Cytoskeletal architecture and immunocytochemical localization of fodrin in the terminal web of the ciliated epithelial cell

Primary Cilia in Pancreatic β- and α-Cells: Time to Revisit the Role of Insulin-Degrading Enzyme

The primary cilium is a narrow organelle located at the surface of the cell in contact with the extracellular environment. Once underappreciated, now is thought to efficiently sense external environmental cues and mediate cell-to-cell communication, because many receptors, ion channels, and signaling molecules are highly or differentially expressed in primary cilium. Rare genetic disorders that affect cilia integrity and function, such as Bardet-Biedl syndrome and Alström syndrome, have awoken interest in studying the biology of cilium. In this review, we discuss recent evidence suggesting emerging roles of primary cilium and cilia-mediated signaling pathways in the regulation of pancreatic β- and α-cell functions, and its implications in regulating glucose homeostasis.

Unveiling the genetic etiology of primary ciliary dyskinesia: When standard genetic approach is not enough

PURPOSE

Primary ciliary dyskinesia (PCD) is a ciliopathy caused by dysfunction of motile cilia. As there is still no standard PCD diagnostics, the final diagnosis requires a combination of several tests. The genetic screening is a hallmark for the final diagnosis and requires high-throughput techniques, such as whole-exome sequencing (WES). Nevertheless, WES has limitations that may prevent a definitive genetic diagnosis. Here we present a case that demonstrates how the PCD genetic diagnosis may not be trivial.

MATERIALS/METHODS

A child with PCD and situs inversus totalis (designated as Kartagener syndrome (KS)) was subjected to clinical assessments, ultrastructural analysis of motile cilia, extensive genetic evaluation by WES and chromosomal array analysis, bioinformatic analysis, gene expression analysis and immunofluorescence to identify the genetic etiology. His parents and sister, as well as healthy controls were also evaluated.

RESULTS

Here we show that a disease-causing variant in the USP11 gene and copy number variations in CRHR1 and KRT34 genes may be involved in the patient PCD phenotype. None of these genes were previously reported in PCD patients and here we firstly show its presence and immunolocalization in respiratory cells.

CONCLUSIONS

This work highlights how the genetic diagnosis can turn to be rather complex and that combining several approaches may be needed. Overall, our results contribute to increase the understanding of the genetic factors involved in the pathophysiology of PCD/KS, which is of paramount importance to assist the current diagnosis and future development of newer therapies.

Zeta-Tubulin Is a Member of a Conserved Tubulin Module and Is a Component of the Centriolar Basal Foot in Multiciliated Cells

There are six members of the tubulin superfamily in eukaryotes. Alpha- and beta-tubulin form a heterodimer that polymerizes to form microtubules, and gamma-tubulin nucleates microtubules as a component of the gamma-tubulin ring complex. Alpha-, beta-, and gamma-tubulin are conserved in all eukaryotes. In contrast, delta- and epsilon-tubulin are conserved in many, but not all, eukaryotes and are associated with centrioles, although their molecular function is unclear. Zeta-tubulin is the sixth and final member of the tubulin superfamily and is largely uncharacterized. We find that zeta-, epsilon-, and delta-tubulin form an evolutionarily co-conserved module, the ZED module, that has been lost at several junctions in eukaryotic evolution and that zeta- and delta-tubulin are evolutionarily interchangeable. Humans lack zeta-tubulin but have delta-tubulin. In Xenopus multiciliated cells, zeta-tubulin is a component of the basal foot, a centriolar appendage that connects centrioles to the apical cytoskeleton, and co-localizes there with epsilon-tubulin. Depletion of zeta-tubulin results in disorganization of centriole distribution and polarity in multiciliated cells. In contrast with multiciliated cells, zeta-tubulin in cycling cells does not localize to centrioles and is associated with the TRiC/CCT cytoplasmic chaperone complex. We conclude that zeta-tubulin facilitates interactions between the centrioles and the apical cytoskeleton as a component of the basal foot in differentiated cells and propose that the ZED tubulins are important for centriole functionalization and orientation of centrioles with respect to cellular polarity axes.

The mechanics of the primary cilium: an intricate structure with complex function

The primary cilium is a non-motile singular cellular structure that extends from the surface of nearly every cell in the body. The cilium has been shown to play numerous roles in maintaining tissue homeostasis, through regulating signaling pathways and sensing both biophysical and biochemical changes in the extracellular environment. The structural performance of the cilium is paramount to its function as defective cilia have been linked to numerous pathologies. In particular, the cilium has demonstrated a mechanosensory role in tissues such as the kidney, liver, endothelium and bone, where cilium deflection under mechanical loading triggers a cellular response. Understanding of how cilium structure and subsequent mechanical behavior contributes to the roles that cilium plays in regulating cellular behavior is a compelling question, yet is a relatively untouched research area. Recent advances in biophysical measurements have demonstrated the cilium to be a structurally intricate organelle containing an array of load bearing proteins. Furthermore advances in modeling of this organelle have revealed the importance of these proteins at regulating the cilium's mechanosensitivity. Remarkably, the cilium is capable of adapting its mechanical state, altering its length and possibly it's bending resistance, to regulate its mechanosensitivity demonstrating the importance of cilium mechanics in cellular responses. In this review, we introduce the cilium as a mechanosensor; discuss the advances in the mechanical modeling of cilia; explore the structural features of the cilium, which contribute to its mechanics and finish with possible mechanisms in which alteration in structure may affect ciliary mechanics, consequently affecting ciliary based mechanosensing.

Alpha-spectrin in detergent-extracted whole-mount cytoskeletons of chicken embryo heart fibroblasts

The distribution of alpha-spectrin, and its relation to other cytoskeletal structures and to the plasma membrane, was studied in detergent-extracted whole-mount cytoskeletons of chicken embryo heart fibroblasts by using immunogold labelling and electron microscopy (IEM). The cell surface was labelled with gold-conjugated wheat germ agglutinin (WGA-gold), microtubules with anti-tubulin antibodies, and spectrin by using antibodies raised to chicken erythrocyte alpha-spectrin. Additionally, the effect of fixation and drying on the labelling pattern was evaluated. In electron microscopy, a three-dimensional filamentous network was observed in detergent-extracted whole-mount preparations. Filaments of diameter 7-10 nm and 15 nm, microtubules of diameter 30 nm, and filament bundles (40-50 nm in diameter) were seen. In IEM, alpha-spectrin was seen on the surface of the cytoskeletal network, especially along the thick filament bundles. In some cells, a distinct membrane skeleton which was labelled with alpha-spectrin antibodies, was seen in close association with the cytoskeletal network. The cells which were labelled first with WGA-gold, and then permeabilized, fixed and labelled with alpha-spectrin, showed a co-localization of the WGA binding sites and alpha-spectrin along the surface of the filament bundles. Reversing the order of the staining, such that fixation was done before WGA labelling and permeabilization, led to a greatly diminished labelling for alpha-spectrin and less pronounced co-localization of spectrin and WGA. Comparison of the conventional critical point drying method with Peldri II, a novel drying agent, indicated a better stability of the cellular structures under the electron beam when Peldri II was used.(ABSTRACT TRUNCATED AT 250 WORDS)

Fodrin immunocytochemical localization in the striated organelles of the rat vestibular hair cells

The immunocytochemical distribution of a spectrin-related protein, fodrin was studied at the electron microscopic level in the rat vestibular hair cells. As previously demonstrated [Scarfone et al., Neurosci. Lett. 93, 13-18, 1988], an intense immunoreactivity was found in the cuticular plates. We demonstrate furthermore, here, for the first time the association of fodrin immunoreactivity with the striated infracuticular structures called striated organelles (SO). Fodrin was found in striated structures clearly identified as SO in both Type I and Type II hair cells. SO were labelled regardless of their location, subcuticular or associated with the plasma membrane of the cells. We suggest that fodrin, as in the cuticular plate, could participate to the Ca2+ dependent cross-linking of the actin filaments of the striated organelles and could play a role in their interaction with the submembraneous cytoskeleton.