Metamorphosis inhibition: an alternative rearing protocol for the newt, Cynops pyrrhogaster.

The newt is an indispensable model animal, of particular utility for regeneration studies. Recently, a high-throughput transgenic protocol was established for the Japanese common newt, Cynops pyrrhogaster. For studies of regeneration, metamorphosed animals may be favorable; however, for this species, there is no efficient protocol for maintaining juveniles after metamorphosis in the laboratory. In these animals, survival drops drastically after metamorphosis as their foraging behaviour changes to adapt to a terrestrial habitat, making feeding in the laboratory with live or moving foods more difficult. To elevate the efficiency of laboratory rearing of this species, we examined metamorphosis inhibition (Ml) protocols to bypass the period (four months to two years after hatching) in which the animal feeds exclusively on moving foods. We found that approximately 30% of animals survived after 2-year Ml, and that the survivors continuously grew, only with static food while maintaining their larval form and foraging behaviour in 0.02% thiourea (TU) aqueous solution, then metamorphosed when returned to a standard rearing solution even after 2-year-MI. The morphology and foraging behavior (feeding on static foods in water) of these metamorphosed newts resembled that of normally developed adult newts. Furthermore, they were able to fully regenerate amputated limbs, suggesting regenerative capacity is preserved in these animals. Thus, controlling metamorphosis with TU allows newts to be reared with the same static food under aqueous conditions, providing an alternative rearing protocol that offers the advantage of bypassing the critical period and obtaining animals that have grown sufficiently for use in regeneration studies.

Controlling gene loss of function in newts with emphasis on lens regeneration.

Here we describe a protocol for gene loss of function during regeneration in newts, specifically applied to lens regeneration. Knockdown with the use of morpholinos can be achieved both in vitro and in vivo, depending on the experimental design. These methods achieve desirable levels of gene knockdown, and thus can be compared with methods developed for use in other animals, such as zebrafish. The technology has been applied to study molecular mechanisms during the process of lens regeneration by knocking down genes at specific stages and examining their effects on other genes and lens differentiation. The protocol can take a few days or up to 20 d to complete, depending on the duration of the experiment.

Expressing exogenous genes in newts by transgenesis.

The great regenerative abilities of newts provide the impetus for studies at the molecular level. However, efficient methods for gene regulation have historically been quite limited. Here we describe a protocol for transgenically expressing exogenous genes in the newt Cynops pyrrhogaster. This method is simple: a reaction mixture of I-SceI meganuclease and a plasmid DNA carrying a transgene cassette flanked by the enzyme recognition sites is directly injected into fertilized eggs. The protocol achieves a high efficiency of transgenesis, comparable to protocols used in other animal systems, and it provides a practical number of transgenic newts (∼20% of injected embryos) that survive beyond metamorphosis and that can be applied to regenerative studies. The entire protocol for obtaining transgenic adult newts takes 4-5 months.

Simple and efficient transgenesis with I-SceI meganuclease in the newt, Cynops pyrrhogaster.

Newts have been recognized as an ideal model for body-parts regeneration after traumatic injury since the 18(th) century. However, molecular mechanisms underlying regeneration remain a mystery because of technical limitations. In the current study, to break this obstacle, we established a simple and efficient transgenic protocol for the newt Cynops pyrrhogaster by adapting an I-SceI microinjection technique, as well as a two-aquarium-tank (TAT) system that allows us to constantly obtain fertilized eggs in the laboratory for transgenesis. Following our protocol, ∼ 20% of injected embryos would exhibit non-mosaic widespread transgene expression and survive beyond metamorphosis. This anticipated success rate is about 10 times higher than that obtained by previous protocols, reaching a practical level. Therefore, our transgenic protocol in conjunction with the TAT-system could provide a key technique to open the way to uncover the long mystery underlying body-parts regeneration of newts.