Expression pattern of cadherins in the naked mole rat (Heterocephalus glaber) suggests innate cortical diversification of the cerebrum

Differential expression of protocadherin-19, protocadherin-17, and cadherin-6 in adult zebrafish brain

Cell adhesion molecule cadherins play important roles in both development and maintenance of adult structures. Most studies on cadherin expression have been carried out in developing organisms, but information on cadherin distribution in adult vertebrate brains is limited. In this study we used in situ hybridization to examine mRNA expression of three cadherins, protocadherin-19, protocadherin-17, and cadherin-6 in adult zebrafish brain. Each cadherin exhibits a distinct expression pattern in the fish brain, with protocadherin-19 and protocadherin-17 showing much wider and stronger expression than that of cadherin-6. Both protocadherin-19 and protocadherin-17-expressing cells occur throughout the brain, with strong expression in the ventromedial telencephalon, periventricular regions of the thalamus and anterior hypothalamus, stratum periventriculare of the optic tectum, dorsal tegmental nucleus, granular regions of the cerebellar body and valvula, and superficial layers of the facial and vagal lobes. Numerous sensory structures (e.g., auditory, gustatory, lateral line, olfactory, and visual nuclei) and motor nuclei (e.g., oculomotor, trochlear, trigeminal motor, abducens, and vagal motor nuclei) contain protocadherin-19 and/or protocadherin-17-expressing cell. Expression of these two protocadherins is similar in the ventromedial telencephalon, thalamus, hypothalamus, facial, and vagal lobes, but substantially different in the dorsolateral telencephalon, intermediate layers of the optic tectum, and cerebellar valvula. In contrast to the two protocadherins, cadherin-6 expression is much weaker and limited in the adult fish brain.

Periostin, a neurite outgrowth-promoting factor, is expressed at high levels in the primate cerebral cortex

Periostin (POSTN or osteoblast specific factor) is an extracellular matrix protein originally identified as a protein highly expressed in osteoblasts. Recently, periostin has been reported to function in axon regeneration and neuroprotection. In the present study, we focused on periostin function in cortical evolution. We performed a comparative gene expression analysis of periostin between rodents (mice) and primates (marmosets and macaques). Periostin was expressed at higher levels in the primate cerebral cortex compared to the mouse cerebral cortex. Furthermore, we performed overexpression experiments of periostin in vivo and in vitro. Periostin exhibited neurite outgrowth activity in cortical neurons. These results suggested the possibility that prolonged and increased periostin expression in the primate cerebral cortex enhances the cortical plasticity of the mammalian cerebral cortex.

Comparative analysis of developmentally regulated expressions of Gadd45a, Gadd45b, and Gadd45g in the mouse and marmoset cerebral cortex

The cerebral cortex is an indispensable region that is involved in higher cognitive function in the mammalian brain, and is particularly evolved in the primate brain. It has been demonstrated that cortical areas are formed by both innate and activity-dependent mechanisms. However, it remains unknown what molecular changes induce cortical expansion and complexity during primate evolution. Active DNA methylation/demethylation is one of the epigenetic mechanisms that can modify gene expression via the methylation/demethylation of promoter regions. Three growth arrest and DNA damage-inducible small nuclear proteins, Gadd45 alpha, beta, and gamma, have been identified as regulators of methylation status. To understand the involvement of epigenetic factors in primate cortical evolution, we started by analyzing expression of these demethylation genes in the developing common marmoset (Callithrix jacchus) and mouse (Mus musculus) brain. In the marmoset brain, we found that cortical expression levels of Gadd45 alpha and gamma were reduced during development, whereas there was high expression of Gadd45 beta in some areas of the adult brain, including the prefrontal, temporal, posterior parietal and insula cortices, which are particularly expanded in greater primates and humans. Compared to the marmoset brain, there were no clear regional differences and constant or reduced Gadd45 expression was seen between juvenile and adult mouse brain. Double staining with a neuronal marker revealed that most Gadd45-expressing cells were NeuN-positive neurons. Thus, these results suggest the possibility that differential Gadd45 expression affects neurons, contributing cortical evolution and diversity.

Mapping arealisation of the visual cortex of non-primate species: lessons for development and evolution

The integration of the visual stimulus takes place at the level of the neocortex, organized in anatomically distinct and functionally unique areas. Primates, including humans, are heavily dependent on vision, with approximately 50% of their neocortical surface dedicated to visual processing and possess many more visual areas than any other mammal, making them the model of choice to study visual cortical arealisation. However, in order to identify the mechanisms responsible for patterning the developing neocortex, specifying area identity as well as elucidate events that have enabled the evolution of the complex primate visual cortex, it is essential to gain access to the cortical maps of alternative species. To this end, species including the mouse have driven the identification of cellular markers, which possess an area-specific expression profile, the development of new tools to label connections and technological advance in imaging techniques enabling monitoring of cortical activity in a behaving animal. In this review we present non-primate species that have contributed to elucidating the evolution and development of the visual cortex. We describe the current understanding of the mechanisms supporting the establishment of areal borders during development, mainly gained in the mouse thanks to the availability of genetically modified lines but also the limitations of the mouse model and the need for alternate species.

Comparative analysis of protocadherin-11 X-linked expression among postnatal rodents, non-human primates, and songbirds suggests its possible involvement in brain evolution

Background

Protocadherin-11 is a cell adhesion molecule of the cadherin superfamily. Since, only in humans, its paralog is found on the Y chromosome, it is expected that protocadherin-11X/Y plays some role in human brain evolution or sex differences. Recently, a genetic mutation of protocadherin-11X/Y was reported to be associated with a language development disorder. Here, we compared the expression of protocadherin-11 X-linked in developing postnatal brains of mouse (rodent) and common marmoset (non-human primate) to explore its possible involvement in mammalian brain evolution. We also investigated its expression in the Bengalese finch (songbird) to explore a possible function in animal vocalization and human language faculties.

Methodology/Principal Findings

Protocadherin-11 X-linked was strongly expressed in the cerebral cortex, hippocampus, amygdala and brainstem. Comparative analysis between mice and marmosets revealed that in certain areas of marmoset brain, the expression was clearly enriched. In Bengalese finches, protocadherin-11 X-linked was expressed not only in nuclei of regions of the vocal production pathway and the tracheosyringeal hypoglossal nucleus, but also in areas homologous to the mammalian amygdala and hippocampus. In both marmosets and Bengalese finches, its expression in pallial vocal control areas was developmentally regulated, and no clear expression was seen in the dorsal striatum, indicating a similarity between songbirds and non-human primates.

Conclusions/Significance

Our results suggest that the enriched expression of protocadherin-11 X-linked is involved in primate brain evolution and that some similarity exists between songbirds and primates regarding the neural basis for vocalization.

Comparative analysis of mineralocorticoid receptor expression among vocal learners (Bengalese finch and budgerigar) and non-vocal learners (quail and ring dove) has implications for the evolution of avian vocal learning

Mineralocorticoid receptor is the receptor for corticosteroids such as corticosterone or aldosterone. Previously, we found that mineralocorticoid receptor was highly expressed in song nuclei of a songbird, Bengalese finch (Lonchura striata var. domestica). Here, to examine the relationship between mineralocorticoid receptor expression and avian vocal learning, we analyzed mineralocorticoid receptor expression in the developing brain of another vocal learner, budgerigar (Melopsittacus undulatus) and non-vocal learners, quail (Coturnix japonica) and ring dove (Streptopelia capicola). Mineralocorticoid receptor showed vocal control area-related expressions in budgerigars as Bengalese finches, whereas no such mineralocorticoid receptor expressions were seen in the telencephalon of non-vocal learners. Thus, these results suggest the possibility that mineralocorticoid receptor plays a role in vocal development of parrots as songbirds and that the acquisition of mineralocorticoid receptor expression is involved in the evolution of avian vocal learning.