Transcriptomic profiling shows brain gene expression associated with learning in the fire-bellied toad, Bombina orientalis.
A key goal in modern neurobiology is to understand the molecular and cellular mechanisms underlying learning and memory. To that end, it is essential to identify the patterns of gene expression and the temporal sequence of molecular events associated with learning and memory processes. Further, in order to advance our knowledge of the evolution of processes that mediate behaviour, we need to understand how these molecular and cellular events vary between organisms. In vertebrates, the acquisition and extinction of a learned response is characterized by distinct phases of molecular activity involving gene transcription, protein synthesis, structural change, and long-term maintenance of such structural change in the nervous system. The fire-bellied toad, Bombina orientalis, is a basal anuran whose neural architecture and molecular pathways may help us describe shared and divergent characteristics of learning and memory mechanisms between amphibians and mammals, and thus help answer questions about the evolution of learning in vertebrates. Utilizing next generation sequencing techniques, I profiled gene expression patterns in the brain of the fire-bellied toad after the acquisition and extinction of prey-catching conditioning, following either short or long training. This allowed me to describe the time-course of learning-related gene expression as well as compare transcriptomic profiles associated with acquisition learning, extinction learning, and resistance to extinction. Differential gene expression following acquisition and extinction training revealed activity in molecular pathways related to neural plasticity (e.g. immediate early genes activity, cytoskeletal modification, axonogenesis, apoptotic processes, mitogen activated protein kinase (MAPK)/GTPase signaling pathways). Further, mechanisms unique to extinction learning and resistance to extinction were found in inhibitory signaling pathways (e.g. chromatin mediated transcriptional suppression, inhibitory neurotransmission, suppression of molecular signaling cascades). While some of these gene expression patterns are similar to those found in mammals submitted to conditioning, many interesting divergent profiles were seen, highlighting potential differences in the mechanisms of learning and memory among tetrapods. Ultimately, this approach has allowed us to describe not only gene expression associated with learning, but also a core set of putative learning related genes in B. orientalis which supports the hypothesis of a general conservation of learning mechanisms between anuran amphibian and mammals.