The first see-through frog created by breeding: description, inheritance patterns, and dermal chromatophore structure

Abstract

We have succeeded in creating see-through frogs from natural color mutants of the Japanese brown frog Rana japonica, which usually possesses an ochre or brown back; this coloration enables the organs, blood vessels, and eggs to be observed through the skin without performing dissection. We crossed two kinds of recessive color mutant (black-eyed and gray-eyed) frogs through artificial insemination, and F2 offspring produced frogs whose skin is translucent throughout the life cycle. Three kinds of dermal chromatophores--xanthophores, iridophores, and melanophores--are observed in a layered arrangement in the skin of wild-type frogs, but few chromatophores were present in the skin of the see-through frogs. The translucent skin enables observation of organ growth and cancer formation and progression in the animal, which can be monitored over its entire life without the need for dissection. See-through frogs thus provide a useful animal model for environmental, medical, and biological research.

Figure 1. See-through, two color mutant, and wild-type adult Rana japonica frogs.

(A) Dorsolateral view of four types. (B) Ventral view of four types. (C) See-through frog (frontal view). (D) See-through frog (ventral view). (E) See-through frog (ventrolateral view). (Scale bar 1 cm)

Figure 2. Internal organs of live see-through frogs and tadpoles visible through the translucent skin.

(A) Breathing see-through frog (dorsolateral view). (B) Heart beating see-through frog (ventral view). (C) See-through tadpole (dorsal view). (D) See-through tadpole (ventral view). (E) Eggs of see-through and wild-type frogs (just after insemination). (F) Ovulated see-through frog (lateral view). (G) Ovulated see-through frog (ventral view). (Scale bar 1 cm)

Figure 3. Electron microphotographs of dermal chromatophores in the dorsal skin.

(A–C) Wild-type frog. (D–F) Gray-eyed frog. (G,H) Black-eyed frog. (I,J) See-through frog. Me: melanophore, Xa: xanthophore, Ir: iridophore, me: melanosome, pt: pterinosome, c.v.: carotenoide vesicle, r.p.: reflecting platelet. Arrows indicate melanosome-like structures. (Scale bar A,D,G,I: 2 μm; B,C,E,F,H,J: 500 nm)