Developmental basis of limblessness and axial patterning in snakes

  title={Developmental basis of limblessness and axial patterning in snakes},
  author={Martin J. Cohn and Cheryll Tickle},
The evolution of snakes involved major changes in vertebrate body plan organization, but the developmental basis of those changes is unknown. The python axial skeleton consists of hundreds of similar vertebrae, forelimbs are absent and hindlimbs are severely reduced. Combined limb loss and trunk elongation is found in many vertebrate taxa, suggesting that these changes may be linked by a common developmental mechanism. Here we show that Hox gene expression domains are expanded along the body… 
Developmental, genetic, and genomic insights into the evolutionary loss of limbs in snakes
The idea that pleiotropy of cis‐regulatory elements may illuminate the convergent genetic changes that occurred in snake‐like lizards is explored, and a number of challenges that remain to be addressed in future studies are discussed.
Regulation of vertebrate forelimb development and wing reduction in the flightless emu
  • Axel H. Newton, C. Smith
  • Biology, Psychology
    Developmental dynamics : an official publication of the American Association of Anatomists
  • 2020
This review summarises the developmental regulation of vertebrate forelimb diversity, with particular focus on wing reduction in the flightless emu as a model for studying limb heterochrony.
Shifts in axial patterning in snake and caecilian embryos
At the molecular level there is a higher degree of body axis regionalization than previously anticipated and it is suggested that, at least in snakes, the formation of ribs is a partially Hox independent.
Patterning mechanisms controlling vertebrate limb development.
The analysis of specific gene functions has revealed the existence of complex interactions between signaling pathways operated by secreted factors of the HH, TGF-beta/BMP, WNT, and FGF superfamilies, which interact with many other genetic networks to control limb positioning, outgrowth, and patterning.
Developmental basis of evolutionary digit loss in the Australian lizard Hemiergis.
A comparative analysis of expression of MSX and Distal-less proteins among embryos from different populations suggests an early role for SHH in specification of digit identity and later importance in maintaining cell proliferation and survival in Hemiergis.
Evolution of Vertebrate Limb Development
The origin and diversification of fins and limbs have long been a focus of interest to both palaeontologists and developmental biologists. Studies conducted in recent decades have resulted in
Competent stripes for diverse positions of limbs/fins in gnathostome embryos
A continuous distribution of competent stripes is hypothesized that represents the common developmental program at the root of appendage formation in gnathostomes.


Hox9 genes and vertebrate limb specification
It is shown that the same population of flank cells can be induced to form either a wing or a leg, and that induction of these ectopic limbs is accompanied by specific changes in expression of three Hox genes in lateral plate mesoderm.
Hox genes and the evolution of vertebrate axial morphology.
A comparative study of the developmental patterns of homeobox gene expression and developmental morphology between animals that have homologous regulatory genes but different morphologies, which contributes a mechanistic level to the assumed homology of these regions in vertebrates.
Dorso-ventral limb polarity and origin of the ridge: on the fringe of independence?
  • R. Zeller, D. Duboule
  • Biology
    BioEssays : news and reviews in molecular, cellular and developmental biology
  • 1997
It is suggested that DV patterning and AER induction, though coordinately regulated during limb bud outgrowth, may early on be more dissociated than expected.
Analysis of Hox gene expression in the chick limb bud.
Comparison of the distributions of Hoxc-6 RNA and protein products reveals posttranscriptional regulation of this gene, suggesting that caution must be exercised in interpreting the functional significance of the RNA distribution of any of the vertebrate Hox genes.
Position-dependent expression of two related homeobox genes in developing vertebrate limbs
Results reported here indicate that both genes are rapidly activated by a signal from the apical ectoderm, which strongly suggest that Hox-7.1 and H Cox-8.1 have fundamental roles in limb-pattern formation.
Cyclopia and defective axial patterning in mice lacking Sonic hedgehog gene function
Targeted gene disruption in the mouse shows that the Sonic hedgehog(Shh) gene plays a critical role in patterning of vertebrate embryonic tissues, including the brain and spinal cord, the axial
Conservation in the Hox code during morphological evolution.
  • S. Gaunt
  • Biology
    The International journal of developmental biology
  • 1994
The results suggest that the Hox code, at least in the development of homologous axial structures, is conserved between species and an evolutionary change in body proportions is accomplished by a shift in the relative positions of Hox expression domains during embryonic development.
Patterns of distal-less gene expression and inductive interactions in the head of the direct developing frog Eleutherodactylus coqui.
It is shown here that inductive interactions in the anterior region of the E. coqui embryo have been modified during the evolution of direct development, and that changes in the competence ofThe E.coqui ectoderm may be responsible for the loss of certain tadpole-specific structures, such as cement gland.
Distribution of Sonic hedgehog peptides in the developing chick and mouse embryo.
Temporal expression of Shh peptides is consistent with induction of sclerotome in somites and floor plate and motor neurons in the CNS, as well as the regulation of anterior-posterior polarity in the limb, but there is no direct evidence for long-range diffusion of the 19 x 10(3) Mr peptide which is thought to mediate both short- and long- range cell interactions.