PMC:4429232 / 35420-38410 JSONTXT

{"project":"0_colil","denotations":[{"id":"26029038-16766701-565891","span":{"begin":117,"end":121},"obj":"16766701"},{"id":"26029038-19726493-565892","span":{"begin":138,"end":142},"obj":"19726493"},{"id":"26029038-11493521-565893","span":{"begin":306,"end":310},"obj":"11493521"},{"id":"26029038-16766701-565894","span":{"begin":337,"end":341},"obj":"16766701"},{"id":"26029038-19168665-565895","span":{"begin":361,"end":365},"obj":"19168665"},{"id":"26029038-16766701-565896","span":{"begin":589,"end":593},"obj":"16766701"},{"id":"26029038-17634059-565897","span":{"begin":610,"end":614},"obj":"17634059"},{"id":"26029038-21609827-565898","span":{"begin":951,"end":955},"obj":"21609827"},{"id":"26029038-23878249-565899","span":{"begin":1613,"end":1617},"obj":"23878249"},{"id":"26029038-23818089-565900","span":{"begin":2427,"end":2431},"obj":"23818089"},{"id":"26029038-18927580-565901","span":{"begin":2904,"end":2908},"obj":"18927580"},{"id":"26029038-19212399-565902","span":{"begin":2925,"end":2929},"obj":"19212399"}],"text":"A hallmark of the evolution of the mammalian neocortex is the emergence of a SVZ in the DP (Martínez-Cerdeño et al., 2006; Cheung et al., 2010), and interestingly the intermediate progenitors (IPc) that populate this germinative layer are mainly involved in the generation of UL neurons (Tarabykin et al., 2001; Martínez-Cerdeño et al., 2006; Kowalczyk et al., 2009). Although, an SVZ is not always evident in sauropsids, studies in turtle and chick showed that putative IP like cells are present in late developmental phases of the LP and VP of turtle and chick (Martínez-Cerdeño et al., 2006; Cheung et al., 2007). The acquisition by DP progenitors of a character (the IPc) that pre-existed in LP/VP progenitors is consistent with our hypothesis. Nonetheless, the IPc step is a common feature in stem cell systems and it has been described for multiple neuronal progenitors populations in both vertebrate and invertebrate brains (Brand and Livesey, 2011). Mammalian DP progenitors may have independently increased the generation of IP to amplify neuron production. Future studies defining the role of the SVZ during pallial development will be necessary to understand the role of this germinative layer in the emergence of the neocortex. While deciphering the developmental program set up by pallial progenitors is a fundamental issue, recent studies also tried to extend previous inter-species comparisons of pallial neuronal types with more modern molecular techniques. The comparison of the chick and mouse transcriptomes of telencephalic regions with either disputed or undisputed homology (Belgard et al., 2013) revealed significant similarities for the hippocampus but failed to identify specific relationships between any other pallial region. The only exception was a weak correlation between the neocortical layer IV and a thalamorecipient field of the nidopallium (a VP derivative). Along with our hypothesis for the evolution of layer II/III it would be interesting to evaluate whether the appearance of stellate cells in layer IV was due to the co-option of the developmental program of the thalamo-recipient VP cells. Unfortunately the olfactory cortex was not analyzed in this study, probably because it is highly reduced in chick. These transcriptomes comparisons supported the view that DP and VP derivatives underwent dramatic changes in morphology and function during amniote evolution (Montiel and Molnár, 2013). At the same time, although such analyses can make a strong case for homology, negative results are more difficult to interpret. Huge differences in the transcriptome do not rule out the occurrence of homologous cell types that greatly changed their relative proportions or mixed with novel cell types. This further indicates the importance of defining the evolutionary history of individual pallial cell types (the so called cell type homology or deep-homology; Arendt, 2008; Shubin et al., 2009) to understand the divergence of DP derivatives in amniotes."}

{"project":"2_test","denotations":[{"id":"26029038-16766701-38462797","span":{"begin":117,"end":121},"obj":"16766701"},{"id":"26029038-19726493-38462798","span":{"begin":138,"end":142},"obj":"19726493"},{"id":"26029038-11493521-38462799","span":{"begin":306,"end":310},"obj":"11493521"},{"id":"26029038-16766701-38462800","span":{"begin":337,"end":341},"obj":"16766701"},{"id":"26029038-19168665-38462801","span":{"begin":361,"end":365},"obj":"19168665"},{"id":"26029038-16766701-38462802","span":{"begin":589,"end":593},"obj":"16766701"},{"id":"26029038-17634059-38462803","span":{"begin":610,"end":614},"obj":"17634059"},{"id":"26029038-21609827-38462804","span":{"begin":951,"end":955},"obj":"21609827"},{"id":"26029038-23878249-38462805","span":{"begin":1613,"end":1617},"obj":"23878249"},{"id":"26029038-23818089-38462806","span":{"begin":2427,"end":2431},"obj":"23818089"},{"id":"26029038-18927580-38462807","span":{"begin":2904,"end":2908},"obj":"18927580"},{"id":"26029038-19212399-38462808","span":{"begin":2925,"end":2929},"obj":"19212399"}],"text":"A hallmark of the evolution of the mammalian neocortex is the emergence of a SVZ in the DP (Martínez-Cerdeño et al., 2006; Cheung et al., 2010), and interestingly the intermediate progenitors (IPc) that populate this germinative layer are mainly involved in the generation of UL neurons (Tarabykin et al., 2001; Martínez-Cerdeño et al., 2006; Kowalczyk et al., 2009). Although, an SVZ is not always evident in sauropsids, studies in turtle and chick showed that putative IP like cells are present in late developmental phases of the LP and VP of turtle and chick (Martínez-Cerdeño et al., 2006; Cheung et al., 2007). The acquisition by DP progenitors of a character (the IPc) that pre-existed in LP/VP progenitors is consistent with our hypothesis. Nonetheless, the IPc step is a common feature in stem cell systems and it has been described for multiple neuronal progenitors populations in both vertebrate and invertebrate brains (Brand and Livesey, 2011). Mammalian DP progenitors may have independently increased the generation of IP to amplify neuron production. Future studies defining the role of the SVZ during pallial development will be necessary to understand the role of this germinative layer in the emergence of the neocortex. While deciphering the developmental program set up by pallial progenitors is a fundamental issue, recent studies also tried to extend previous inter-species comparisons of pallial neuronal types with more modern molecular techniques. The comparison of the chick and mouse transcriptomes of telencephalic regions with either disputed or undisputed homology (Belgard et al., 2013) revealed significant similarities for the hippocampus but failed to identify specific relationships between any other pallial region. The only exception was a weak correlation between the neocortical layer IV and a thalamorecipient field of the nidopallium (a VP derivative). Along with our hypothesis for the evolution of layer II/III it would be interesting to evaluate whether the appearance of stellate cells in layer IV was due to the co-option of the developmental program of the thalamo-recipient VP cells. Unfortunately the olfactory cortex was not analyzed in this study, probably because it is highly reduced in chick. These transcriptomes comparisons supported the view that DP and VP derivatives underwent dramatic changes in morphology and function during amniote evolution (Montiel and Molnár, 2013). At the same time, although such analyses can make a strong case for homology, negative results are more difficult to interpret. Huge differences in the transcriptome do not rule out the occurrence of homologous cell types that greatly changed their relative proportions or mixed with novel cell types. This further indicates the importance of defining the evolutionary history of individual pallial cell types (the so called cell type homology or deep-homology; Arendt, 2008; Shubin et al., 2009) to understand the divergence of DP derivatives in amniotes."}