Centriole amplification in multiciliated cells occurs in a pseudo-cell cycle regulated process that typically utilizes a poorly characterized molecularly dense structure called the deuterosome. We identified the centrosomal protein Cep70 as a novel deuterosome-associated protein that forms a complex with other deuterosome proteins, CCDC78 and Deup1. Cep70 dynamically associates with deuterosomes during centriole amplification in the ciliated epithelia of Xenopus embryos. Cep70 is not found in nascent deuterosomes prior to amplification. However, it becomes localized at deuterosomes at the onset of centriole biogenesis and remains there after the completion of centriole amplification. Deuterosome localization requires a conserved C-terminal "Cep70" motif. Depletion of Cep70 using morpholino oligos or CRISPR/Cas9 editing in F0 embryos leads to a severe decrease in centriole formation in both endogenous MCCs, as well as ectopically induced MCCs. Consistent with a decrease in centrioles, endogenous MCCs have defects in the process of radial intercalation. We propose that Cep70 represents a novel regulator of centriole biogenesis in MCCs.

Mcidas mutant mice reveal a two-step process for the specification and differentiation of multiciliated cells in mammals

Motile cilia on multiciliated cells (MCCs) function in fluid clearance over epithelia. Studies with Xenopus embryos and individuals with the congenital respiratory disorder reduced generation of multiple motile cilia (RGMC), have implicated the nuclear protein MCIDAS (MCI), in the transcriptional regulation of MCC specification and differentiation. Recently, a paralogous protein, geminin coiled-coil domain containing (GMNC), was also shown to be required for MCC formation. Surprisingly, in contrast to the presently held view, we find that Mci mutant mice can specify MCC precursors. However, these precursors cannot produce multiple basal bodies, and mature into single ciliated cells. We identify an essential role for MCI in inducing deuterosome pathway components for the production of multiple basal bodies. Moreover, GMNC and MCI associate differentially with the cell-cycle regulators E2F4 and E2F5, which enables them to activate distinct sets of target genes (ciliary transcription factor genes versus basal body amplification genes). Our data establish a previously unrecognized two-step model for MCC development: GMNC functions in the initial step for MCC precursor specification. GMNC induces Mci expression that drives the second step of basal body production for multiciliation.

Distinct requirements of E2f4 versus E2f5 activity for multiciliated cell development in the zebrafish embryo

Multiciliated cells (MCCs) differentiate arrays of motile cilia that beat to drive fluid flow over epithelia. Recent studies have established two Geminin family coiled-coil containing nuclear regulatory proteins, Gmnc and Multicilin (Mci), in the specification and differentiation of the MCCs. Both Gmnc and Mci are devoid of a DNA binding domain: they regulate transcription by associating with E2f family transcription factors, notably E2f4 and E2f5. Here, we have studied the relative contribution of these two E2f factors in MCC development using the zebrafish embryo, which differentiates MCCs within kidney tubules and the nose. We found that while E2f4 is fully dispensable, E2f5 is essential for MCCs to form in the kidney tubules. Moreover, using a variety of double mutant combinations we show that E2f5 has a more prominent role in MCC development in the zebrafish than E2f4. This contrasts with current evidence from the mouse, where E2f4 seems to be more important. Thus, distinct combinatorial activities of the E2f4 and E2f5 proteins regulate the specification and differentiation of MCCs in zebrafish and mice.

Protein localization screening in vivo reveals novel regulators of multiciliated cell development and function

Multiciliated cells (MCCs) drive fluid flow in diverse tubular organs and are essential for the development and homeostasis of the vertebrate central nervous system, airway and reproductive tracts. These cells are characterized by dozens or hundreds of motile cilia that beat in a coordinated and polarized manner. In recent years, genomic studies have not only elucidated the transcriptional hierarchy for MCC specification but also identified myriad new proteins that govern MCC ciliogenesis, cilia beating and cilia polarization. Interestingly, this burst of genomic data has also highlighted that proteins with no obvious role in cilia do, in fact, have important ciliary functions. Understanding the function of proteins with little prior history of study presents a special challenge, especially when faced with large numbers of such proteins. Here, we define the subcellular localization in MCCs of ∼200 proteins not previously implicated in cilia biology. Functional analyses arising from the screen provide novel links between actin cytoskeleton and MCC ciliogenesis.

Manipulating and Analyzing Cell Type Composition of the Xenopus Mucociliary Epidermis

The Xenopus embryonic epidermis serves as a model to investigate the development, cell biology, and regeneration of vertebrate mucociliary epithelia. Its fast development as well as the ease of manipulation and analysis in this system facilitate novel approaches and sophisticated experiments addressing the principle mechanisms of mucociliary signaling, transcriptional regulation, and morphogenesis. This protocol describes how cell type composition can be manipulated and analyzed, and how mucociliary organoids can be generated and used for "omics"-type of experiments.

Basal bodies across eukaryotes series: basal bodies in the freshwater planarian Schmidtea mediterranea

The freshwater planarian Schmidtea mediterranea has recently emerged as a valuable model system to study basal bodies (BBs) and cilia. Planarians are free-living flatworms that use cilia beating at the surface of their ventral epidermis for gliding along substrates. The ventral epidermis is composed of multiciliated cells (MCCs) that are similar to the MCCs in the respiratory airways, the brain ventricles, and the oviducts in vertebrates. In the planarian epidermis, each cell assembles approximately eighty cilia that beat in a coordinate fashion across the tissue. The BBs that nucleate these cilia all assemble de novo during terminal differentiation of MCCs. The genome of the planarian S. mediterranea has been sequenced and efficient methods for targeting gene expression by RNA interference are available. Defects induced by perturbing the expression of BB proteins can be detected simply by analyzing the locomotion of planarians. BBs are present in large numbers and in predictable orientation, which greatly facilitates analyses by immunofluorescence and electron microscopy. The great ease in targeting gene expression and analyzing associated defects allowed to identify a set of proteins required for BB assembly and function in planarian MCCs. Future technological developments, including methods for transgenic expression in planarians and in related species, will achieve turning free-living flatworms into powerful model systems to study MCCs and the associated human pathologies.

Control of vertebrate core planar cell polarity protein localization and dynamics by Prickle 2

Planar cell polarity (PCP) is a ubiquitous property of animal tissues and is essential for morphogenesis and homeostasis. In most cases, this fundamental property is governed by a deeply conserved set of 'core PCP' proteins, which includes the transmembrane proteins Van Gogh-like (Vangl) and Frizzled (Fzd), as well as the cytoplasmic effectors Prickle (Pk) and Dishevelled (Dvl). Asymmetric localization of these proteins is thought to be central to their function, and understanding the dynamics of these proteins is an important challenge in developmental biology. Among the processes that are organized by the core PCP proteins is the directional beating of cilia, such as those in the vertebrate node, airway and brain. Here, we exploit the live imaging capabilities of Xenopus to chart the progressive asymmetric localization of fluorescent reporters of Dvl1, Pk2 and Vangl1 in a planar polarized ciliated epithelium. Using this system, we also characterize the influence of Pk2 on the asymmetric dynamics of Vangl1 at the cell cortex, and we define regions of Pk2 that control its own localization and those impacting Vangl1. Finally, our data reveal a striking uncoupling of Vangl1 and Dvl1 asymmetry. This study advances our understanding of conserved PCP protein functions and also establishes a rapid, tractable platform to facilitate future in vivo studies of vertebrate PCP protein dynamics.

Mcidas and GemC1 are key regulators for the generation of multiciliated ependymal cells in the adult neurogenic niche

Multiciliated cells are abundant in the epithelial surface of different tissues, including cells lining the walls of the lateral ventricles in the brain and the airway epithelium. Their main role is to control fluid flow and defects in their differentiation are implicated in many human disorders, such as hydrocephalus, accompanied by defects in adult neurogenesis and mucociliary disorder in the airway system. Here we show that Mcidas, which is mutated in human mucociliary clearance disorder, and GemC1 (Gmnc or Lynkeas), previously implicated in cell cycle progression, are key regulators of multiciliated ependymal cell generation in the mouse brain. Overexpression and knockdown experiments show that Mcidas and GemC1 are sufficient and necessary for cell fate commitment and differentiation of radial glial cells to multiciliated ependymal cells. Furthermore, we show that GemC1 and Mcidas operate in hierarchical order, upstream of Foxj1 and c-Myb transcription factors, which are known regulators of ependymal cell generation, and that Notch signaling inhibits GemC1 and Mcidas function. Our results suggest that Mcidas and GemC1 are key players in the generation of multiciliated ependymal cells of the adult neurogenic niche.

Centriole biogenesis and function in multiciliated cells

The use of Xenopus embryonic skin as a model system for the development of ciliated epithelia is well established. This tissue is comprised of numerous cell types, most notably the multiciliated cells (MCCs) that each contain approximately 150 motile cilia. At the base of each cilium lies the centriole-based structure called the basal body. Centriole biogenesis is typically restricted to two new centrioles per cell cycle, each templating from an existing "mother" centriole. In contrast, MCCs are post-mitotic cells in which the majority of centrioles arise "de novo" without templating from a mother centriole, instead, these centrioles nucleate from an electron-dense structure termed the deuterostome. How centriole number is regulated in these cells and the mechanism by which the deuterosome templates nascent centrioles is still poorly understood. Here, we describe methods for regulating MCC cell fate as well as for visualizing and manipulating centriole biogenesis.