image: Figure 1. Genome assemblies of three limbless lizards and independent limb loss in Squamata view more
Credit: ©Science China Press
This study is reported by Jia-Tang Li’s group from the Chengdu Institute of Biology, Chinese Academy of Sciences. The development of limbs is significant for the origin and evolution of tetrapods, providing multiple functions and capabilities. Although limb loss has occurred in many clades to adapt to new environments, it is particularly common in Squamata, which have evolved independently at least 26 times. Squamates are therefore an ideal model for studying the evolution of limb loss.
The team performed de novo-assembled genomes of three limbless lizards from different clades of Squamata (i.e. European glass lizard, Hart’s glass lizard, and Bourret’s blind skink). The constructed topology indicated the independent limb losses in the squamate lineages.
Focusing on the conserved non-coding elements (CNEs), the team identified convergent signals both in the snake and limbless lizard pair and in the limbless lizard pair. These convergently divergent CNEs (dCNEs) are associated with regulatory signals during early limb development, and the associated genes are required for limb initiation and outgrowth. Experiments suggest that the regulatory functions of these CNEs have been altered and that mutations in the transcription factor binding sites are the major cause.
The team further found the extensive existence of lineage-specific insertions and deletions (InDels) in the CNEs across limbless squamates. These InDel CNEs, together with the dCNEs, overlap with regulatory signals in limb development. Nearby genes of these InDel CNEs are involved in limb bud formation, such as Tbx4, Fgf10, and Gli3. Based on experiments, the authors found that the functions of these CNEs are affected by InDels, leading to an increase or decrease in the expression of downstream genes. This may be the important genetic mechanism for limb loss in squamates.
In this paper, the team presents the genetic mechanism that contributes to limb loss in squamates and their research sheds light on the importance of the regulatory element InDels in phenotypic evolution. This is important for understanding the genetic mechanism for the evolution of complex biological traits.
See the article:
Developmental regulation of conserved non-coding element evolution provides insights into limb loss in squamates
Journal
Science China Life Sciences