Mutation of an axonemal dynein affects left-right asymmetry in inversus viscerum mice

Mirror, mirror? An evaluation of identical twin mirroring in tooth crown morphology

It has been estimated that 25% of monozygotic ("identical") twin pairs exhibit reverse asymmetry (RA) or "mirroring" of minor anatomical features as a result of delayed zygote division. Here, we examine whether identical twin mirroring accounts for patterns of dental asymmetry in a sample of monozygotic and dizygotic ("fraternal") twins. We focus on crown morphology to approach the following question: is there an association between dental RA frequency and twin type suggestive of the presence of mirror image twins in our sample? Data were collected from 208 deciduous and 196 permanent dentitions of participants of the University of Adelaide Twin Study using Arizona State University Dental Anthropology System standards. RA frequencies were compared across morphological complexes (deciduous, permanent), twin types (monozygotic, dizygotic), and traits. Fisher's exact tests were performed to formally evaluate the association between twin type and dental RA. Across the entire dataset, RA rates failed to exceed 8% for any twin type. In monozygotic twins, deciduous mirroring totaled 5.3% of observed cases, while permanent mirroring totaled 7.8% of observed cases. We found no statistically significant association between RA and twin type for any morphological character (p-value range: 0.07-1.00). Our results suggest the timing of monozygotic twin division does not explain the structure of asymmetry for our morphology dataset and that published estimates of identical twin mirroring rates may be inflated or contingent upon phenotype. Instead, rates reported for this sample more closely align with the proposed etiology of this condition.

Investigation of the genetic and clinical features of laterality disorders in prenatal diagnosis: discovery of a novel compound heterozygous mutation in the DNAH11 gene

BACKGROUND

Left-right laterality disorders are a heterogeneous group of disorders caused by an altered position or orientation of the thoracic and intra-abdominal organs and vasculature across the left-right axis. They mainly include situs inversus and heterotaxy. Those disorders are complicated by cardiovascular abnormalities significantly more frequently than situs solitus.

METHODS

In this study, 16 patients with a fetal diagnosis of laterality disorder with congenital heart defects (CHD) were evaluated with a single nucleotide polymorphism array (SNP-arry) combined with whole-exome sequencing (WES).

RESULTS

Although the diagnostic rate of copy number variations was 0 and the diagnostic rate of WES was 6.3% (1/16), the likely pathogenic gene DNAH11 and the candidate gene OFD1 were ultimately identified. In addition, novel compound heterozygous mutations in the DNAH11 gene and novel hemizygous variants in the OFD1 gene were found. Among the combined CHD, a single atrium/single ventricle had the highest incidence (50%, 8/16), followed by atrioventricular septal defects (37.5%, 6/16). Notably, two rare cases of common pulmonary vein atresia (CPVA) were also found on autopsy.

CONCLUSION

This study identified the types of CHD with a high incidence in patients with laterality disorders. It is clear that WES is an effective tool for diagnosing laterality disorders and can play an important role in future research.

Optical microscopic imaging, manipulation, and analysis methods for morphogenesis research

Morphogenesis is a developmental process of organisms being shaped through complex and cooperative cellular movements. To understand the interplay between genetic programs and the resulting multicellular morphogenesis, it is essential to characterize the morphologies and dynamics at the single-cell level and to understand how physical forces serve as both signaling components and driving forces of tissue deformations. In recent years, advances in microscopy techniques have led to improvements in imaging speed, resolution and depth. Concurrently, the development of various software packages has supported large-scale, analyses of challenging images at the single-cell resolution. While these tools have enhanced our ability to examine dynamics of cells and mechanical processes during morphogenesis, their effective integration requires specialized expertise. With this background, this review provides a practical overview of those techniques. First, we introduce microscopic techniques for multicellular imaging and image analysis software tools with a focus on cell segmentation and tracking. Second, we provide an overview of cutting-edge techniques for mechanical manipulation of cells and tissues. Finally, we introduce recent findings on morphogenetic mechanisms and mechanosensations that have been achieved by effectively combining microscopy, image analysis tools and mechanical manipulation techniques.

The molecular and cellular choreography of early mammalian lung development

Mammalian lung development starts from a specific cluster of endodermal cells situated within the ventral foregut region. With the orchestrating of delicate choreography of transcription factors, signaling pathways, and cell-cell communications, the endodermal diverticulum extends into the surrounding mesenchyme, and builds the cellular and structural basis of the complex respiratory system. This review provides a comprehensive overview of the current molecular insights of mammalian lung development, with a particular focus on the early stage of lung cell fate differentiation and spatial patterning. Furthermore, we explore the implications of several congenital respiratory diseases and the relevance to early organogenesis. Finally, we summarize the unprecedented knowledge concerning lung cell compositions, regulatory networks as well as the promising prospect for gaining an unbiased understanding of lung development and lung malformations through state-of-the-art single-cell omics.

Molecular Pathways and Animal Models of Defects in Situs

Left-right patterning is among the least well understood of the three axes defining the body plan, and yet it is no less important, with left-right patterning defects causing structural birth defects with high morbidity and mortality, such as complex congenital heart disease, biliary atresia, or intestinal malrotation. The cell signaling pathways governing left-right asymmetry are highly conserved and involve multiple components of the TGF-β superfamily of cell signaling molecules. Central to left-right patterning is the differential activation of Nodal on the left, and BMP signaling on the right. In addition, a plethora of other cell signaling pathways including Shh, FGF, and Notch also contribute to the regulation of left-right patterning. In vertebrate embryos such as the mouse, frog, or zebrafish, the specification of left-right identity requires the left-right organizer (LRO) containing cells with motile and primary cilia that mediate the left-sided propagation of Nodal signaling, followed by left-sided activation of Lefty and then Pitx2, a transcription factor that specifies visceral organ asymmetry. While this overall scheme is well conserved, there are striking species differences, including the finding that motile cilia do not play a role in left-right patterning in some vertebrates. Surprisingly, the direction of heart looping, one of the first signs of organ left-right asymmetry, was recently shown to be specified by intrinsic cell chirality, not Nodal signaling, possibly a reflection of the early origin of Nodal signaling in radially symmetric organisms. How this intrinsic chirality interacts with downstream molecular pathways regulating visceral organ asymmetry will need to be further investigated to elucidate how disturbance in left-right patterning may contribute to complex CHD.

Molecular Pathways and Animal Models of d-Transposition of the Great Arteries

During normal cardiovascular development, the outflow tract becomes septated and rotates so that the separate aorta and pulmonary trunk are correctly aligned with the left and right ventricles, respectively. However, when this process goes wrong, the aorta and pulmonary trunk are incorrectly positioned, resulting in oxygenated blood being directly returned to the lungs, with deoxygenated blood being delivered to the systemic circulation. This is termed transposition of the great arteries (TGA). The precise etiology of TGA is not known, but the use of animal models has elucidated that genes involved in determination of the left- embryonic body axis play key roles. Other factors such as retinoic acid levels are also crucial. This chapter reviews the animal models presenting with TGA that have been generated by genetic manipulation or with exogenous agents.

Identification of Greb1l as a genetic determinant of crisscross heart in mice showing torsion of the heart tube by shortage of progenitor cells

Despite their burden, most congenital defects remain poorly understood, due to lack of knowledge of embryological mechanisms. Here, we identify Greb1l mutants as a mouse model of crisscross heart. Based on 3D quantifications of shape changes, we demonstrate that torsion of the atrioventricular canal occurs together with supero-inferior ventricles at E10.5, after heart looping. Mutants phenocopy partial deficiency in retinoic acid signaling, which reflect overlapping pathways in cardiac precursors. Spatiotemporal gene mapping and cross-correlated transcriptomic analyses further reveal the role of Greb1l in maintaining a pool of dorsal pericardial wall precursor cells during heart tube elongation, likely by controlling ribosome biogenesis and cell differentiation. Consequently, we observe growth arrest and malposition of the outflow tract, which are predictive of abnormal tube remodeling in mutants. Our work on a rare cardiac malformation opens novel perspectives on the origin of a broader spectrum of congenital defects associated with GREB1L in humans.

Time space and single-cell resolved tissue lineage trajectories and laterality of body plan at gastrulation

Understanding of the molecular drivers of lineage diversification and tissue patterning during primary germ layer development requires in-depth knowledge of the dynamic molecular trajectories of cell lineages across a series of developmental stages of gastrulation. Through computational modeling, we constructed at single-cell resolution, a spatio-temporal transcriptome of cell populations in the germ-layers of gastrula-stage mouse embryos. This molecular atlas enables the inference of molecular network activity underpinning the specification and differentiation of the germ-layer tissue lineages. Heterogeneity analysis of cellular composition at defined positions in the epiblast revealed progressive diversification of cell types. The single-cell transcriptome revealed an enhanced BMP signaling activity in the right-side mesoderm of late-gastrulation embryo. Perturbation of asymmetric BMP signaling activity at late gastrulation led to randomization of left-right molecular asymmetry in the lateral mesoderm of early-somite-stage embryo. These findings indicate the asymmetric BMP activity during gastrulation may be critical for the symmetry breaking process.

Morphological phenotyping after mouse whole embryo culture

Morphological phenotyping of the mouse embryo is described at neurulation stages, primarily as a guide to evaluating the outcome of whole embryo cultures between embryonic days 8.5 and 9.5. During this period, neural tube closure is initiated and progresses to completion in the cranial region. Spinal closure is still underway at the end of the culture period. The focus of this article is particularly on phenotyping that can be performed at the bench, using a stereomicroscope. This involves assessment of embryonic health, through observation and scoring of yolk sac blood circulation, measurement of developmental stage by somite counting, and determination of crown-rump length as a measure of growth. Axial rotation ("turning") can also be assessed using a simple scoring system. Neural tube closure assessment includes: 1) determining whether closure has been initiated at the Closure 1 site; 2) evaluating the complex steps of cranial neurulation including initiation at Closure sites 2 and 3, and completion of closure at the anterior and hindbrain neuropores; 3) assessment of spinal closure by measurement of posterior neuropore length. Interpretation of defects in neural tube closure requires an appreciation of, first, the stages that particular events are expected to be completed and, second, the correspondence between embryonic landmarks, for example, somite position, and the resulting adult axial levels. Detailed embryonic phenotyping, as described in this article, when combined with the versatile method of whole embryo culture, can form the basis for a wide range of experimental studies in early mouse neural development.

Siewert-Kartagener's syndrome in a dog

Siewert-Kartagener's syndrome, a type of primary ciliary dyskinesia, is a complex disease comprising situs inversus, rhinosinusitis, and bronchiectasis. Situs inversus totalis is a condition in which all organs in the thoracic and abdominal cavities are reversed. Furthermore, primary ciliary dyskinesia, an autosomal genetic disease, may coexist with situs inversus totalis. Reports on Siewert-Kartagener's syndrome in veterinary medicine are limited. We report a rare case of primary ciliary dyskinesia with Siewert-Kartagener's syndrome in a dog, concurrently infected with canine distemper virus and type-2 adenovirus. This case highlights that situs inversus totalis can cause primary ciliary dyskinesia, and concurrent infections are possible.

Identification of novel compound heterozygous variants in the DNAH1 gene of a Chinese family with left-right asymmetry disorder

Most internal organs in humans and other vertebrates exhibit striking left-right asymmetry in position and structure. Variation of normal organ positioning results in left-right asymmetry disorders and presents as internal organ reversal or randomization. Up to date, at least 82 genes have been identified as the causative genetic factors of left-right asymmetry disorders. This study sought to discover potential pathogenic variants responsible for left-right asymmetry disorder present in a Han-Chinese family using whole exome sequencing combined with Sanger sequencing. Novel compound heterozygous variants, c.5690A>G (p.Asn1897Ser) and c.7759G>A (p.Val2587Met), in the dynein axonemal heavy chain 1 gene (DNAH1), were found in the proband and absent in unaffected family members. Conservation analysis has shown that the variants affect evolutionarily conserved residues, which may impact the tertiary structure of the DNAH1 protein. The novel compound heterozygous variants may potentially bear responsibility for left-right asymmetry disorder, which results from a perturbation of left-right axis coordination at the earliest embryonic development stages. This study broadens the variant spectrum of left-right asymmetry disorders and may be helpful for genetic counseling and healthcare management for the diagnosed individual, and promotes a greater understanding of the pathophysiology.

DNALI1 interacts with the MEIG1/PACRG complex within the manchette and is required for proper sperm flagellum assembly in mice

The manchette is a transient and unique structure present in elongating spermatids and required for proper differentiation of the germ cells during spermatogenesis. Previous work indicated that the MEIG1/PACRG complex locates in the manchette and is involved in the transport of cargos, such as SPAG16L, to build the sperm flagellum. Here, using co-immunoprecipitation and pull-down approaches in various cell systems, we established that DNALI1, an axonemal component originally cloned from Chlamydomonas reinhardtii, recruits and stabilizes PACRG and we confirm in vivo, the co-localization of DNALI1 and PACRG in the manchette by immunofluorescence of elongating murine spermatids. We next generated mice with a specific deficiency of DNALI1 in male germ cells, and observed a dramatic reduction of the sperm cells, which results in male infertility. In addition, we observed that the majority of the sperm cells exhibited abnormal morphology including misshapen heads, bent tails, enlarged midpiece, discontinuous accessory structure, emphasizing the importance of DNALI1 in sperm differentiation. Examination of testis histology confirmed impaired spermiogenesis in the mutant mice. Importantly, while testicular levels of MEIG1, PACRG, and SPAG16L proteins were unchanged in the Dnali1 mutant mice, their localization within the manchette was greatly affected, indicating that DNALI1 is required for the formation of the MEIG1/PACRG complex within the manchette. Interestingly, in contrast to MEIG1 and PACRG-deficient mice, the DNALI1-deficient mice also showed impaired sperm spermiation/individualization, suggesting additional functions beyond its involvement in the manchette structure. Overall, our work identifies DNALI1 as a protein required for sperm development.

Immotile cilia mechanically sense the direction of fluid flow for left-right determination

Immotile cilia at the ventral node of mouse embryos are required for sensing leftward fluid flow that breaks left-right symmetry of the body. However, the flow-sensing mechanism has long remained elusive. In this work, we show that immotile cilia at the node undergo asymmetric deformation along the dorsoventral axis in response to the flow. Application of mechanical stimuli to immotile cilia by optical tweezers induced calcium ion transients and degradation of Dand5 messenger RNA (mRNA) in the targeted cells. The Pkd2 channel protein was preferentially localized to the dorsal side of immotile cilia, and calcium ion transients were preferentially induced by mechanical stimuli directed toward the ventral side. Our results uncover the biophysical mechanism by which immotile cilia at the node sense the direction of fluid flow.

Morphological changes and two Nodal paralogs drive left-right asymmetry in the squamate veiled chameleon (C. calyptratus)

The ancestral mode of left-right (L-R) patterning involves cilia in the L-R organizer. However, the mechanisms regulating L-R patterning in non-avian reptiles remains an enigma, since most squamate embryos are undergoing organogenesis at oviposition. In contrast, veiled chameleon (Chamaeleo calyptratus) embryos are pre-gastrula at oviposition, making them an excellent organism for studying L-R patterning evolution. Here we show that veiled chameleon embryos lack motile cilia at the time of L-R asymmetry establishment. Thus, the loss of motile cilia in the L-R organizers is a synapomorphy of all reptiles. Furthermore, in contrast to avians, geckos and turtles, which have one Nodal gene, veiled chameleon exhibits expression of two paralogs of Nodal in the left lateral plate mesoderm, albeit in non-identical patterns. Using live imaging, we observed asymmetric morphological changes that precede, and likely trigger, asymmetric expression of the Nodal cascade. Thus, veiled chameleons are a new and unique model for studying the evolution of L-R patterning.

Understanding laterality disorders and the left-right organizer: Insights from zebrafish

Vital internal organs display a left-right (LR) asymmetric arrangement that is established during embryonic development. Disruption of this LR asymmetry-or laterality-can result in congenital organ malformations. Situs inversus totalis (SIT) is a complete concordant reversal of internal organs that results in a low occurrence of clinical consequences. Situs ambiguous, which gives rise to Heterotaxy syndrome (HTX), is characterized by discordant development and arrangement of organs that is associated with a wide range of birth defects. The leading cause of health problems in HTX patients is a congenital heart malformation. Mutations identified in patients with laterality disorders implicate motile cilia in establishing LR asymmetry. However, the cellular and molecular mechanisms underlying SIT and HTX are not fully understood. In several vertebrates, including mouse, frog and zebrafish, motile cilia located in a "left-right organizer" (LRO) trigger conserved signaling pathways that guide asymmetric organ development. Perturbation of LRO formation and/or function in animal models recapitulates organ malformations observed in SIT and HTX patients. This provides an opportunity to use these models to investigate the embryological origins of laterality disorders. The zebrafish embryo has emerged as an important model for investigating the earliest steps of LRO development. Here, we discuss clinical characteristics of human laterality disorders, and highlight experimental results from zebrafish that provide insights into LRO biology and advance our understanding of human laterality disorders.

Structures and functions of cilia during vertebrate embryo development

Cilia are hair-like structures that project from the surface of cells. In vertebrates, most cells have an immotile primary cilium that mediates cell signaling, and some specialized cells assemble one or multiple cilia that are motile and beat synchronously to move fluids in one direction. Gene mutations that alter cilia structure or function cause a broad spectrum of disorders termed ciliopathies that impact virtually every system in the body. A wide range of birth defects associated with ciliopathies underscores critical functions for cilia during embryonic development. In many cases, the mechanisms underlying cilia functions during development and disease remain poorly understood. This review describes different types of cilia in vertebrate embryos and discusses recent research results from diverse model systems that provide novel insights into how cilia form and function during embryo development. The work discussed here not only expands our understanding of in vivo cilia biology, but also opens new questions about cilia and their roles in establishing healthy embryos.

Extended reality visualization of medical museum specimens: Online presentation of conjoined twins curated by Dr. Jacob Henle between 1844-1852

Background

The purpose of this study is to characterize a full-term conjoined twins' cadaver curated by Dr. Jacob Henle sometime between 1844 and 1852 and demonstrate digital distribution of an old and rare medical museum specimen using an extended reality (XR) model workflow.

Methods

The cadaver (Preparation 296) is in the Department of Anatomy and Cell Biology at the University of Heidelberg. An XR display workflow comprises image capture, segmentation, and visualization using CT/MR scans derived from the cadaver. Online radiology presentation to medical students focuses on diagnostic characteristics of anatomical systems depicted with XR models.

Results

Developmental defects in Preparation 296 include duplicated supradiaphragmatic structures and abnormal osteological features. Subdiaphragmatically, the gut is continuous on the right, but terminates at the distal esophagus on the left. One large liver occupies the abdomen with one spleen located on the left side. Observations suggest duplication of the primitive streak and separate notochords rostrally. Duplication occurs near the yolk sac and involves midgut formation while secondary midline fusion of the upper extremities and ribs likely results from the proximity of the embryos during development. Medical students access the model with device agnostic software during the curricular topic "Human Body Plan" that includes embryology concepts covering mechanisms of twinning.

Conclusions

The workflow enables ease-of-access XR visualizations of an old and rare museum specimen. This study also demonstrates digital distribution and utilization of XR models applicable to embryology education.

Cerebral Polymorphisms for Lateralisation: Modelling the Genetic and Phenotypic Architectures of Multiple Functional Modules

Recent fMRI and fTCD studies have found that functional modules for aspects of language, praxis, and visuo-spatial functioning, while typically left, left and right hemispheric respectively, frequently show atypical lateralisation. Studies with increasing numbers of modules and participants are finding increasing numbers of module combinations, which here are termed cerebral polymorphisms—qualitatively different lateral organisations of cognitive functions. Polymorphisms are more frequent in left-handers than right-handers, but it is far from the case that right-handers all show the lateral organisation of modules described in introductory textbooks. In computational terms, this paper extends the original, monogenic McManus DC (dextral-chance) model of handedness and language dominance to multiple functional modules, and to a polygenic DC model compatible with the molecular genetics of handedness, and with the biology of visceral asymmetries found in primary ciliary dyskinesia. Distributions of cerebral polymorphisms are calculated for families and twins, and consequences and implications of cerebral polymorphisms are explored for explaining aphasia due to cerebral damage, as well as possible talents and deficits arising from atypical inter- and intra-hemispheric modular connections. The model is set in the broader context of the testing of psychological theories, of issues of laterality measurement, of mutation-selection balance, and the evolution of brain and visceral asymmetries.

A Novel Compound Heterozygous Mutation in the DNAH11 Gene Found in Neonatal Twins With Primary Ciliary Dyskinesis

Background: Primary ciliary dyskinesia (PCD) is a rare genetically heterogeneous disorder of motile cilia. Common features of PCD include upper and lower respiratory tract disease, secretory otitis media, situs inversus and fertility problems. To date, although several PCD-associated genes have been identified, the genetic causes of most PCD cases remain elusive.

Methods: In this case study, we analyzed the clinical and genetic data of one case of monochorionic diamniotic twins which were suspected of having PCD on the basis of clinical and radiological features including situs inversus, recurrent wet cough and sinusitis as well as varying degrees of respiratory distress. Whole-exome sequencing was performed to identify variants of the DNAH11 gene in the twins. Sanger sequencing and real-time quantitative polymerase chain reaction (RT-qPCR) were used for validation of DNAH11 variants both in the patient and the twins.

Results: In the twins, we found a novel mutation at c.2436C > G (p.Y812 *) and a pathogenic deletion encompassing 2.0 Kb of 7P15.3 ([GRCh38] chr7: g.21,816,397-21,818,402). The deleted region included exons 64 and 65 of DNAH11. Sanger sequencing also revealed that the twins’ father was a carrier of heterozygous C.2436C > G and a heterozygous deletion was detected in the mother. No other clinically relevant genetic variants were identified.

Conclusion: We describe a novel DNAH11 gene compound heterozygous mutation in newborn twins with PCD and recommend that PCD diagnosis should be considered in newborns presenting with respiratory distress and/or situs inversus. Early diagnosis and treatment of PCD will help control disease progression and improve the patient’s quality of life.

Primary ciliary dyskinesia in Volendam: Diagnostic and phenotypic features in patients with a CCDC114 mutation

Primary ciliary dyskinesia (PCD) is a heterogeneous disease, with impaired mucociliary clearance causing respiratory tract infections. A founding CCDC114 mutation has led to a relatively homogeneous and large Dutch PCD population in Volendam. Our aim was to describe their phenotype. Therefore, all Volendam PCD patients seen at the Amsterdam UMC were included in this study. Data were collected on lung function, microbiology, radiology, and ear‐nose‐throat (ENT) symptoms. A mixed effects model estimated lung function decline in %point per year (95% confidence interval [CI]). Thirty‐three (60%) out of approximately 56 Volendam PCD patients were treated at our center and included in this study. Only 30% of patients had situs inversus. FEV₁ declined in children (−1.43%/year, CI: −1.80/−1.05), but not in adults (0.01%/year, CI: −0.36/0.38). Pseudomonas aeruginosa was cultured in 21% of children and 60% of adults, respectively. Patients who have been infected at some point with P. aeruginosa had a steeper decline in FEV₁ as compared to patients that have never been infected. Neonatal symptoms (79%) and ENT problems (94%) were common; fertility issues however, were not (11%) common. Compared to other PCD cohorts, the Volendam/CCDC114 patients have a moderately severe phenotype with lung function decline predominantly occurring in childhood.

Spontaneously Beating Biomimetic Structures

The propulsion of motile cells such as sperms and the transport of fluids on cell surfaces rely on oscillatory bending of cellular appendages that can perform periodic oscillations. These structures are flagella and cilia. Their beating is driven by the interaction between microtubules and motor proteins and the mechanism regulating this is still a puzzle. One approach to address this issue is the assembling of synthetic minimal systems by using natural building blocks, e.g., microtubules and kinesin motors, which undergo persistent oscillation in the presence of ATP. An example of an autonomous molecular system is reported in this chapter. It dynamically self-organizes through its elasticity and the interaction with the environment represented by the active forces exerted by motor proteins. The resulting motion resembles the beating of sperm flagella. Assembling such minimal systems able to mimic the behavior of complex biological structures might help to unveil basic mechanisms underlying the beating of natural cilia and flagella.

Identification of compound heterozygous DNAH11 variants in a Han-Chinese family with primary ciliary dyskinesia

Primary ciliary dyskinesia (PCD) is a group of genetically and clinically heterogeneous disorders with motile cilia dysfunction. It is clinically characterized by oto‐sino‐pulmonary diseases and subfertility, and half of the patients have situs inversus (Kartagener syndrome). To identify the genetic cause in a Han‐Chinese pedigree, whole‐exome sequencing was conducted in the 37‐year‐old proband, and then, Sanger sequencing was performed on available family members. Minigene splicing assay was applied to verify the impact of the splice‐site variant. Compound heterozygous variants including a splice‐site variant (c.1974‐1G>C, rs1359107415) and a missense variant (c.7787G>A, p.(Arg2596Gln), rs780492669), in the dynein axonemal heavy chain 11 gene (DNAH11) were identified and confirmed as the disease‐associated variants of this lineage. The minigene expression in vitro revealed that the c.1974‐1G>C variant could cause skipping over exon 12, predicted to result in a truncated protein. This discovery may enlarge the DNAH11 variant spectrum of PCD, promote accurate genetic counselling and contribute to PCD diagnosis.

Fluid flow-induced left-right asymmetric decay of Dand5 mRNA in the mouse embryo requires a Bicc1-Ccr4 RNA degradation complex

Molecular left-right (L-R) asymmetry is established at the node of the mouse embryo as a result of the sensing of a leftward fluid flow by immotile cilia of perinodal crown cells and the consequent degradation of Dand5 mRNA on the left side. We here examined how the fluid flow induces Dand5 mRNA decay. We found that the first 200 nucleotides in the 3' untranslated region (3'-UTR) of Dand5 mRNA are necessary and sufficient for the left-sided decay and to mediate the response of a 3'-UTR reporter transgene to Ca2+, the cation channel Pkd2, the RNA-binding protein Bicc1 and their regulation by the flow direction. We show that Bicc1 preferentially recognizes GACR and YGAC sequences, which can explain the specific binding to a conserved GACGUGAC motif located in the proximal Dand5 3'-UTR. The Cnot3 component of the Ccr4-Not deadenylase complex interacts with Bicc1 and is also required for Dand5 mRNA decay at the node. These results suggest that Ca2+ currents induced by leftward fluid flow stimulate Bicc1 and Ccr4-Not to mediate Dand5 mRNA degradation specifically on the left side of the node.

A genome-wide library of MADM mice for single-cell genetic mosaic analysis

Mosaic analysis with double markers (MADM) offers one approach to visualize and concomitantly manipulate genetically defined cells in mice with single-cell resolution. MADM applications include the analysis of lineage, single-cell morphology and physiology, genomic imprinting phenotypes, and dissection of cell-autonomous gene functions in vivo in health and disease. Yet, MADM can only be applied to <25% of all mouse genes on select chromosomes to date. To overcome this limitation, we generate transgenic mice with knocked-in MADM cassettes near the centromeres of all 19 autosomes and validate their use across organs. With this resource, >96% of the entire mouse genome can now be subjected to single-cell genetic mosaic analysis. Beyond a proof of principle, we apply our MADM library to systematically trace sister chromatid segregation in distinct mitotic cell lineages. We find striking chromosome-specific biases in segregation patterns, reflecting a putative mechanism for the asymmetric segregation of genetic determinants in somatic stem cell division.

DNAH11 compound heterozygous variants cause heterotaxy and congenital heart disease

Heterotaxy (HTX), a condition characterized by internal organs not being arranged as expected relative to each other and to the left-right axis, is often accompanied with congenital heart disease (CHD). The purpose was to detect the pathogenic variants in a Chinese family with HTX and CHD. A non-consanguineous Han Chinese family with HTX and CHD, and 200 unrelated healthy subjects were enlisted. Exome sequencing and Sanger sequencing were applied to identify the genetic basis of the HTX family. Compound heterozygous variants, c.3426-1G>A and c.4306C>T (p.(Arg1436Trp)), in the dynein axonemal heavy chain 11 gene (DNAH11) were identified in the proband via exome sequencing and further confirmed by Sanger sequencing. Neither c.3426-1G>A nor c.4306C>T variant in the DNAH11 gene was detected in 200 healthy controls. The DNAH11 c.3426-1G>A variant was predicted as altering the acceptor splice site and most likely affecting splicing. The DNAH11 c.4306C>T variant was predicted to be damaging, which may reduce the phenotype severity. The compound heterozygous variants, c.3426-1G>A and c.4306C>T, in the DNAH11 gene might be the pathogenic alterations resulting in HTX and CHD in this family. These findings broaden the variant spectrum of the DNAH11 gene and increase knowledge used in genetic counseling for the HTX family.

Heart Development and Congenital Structural Heart Defects

Congenital heart disease is the most frequent birth defect and the leading cause of death for the fetus and in the first year of life. The wide phenotypic diversity of congenital heart defects requires expert diagnosis and sophisticated repair surgery. Although these defects have been described since the seventeenth century, it was only in 2005 that a consensus international nomenclature was adopted, followed by an international classification in 2017 to help provide better management of patients. Advances in genetic engineering, imaging, and omics analyses have uncovered mechanisms of heart formation and malformation in animal models, but approximately 80% of congenital heart defects have an unknown genetic origin. Here, we summarize current knowledge of congenital structural heart defects, intertwining clinical and fundamental research perspectives, with the aim to foster interdisciplinary collaborations at the cutting edge of each field. We also discuss remaining challenges in better understanding congenital heart defects and providing benefits to patients.

The Axenfeld-Rieger Syndrome Gene FOXC1 Contributes to Left-Right Patterning

Precise spatiotemporal expression of the Nodal-Lefty-Pitx2 cascade in the lateral plate mesoderm establishes the left–right axis, which provides vital cues for correct organ formation and function. Mutations of one cascade constituent PITX2 and, separately, the Forkhead transcription factor FOXC1 independently cause a multi-system disorder known as Axenfeld–Rieger syndrome (ARS). Since cardiac involvement is an established ARS phenotype and because disrupted left–right patterning can cause congenital heart defects, we investigated in zebrafish whether foxc1 contributes to organ laterality or situs. We demonstrate that CRISPR/Cas9-generated foxc1a and foxc1b mutants exhibit abnormal cardiac looping and that the prevalence of cardiac situs defects is increased in foxc1a^−/−; foxc1b^−/− homozygotes. Similarly, double homozygotes exhibit isomerism of the liver and pancreas, which are key features of abnormal gut situs. Placement of the asymmetric visceral organs relative to the midline was also perturbed by mRNA overexpression of foxc1a and foxc1b. In addition, an analysis of the left–right patterning components, identified in the lateral plate mesoderm of foxc1 mutants, reduced or abolished the expression of the NODAL antagonist lefty2. Together, these data reveal a novel contribution from foxc1 to left–right patterning, demonstrating that this role is sensitive to foxc1 gene dosage, and provide a plausible mechanism for the incidence of congenital heart defects in Axenfeld–Rieger syndrome patients.

Motile cilia genetics and cell biology: big results from little mice

Our understanding of motile cilia and their role in disease has increased tremendously over the last two decades, with critical information and insight coming from the analysis of mouse models. Motile cilia form on specific epithelial cell types and typically beat in a coordinated, whip-like manner to facilitate the flow and clearance of fluids along the cell surface. Defects in formation and function of motile cilia result in primary ciliary dyskinesia (PCD), a genetically heterogeneous disorder with a well-characterized phenotype but no effective treatment. A number of model systems, ranging from unicellular eukaryotes to mammals, have provided information about the genetics, biochemistry, and structure of motile cilia. However, with remarkable resources available for genetic manipulation and developmental, pathological, and physiological analysis of phenotype, the mouse has risen to the forefront of understanding mammalian motile cilia and modeling PCD. This is evidenced by a large number of relevant mouse lines and an extensive body of genetic and phenotypic data. More recently, application of innovative cell biological techniques to these models has enabled substantial advancement in elucidating the molecular and cellular mechanisms underlying the biogenesis and function of mammalian motile cilia. In this article, we will review genetic and cell biological studies of motile cilia in mouse models and their contributions to our understanding of motile cilia and PCD pathogenesis.

Role of Ca2+ transients at the node of the mouse embryo in breaking of left-right symmetry

Immotile cilia sense extracellular signals such as fluid flow, but whether Ca²⁺ plays a role in flow sensing has been unclear. Here, we examined the role of ciliary Ca²⁺ in the flow sensing that initiates the breaking of left-right (L-R) symmetry in the mouse embryo. Intraciliary and cytoplasmic Ca²⁺ transients were detected in the crown cells at the node. These Ca²⁺ transients showed L-R asymmetry, which was lost in the absence of fluid flow or the PKD2 channel. Further characterization allowed classification of the Ca²⁺ transients into two types: cilium-derived, L-R-asymmetric transients (type 1) and cilium-independent transients without an L-R bias (type 2). Type 1 intraciliary transients occurred preferentially at the left posterior region of the node, where L-R symmetry breaking takes place. Suppression of intraciliary Ca²⁺ transients delayed L-R symmetry breaking. Our results implicate cilium-derived Ca²⁺ transients in crown cells in initiation of L-R symmetry breaking in the mouse embryo.

Genetics of atrioventricular canal defects

Atrioventricular canal defect (AVCD) represents a quite common congenital heart defect (CHD) accounting for 7.4% of all cardiac malformations. AVCD is a very heterogeneous malformation that can occur as a phenotypical cardiac aspect in the context of different genetic syndromes but also as an isolated, non-syndromic cardiac defect. AVCD has also been described in several pedigrees suggesting a pattern of familiar recurrence. Targeted Next Generation Sequencing (NGS) techniques are proved to be a powerful tool to establish the molecular heterogeneity of AVCD.

Given the complexity of cardiac embryology, it is not surprising that multiple genes deeply implicated in cardiogenesis have been described mutated in patients with AVCD. This review attempts to examine the recent advances in understanding the molecular basis of this complex CHD in the setting of genetic syndromes or in non-syndromic patients.

A null allele of Dnaaf2 displays embryonic lethality and mimics human ciliary dyskinesia

The dynein axonemal assembly factor (Dnaaf) protein family is involved in preassembly and stability of dynein arms before they are transported into the cilia. In humans, mutations in DNAAF genes lead to several diseases related to cilia defects such as primary ciliary dyskinesia (PCD; OMIM: 612518). Patients with PCD experience malfunctions in cilia motility, which can result in inflammation and infection of the respiratory tract among other defects. Previous studies have identified that a mutation in DNAAF2 results in PCD and that 40% of these patients also experience laterality defects. In an outbred genetic background, Dnaaf2 homozygotes die after birth and have left/right defects among other phenotypes. Here we characterize a novel null allele of Dnaaf2 obtained from the International Mouse Phenotyping Consortium. Our data indicate that on a defined C57bl/6NJ genetic background, homozygous Dnaaf2 mouse embryos fail to progress beyond organogenesis stages with many abnormalities including left-right patterning defects. These findings support studies indicating that hypomorphic mutations of human DNAAF2 can result in ciliary dyskinesia and identify Dnaaf2 as an essential component of cilia function in vivo.

Comorbidities in situs inversus totalis: A hospital-based study

BACKGROUND AND OBJECTIVE

Few studies have assessed the comorbid diseases in situs inversus totalis (SIT) comprehensively. The aim of this study was to provide insight into the spectrum and prevalence of comorbidities in SIT.

METHODS

Children ≤18 years of age with SIT were enrolled in this retrospective observational study. Situs status and comorbidities were independently confirmed by two physicians, based on review of radiologic, ultrasonic examination, operative records, and case notes.

RESULTS

A total of 155 children (median age: 1.24 years; range: 1 day-17.8 years) confirmed to have SIT were recruited between January 2008 and December 2018. Associated conditions were diagnosed in 114 children (73.5%). Among them, 25 children (16.1%) had multiple anomalies affecting two or more organ systems. The most commonly associated conditions were congenital heart defects (n = 72, 46.5%) followed by primary ciliary dyskinesia (n = 19, 12.3%), renal disorders (n = 12, 7.7%), biliary atresia (n = 7, 4.5%), skeletal dysplasia (n = 8, 5.2%), and mental retardation (n = 4, 2.6%).

CONCLUSION

A substantial proportion of children with SIT have comorbidities affecting multiple systems, especially cardiovascular and respiratory abnormalities. Children with SIT warrant careful examination for the presence of congenital and acquired abnormalities.

Molecular and cellular basis of left-right asymmetry in vertebrates

Although the human body appears superficially symmetrical with regard to the left-right (L-R) axis, most visceral organs are asymmetric in terms of their size, shape, or position. Such morphological asymmetries of visceral organs, which are essential for their proper function, are under the control of a genetic pathway that operates in the developing embryo. In many vertebrates including mammals, the breaking of L-R symmetry occurs at a structure known as the L-R organizer (LRO) located at the midline of the developing embryo. This symmetry breaking is followed by transfer of an active form of the signaling molecule Nodal from the LRO to the lateral plate mesoderm (LPM) on the left side, which results in asymmetric expression of Nodal (a left-side determinant) in the left LPM. Finally, L-R asymmetric morphogenesis of visceral organs is induced by Nodal-Pitx2 signaling. This review will describe our current understanding of the mechanisms that underlie the generation of L-R asymmetry in vertebrates, with a focus on mice.

Loss of ciliary transition zone protein TMEM107 leads to heterotaxy in mice

Cilia in most vertebrate left-right organizers are involved in the original break in left-right (L-R) symmetry, however, less is known about their roles in subsequent steps of the cascade - relaying the signaling and maintaining the established asymmetry. Here we describe the L-R patterning cascades in two mutants of a ciliary transition zone protein TMEM107, revealing that near-complete loss of cilia in Tmem107^null leads to left pulmonary isomerism due to the failure of the midline barrier. Contrary, partially retained cilia in the node and the midline of a hypomorphic Tmem107^schlei mutant appear sufficient for the formation of the midline barrier and establishment and maintenance of the L-R asymmetry. Despite misregulation of Shh signaling in both mutants, the presence of normal Lefty1 expression and midline barrier formation in Tmem107^schlei mutants, suggests a requirement for cilia, but not necessarily Shh signaling for Lefty1 expression and midline barrier formation.

MNS1 variant associated with situs inversus and male infertility

Ciliopathy disorders due to abnormalities of motile cilia encompass a range of autosomal recessive conditions typified by chronic otosinopulmonary disease, infertility, situs abnormalities and hydrocephalus. Using a combination of genome-wide SNP mapping and whole exome sequencing (WES), we investigated the genetic cause of a form of situs inversus (SI) and male infertility present in multiple individuals in an extended Amish family, assuming that an autosomal recessive founder variant was responsible. This identified a single shared (2.34 Mb) region of autozygosity on chromosome 15q21.3 as the likely disease locus, in which we identified a single candidate biallelic frameshift variant in MNS1 [NM_018365.2: c.407_410del; p.(Glu136Glyfs*16)]. Genotyping of multiple family members identified randomisation of the laterality defects in other homozygous individuals, with all wild type or MNS1 c.407_410del heterozygous carriers being unaffected, consistent with an autosomal recessive mode of inheritance. This study identifies an MNS1 variant as a cause of laterality defects and male infertility in humans, mirroring findings in Mns1-deficient mice which also display male infertility and randomisation of left–right asymmetry of internal organs, confirming a crucial role for MNS1 in nodal cilia and sperm flagella formation and function.

New insights into ion channel-dependent signalling during left-right patterning

The left-right organizer (LRO) in the mouse consists of pit cells within the depression, located at the end of the developing notochord, also known as the embryonic node and crown cells lining the outer periphery of the node. Cilia on pit cells are posteriorly tilted, rotate clockwise and generate leftward fluid flow. Primary cilia on crown cells are required to interpret the directionality of fluid movement and initiate flow-dependent gene transcription. Crown cells express PC1-L1 and PC2, which may form a heteromeric polycystin channel complex on primary cilia. It is still only poorly understood how fluid flow activates the ciliary polycystin complex. Besides polycystin channels voltage gated channels like HCN4 and KCNQ1 have been implicated in establishing asymmetry. How this electrical network of ion channels initiates left-sided signalling cascades and differential gene expression is currently only poorly defined.

Association Between the Catechol-O-Methyltransferase (COMT) Val158Met Polymorphism and Manual Performance Asymmetries

Within the cognitive domain, neuroscience and cognitive psychology researchers have investigated the relationship between handedness and cognitive skills. However, there have been few studies of the three-way association between manual asymmetry, its genetic components, and cognition even though this line of research could further an understanding of asymmetry. One enzyme involved in cognitive functions related to the dopaminergic system and to the prefrontal cortex is the catechol-O-methyltransferase (COMT), and it has a trimodal activity distribution in the human population due to its functional polymorphism known as Val158Met. This study investigated whether this COMT polymorphism is associated with asymmetries in the performance of a manual dexterity task. Forty-two right-handed undergraduate students ( M_age = 25.12, SD = 5.84; 15 women, 27 men) performed two trials each of place and remove conditions of the Grooved Pegboard Test with each hand (right and left), counterbalancing the order of the initial or starting hand. We calculated the mean time to perform the task for both hands on both trials and found, as hypothesized, that the Met/Met group gave a more asymmetrical performance than the Val/Met group under the place condition because dopamine levels reduced flexible behavior for the Val/Met group. We suspect that the place condition requires greater interhemispheric connectivity, as it requires a greater cognitive flexibility, and highly asymmetrical individuals are said to be less flexible. The findings of this study suggest a significant association between the COMT polymorphism and manual asymmetry in healthy populations.

Atrioventricular canal defect and genetic syndromes: The unifying role of sonic hedgehog

The atrioventricular canal defect (AVCD) is a congenital heart defect (CHD) frequently associated with extracardiac anomalies (75%). Previous observations from a personal series of patients with AVCD and "polydactyly syndromes" showed that the distinct morphology and combination of AVCD features in some of these syndromes is reminiscent of the cardiac phenotype found in heterotaxy, a malformation complex previously associated with functional cilia abnormalities and aberrant Hedgehog (Hh) signaling. Hh signaling coordinates multiple aspects of left-right lateralization and cardiovascular growth. Being active at the venous pole the secondary heart field (SHF) is essential for normal development of dorsal mesenchymal protrusion and AVCD formation and septation. Experimental data show that perturbations of different components of the Hh pathway can lead to developmental errors presenting with partially overlapping manifestations and AVCD as a common denominator. We review the potential role of Hh signaling in the pathogenesis of AVCD in different genetic disorders. AVCD can be viewed as part of a "developmental field," according to the concept that malformations can be due to defects in signal transduction cascades or pathways, as morphogenetic units which may be altered by Mendelian mutations, aneuploidies, and environmental causes.

Congenital Heart Defects and Ciliopathies Associated With Renal Phenotypes

Congenital heart disease (CHD) is one of the most common birth defects, and recent studies indicate cilia-related mutations play a central role in the genetic etiology of CHD. As cilia are also known to have important roles in kidney development and disease, it is not surprising that renal anomalies were found to be enriched among CHD mutant mice recovered in a large-scale mouse forward genetic screen. Indeed 42% of mutations identified to cause both CHD and renal anomalies were cilia-related. Many of these cilia mutations comprise cilia transition zone or inversin compartment components, consistent with the known role of these cilia proteins in a wide variety of ciliopathies. The high prevalence of CHD with congenital anomalies of the kidney and urinary tract (CAKUT) observed in mice was also corroborated with clinical studies that showed 20-30% of CHD patients have renal anomalies. Together these findings suggest CHD patients may benefit from early screening for renal anomalies to allow early diagnosis and intervention to improve outcome for this vulnerable patient population.

Vertebrate Left-Right Asymmetry: What Can Nodal Cascade Gene Expression Patterns Tell Us?

Laterality of inner organs is a wide-spread characteristic of vertebrates and beyond. It is ultimately controlled by the left-asymmetric activation of the Nodal signaling cascade in the lateral plate mesoderm of the neurula stage embryo, which results from a cilia-driven leftward flow of extracellular fluids at the left-right organizer. This scenario is widely accepted for laterality determination in wildtype specimens. Deviations from this norm come in different flavors. At the level of organ morphogenesis, laterality may be inverted (situs inversus) or non-concordant with respect to the main body axis (situs ambiguus or heterotaxia). At the level of Nodal cascade gene activation, expression may be inverted, bilaterally induced, or absent. In a given genetic situation, patterns may be randomized or predominantly lacking laterality (absence or bilateral activation). We propose that the distributions of patterns observed may be indicative of the underlying molecular defects, with randomizations being primarily caused by defects in the flow-generating ciliary set-up, and symmetrical patterns being the result of impaired flow sensing, on the left, the right, or both sides. This prediction, the reasoning of which is detailed in this review, pinpoints functions of genes whose role in laterality determination have remained obscure.

Antagonistic interactions in the zebrafish midline prior to the emergence of asymmetric gene expression are important for left-right patterning

Left-right (L-R) asymmetry of the internal organs of vertebrates is presaged by domains of asymmetric gene expression in the lateral plate mesoderm (LPM) during somitogenesis. Ciliated L-R coordinators (LRCs) are critical for biasing the initiation of asymmetrically expressed genes, such as nodal and pitx2, to the left LPM. Other midline structures, including the notochord and floorplate, are then required to maintain these asymmetries. Here we report an unexpected role for the zebrafish EGF-CFC gene one-eyed pinhead (oep) in the midline to promote pitx2 expression in the LPM. Late zygotic oep (LZoep) mutants have strongly reduced or absent pitx2 expression in the LPM, but this expression can be rescued to strong levels by restoring oep in midline structures only. Furthermore, removing midline structures from LZoep embryos can rescue pitx2 expression in the LPM, suggesting the midline is a source of an LPM pitx2 repressor that is itself inhibited by oep Reducing lefty1 activity in LZoep embryos mimics removal of the midline, implicating lefty1 in the midline-derived repression. Together, this suggests a model where Oep in the midline functions to overcome a midline-derived repressor, involving lefty1, to allow for the expression of left side-specific genes in the LPM.This article is part of the themed issue 'Provocative questions in left-right asymmetry'.

Multiple Roles of Pitx2 in Cardiac Development and Disease

Cardiac development is a complex morphogenetic process initiated as bilateral cardiogenic mesoderm is specified at both sides of the gastrulating embryo. Soon thereafter, these cardiogenic cells fuse at the embryonic midline configuring a symmetrical linear cardiac tube. Left/right bilateral asymmetry is first detected in the forming heart as the cardiac tube bends to the right, and subsequently, atrial and ventricular chambers develop. Molecular signals emanating from the node confer distinct left/right signalling pathways that ultimately lead to activation of the homeobox transcription factor Pitx2 in the left side of distinct embryonic organ anlagen, including the developing heart. Asymmetric expression of Pitx2 has therefore been reported during different cardiac developmental stages, and genetic deletion of Pitx2 provided evidence of key regulatory roles of this transcription factor during cardiogenesis and thus congenital heart diseases. More recently, impaired Pitx2 function has also been linked to arrhythmogenic processes, providing novel roles in the adult heart. In this manuscript, we provide a state-of-the-art review of the fundamental roles of Pitx2 during cardiogenesis, arrhythmogenesis and its contribution to congenital heart diseases.

Cilia in Left-Right Symmetry Breaking

Visceral organs of vertebrates show left-right (L-R) asymmetry with regard to their position and morphology. Cilia play essential role in generating L-R asymmetry. A number of genes required for L-R asymmetry have now been identified in vertebrates, including human, many of which contribute to the formation and motility of cilia. In the mouse embryo, breaking of L-R symmetry occurs in the ventral node, where two types of cilia (motile and immotile) are present. Motile cilia are located at the central region of the node, and generate a leftward fluid flow. These motile cilia at the node are unique in that they rotate in the clockwise direction, unlike other immotile cilia such as airway cilia that show planar beating. The second type of cilia essential for L-R asymmetry is immotile cilia that are peripherally located immotile cilia. They sense a flow-dependent signal, which is either chemical or mechanical in nature. Although Ca²⁺ signaling is implicated in flow sensing, the precise mechanism remains unknown.

DNAH11 Localization in the Proximal Region of Respiratory Cilia Defines Distinct Outer Dynein Arm Complexes

Primary ciliary dyskinesia (PCD) is a recessively inherited disease that leads to chronic respiratory disorders owing to impaired mucociliary clearance. Conventional transmission electron microscopy (TEM) is a diagnostic standard to identify ultrastructural defects in respiratory cilia but is not useful in approximately 30% of PCD cases, which have normal ciliary ultrastructure. DNAH11 mutations are a common cause of PCD with normal ciliary ultrastructure and hyperkinetic ciliary beating, but its pathophysiology remains poorly understood. We therefore characterized DNAH11 in human respiratory cilia by immunofluorescence microscopy (IFM) in the context of PCD. We used whole-exome and targeted next-generation sequence analysis as well as Sanger sequencing to identify and confirm eight novel loss-of-function DNAH11 mutations. We designed and validated a monoclonal antibody specific to DNAH11 and performed high-resolution IFM of both control and PCD-affected human respiratory cells, as well as samples from green fluorescent protein (GFP)-left-right dynein mice, to determine the ciliary localization of DNAH11. IFM analysis demonstrated native DNAH11 localization in only the proximal region of wild-type human respiratory cilia and loss of DNAH11 in individuals with PCD with certain loss-of-function DNAH11 mutations. GFP-left-right dynein mice confirmed proximal DNAH11 localization in tracheal cilia. DNAH11 retained proximal localization in respiratory cilia of individuals with PCD with distinct ultrastructural defects, such as the absence of outer dynein arms (ODAs). TEM tomography detected a partial reduction of ODAs in DNAH11-deficient cilia. DNAH11 mutations result in a subtle ODA defect in only the proximal region of respiratory cilia, which is detectable by IFM and TEM tomography.

PirB regulates asymmetries in hippocampal circuitry

Left-right asymmetry is a fundamental feature of higher-order brain structure; however, the molecular basis of brain asymmetry remains unclear. We recently identified structural and functional asymmetries in mouse hippocampal circuitry that result from the asymmetrical distribution of two distinct populations of pyramidal cell synapses that differ in the density of the NMDA receptor subunit GluRε2 (also known as NR2B, GRIN2B or GluN2B). By examining the synaptic distribution of ε2 subunits, we previously found that β2-microglobulin-deficient mice, which lack cell surface expression of the vast majority of major histocompatibility complex class I (MHCI) proteins, do not exhibit circuit asymmetry. In the present study, we conducted electrophysiological and anatomical analyses on the hippocampal circuitry of mice with a knockout of the paired immunoglobulin-like receptor B (PirB), an MHCI receptor. As in β2-microglobulin-deficient mice, the PirB-deficient hippocampus lacked circuit asymmetries. This finding that MHCI loss-of-function mice and PirB knockout mice have identical phenotypes suggests that MHCI signals that produce hippocampal asymmetries are transduced through PirB. Our results provide evidence for a critical role of the MHCI/PirB signaling system in the generation of asymmetries in hippocampal circuitry.