Advancing genetic and genomic technologies deepen the pool for discovery in Xenopus tropicalis

Abstract

Xenopus laevis and Xenopus tropicalis have long been used to drive discovery in developmental, cell, and molecular biology. These dual frog species boast experimental strengths for embryology including large egg sizes that develop externally, well‐defined fate maps, and cell‐intrinsic sources of nutrients that allow explanted tissues to grow in culture. Development of the Xenopus cell extract system has been used to study cell cycle and DNA replication. Xenopus tadpole tail and limb regeneration have provided fundamental insights into the underlying mechanisms of this processes, and the loss of regenerative competency in adults adds a complexity to the system that can be more directly compared to humans. Moreover, Xenopus genetics and especially disease‐causing mutations are highly conserved with humans, making them a tractable system to model human disease. In the last several years, genome editing, expanding genomic resources, and intersectional approaches leveraging the distinct characteristics of each species have generated new frontiers in cell biology. While Xenopus have enduringly represented a leading embryological model, new technologies are generating exciting diversity in the range of discoveries being made in areas from genomics and proteomics to regenerative biology, neurobiology, cell scaling, and human disease modeling.

Parallel in vivo analysis of large-effect autism genes implicates cortical neurogenesis and estrogen in risk and resilience

“…Xenopus has several key advantages for this purpose, including being relatively high throughput and low cost for an in vivo model and providing the opportunity for unilateral mutagenesis by CRISPR-Cas9 injection, allowing the comparison of mutated and control halves of the brain within the same animal throughout vertebrate development (Exner and Willsey, 2020). In addition, its conserved and syntenic diploid genome allows for unambiguous identification of orthologous genes with humans, and a host of studies of human physiology and development have produced important mechanistic insights into congenital heart, kidney, and brain disorders, among others (Exner and Willsey, 2020;Krneta-Stankic et al, 2017;Deniz et al, 2018;Duncan and Khokha, 2016;Garfinkel and Khokha, 2017;Kakebeen and Wills, 2019;Willsey et al, 2018aWillsey et al, , 2018bDeLay et al, 2018). Finally, the approach facilitates not only the investigation of convergent pathology but also an evaluation of in vivo resilience mechanisms through small-molecule, chemical, and genetic suppressor screens.…”

Embryo, larval, and juvenile staging of Lytechinus pictus from fertilization through sexual maturation

“…Knowing the precise timing of specification and differentiation of important cell populations is essential to being able to manipulate the embryo and provide a common language for discussion of development. Perhaps the most well-recognized standardized staging schemes come from Xenopus, [46][47][48] zebrafish, 49 and chick. 50 Each of these vertebrate models has unique advantages and improved accessibility for studying specific processes in development such as nervous system development, regeneration, or formation of limb buds.…”

Xenopus leads the way: Frogs as a pioneering model to understand the human brain

“…Injectable reagents include plasmids and mRNA for overexpression experiments, morpholinos for knockdown of maternal or zygotic expression, and, recently, CRISPR/Cas9 for genome editing (Aslan, Tadjuidje, Zorn, & Cha, 2017; Bhattacharya, Marfo, Li, Lane, & Khokha, 2015; Blitz, Biesinger, Xie, & Cho, 2013; Guo et al, 2014; Naert et al, 2020; Naert & Vleminckx, 2018; Nakayama, Grainger, & Cha, 2020; Tandon, Frank, David Furlow, & Horb, 2017). Although all of these tools can be used in X. laevis or X. tropicalis , CRISPR approaches have more commonly been deployed in X. tropicalis due to its diploid genome, whereas the pseudotetraploid X. laevis is often preferred for overexpression experiments and for embryological, cell biological, and biochemical approaches because of its larger size (Harland & Grainger, 2011; Kakebeen & Wills, 2019a, 2019b).…”