FoxP1, FoxP2 and FoxP4 in the song control system of zebra finches: molecular interactions and relevance for vocal learning ; FoxP Sub-Familien Proteinmitglieder, die beim Gesangserwerb der Zebrafinken beteiligt sind

The Forkhead transcription factor FoxP2 is important both for human speech and for bird song learning. In vitro, transcriptional activity of FoxP2 requires dimerization, either with itself of with other members of the Forkhead P family, FoxP1 and FoxP4. In vivo, the brain expression patterns of FoxP1, FoxP2 and FoxP4 have not been systematically compared for regional or cellular co-localization. To provide the means for future functional studies I cloned FoxP4 from zebra finches and compared both the mRNA and protein expression patterns of FoxP1, FoxP2 and FoxP4 at different ages. I found overlapping expression of FoxP1, FoxP2 and FoxP4 in striatum and there, in Area X, a nuclei important for song learning. HVC and RA, two important nuclei of the motor pathway of the song system, express FoxP1 and FoxP4. All FoxP subfamily members studied had a specific pattern of expression, shown in regions of overlapping expression and regions were there are either expressed alone or with another FoxP member. I further characterize HVC neurons expressing FoxP1 and FoxP4 as Area X and RA projecting neurons. To address whether specific combinations of FoxP expression existed I analyzed co-expression in the most important song nuclei using double in situ hybridization and triple immunohistochemistry. I provide the first evidence that FoxP subfamily members can be co-express in the same neurons. In Area X and striatum, I found neurons expressing all combinations of FoxP expression consistently during the different ages assessed. Surprisingly I found few cells that expressed only FoxP2, the majority of cells were FoxP1+/FoxP2+/FoxP4+, FoxP1+/FoxP4+ or FoxP1 alone. In addition all Purkinje cells express FoxP2 and FoxP4, HVC projecting neurons express FoxP1 and FoxP4 as well as RA neurons. A second part of my work focus on the interaction of zebra finch FoxP1, FoxP2 and FoxP4 proteins and what the functional implication of this interaction would be. I first show in vitro that zebra finch FoxP1/2/4 proteins are able to homo- and ...