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.

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.

Mechanical strain breaks planar symmetry in embryonic epithelia via polarized microtubules.

Mechanical strain can act as a global cue to orient the core planar cell polarity pathway (Fz-PCP) in developing epithelia, but how strain directs a Fz-PCP vector is not known. Here we use live cell imaging of apical microtubules (MTs) and components of the Fz-PCP pathway to analyze epithelial cells in Xenopus embryos as they respond to anisotropic mechanical strain and form a Fz-PCP axis. We find that a Fz-PCP axis can be detected approximately 40 min after the application of strain.

Emi2 enables centriole amplification during multiciliated cell differentiation.

Massive centriole amplification during multiciliated cell (MCC) differentiation is a notable example of organelle biogenesis. This process is thought to be enabled by a derived cell cycle state, but the key cell cycle components required for centriole amplification in MCC progenitors remain poorly defined. Here, we show that () expression is up-regulated and acts in MCC progenitors after cell cycle exit to transiently inhibit anaphase-promoting complex/cyclosome (APC/C) activity.

Rabies in a Dog Imported from Egypt - Kansas, 2019.

Although canine rabies virus variant (CRVV) was successfully eliminated from the United States after approximately 6 decades of vaccination campaigns, licensing requirements, and stray animal control, dogs remain the principal source of human rabies infections worldwide. A rabies vaccination certificate is required for dogs entering the United States from approximately 100 countries with endemic CRVV, including Egypt (1). On February 25, 2019, rabies was diagnosed in a dog imported from Egypt, representing the third canine rabies case imported from Egypt in 4 years (2,3).

Differential Loss of Spinal Interneurons in a Mouse Model of ALS.

Amyotrophic lateral sclerosis (ALS) leads to a loss of specific motor neuron populations in the spinal cord and cortex. Emerging evidence suggests that interneurons may also be affected, but a detailed characterization of interneuron loss and its potential impacts on motor neuron loss and disease progression is lacking. To examine this issue, the fate of V1 inhibitory neurons during ALS was assessed in the ventral spinal cord using the SOD mouse model.

Multicilin and activated E2f4 induce multiciliated cell differentiation in primary fibroblasts.

Multiciliated cells (MCCs) are specialized epithelial cells that project hundreds of motile cilia. To form these cilia, MCCs differentiate by dramatically expanding centriole number, using assembly factors required for centriole duplication during the cell cycle and multiple, novel assembly sites, called the deuterosome. The small coiled-coil protein, Multicilin, acting in a complex with the E2F proteins can initiate multiciliated cell differentiation, but reportedly only in a limited range of epithelial progenitors.

Mechanical Strain Determines Cilia Length, Motility, and Planar Position in the Left-Right Organizer.

The Xenopus left-right organizer (LRO) breaks symmetry along the left-right axis of the early embryo by producing and sensing directed ciliary flow as a patterning cue. To carry out this process, the LRO contains different ciliated cell types that vary in cilia length, whether they are motile or sensory, and how they position their cilia along the anterior-posterior (A-P) planar axis. Here, we show that these different cilia features are specified in the prospective LRO during gastrulation, based on anisotropic mechanical strain that is oriented along the A-P axis, and graded in levels along the medial-lateral axis.

Origin and Segmental Diversity of Spinal Inhibitory Interneurons.

Motor output varies along the rostro-caudal axis of the tetrapod spinal cord. At limb levels, ∼60 motor pools control the alternation of flexor and extensor muscles about each joint, whereas at thoracic levels as few as 10 motor pools supply muscle groups that support posture, inspiration, and expiration. Whether such differences in motor neuron identity and muscle number are associated with segmental distinctions in interneuron diversity has not been resolved.

Rfx2 Stabilizes Foxj1 Binding at Chromatin Loops to Enable Multiciliated Cell Gene Expression.

Cooperative transcription factor binding at cis-regulatory sites in the genome drives robust eukaryotic gene expression, and many such sites must be coordinated to produce coherent transcriptional programs. The transcriptional program leading to motile cilia formation requires members of the DNA-binding forkhead (Fox) and Rfx transcription factor families and these factors co-localize to cilia gene promoters, but it is not clear how many cilia genes are regulated by these two factors, whether these factors act directly or indirectly, or how these factors act with specificity in the context of a 3-dimensional genome. Here, we use genome-wide approaches to show that cilia genes reside at the boundaries of topological domains and that these areas have low enhancer density.

Foxn4 promotes gene expression required for the formation of multiple motile cilia.

Multiciliated cell (MCC) differentiation involves extensive organelle biogenesis required to extend hundreds of motile cilia. Key transcriptional regulators known to drive the gene expression required for this organelle biogenesis are activated by the related coiled-coil proteins Multicilin and Gemc1. Here we identify foxn4 as a new downstream target of Multicilin required for MCC differentiation in Xenopus skin.

Ciliary transcription factors and miRNAs precisely regulate Cp110 levels required for ciliary adhesions and ciliogenesis.

Upon cell cycle exit, centriole-to-basal body transition facilitates cilia formation. The centriolar protein Cp110 is a regulator of this process and cilia inhibitor, but its positive roles in ciliogenesis remain poorly understood. Using we show that Cp110 inhibits cilia formation at high levels, while optimal levels promote ciliogenesis.

Systematic Analysis of CCNO Variants in a Defined Population: Implications for Clinical Phenotype and Differential Diagnosis.

Reduced generation of multiple motile cilia (RGMC) is a novel chronic destructive airway disease within the group of mucociliary clearance disorders with only few cases reported. Mutations in two genes, CCNO and MCIDAS, have been identified as a cause of this disease, both leading to a greatly reduced number of cilia and causing impaired mucociliary clearance. This study was designed to identify the prevalence of CCNO mutations in Israel and further delineate the clinical characteristics of RGMC.

Prdm12 specifies V1 interneurons through cross-repressive interactions with Dbx1 and Nkx6 genes in Xenopus.

V1 interneurons are inhibitory neurons that play an essential role in vertebrate locomotion. The molecular mechanisms underlying their genesis remain, however, largely undefined. Here, we show that the transcription factor Prdm12 is selectively expressed in p1 progenitors of the hindbrain and spinal cord in the frog embryo, and that a similar restricted expression profile is observed in the nerve cord of other vertebrates as well as of the cephalochordate amphioxus.

Mechanical strain determines the axis of planar polarity in ciliated epithelia.

Epithelia containing multiciliated cells align beating cilia along a common planar axis specified by the conserved planar cell polarity (PCP) pathway. Specification of the planar axis is also thought to require a long-range cue to align the axis globally, but the nature of this cue in ciliated and other epithelia remains poorly understood. We examined this issue using the Xenopus larval skin, where ciliary flow aligns to the anterior-posterior (A-P) axis.

MCIDAS mutations result in a mucociliary clearance disorder with reduced generation of multiple motile cilia.

Reduced generation of multiple motile cilia (RGMC) is a rare mucociliary clearance disorder. Affected persons suffer from recurrent infections of upper and lower airways because of highly reduced numbers of multiple motile respiratory cilia. Here we report recessive loss-of-function and missense mutations in MCIDAS-encoding Multicilin, which was shown to promote the early steps of multiciliated cell differentiation in Xenopus.

Multicilin drives centriole biogenesis via E2f proteins.

Multiciliate cells employ hundreds of motile cilia to produce fluid flow, which they nucleate and extend by first assembling hundreds of centrioles. In most cells, entry into the cell cycle allows centrioles to undergo a single round of duplication, but in differentiating multiciliate cells, massive centriole assembly occurs in G0 by a process initiated by a small coiled-coil protein, Multicilin. Here we show that Multicilin acts by forming a ternary complex with E2f4 or E2f5 and Dp1 that binds and activates most of the genes required for centriole biogenesis, while other cell cycle genes remain off.

Mutations in CCNO result in congenital mucociliary clearance disorder with reduced generation of multiple motile cilia.

Using a whole-exome sequencing strategy, we identified recessive CCNO (encoding cyclin O) mutations in 16 individuals suffering from chronic destructive lung disease due to insufficient airway clearance. Respiratory epithelial cells showed a marked reduction in the number of multiple motile cilia (MMC) covering the cell surface. The few residual cilia that correctly expressed axonemal motor proteins were motile and did not exhibit obvious beating defects.

Myb promotes centriole amplification and later steps of the multiciliogenesis program.

The transcriptional control of primary cilium formation and ciliary motility are beginning to be understood, but little is known about the transcriptional programs that control cilium number and other structural and functional specializations. One of the most intriguing ciliary specializations occurs in multiciliated cells (MCCs), which amplify their centrioles to nucleate hundreds of cilia per cell, instead of the usual monocilium. Here we report that the transcription factor MYB, which promotes S phase and drives cycling of a variety of progenitor cells, is expressed in postmitotic epithelial cells of the mouse airways and ependyma destined to become MCCs.

Neural induction and early patterning in vertebrates.

In vertebrates, the development of the nervous system is triggered by signals from a powerful 'organizing' region of the early embryo during gastrulation. This phenomenon--neural induction--was originally discovered and given conceptual definition by experimental embryologists working with amphibian embryos. Work on the molecular circuitry underlying neural induction, also in the same model system, demonstrated that elimination of ongoing transforming growth factor-β (TGFβ) signaling in the ectoderm is the hallmark of anterior neural-fate acquisition.

Bbof1 is required to maintain cilia orientation.

Multiciliate cells (MCCs) are highly specialized epithelial cells that employ hundreds of motile cilia to produce a vigorous directed flow in a variety of organ systems. The production of this flow requires the establishment of planar cell polarity (PCP) whereby MCCs align hundreds of beating cilia along a common planar axis. The planar axis of cilia in MCCs is known to be established via the PCP pathway and hydrodynamic cues, but the downstream steps required for cilia orientation remain poorly defined.

Molecular determinants of lung development.

Development of the pulmonary system is essential for terrestrial life. The molecular pathways that regulate this complex process are beginning to be defined, and such knowledge is critical to our understanding of congenital and acquired lung diseases. A recent workshop was convened by the National Heart, Lung, and Blood Institute to discuss the developmental principles that regulate the formation of the pulmonary system.

Multicilin promotes centriole assembly and ciliogenesis during multiciliate cell differentiation.

Multiciliate cells function prominently in the respiratory system, brain ependyma and female reproductive tract to produce vigorous fluid flow along epithelial surfaces. These specialized cells form during development when epithelial progenitors undergo an unusual form of ciliogenesis, in which they assemble and project hundreds of motile cilia. Notch inhibits multiciliate cell formation in diverse epithelia, but how progenitors overcome lateral inhibition and initiate multiciliate cell differentiation is unknown.