Multiciliated Cells: Rise and Fall of the Deuterosomes

RBL2 represses the transcriptional activity of Multicilin to inhibit multiciliogenesis

A core pathophysiologic feature underlying many respiratory diseases is multiciliated cell dysfunction, leading to inadequate mucociliary clearance. Due to the prevalence and highly variable etiology of mucociliary dysfunction in respiratory diseases, it is critical to understand the mechanisms controlling multiciliogenesis that may be targeted to restore functional mucociliary clearance. Multicilin, in a complex with E2F4, is necessary and sufficient to drive multiciliogenesis in airway epithelia, however this does not apply to all cell types, nor does it occur evenly across all cells in the same cell population. In this study we further investigated how co-factors regulate the ability of Multicilin to drive multiciliogenesis. Combining data in mouse embryonic fibroblasts and human bronchial epithelial cells, we identify RBL2 as a repressor of the transcriptional activity of Multicilin. Knockdown of RBL2 in submerged cultures or phosphorylation of RBL2 in response to apical air exposure, in the presence of Multicilin, allows multiciliogenesis to progress. These data demonstrate a dynamic interaction between RBL2 and Multicilin that regulates the capacity of cells to differentiate and multiciliate. Identification of this mechanism has important implications for facilitating MCC differentiation in diseases with impaired mucociliary clearance.

RBL2 represses the transcriptional activity of Multicilin to inhibit multiciliogenesis

A core pathophysiologic feature underlying many respiratory diseases is multiciliated cell dysfunction, leading to inadequate mucociliary clearance. Due to the prevalence and highly variable etiology of mucociliary dysfunction in respiratory diseases, it is critical to understand the mechanisms controlling multiciliogenesis that may be targeted to restore functional mucociliary clearance. Multicilin, in a complex with E2F4, is necessary and sufficient to drive multiciliogenesis in airway epithelia, however this does not apply to all cell types, nor does it occur evenly across all cells in the same cell population. In this study we further investigated how co-factors regulate the ability of Multicilin to drive multiciliogenesis. Combining data in mouse embryonic fibroblasts and human bronchial epithelial cells, we identify RBL2 as a repressor of the transcriptional activity of Multicilin. Knockdown of RBL2 in submerged cultures or phosphorylation of RBL2 in response to apical air exposure, in the presence of Multicilin, allows multiciliogenesis to progress. These data demonstrate a dynamic interaction between RBL2 and Multicilin that regulates the capacity of cells to differentiate and multiciliate. Identification of this mechanism has important implications for facilitating MCC differentiation in diseases with impaired mucociliary clearance.

Temporal Whole-Transcriptomic Analysis of Characterized In Vitro and Ex Vivo Primary Nasal Epithelia

Air-liquid interface (ALI) cell culture of primary airway progenitors enables the differentiation and recapitulation of a pseudostratified epithelium in vitro, providing a highly useful tool for researching respiratory health and disease. Previous studies into gene expression in ALI-cultures compared to ex vivo nasal brushings have been limited in the number of time-points and/or the number of genes studied. In this study physiological and global transcriptomic changes were assessed in an extended in vitro 63-day human healthy nasal epithelium ALI-culture period and compared to ex vivo nasal brushing samples. Ex vivo nasal brushing samples formed distinct transcriptome clusters to in vitro ALI-cultured nasal epithelia, with from day 14 onwards ALI samples best matching the ex vivo samples. Immune response regulation genes were not expressed in the in vitro ALI-culture compared to the ex vivo nasal brushing samples, likely because the in vitro cultures lack an airway microbiome, lack airborne particles stimulation, or did not host an immune cell component. This highlights the need for more advanced co-cultures with immune cell representation to better reflect the physiological state. During the first week of ALI-culture genes related to metabolism and proliferation were increased. By the end of week 1 epithelial cell barrier function plateaued and multiciliated cell differentiation started, although widespread ciliation was not complete until day 28. These results highlight that time-points at which ALI-cultures are harvested for research studies needs to be carefully considered to suit the purpose of investigation (transcriptomic and/or functional analysis).

Bi-allelic mutations in MCIDAS and CCNO cause human infertility associated with abnormal gamete transport

Reduced generation of multiple motile cilia (RGMC) and the consequent primary ciliary dyskinesia (PCD) cause infertility due to a substantial reduction in the number of multiciliated cells (MCCs) in the efferent ducts (EDs)/oviducts. MCIDAS acts upstream of CCNO to regulate the biogenesis of basal bodies (BBs); therefore, both genes play a vital role in the multiciliogenesis of the reproductive tract epithelium. In this study, whole-exome sequencing was performed to identify the causative genes in 10 unrelated infertile patients with PCD: seven males and three females. Notably, homozygous frameshift mutations in MCIDAS (c.186dupT, p.Pro63Serfs*22) and CCNO (c.262_263insGGCCC, p.Gln88Argfs*8) were identified in one male and one female participant from two unrelated consanguineous families. Haematoxylin-eosin staining/scanning electron microscopy revealed abnormal MCCs in the mutated EDs/oviducts. Furthermore, transmission electron microscopy revealed significantly reduced BBs. Immunofluorescence staining showed the absence of MCIDAS and CCNO signals in the affected tissues and confirmed that MCIDAS acts upstream of CCNO in the context of multiciliogenesis in the reproductive tract epithelium. In vitro fertilization (IVF)/intracytoplasmic sperm injection (ICSI) was successful, with a positive pregnancy outcome in both MCIDAS- and CCNO-mutated patients. Our results support the use of IVF/ICSI interventions to treat infertility due to RGMC in couples.