Selective requirement of Pax6, but not Emx2, in the specification and development of several nuclei of the amygdaloid complex.
ABSTRACT The amygdaloid complex is a group of nuclei that are thought to originate from multiple sites of the dorsal and ventral telencephalic neuroepithelium. The mechanisms that regulate their development are essentially unknown. We studied the role of Pax6 and Emx2, two transcription factors that regulate regional specification and growth of the telencephalon, in the morphogenesis of the amygdaloid complex. We used a set of specific marker genes that identify distinct amygdaloid nuclei to analyze Pax6/Small eye and Emx2 knock-out mutant mouse brains. We found that there is a selective requirement for Pax6, but not Emx2, in the formation a subset of nuclei within the amygdaloid complex. Specifically, structures that were not previously considered to be developmentally linked, the nucleus of the lateral olfactory tract and the lateral, basolateral, and basomedial nuclei, all appear to have a common requirement for Pax6. Together, our findings provide new insights into the origins and mechanisms underlying the development of the amygdaloid complex.
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ABSTRACT: The anatomical organization of the mammalian neocortex stands out among vertebrates for its laminar and columnar arrangement, featuring vertically oriented, excitatory pyramidal neurons. The evolutionary origin of this structure is discussed here in relation to the brain organization of other amniotes, i.e., the sauropsids (reptiles and birds). Specifically, we address the developmental modifications that had to take place to generate the neocortex, and to what extent these modifications were shared by other amniote lineages or can be considered unique to mammals. In this article, we propose a hypothesis that combines the control of proliferation in neural progenitor pools with the specification of regional morphogenetic gradients, yielding different anatomical results by virtue of the differential modulation of these processes in each lineage. Thus, there is a highly conserved genetic and developmental battery that becomes modulated in different directions according to specific selective pressures. In the case of early mammals, ecological conditions like nocturnal habits and reproductive strategies are considered to have played a key role in the selection of the particular brain patterning mechanisms that led to the origin of the neocortex.Frontiers in Neuroanatomy 11/2013; 7:38. DOI:10.3389/fnana.2013.00038 · 4.18 Impact Factor
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ABSTRACT: In tetrapods, the medial amygdala is a forebrain center that integrates olfactory and/or vomeronasal signals with the endocrine and autonomic systems, playing a key role in different social behaviors. The vomeronasal system has undergone important changes during evolution, which may be behind some interspecies differences in chemosensory-mediated social behavior. These evolutionary changes are associated with variations in vomeronasal-recipient brain structures, including the medial amygdala. Herein, we employed an evolutionary developmental biology approach for trying to understand the function and evolution of the medial amygdala. For that purpose, we reviewed published data on fate mapping in mouse, and the expression of orthologous developmental regulatory genes (Nkx2.1, Lhx6, Shh, Tbr1, Lhx9, Lhx5, Otp, and Pax6) in embryos of mouse, chicken, emydid turtles, and a pipid frog. We also analyzed novel data on Lhx9 and Otp in a lacertid lizard. Based on distinct embryonic origin and genetic profile, at least five neuronal subpopulations exist in the medial amygdala of rodents, expressing either Nkx2.1/Lhx6, Shh, Lhx9, Otp/Lhx5, or Pax6. Each neuronal subpopulation appears involved in different functional pathways. For example, Lhx6 cells are specifically activated by sex pheromones and project to preoptic and hypothalamic centers involved in reproduction. Based on data in nonmammals, at least three of these neuronal subtypes might have been present in the medial amygdala of the amniote common ancestor. During mammalian evolution, the downregulation of Nkx2.1 in the alar hypothalamus may have been a driving force for an increment of the Otp/Lhx5 subpopulation. Anat Rec, 2013. © 2013 Wiley Periodicals, Inc.The Anatomical Record Advances in Integrative Anatomy and Evolutionary Biology 09/2013; 296(9). DOI:10.1002/ar.22744 · 1.53 Impact Factor
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ABSTRACT: The mammalian neocortex is a structure with no equals in the vertebrates and is the seat of the highest cerebral functions, such as thoughts and consciousness. It is radially organized into six layers and tangentially subdivided into functional areas deputed to the elaboration of sensory information, association between different stimuli, and selection and triggering of voluntary movements. The process subdividing the neocortical field into several functional areas is called \arealization". Each area has its own cytoarchitecture, connectivity, and peculiar functions. In the last century, several neuroscientists have investigated areal structure and the mechanisms that have led during evolution to the rising of the neocortex and its organization. The extreme conservation in the positioning and wiring of neocortical areas among different mammalian families suggests a conserved genetic program orchestrating neocortical patterning. However, the impressive plasticity of the neocortex, which is able to rewire and reorganize areal structures and connectivity after impairments of sensory pathways, argues for a more complex scenario. Indeed, even if genetics and molecular biology helped in identifying several genes involved in the arealization process, the logic underlying the neocortical bauplan is still beyond our comprehension. In this review, we will introduce the present knowledge and hypotheses on the ontogenesis and evolution of neocortical areas. Then, we will focus our attention on some open issues, which are still unresolved, and discuss some recent studies that might open new directions to be explored in the next few years.Developmental Neurobiology 06/2013; 73(6):411-477. DOI:10.1002/dneu.22067 · 4.19 Impact Factor