Sequential pattern of sublayer formation in the paleocortex and neocortex
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ORIGINAL PAPER
Sequential pattern of sublayer formation in the paleocortex and neocortex Makoto Nasu1 · Kenji Shimamura2 · Shigeyuki Esumi1 · Nobuaki Tamamaki1 Received: 17 December 2019 / Accepted: 13 January 2020 © The Japanese Society for Clinical Molecular Morphology 2020
Abstract The piriform cortex (paleocortex) is the olfactory cortex or the primary cortex for the sense of smell. It receives the olfactory input from the mitral and tufted cells of the olfactory bulb and is involved in the processing of information pertaining to odors. The piriform cortex and the adjoining neocortex have different cytoarchitectures; while the former has a three-layered structure, the latter has a six-layered structure. The regulatory mechanisms underlying the building of the six-layered neocortex are well established; in contrast, less is known about of the regulatory mechanisms responsible for structure formation of the piriform cortex. The differences as well as similarities in the regulatory mechanisms between the neocortex and the piriform cortex remain unclear. Here, the expression of neocortical layer-specific genes in the piriform cortex was examined. Two sublayers were found to be distinguished in layer II of the piriform cortex using Ctip2/Bcl11b and Brn1/Pou3f3. The sequential expression pattern of Ctip2 and Brn1 in the piriform cortex was similar to that detected in the neocortex, although the laminar arrangement in the piriform cortex exhibited an outside-in arrangement, unlike that observed in the neocortex. Keywords Piriform cortex (paleocortex) · Sublayer · Sequential expression · Ctip2/Bcl11b · Brn1/Pou3f3
Introduction The piriform cortex (paleocortex) is the olfactory cortex or the primary cortex for the sense of smell. It receives the olfactory input from the mitral and tufted cells in the olfactory bulb and is involved in the processing of information pertaining to odors [1, 2]. Neurons originating from the lateral pallium (LP) in the telencephalon migrate laterally or ventrally into the piriform cortex [3, 4]. The dorsally adjoining dorsal pallium (DP) gives rise to the neocortex, which is responsible for higher mental functions, including memory, speech, value judgments, and sociality. The adjoining LP and DP have different cytoarchitectures; LP is a three-layered structure, while DP is a six-layered structure [5–7]. The regulatory mechanisms underlying the building of the * Makoto Nasu mnas@kumamoto‑u.ac.jp 1
Department of Morphological Neural Science, Graduate School of Medical Sciences, Kumamoto University, 1‑1‑1, Honjo, Chuo‑ku, Kumamoto 860‑8556, Japan
Department of Brain Morphogenesis, Institute of Molecular Embryology and Genetics (IMEG), Kumamoto University, 2‑2‑1, Honjo, Chuo‑ku, Kumamoto 860‑0811, Japan
2
six-layered cortex, which is a mammal-specific feature, are well established; sequential expression of transcription factors is involved in determining cell identities, and late-born neurons migrate to pass through and take their place outside earlier-born neurons, i.e., in an in
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