51
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Affiliation(s)
| | - Shyam Srinivasan
- The Salk Institute for Biological Sciences, La Jolla, California 92037;
- Kavli Institute for Brain and Mind, University of California, San Diego, La Jolla, California 92037
| | - Edwin S. Monuki
- Department of Pathology and Laboratory Medicine, University of California, Irvine, California 92697; ,
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52
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Neurodevelopmental LincRNA Microsyteny Conservation and Mammalian Brain Size Evolution. PLoS One 2015; 10:e0131818. [PMID: 26134977 PMCID: PMC4489927 DOI: 10.1371/journal.pone.0131818] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2015] [Accepted: 06/07/2015] [Indexed: 11/19/2022] Open
Abstract
The mammalian neocortex has undergone repeated selection for increases and decreases in size and complexity, often over relatively short evolutionary time. But because probing developmental mechanisms across many species is experimentally unfeasible, it is unknown whether convergent morphologies in distantly related species are regulated by conserved developmental programs. In this work, we have taken advantage of the abundance of available mammalian genomes to find evidence of selection on genomic regions putatively regulating neurogenesis in large- versus small-brained species. Using published fetal human RNA-seq data, we show that the gene-neighborhood (i.e., microsynteny) of long intergenic non-coding RNAs (lincRNAs) implicated in cortical development is differentially conserved in large-brained species, lending support to the hypothesis that lincRNAs regulating neurogenesis are selectively lost in small-brained species. We provide evidence that this is not a phenomenon attributable to lincRNA expressed in all tissue types and is therefore likely to represent an adaptive function in the evolution of neurogenesis. A strong correlation between transcription factor-adjacency and lincRNA sequence conservation reinforces this conclusion.
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53
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Affiliation(s)
- Mareike Albert
- MPI of Molecular Cell Biology & Genetics, Dresden, Germany
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54
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Dehay C, Kennedy H, Kosik KS. The outer subventricular zone and primate-specific cortical complexification. Neuron 2015; 85:683-94. [PMID: 25695268 DOI: 10.1016/j.neuron.2014.12.060] [Citation(s) in RCA: 206] [Impact Index Per Article: 22.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
Evolutionary expansion and complexification of the primate cerebral cortex are largely linked to the emergence of the outer subventricular zone (OSVZ), a uniquely structured germinal zone that generates the expanded primate supragranular layers. The primate OSVZ departs from rodent germinal zones in that it includes a higher diversity of precursor types, inter-related in bidirectional non-hierarchical lineages. In addition, primate-specific regulatory mechanisms are operating in primate cortical precursors via the occurrence of novel miRNAs. Here, we propose that the origin and evolutionary importance of the OSVZ is related to genetic changes in multiple regulatory loops and that cell-cycle regulation is a favored target for evolutionary adaptation of the cortex.
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Affiliation(s)
- Colette Dehay
- Stem Cell and Brain Research Institute, INSERM U846, 18 Avenue Doyen Lepine, 69500 Bron, France; Université de Lyon, Université Lyon I, 69003, Lyon, France.
| | - Henry Kennedy
- Stem Cell and Brain Research Institute, INSERM U846, 18 Avenue Doyen Lepine, 69500 Bron, France; Université de Lyon, Université Lyon I, 69003, Lyon, France.
| | - Kenneth S Kosik
- Neuroscience Research Institute and Dept Cellular Molecular and Developmental Biology, University of California, Santa Barbara, CA 93106, USA.
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55
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Progenitor genealogy in the developing cerebral cortex. Cell Tissue Res 2014; 359:17-32. [PMID: 25141969 DOI: 10.1007/s00441-014-1979-5] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2014] [Accepted: 07/28/2014] [Indexed: 10/24/2022]
Abstract
The mammalian cerebral cortex is characterized by a complex histological organization that reflects the spatio-temporal stratifications of related stem and neural progenitor cells, which are responsible for the generation of distinct glial and neuronal subtypes during development. Some work has been done to shed light on the existing filiations between these progenitors as well as their respective contribution to cortical neurogenesis. The aim of the present review is to summarize the current views of progenitor hierarchy and relationship in the developing cortex and to further discuss future research directions that would help us to understand the molecular and cellular regulating mechanisms involved in cerebral corticogenesis.
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56
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Florio M, Huttner WB. Neural progenitors, neurogenesis and the evolution of the neocortex. Development 2014; 141:2182-94. [PMID: 24866113 DOI: 10.1242/dev.090571] [Citation(s) in RCA: 433] [Impact Index Per Article: 43.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
The neocortex is the seat of higher cognitive functions and, in evolutionary terms, is the youngest part of the mammalian brain. Since its origin, the neocortex has expanded in several mammalian lineages, and this is particularly notable in humans. This expansion reflects an increase in the number of neocortical neurons, which is determined during development and primarily reflects the number of neurogenic divisions of distinct classes of neural progenitor cells. Consequently, the evolutionary expansion of the neocortex and the concomitant increase in the numbers of neurons produced during development entail interspecies differences in neural progenitor biology. Here, we review the diversity of neocortical neural progenitors, their interspecies variations and their roles in determining the evolutionary increase in neuron numbers and neocortex size.
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Affiliation(s)
- Marta Florio
- Max Planck Institute of Molecular Cell Biology and Genetics, Pfotenhauerstrasse 108, Dresden 01307, Germany
| | - Wieland B Huttner
- Max Planck Institute of Molecular Cell Biology and Genetics, Pfotenhauerstrasse 108, Dresden 01307, Germany
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57
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Montgomery SH, Mundy NI. Microcephaly genes evolved adaptively throughout the evolution of eutherian mammals. BMC Evol Biol 2014; 14:120. [PMID: 24898820 PMCID: PMC4055943 DOI: 10.1186/1471-2148-14-120] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2014] [Accepted: 05/23/2014] [Indexed: 10/27/2022] Open
Abstract
BACKGROUND Genes associated with the neurodevelopmental disorder microcephaly display a strong signature of adaptive evolution in primates. Comparative data suggest a link between selection on some of these loci and the evolution of primate brain size. Whether or not either positive selection or this phenotypic association are unique to primates is unclear, but recent studies in cetaceans suggest at least two microcephaly genes evolved adaptively in other large brained mammalian clades. RESULTS Here we analyse the evolution of seven microcephaly loci, including three recently identified loci, across 33 eutherian mammals. We find extensive evidence for positive selection having acted on the majority of these loci not just in primates but also across non-primate mammals. Furthermore, the patterns of selection in major mammalian clades are not significantly different. Using phylogenetically corrected comparative analyses, we find that the evolution of two microcephaly loci, ASPM and CDK5RAP2, are correlated with neonatal brain size in Glires and Euungulata, the two most densely sampled non-primate clades. CONCLUSIONS Together with previous results, this suggests that ASPM and CDK5RAP2 may have had a consistent role in the evolution of brain size in mammals. Nevertheless, several limitations of currently available data and gene-phenotype tests are discussed, including sparse sampling across large evolutionary distances, averaging gene-wide rates of evolution, potential phenotypic variation and evolutionary reversals. We discuss the implications of our results for studies of the genetic basis of brain evolution, and explicit tests of gene-phenotype hypotheses.
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Affiliation(s)
- Stephen H Montgomery
- Department Genetics, Evolution & Environment, University College London, Gower Street, London WC1E 6BT, UK.
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58
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González-Gómez M, Meyer G. Dynamic expression of calretinin in embryonic and early fetal human cortex. Front Neuroanat 2014; 8:41. [PMID: 24917793 PMCID: PMC4042362 DOI: 10.3389/fnana.2014.00041] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2014] [Accepted: 05/16/2014] [Indexed: 02/04/2023] Open
Abstract
Calretinin (CR) is one of the earliest neurochemical markers in human corticogenesis. In embryos from Carnegie stages (CS) 17 to 23, calbindin (CB) and CR stain opposite poles of the incipient cortex suggesting early regionalization: CB marks the neuroepithelium of the medial boundary of the cortex with the choroid plexus (cortical hem). By contrast, CR is confined to the subventricular zone (SVZ) of the lateral and caudal ganglionic eminences at the pallial-subpallial boundary (PSB, or antihem), from where CR+/Tbr1- neurons migrate toward piriform cortex and amygdala as a component of the lateral cortical stream. At CS 19, columns of CR+ cells arise in the rostral cortex, and contribute at CS 20 to the “monolayer” of horizontal Tbr1+/CR+ and GAD+ cells in the preplate. At CS 21, the “pioneer cortical plate” appears as a radial aggregation of CR+/Tbr1+ neurons, which cover the entire future neocortex and extend the first corticofugal axons. CR expression in early human corticogenesis is thus not restricted to interneurons, but is also present in the first excitatory projection neurons of the cortex. At CS 21/22, the cortical plate is established following a lateral to medial gradient, when Tbr1+/CR- neurons settle within the pioneer cortical plate, and thus separate superficial and deep pioneer neurons. CR+ pioneer neurons disappear shortly after the formation of the cortical plate. Reelin+ Cajal-Retzius cells begin to express CR around CS21 (7/8 PCW). At CS 21–23, the CR+ SVZ at the PSB is the source of CR+ interneurons migrating into the cortical SVZ. In turn, CB+ interneurons migrate from the subpallium into the intermediate zone following the fibers of the internal capsule. Early CR+ and CB+ interneurons thus have different origins and migratory routes. CR+ cell populations in the embryonic telencephalon take part in a complex sequence of events not analyzed so far in other mammalian species, which may represent a distinctive trait of the initial steps of human corticogenesis.
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Affiliation(s)
- Miriam González-Gómez
- Departamento de Anatomía, Facultad de Medicina, Universidad de La Laguna Tenerife, Spain
| | - Gundela Meyer
- Departamento de Anatomía, Facultad de Medicina, Universidad de La Laguna Tenerife, Spain
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59
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Sun T, Hevner RF. Growth and folding of the mammalian cerebral cortex: from molecules to malformations. Nat Rev Neurosci 2014; 15:217-32. [PMID: 24646670 DOI: 10.1038/nrn3707] [Citation(s) in RCA: 340] [Impact Index Per Article: 34.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
The size and extent of folding of the mammalian cerebral cortex are important factors that influence a species' cognitive abilities and sensorimotor skills. Studies in various animal models and in humans have provided insight into the mechanisms that regulate cortical growth and folding. Both protein-coding genes and microRNAs control cortical size, and recent progress in characterizing basal progenitor cells and the genes that regulate their proliferation has contributed to our understanding of cortical folding. Neurological disorders linked to disruptions in cortical growth and folding have been associated with novel neurogenetic mechanisms and aberrant signalling pathways, and these findings have changed concepts of brain evolution and may lead to new medical treatments for certain disorders.
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Affiliation(s)
- Tao Sun
- Department of Cell and Developmental Biology, Weill Medical College of Cornell University, 1300 York Avenue, BOX 60, New York, New York 10065, USA
| | - Robert F Hevner
- Department of Neurological Surgery and Center for Integrative Brain Research, Seattle Children's Research Institute, Seattle, Washington 98101, USA
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60
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Borrell V, Calegari F. Mechanisms of brain evolution: regulation of neural progenitor cell diversity and cell cycle length. Neurosci Res 2014; 86:14-24. [PMID: 24786671 DOI: 10.1016/j.neures.2014.04.004] [Citation(s) in RCA: 59] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2014] [Revised: 02/06/2014] [Accepted: 02/14/2014] [Indexed: 12/31/2022]
Abstract
In the last few years, several studies have revisited long-held assumptions in the field of brain development and evolution providing us with a fundamentally new vision on the mechanisms controlling its size and shape, hence function. Among these studies, some described hitherto unforeseeable subtypes of neural progenitors while others reinterpreted long-known observations about their cell cycle in alternative new ways. Most remarkably, this knowledge combined has allowed the generation of mammalian model organisms in which brain size and folding has been selectively increased giving us the means to understand the mechanisms underlying the evolution of the most complex and sophisticated organ. Here we review the key findings made in this area and make a few conjectures about their evolutionary meaning including the likelihood of Martians conquering our planet.
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Affiliation(s)
- Victor Borrell
- Instituto de Neurociencias, CSIC & Universidad Miguel Hernández, Av. Ramón y Cajal s/n, San Juan de Alicante 03550, Spain.
| | - Federico Calegari
- CRTD - DFG Research Center for Regenerative Therapies Dresden, Technische Universität Dresden, Fetscherstrasse 105, 01307 Dresden, Germany.
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61
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Abstract
The layout of areas in the cerebral cortex of different primates is quite similar, despite significant variations in brain size. However, it is clear that larger brains are not simply scaled up versions of smaller brains: some regions of the cortex are disproportionately large in larger species. It is currently debated whether these expanded areas arise through natural selection pressures for increased cognitive capacity or as a result of the application of a common developmental sequence on different scales. Here, we used computational methods to map and quantify the expansion of the cortex in simian primates of different sizes to investigate whether there is any common pattern of cortical expansion. Surface models of the marmoset, capuchin, and macaque monkey cortex were registered using the software package CARET and the spherical landmark vector difference algorithm. The registration was constrained by the location of identified homologous cortical areas. When comparing marmosets with both capuchins and macaques, we found a high degree of expansion in the temporal parietal junction, the ventrolateral prefrontal cortex, and the dorsal anterior cingulate cortex, all of which are high-level association areas typically involved in complex cognitive and behavioral functions. These expanded maps correlated well with previously published macaque to human registrations, suggesting that there is a general pattern of primate cortical scaling.
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