Expression analysis of the polypyrimidine tract binding protein (PTBP1) and its paralogs PTBP2 and PTBP3 during Xenopus tropicalis embryogenesis.

The PTB (polypyrimidine tract binding protein) family of RNA-binding proteins plays a critical role in development through the regulation of post-transcriptional events. We have determined expression patterns of the three members of this gene family ptbp1, ptbp2 and ptbp3 during Xenopus tropicalis embryogenesis using whole-mount in situ hybridization. Our results show that each paralog presents a unique pattern of expression. ptbp1 is the prevalent maternal mRNA and is differentially expressed in the three germ layers. Later in development, it is widely expressed in the embryo including the epidermis, the dermatome, the intermediate mesoderm, the lateral plate mesoderm and the neural crest. ptbp2 expression is restricted to the nervous system including the brain, the neural retina and the spinal cord and the intermediate mesoderm. In addition to being expressed in erythroid precursors, ptbp3 is present in specific subdomains of the brain and the spinal cord, as well as in the posterior part of the notochord, suggesting it may play a role in the patterning of the nervous system. In the eye, each of the three genes is expressed in a specific structure which emphasizes their non-redundant function during development. Strickingly, our experiments also revealed that none of the three paralogs was expressed in the myotome, suggesting that the absence of PTB activity is a key determinant to display myotomal splicing patterns.