The road to the vertebral formula

Abstract

In vertebrates, the paraxial mesoderm differentiates into several structures, including the axial skeleton. The genetic mechanisms that control positional information in the paraxial mesoderm along the anterior-posterior axis are responsible for the development of a skeleton with the appropriate vertebral formula, i.e. a specific number of cervical, thoracic, lumbar, sacral and caudal vertebrae. These control mechanisms are complex and involve molecules of different kinds, including transcription factors, like those encoded by the Hox genes, and signalling molecules, like those involved in Gdf11, FGF, retinoic acid or WNT signalling. Recent experiments indicate that most of the positional information for the paraxial mesoderm is encoded during the initial steps of its development in the presomitic mesoderm, although it is only decoded later during differentiation of the somites. The genesis of positional identity may be linked to the process of somitogenesis, which also occurs in the presomitic mesoderm as a result of complex interactions involving oscillatory activity of components of the Notch and WNT signalling pathways and antagonistic gradients of FGF/WNT and retinoic acid. The possible connections between Hox genes and all these signalling processes to generate a properly patterned axial skeleton are discussed in this review.

Hox11 genes are required for regional patterning and integration of muscle, tendon and bone

“…There is a high degree of sequence similarity and functional redundancy between members within a Hox paralogous group (Mallo et al, 2009;Wellik, 2007). Loss of function of Abdominal-B class Hox genes from paralogous groups 9-13 results in disrupted patterning of limb skeletal elements within specific proximal-distal regions whereas other regions of the limb are largely unaffected.…”

Desarrollo neural, somitogénesis y morfología interna de los embriones de Hyloxalus vertebralis y Dendrobates auratus (Anura: Dendrobatidae)

“…La somitogénesis es el desarrollo de los somitas a partir del mesodermo paraxial localizado a cada lado de la línea media del cuerpo (Mallo et al, 2009;Pourquié, 2003).…”

“…De los somitas se originarán los tejidos óseo, cartilaginoso, muscular y la dermis (Krneta-Stankic et al, 2010;Mallo et al, 2009;Wolpert et al, 2007;Radice et al, 1989).…”

Hoxb6 can interfere with somitogenesis in the posterior embryo through a mechanism independent of its rib-promoting activity

“…A variety of genetic studies revealed that Hox proteins have a high degree of functional specificity, often shared by the different members of the same PG (Casaca et al, 2014). It is thought that morphological diversity in the axial skeleton results from the combined activities provided by the different Hox PGs (Mallo et al, 2009;Wellik, 2009).…”