Balanced expression of various TrkB receptor isoforms from the Ntrk2 gene locus in the mouse nervous system.

A brain-derived neurotrophic factor (BDNF) receptor TrkB involves three spliced variants, namely the tyrosine kinase domain (TK) intact (+) and two TK(-) isoforms T1 and T2, yet their precise roles are largely unknown. Here we extensively map the mRNA expression patterns of BDNF and TrkB variants, further to gain insights in TK(-) specific functions during mouse development. Consequently, we found that TK(+), T1 and T2 were expressed in distinct regions of the mouse nervous system at the embryonic and postnatal stages, implicating separable functions of TK(-) forms. Additionally we uncovered five expressed segments in the intron between T2 and T1 specific exons, and one of these segments was revealed to code novel TK(-) receptors with unique responsiveness in vitro. These results suggest dynamic modes of expression from the Ntrk2 gene locus and multiple roles of TK(-) forms in the developing mouse nervous system.