Resegmentation in the mexican axolotl, Ambystoma mexicanum

Abstract

The segmental series of somites in the vertebrate embryo gives rise to the axial skeleton. In amniote models, single vertebrae are derived from the sclerotome of two adjacent somites. This process, known as resegmentation, is well-studied using the quail-chick chimeric system, but the presumed generality of resegmentation across vertebrates remains poorly evaluated. Resegmentation has been questioned in anamniotes, given that the sclerotome is much smaller and lacks obvious differentiation between cranial and caudal portions. Here, we provide the first experimental evidence that resegmentation does occur in a species of amphibian. Fate mapping of individual somites in the Mexican axolotl (Ambystoma mexicanum) revealed that individual vertebrae receive cells from two adjacent somites as in the chicken. These findings suggest that large size and segmentation of the sclerotome into distinct cranial and caudal portions are not requirements for resegmentation. Our results, in addition to those for zebrafish, indicate that resegmentation is a general process in building the vertebral column in vertebrates, although it may be achieved in different ways in different groups.

Building the backbone: the development and evolution of vertebral patterning

“…Resegmentation has also been confirmed recently during urodele amphibian development (Piekarski and Olsson, 2014). It therefore operates in diverse tetrapods, and, in exploring its evolutionary origins, it will be interesting to assess its status in basal vertebrates.…”

Embryonic development of the axial column in the little skate,Leucoraja erinacea

“…In tetrapods (salamander, chick, and mouse), vertebrae have been documented to form entirely from migrating sclerotomal cells that condense around the notochord to form a perichordal tube of tissue that then differentiates into individual vertebral units (Bagnall et al, ; Christ and Wilting, ; Piekarski and Olsson, ). In chick ( Gallus gallus ), the ventral portion of the somite has been fate mapped to specific vertebral components, with the medial‐most cell population contributing to the centra, the dorsal sclerotomal cells giving rise to neural spines, and the lateral portion of the sclerotome making up the remainder of the neural arches and ribs (Bagnall et al, ; Christ et al, ).…”

“…In chick ( Gallus gallus ), the ventral portion of the somite has been fate mapped to specific vertebral components, with the medial‐most cell population contributing to the centra, the dorsal sclerotomal cells giving rise to neural spines, and the lateral portion of the sclerotome making up the remainder of the neural arches and ribs (Bagnall et al, ; Christ et al, ). In the axolotl ( Ambystoma mexicanum ), a urodele amphibian, fate mapping of somites three to five shows somitic contributions to all vertebral parts, including the centra, arches, and intervertebral discs (Piekarski and Olsson, ). This variation in vertebral development across vertebrates highlights the need for more data from the sister group of osteichthyans, the cartilaginous fishes (chondrichthyans).…”

Osseous pathologies in the lungless salamander Desmognathus fuscus (Plethodontidae)

“…In teleost fishes, on the contrary, centrum formation can be induced by the notochord (Nordvik, Kryvi, Totland, & Grotmol, 2005) or formed by the so‐called "leaky‐resegmentation," in which the centra are formed from cells originated from numerous somites (Morin‐Kensicki, Melancon, & Eisen, 2002). Lissamphibians are characterized by a small amount of sclerotomal cells and resegmentation was first documented in caecilians by Wake and Wake (2000) which was followed by its discovery in salamanders by Piekarski and Olsson (2014). Vertebral formation in frogs is still without evidence of resegmentation (Blanco & Sanchiz, 2000; Handrigan & Wassersug, 2007; Wake & Lawson, 1973).…”