Evolutionary Expression of the Orthopedia Transcription Factor in the Alar Hypothalamus: Implications for Amygdala Formation across Vertebrates.

Introduction: This study analyzes the expression of the transcription factor orthopedia (Otp) in the alar hypothalamus and its evolutionary relationship with the amygdaloid complex.

Methods: Immunofluorescence analysis was used in several representative vertebrates, including sarcopterygians (mice, chickens, turtles, anuran amphibians, and lungfish) and actinopterygian fish (teleosts and polypteriforms).

Results: We reveal highly conserved Otp expression in all species used, supporting its critical role in hypothalamic regional specification and in the development of neuroendocrine cells and the amygdaloid complex. Our results show that hypothalamic radial migration of Otp contributes to amygdaloid populations, particularly in those with subpallial origin, in a highly conserved manner from basal actinopterygians.

Conclusion: Differences between sarcopterygians and actinopterygians in the Otp expression patterns in cells migrated to the pallial amygdala highlight an evolutionary divergence, particularly in the complexity and cellular composition of this region, tracing its evolutionary emergence by using the studied species as reference. Moreover, present results emphasize the evolutionary and functional importance of hypothalamic-amygdaloid interactions.