Xenopus to the rescue: A model to validate and characterize candidate ciliopathy genes

Abstract

Summary Cilia are present on most vertebrate cells and play a central role in development, growth, and homeostasis. Thus, cilia dysfunction can manifest into an array of diseases, collectively termed ciliopathies, affecting millions of lives worldwide. Yet, our understanding of the gene regulatory networks that control cilia assembly and functions remain incomplete. With the advances in next‐generation sequencing technologies, we can now rapidly predict pathogenic variants from hundreds of ciliopathy patients. While the pace of candidate gene discovery is exciting, most of these genes have never been previously implicated in cilia assembly or function. This makes assigning the disease causality difficult. This review discusses how Xenopus, a genetically tractable and high‐throughput vertebrate model, has played a central role in identifying, validating, and characterizing candidate ciliopathy genes. The review is focused on multiciliated cells (MCCs) and diseases associated with MCC dysfunction. MCCs harbor multiple motile cilia on their apical surface to generate extracellular fluid flow inside the airway, the brain ventricles, and the oviduct. In Xenopus, these cells are external and present on the embryonic epidermal epithelia, facilitating candidate genes analysis in MCC development in vivo. The ability to introduce patient variants to study their effects on disease progression makes Xenopus a powerful model to improve our understanding of the underlying disease mechanisms and explain the patient phenotype.

Microridge-like structures anchor motile cilia

“…The genetically tractable Xenopus has become an important model to characterize the function of motile cilia and cilia-associated molecules 7 , 8 . Multiciliated cells (MCCs) of the Xenopus epidermis develop from precursor cells that arise from deeper epidermal layers and penetrate the superficial cell layer by radial intercalation 9 – 11 .…”

PCD Genes—From Patients to Model Organisms and Back to Humans

“…Cells assembling motile cilia are bordered by cells forming non-motile cilia [247]. The effect of LRO cilia activity (position of developing heart and other organs) can be analyzed in 3-4 days old larvae [248,251].…”

“…Cells destined to become multiciliated start to express cilia-specific genes ~12 hpf (stage 11.5), and ciliogenesis starts around stage 20 (~21 hpf). By stage 28 (~32 hpf), assembled cilia are properly oriented [251,256,257].…”

An updated SYSCILIA gold standard (SCGSv2) of known ciliary genes, revealing the vast progress that has been made in the cilia research field

“…Caenorhabditis elegans and Drosophila melanogaster were useful models for early characterisation of genes encoding ciliary proteins, through genome-wide identification of promoters containing an X-box, and study of genes under control of ciliary transcription factors (Blacque et al, 2005;Efimenko et al, 2005;Laurençon et al, 2007). These simple model organisms show some striking conservation with humans and have been useful for identifying and characterising orthologs of human ciliopathy genes (Keller et al, 2005;Chen et al, 2006), further developed through studies of vertebrate models such as Xenopus tropicalis and laevis and zebrafish (Song et al, 2016;Rao and Kulkarni, 2021). Rat and mouse have been important mammalian models for understanding and modelling the role of cilia in human health and disease (Norris and Grimes, 2012).…”

“…, 2006 ), further developed through studies of vertebrate models such as Xenopus tropicalis , X. laevis , and zebrafish ( Song et al. , 2016 ; Rao and Kulkarni, 2021 ). Rat and mouse have been important mammalian models for understanding and modelling the role of cilia in human health and disease ( Norris and Grimes, 2012 ).…”