PMC:4429232 / 19851-23505
Annnotations
{"target":"https://pubannotation.org/docs/sourcedb/PMC/sourceid/4429232","sourcedb":"PMC","sourceid":"4429232","source_url":"https://www.ncbi.nlm.nih.gov/pmc/4429232","text":"Notably, in the lizard L. Muralis we identified DCX+/Tbr1+ cells morphologically similar to those of mammals in the layer II of the olfactory cortex and DVR, with a preferential distribution in higher order areas, but not in the dorsal cortex (Figure 2B). When compared to the DCX+/Tbr1+ cells in the neocortex, the general distribution of these cells in the lizard was consistent with the homologies proposed by Karten (Karten, 1969; Butler et al., 2011). Indeed, the DVR has been proposed to be homologous to temporal neocortical areas, such as auditory and secondary somatosensory and visual cortices, that in mammals show high numbers of DCX+/Tbr1+ cells. By contrast, the neocortical regions proposed as homologous of the dorsal cortex, that include primary somatosensory and visual cortices as well as the posterior cingulate, retrosplenial, and postrhinal cortices, are largely devoid of DCX+/Tbr1+ cells. Collectively, these data strongly support that layer II DCX+/Tbr1+ cells represent a conserved cell type in amniotes. In addition, although the sauropsids homologs of mammalian MEC and LEC associated circuits are still poorly defined (Rattenborg and Martinez-Gonzalez, 2011; Allen and Fortin, 2013; Abellán et al., 2014), it is tempting to speculate that non-newly generated DCX+/Tbr1+ cells may be involved in a conserved form of structural plasticity selectively associated to higher order areas of non-spatial learning and memory networks in amniotes. At the same time, our data suggests that the presence of DCX+/Tbr1+ cells in DP derivatives may represent a mammalian innovation. This supports the hypothesis of Reiner that the UL are an evolutionary novelty, but in parallel introduces the possibility that this novelty has been produced by re-using (or co-opting) pre-existing cell types. In particular, we propose that in the transition from the stem-amniote to mammals, DP progenitors instead of exiting from the cell cycle after the production of the DL neurons homologs, continued to proliferate by setting up a LP and/or VP developmental program, giving rise to the UL of the NC. Thus, the evolution of the neocortex could be attributed to a spatial to temporal patterning switch involving DP and LP/VP developmental programs. An interesting aspect of this model is that it could reconcile the developmental data supporting the field homology of the primary progenitors, with the striking similarities existing between neurons of the neocortex and LP and VP derivatives of sauropsids. Future studies in other reptilian species will be required to understand if the distribution of DCX+/Tbr1+ cells in L. Muralis represents the basal reptilian condition or, as happen in mice, this species simply lack this feature. An important point will be also to define where and when these cells are generated in different tetrapod species. Indeed, previous studies have shown that the VP and LP progenitors give rise to neurons that tangentially migrate to the neocortex in mice (Puelles, 2011; Teissier et al., 2012). Most of these VP/LP derived cells have a transient existence in mice, but we cannot exclude that in other mammalian species some of these cells may persist for longer post-natal periods (Teissier et al., 2010, 2012). Finally, molecular and functional analyses will be necessary to understand if these cells in different amniote species and pallial derivatives actually represent sister cell types. Nonetheless, as we will discuss in the next paragraphs, beside this intriguing cell population the hypothesis of the co-option of the LP/VP developmental program is supported also by other anatomical and developmental data.","tracks":[{"project":"0_colil","denotations":[{"id":"26029038-21534989-565853","span":{"begin":450,"end":454},"obj":"21534989"},{"id":"26029038-21420438-565854","span":{"begin":1182,"end":1186},"obj":"21420438"},{"id":"26029038-23754432-565855","span":{"begin":1206,"end":1210},"obj":"23754432"},{"id":"26029038-25071464-565856","span":{"begin":1228,"end":1232},"obj":"25071464"},{"id":"26029038-21701143-565857","span":{"begin":3003,"end":3007},"obj":"21701143"},{"id":"26029038-21666133-565858","span":{"begin":3026,"end":3030},"obj":"21666133"},{"id":"26029038-20685999-565859","span":{"begin":3237,"end":3241},"obj":"20685999"},{"id":"26029038-21666133-565860","span":{"begin":3243,"end":3247},"obj":"21666133"}],"attributes":[{"subj":"26029038-21534989-565853","pred":"source","obj":"0_colil"},{"subj":"26029038-21420438-565854","pred":"source","obj":"0_colil"},{"subj":"26029038-23754432-565855","pred":"source","obj":"0_colil"},{"subj":"26029038-25071464-565856","pred":"source","obj":"0_colil"},{"subj":"26029038-21701143-565857","pred":"source","obj":"0_colil"},{"subj":"26029038-21666133-565858","pred":"source","obj":"0_colil"},{"subj":"26029038-20685999-565859","pred":"source","obj":"0_colil"},{"subj":"26029038-21666133-565860","pred":"source","obj":"0_colil"}]},{"project":"2_test","denotations":[{"id":"26029038-21534989-38462759","span":{"begin":450,"end":454},"obj":"21534989"},{"id":"26029038-21420438-38462760","span":{"begin":1182,"end":1186},"obj":"21420438"},{"id":"26029038-23754432-38462761","span":{"begin":1206,"end":1210},"obj":"23754432"},{"id":"26029038-25071464-38462762","span":{"begin":1228,"end":1232},"obj":"25071464"},{"id":"26029038-21701143-38462763","span":{"begin":3003,"end":3007},"obj":"21701143"},{"id":"26029038-21666133-38462764","span":{"begin":3026,"end":3030},"obj":"21666133"},{"id":"26029038-20685999-38462765","span":{"begin":3237,"end":3241},"obj":"20685999"},{"id":"26029038-21666133-38462766","span":{"begin":3243,"end":3247},"obj":"21666133"}],"attributes":[{"subj":"26029038-21534989-38462759","pred":"source","obj":"2_test"},{"subj":"26029038-21420438-38462760","pred":"source","obj":"2_test"},{"subj":"26029038-23754432-38462761","pred":"source","obj":"2_test"},{"subj":"26029038-25071464-38462762","pred":"source","obj":"2_test"},{"subj":"26029038-21701143-38462763","pred":"source","obj":"2_test"},{"subj":"26029038-21666133-38462764","pred":"source","obj":"2_test"},{"subj":"26029038-20685999-38462765","pred":"source","obj":"2_test"},{"subj":"26029038-21666133-38462766","pred":"source","obj":"2_test"}]}],"config":{"attribute types":[{"pred":"source","value type":"selection","values":[{"id":"0_colil","color":"#93ece7","default":true},{"id":"2_test","color":"#eccd93"}]}]}}