Homozygous knockout of the piezo1 gene in the zebrafish is not associated with anemia

A mutation in F-actin polymerization factor suppresses the distal arthrogryposis type 5 PIEZO2 pathogenic variant in Caenorhabditis elegans

The mechanosensitive PIEZO channel family has been linked to over 26 disorders and diseases. Although progress has been made in understanding these channels at the structural and functional levels, the underlying mechanisms of PIEZO-associated diseases remain elusive. In this study, we engineered four PIEZO-based disease models using CRISPR/Cas9 gene editing. We performed an unbiased chemical mutagen-based genetic suppressor screen to identify putative suppressors of a conserved gain-of-function variant pezo-1[R2405P] that in human PIEZO2 causes distal arthrogryposis type 5 (DA5; p. R2718P). Electrophysiological analyses indicate that pezo-1(R2405P) is a gain-of-function allele. Using genomic mapping and whole-genome sequencing approaches, we identified a candidate suppressor allele in the C. elegans gene gex-3. This gene is an ortholog of human NCKAP1 (NCK-associated protein 1), a subunit of the Wiskott-Aldrich syndrome protein (WASP)-verprolin homologous protein (WAVE/SCAR) complex, which regulates F-actin polymerization. Depletion of gex-3 by RNAi, or with the suppressor allele gex-3(av259[L353F]), significantly increased brood size and ovulation rate, as well as alleviating the crushed oocyte phenotype of the pezo-1(R2405P) mutant. Expression of GEX-3 in the soma is required to rescue the brood size defects in pezo-1(R2405P) animals. Actin organization and orientation were disrupted and distorted in the pezo-1 mutants. Mutation of gex-3(L353F) partially alleviated these defects. The identification of gex-3 as a suppressor of the pathogenic variant pezo-1(R2405P) suggests that the PIEZO coordinates with the cytoskeleton regulator to maintain the F-actin network and provides insight into the molecular mechanisms of DA5 and other PIEZO-associated diseases.

Mutation in F-actin Polymerization Factor Suppresses Distal Arthrogryposis Type 5 (DA5) PIEZO2 Pathogenic Variant in Caenorhabditis elegans

The mechanosensitive PIEZO channel family has been linked to over 26 disorders and diseases. Although progress has been made in understanding these channels at the structural and functional levels, the underlying mechanisms of PIEZO-associated diseases remain elusive. In this study, we engineered four PIEZO-based disease models using CRISPR/Cas9 gene editing. We performed an unbiased chemical mutagen-based genetic suppressor screen to identify putative suppressors of a conserved gain-of-function variant pezo-1[R2405P] that in human PIEZO2 causes distal arthrogryposis type 5 (DA5; p. R2718P). Electrophysiological analyses indicate that pezo-1(R2405P) is a gain-of-function allele. Using genomic mapping and whole genome sequencing approaches, we identified a candidate suppressor allele in the C. elegans gene gex-3. This gene is an ortholog of human NCKAP1 (NCK-associated protein 1), a subunit of the Wiskott-Aldrich syndrome protein (WASP)-verprolin homologous protein (WAVE/SCAR) complex, which regulates F-actin polymerization. Depletion of gex-3 by RNAi, or with the suppressor allele gex-3(av259[L353F]) , significantly restored the small brood size and low ovulation rate, as well as alleviated the crushed oocyte phenotype of the pezo-1(R2405P) mutant. Auxin-inducible degradation of GEX-3 revealed that only somatic-specific degradation of GEX-3 restored the reduced brood size in the pezo-1(R2405P) mutants. Additionally, actin organization and orientation were disrupted and distorted in the pezo-1 mutants. Mutation of gex-3(L353F) partially alleviated these defects. The identification of gex-3 as a suppressor of the pathogenic variant pezo-1(R2405P) suggests that the cytoskeleton plays an important role in regulating PIEZO channel activity and provides insight into the molecular mechanisms of DA5 and other PIEZO-associated diseases.

Levering Mechanically Activated Piezo Channels for Potential Pharmacological Intervention

The mechanically activated Piezo channels, including Piezo1 and Piezo2 in mammals, function as key mechanotransducers for converting mechanical force into electrochemical signals. This review highlights key evidence for the potential of Piezo channel drug discovery. First, both mouse and human genetic studies have unequivocally demonstrated the prominent role of Piezo channels in various mammalian physiologies and pathophysiologies, validating their potential as novel therapeutic targets. Second, the cryo-electron microscopy structure of the 2,547-residue mouse Piezo1 trimer has been determined, providing a solid foundation for studying its structure-function relationship and drug action mechanisms and conducting virtual drug screening. Third, Piezo1 chemical activators, named Yoda1 and Jedi1/2, have been identified through high-throughput screening assays, demonstrating the drugability of Piezo channels. However, the pharmacology of Piezo channels is in its infancy. By establishing an integrated drug discovery platform, we may hopefully discover and develop a fleet of Jedi masters for battling Piezo-related human diseases.

Loss-of-function approaches in comparative physiology: is there a future for knockdown experiments in the era of genome editing?

Loss-of-function technologies, such as morpholino- and RNAi-mediated gene knockdown, and TALEN- and CRISPR/Cas9-mediated gene knockout, are widely used to investigate gene function and its physiological significance. Here, we provide a general overview of the various knockdown and knockout technologies commonly used in comparative physiology and discuss the merits and drawbacks of these technologies with a particular focus on research conducted in zebrafish. Despite their widespread use, there is an ongoing debate surrounding the use of knockdown versus knockout approaches and their potential off-target effects. This debate is primarily fueled by the observations that, in some studies, knockout mutants exhibit phenotypes different from those observed in response to knockdown using morpholinos or RNAi. We discuss the current debate and focus on the discrepancies between knockdown and knockout phenotypes, providing literature and primary data to show that the different phenotypes are not necessarily a direct result of the off-target effects of the knockdown agents used. Nevertheless, given the recent evidence of some knockdown phenotypes being recapitulated in knockout mutants lacking the morpholino or RNAi target, we stress that results of knockdown experiments need to be interpreted with caution. We ultimately argue that knockdown experiments should not be discontinued if proper control experiments are performed, and that with careful interpretation, knockdown approaches remain useful to complement the limitations of knockout studies (e.g. lethality of knockout and compensatory responses).

PIEZO1 Hypomorphic Variants in Congenital Lymphatic Dysplasia Cause Shape and Hydration Alterations of Red Blood Cells

PIEZO1 is a cation channel activated by mechanical force. It plays an important physiological role in several biological processes such as cardiovascular, renal, endothelial and hematopoietic systems. Two different diseases are associated with alteration in the DNA sequence of PIEZO1: (i) dehydrated hereditary stomatocytosis (DHS1, #194380), an autosomal dominant hemolytic anemia caused by gain-of-function mutations; (ii) lymphatic dysplasia with non-immune fetal hydrops (LMPH3, #616843), an autosomal recessive condition caused by biallelic loss-of-function mutations. We analyzed a 14-year-old boy affected by severe lymphatic dysplasia already present prenatally, with peripheral edema, hydrocele, and chylothoraces. By whole exome sequencing, we identified compound heterozygosity for PIEZO1, with one splicing and one deletion mutation, the latter causing the formation of a premature stop codon that leads to mRNA decay. The functional analysis of the erythrocytes of the patient highlighted altered hydration with the intracellular loss of the potassium content and structural abnormalities with anisopoikolocytosis and presence of both spherocytes and stomatocytes. This novel erythrocyte trait, sharing features with both hereditary spherocytosis and overhydrated hereditary stomatocytosis, complements the clinical features associated with loss-of-function mutations of PIEZO1 in the context of the generalized lymphatic dysplasia of LMPH3 type.

Versatile Genome Engineering Techniques Advance Human Ocular Disease Researches in Zebrafish

Over recent decades, zebrafish has been established as a sophisticated vertebrate model for studying human ocular diseases due to its high fecundity, short generation time and genetic tractability. With the invention of morpholino (MO) technology, it became possible to study the genetic basis and relevant genes of ocular diseases in vivo. Many genes have been shown to be related to ocular diseases. However, the issue of specificity is the major concern in defining gene functions with MO technology. The emergence of the first- and second-generation genetic modification tools zinc-finger nucleases (ZFNs) and TAL effector nucleases (TALENs), respectively, eliminated the potential phenotypic risk induced by MOs. Nevertheless, the efficiency of these nucleases remained relatively low until the third technique, the clustered regularly interspersed short palindromic repeats (CRISPR)/CRISPR-associated protein 9 (Cas9) system, was discovered. This review highlights the application of multiple genome engineering techniques, especially the CRISPR/Cas9 system, in the study of human ocular diseases in zebrafish.

Sickle cell dehydration: Pathophysiology and therapeutic applications

Cell dehydration is a distinguishing characteristic of sickle cell disease and an important contributor to disease pathophysiology. Due to the unique dependence of Hb S polymerization on cellular Hb S concentration, cell dehydration promotes polymerization and sickling. In double heterozygosis for Hb S and C (SC disease) dehydration is the determining factor in disease pathophysiology. Three major ion transport pathways are involved in sickle cell dehydration: the K-Cl cotransport (KCC), the Gardos channel (KCNN4) and Psickle, the polymerization induced membrane permeability, most likely mediated by the mechano-sensitive ion channel PIEZO1. Each of these pathways exhibit unique characteristics in regulation by oxygen tension, intracellular and extracellular environment, and functional expression in reticulocytes and mature red cells. The unique dependence of K-Cl cotransport on intracellular Mg and the abnormal reduction of erythrocyte Mg content in SS and SC cells had led to clinical studies assessing the effect of oral Mg supplementation. Inhibition of Gardos channel by clotrimazole and senicapoc has led to Phase 1,2,3 trials in patients with sickle cell disease. While none of these studies has resulted in the approval of a novel therapy for SS disease, they have highlighted the key role played by these pathways in disease pathophysiology.

Hereditary stomatocytosis: An underdiagnosed condition

Hereditary stomatocytoses are a wide class of hemolytic anemias characterized by alterations of ionic flux with increased cation permeability that results in inappropriate shrinkage or swelling of the erythrocytes, and water lost or gained osmotically. The last few years have been crucial for new acquisitions in this field in terms of identifying new causative genes and of studying their pathogenetic mechanisms. This review summarizes the main features of erythrocyte membrane transport diseases, dividing them into forms with either isolated erythroid phenotype (nonsyndromic) or extra-hematological manifestations (syndromic), and focusing particularly on the most recent advances regarding dehydrated forms of hereditary stomatocytosis and familial pseudohyperkalemia.

Piezos thrive under pressure: mechanically activated ion channels in health and disease

Cellular mechanotransduction, the process of translating mechanical forces into biological signals, is crucial for a wide range of physiological processes. A role for ion channels in sensing mechanical forces has been proposed for decades, but their identity in mammals remained largely elusive until the discovery of Piezos. Recent research on Piezos has underscored their importance in somatosensation (touch perception, proprioception and pulmonary respiration), red blood cell volume regulation, vascular physiology and various human genetic disorders.

Genetic Diseases of PIEZO1 and PIEZO2 Dysfunction

Mutations in the genes encoding the mechanosensitive cation channels PIEZO1 and PIEZO2 are responsible for multiple hereditary human diseases. Loss-of-function mutations in the human PIEZO1 gene cause autosomal recessive congenital lymphatic dysplasia. Gain-of-function mutations in the human PIEZO1 gene cause the autosomal dominant hemolytic anemia, hereditary xerocytosis (also known as dehydrated stomatocytosis). Loss-of-function mutations in the human PIEZO2 gene cause an autosomal recessive syndrome of muscular atrophy with perinatal respiratory distress, arthrogryposis, and scoliosis. Gain-of-function mutations in the human PIEZO2 gene cause three clinical types of autosomal dominant distal arthrogryposis. This chapter will review the hereditary diseases caused by mutations in the PIEZO genes and will discuss additional physiological systems in which PIEZO channel dysfunction may contribute to human disease pathophysiology.

Comparison of Zebrafish tmem88a mutant and morpholino knockdown phenotypes

Tmem88a is a transmembrane protein that is thought to be a negative regulator of the Wnt signalling pathway. Several groups have used antisense morpholino oligonucleotides in an effort to characterise the role of tmem88a in zebrafish cardiovascular development, but they have not obtained consistent results. Here, we generate an 8 bp deletion in the coding region of the tmem88a locus using TALENs, and we have gone on to establish a viable homozygous tmem88aΔ8 mutant line. Although tmem88aΔ8 mutants have reduced expression of some key haematopoietic genes, differentiation of erythrocytes and neutrophils is unaffected, contradicting our previous study using antisense morpholino oligonucleotides. We find that expression of the tmem88a paralogue tmem88b is not significantly changed in tmem88aΔ8 mutants and injection of the tmem88a splice-blocking morpholino oligonucleotide into tmem88aΔ8 mutants recapitulates the reduction of erythrocytes observed in morphants using o-Dianisidine. This suggests that there is a partial, but inessential, requirement for tmem88a during haematopoiesis and that morpholino injection exacerbates this phenotype in tmem88a morpholino knockdown embryos.

The Power of Zebrafish in Personalised Medicine

The goal of personalised medicine is to develop tailor-made therapies for patients in whom currently available therapeutics fail. This approach requires correlating individual patient genotype data to specific disease phenotype data and using these stratified data sets to identify bespoke therapeutics. Applications for personalised medicine include common complex diseases which may have multiple targets, as well as rare monogenic disorders, for which the target may be unknown. In both cases, whole genome sequence analysis (WGS) is discovering large numbers of disease associated mutations in new candidate genes and potential modifier genes. Currently, the main limiting factor is the determination of which mutated genes are important for disease progression and therefore represent potential targets for drug discovery. Zebrafish have gained popularity as a model organism for understanding developmental processes, disease mechanisms and more recently for drug discovery and toxicity testing. In this chapter, we will examine the diverse roles that zebrafish can make in the expanding field of personalised medicine, from generating humanised disease models to xenograft screening of different cancer cell lines, through to finding new drugs via in vivo phenotypic screens. We will discuss the tools available for zebrafish research and recent advances in techniques, highlighting the advantages and potential of using zebrafish for high throughput disease modeling and precision drug discovery.

Neural Crest Migration and Survival Are Susceptible to Morpholino-Induced Artifacts

The neural crest (NC) is a stem cell-like embryonic population that is essential for generating and patterning the vertebrate body, including the craniofacial skeleton and peripheral nervous system. Defects in NC development underlie many birth defects and contribute to formation of some of the most malignant cancers in humans, such as melanoma and neuroblastoma. For these reasons, significant research efforts have been expended to identify genes that control NC development, as it is expected to lead to a deeper understanding of the genetic mechanisms controlling vertebrate development and identify new treatments for NC-derived diseases and cancers. However, a number of inconsistencies regarding gene function during NC development have emerged from comparative analyses of gene function between mammalian and non-mammalian systems (chick, frog, zebrafish). This poses a significant barrier to identification of single genes and/or redundant pathways to target in NC diseases. Here, we determine whether technical differences, namely morpholino-based approaches used in non-mammalian systems, could contribute to these discrepancies, by examining the extent to which NC phenotypes in fascin1a (fscn1a) morphant embryos are similar to or different from fscn1a null mutants in zebrafish. Analysis of fscn1a morphants showed that they mimicked early NC phenotypes observed in fscn1a null mutants; however, these embryos also displayed NC migration and derivative phenotypes not observed in null mutants, including accumulation of p53-independent cell death. These data demonstrate that morpholinos can cause seemingly specific NC migration and derivative phenotypes, and thus have likely contributed to the inconsistencies surrounding NC gene function between species. We suggest that comparison of genetic mutants between different species is the most rigorous method for identifying conserved genetic mechanisms controlling NC development and is critical to identify new treatments for NC diseases.

New insights on hereditary erythrocyte membrane defects

After the first proposed model of the red blood cell membrane skeleton 36 years ago, several additional proteins have been discovered during the intervening years, and their relationship with the pathogenesis of the related disorders have been somewhat defined. The knowledge of erythrocyte membrane structure is important because it represents the model for spectrin-based membrane skeletons in all cells and because defects in its structure underlie multiple hemolytic anemias. This review summarizes the main features of erythrocyte membrane disorders, dividing them into structural and altered permeability defects, focusing particularly on the most recent advances. New proteins involved in alterations of the red blood cell membrane permeability were recently described. The mechanoreceptor PIEZO1 is the largest ion channel identified to date, the fundamental regulator of erythrocyte volume homeostasis. Missense, gain-of-function mutations in the PIEZO1 gene have been identified in several families as causative of dehydrated hereditary stomatocytosis or xerocytosis. Similarly, the KCNN4 gene, codifying the so called Gardos channel, has been recently identified as a second causative gene of hereditary xerocytosis. Finally, ABCB6 missense mutations were identified in different pedigrees of familial pseudohyperkalemia. New genomic technologies have improved the quality and reduced the time of diagnosis of these diseases. Moreover, they are essential for the identification of the new causative genes. However, many questions remain to solve, and are currently objects of intensive studies.