This study characterizes regulatory elements of collagen2 alpha 7 (col2a1) in Xenopus that enable transgene expression in cartilage-forming chondrocytes. The reporters described in this study drive strong cartilage-specific gene expression, which will be a valuable tool for further investigations of Xenopus skeletal development. While endogenous col2a1 mRNA is expressed in many embryonic tissues, its expression becomes restricted to tadpole and adult chondrocytes. This chondrocyte-specific expression is recapitulated by col2a1 reporter constructs, which were tested through I-Scel meganuclease-mediated transgenesis. These constructs contain a portion of the Xenopus tropicalis col2a1 intron, which aligns to a cartilage-specific intronic enhancer that has been well characterized in mammals. Two overlapping regions of the first intron that are 1.5-Kb and 665-bp long, both of which contain this enhancer sequence, drove EGFP expression in both larval and adult chondrocytes when connected to an upstream promoter. However, neither a truncated 155-bp region that also contains the enhancer, nor a separate 347-bp intronic region that lacks it, was able to drive cartilaginous transgene expression. The two cartilage-specific transgenes are heritable in F1 progeny, which exhibit none of the background expression observed in the injected founders. This study is the first to use the I-Scel technique to characterize an enhancer element in Xenopus, and the first to generate chondrocyte-specific gene expression in a non-mammalian vertebrate. The creation of novel cartilage-specific gene expression provides a new tool for further studies of anuran skeletal development.
A new species of Asian warty newt, Paramesotriton ermizhaoi, is described from Guangxi Zhuang Autonomous Region in southern China. This species is easily distinguished from other congeners by external morphology and osteology. Phylogenetic analyses based on mitochondrial data place P. ermizhaoi as a possible sister taxon to P. hongkongensis and P. chinensis. The number of trunk vertebrae varies from 12 to 13 in the new species. The relationship between P. ermizhaoi and a potentially new Pachytriton species (Pachytriton C), and the Guangxi population of P. chinensis is briefly discussed.