Expression of cyclin D1, cyclin D2, and N-myc in embryos of the direct developing frog Eleutherodactylus coqui, with a focus on limbs

► Ccnd1 expression in E. coqui mandibular neural crest correlates with early formation of adult jaw. ► Ccnd2 midbrain expression in E. coqui correlates with early formation of the adult visual system. ► Ccnd2 and mycn expression in E. coqui define early, large limb fields, not seen in X. laevis. ► Ccnd1 and mycn expression in autopods indicates frog digit formation by differential growth. Species of frogs that develop directly have removed the tadpole from their ontogeny and form adult structures precociously. To see whether cell cycle regulators could be involved in this altered embryogenesis, we examined the expression of ccnd1, ccnd2, and mycn in embryos of the direct developing frog, Eleutherodactylus coqui. Notable differences compared to embryos of Xenopus laevis, a species with a tadpole, included prominent expression of ccnd2 in the midbrain and ccnd1 in the mandibular neural crest. The former may contribute to the precocious appearance of the adult-type visual system and the latter to the adult-type jaw. Large domains of ccnd2 and mycn presage the early appearance of limb buds, and ccnd1 and mycn are implicated in digit development.