The International Journal of Developmental Biology

Int. J. Dev. Biol. 65: 177 - 186 (2021)

Vol 65, Issue 4-5-6

Special Issue: Developmental Biology in Ibero-America - Part 2

Delineating the anuran axial skeleton

Published: 27 August 2020

Sara S. Sánchez*,1 and Romel S. Sánchez1,2,3

1Instituto Superior de Investigaciones Biológicas (INSIBIO), CONICET-UNT, and Instituto de Biología “Dr. Francisco D. Barbieri”, Facultad de Bioquímica, Química y Farmacia, 2Cátedra de Biología General, Facultad de Ciencias Naturales e Instituto Miguel Lillo and 3Instituto Superior de Investigaciones Biológicas (INSIBIO), CONICET-UNT. Cátedra de Fisiología, Departamento Biomédico-Fisiología, Facultad de Medicina, Universidad Nacional de Tucumán, San Miguel de Tucumán, Argentina


The axial skeleton of the anurans has undergone an evolutionary reduction of its bone elements. This structural plan is strongly preserved throughout the order and would have emerged as a highly specialized anatomical adaptation to its locomotor jumping pattern. The development programs that direct the vertebral morphogenesis of the anurans are poorly described and the molecular bases that have caused their pattern to differ from other tetrapods are completely unknown. In this work, we review the ontogeny of the spinal column of the anurans and explore the genetic mechanisms that could explain the morphological difference and the maintenance of the body plan during evolution. Here, we propose that the absence of caudal osseous elements, as a consequence of the inability of sclerotomes to form cartilaginous condensations in frogs, could be due to changes in both pattern and expression levels of Hox, Pax1, Pax9 and Uncx4.1 genes along the anteroposterior axis. The anteriorised expression of the Hox genes together with the reduction in the expression levels of Pax1, Pax9 and Uncx4 in the posterior somites could explain, at least partly, the loss of caudal vertebrae in the anurans during evolution.


anurans, Xenopus, vertebral column, sclerotome, pax1, pax9, uncx, Hox

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