FoxP1 Protein Shows Differential Layer Expression in the Parahippocampal Domain among Bird Species

Abstract

Different bird orders show diversity in neural capabilities supported by variations in brain morphology. The parahippocampal domain in the medial pallium, together with the hippocampus proper, plays an important role in memory skills. In the present work, we analyze the expression pattern of the FoxP1 protein in the parahippocampal area of four different bird species: the nonvocal learner birds quail and chicken (Galliformes) and two vocal learner birds, i.e. the zebra finch (Passeriformes) and the budgerigar (Psittaciformes), at different developmental and adult stages. We also analyze the expression of the calbindin protein in quails and zebra finches. We observed differences in the FoxP1 parahippocampal layer among bird species. In quails, chickens, and budgerigar, FoxP1 cells were located in the outer layers of the lateral and caudolateral parahippocampal sectors. In contrast, FoxP1 immunoreactive cells appeared in the inner layer of the same sectors in the zebra finch parahippocampal domain. These differences suggest two possibilities: either the FoxP1-positive cells described in quails, chickens, and budgerigars are a different population than the one described in the zebra finch, or there are changes in the pattern of radial migration in the parahippocampal area among birds. In the present study, we show that FoxP1 expression is more similar between quails, chickens, and budgerigars than between budgerigars and zebra finches in the parahippocampal area. This result contrasts with previous data in other telencephalic structures, like the calbindin-positive projection neurons described in the striatum of budgerigars and zebra finches but not in quails and chickens. All of these data point to diversity in the evolution of different morphological characters and, therefore, a mosaic model for telencephalic evolution in birds.

Brain evolution and development: adaptation, allometry and constraint

“…Human FOXP2 has two derived amino acid substitutions that specifically alter dopamine concentrations, dendrite length and synaptic plasticity in the basal ganglia of a transgenic mouse model [73], and purkinje cell function in the cerebellum [75]. Differential expression of another FOX family gene, FOXP1, in the avian telencephalon also provides support for the regionspecific action of key transcription factors in moderating mosaic patterns of brain evolution [76]. The human-specific duplication of SRGAP2 provides a further example of localized effects, in which antagonistic interactions between the duplicated copies result in altered expression profiles that affect dendritic morphology during neocortical maturation [74,77].…”

On the Value of Reptilian Brains to Map the Evolution of the Hippocampal Formation

“…Comparable data on reptiles remain exceedingly scarce [Nomura et al, 2013b]. The general cortical markers Tbr1 and Ctip2 are present in the reptilian medial cortex, whereas Er81 and Foxp1 are differentially expressed in medial cortex subregions [Moreno et al, 2010;Nomura et al, 2013a;Suzuki and Hirata, 2014;Garcia-Calero and Martinez, 2016]. However, using classical methods for detecting genes and proteins, only a few genes can be surveyed at a time.…”