Tole, S., Remedios, R., Saha, B. & Stoykova, A. Selective requirement of Pax6, but not Emx2, in the specification and development of several nuclei of the amygdaloid complex. J. Neurosci. 25, 2753-2760

Department of Biological Sciences, Tata Institute of Fundamental Research, Mumbai 400005, India.
The Journal of Neuroscience : The Official Journal of the Society for Neuroscience (Impact Factor: 6.34). 04/2005; 25(10):2753-60. DOI: 10.1523/JNEUROSCI.3014-04.2005
Source: PubMed


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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Available from: Anastassia Stoykova, Jan 04, 2016
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    • "The molecular analysis corroborating the distinctness as a pallial sec-tor of the VPall has been influential in recent years, leading to widespread usage of the corresponding tetrapartite pallial model (e.g. Lindsay et al., 2005; Remedios et al., 2004; Stenman et al., 2003; Teissier et al., 2010 Teissier et al., , 2012 Tole et al., 2005), and also to its extrapolation to gnathostomes in general (Nieuwenhuys, 2009). The presence of a tetrapartite pallium in agnatha is still a controversial issue, but not because of a lack of VPall or LPall; it has been questioned whether these animals have a DPall (Pombal et al., 2009; Puelles, 2001). "
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    ABSTRACT: The mammalian claustrum is a pallial nucleus embedded in the telencephalic white matter under the insula. It is a Cinderella-like anatomic entity, which is not well understood in many ways, but whose constancy suggests it performs an essential function. This embryological essay first discusses in detail the diverse historic conceptions about how it develops, pointing out both critical data obtained and faulty assumptions that led to erroneous conclusions. Five successive models have been produced about the origin of the claustrum. Initial debates considered whether the claustrum is pallial or subpallial, finally establishing its pallial nature. It was also discussed whether it delaminates from the insular cortex next to it or arises independently from an adjacent pallial progenitor area that also produces the olfactory cortex. The non-insular source was eventually held to be subdivided in two parallel domains with distinct properties (and several parts of claustrum), consistently with observations in birds and reptiles. In contrast, comparative studies in basal mammals suggested that the claustrum is hidden or partly hidden inside the insular cortex (particularly in monotremes, where at first it was said not to exist). Claustral parts therefore may be understood as internal cortical elements. Neurogenetic studies indicated that claustral neurons are among the earliest cells to be born in the pallium. Modern results with gene mapping methods are examined next. These tended to corroborate a tetrapartite pallium model, with a non-insular claustrum origin in ventral and lateral pallium. However, some predictions have not been verified. Very recent reexamination in the mouse of claustral development, using the gene Nr4a2 as a characteristic marker, corroborated its early origin and its intimate association with insular cortex via a shared packet of radial glial fibers. Insular neurons are born after the claustrum is present subpially, and migrate across it to form the insular cortical plate, in so doing pushing the claustrum into the depths. The concept of "lateral pallium" was thus redefined as a claustro-insular and claustro-rhinal, longitudinal histogenetic unit wholly parallel to olfactory cortex. It does not enter the amygdala. Various interesting examples of pallio-pallial migration could be traced from the claustral primordium into neighboring pallial domains, and in particular the precocious subplate cells. The "ventral pallium" concept was also redefined, since the olfactory cortex is now wholly ascribed to it. The insula is no longer considered to be part of the "dorsal pallium" or neocortex. These novelties imply a modified tetrapartite pallium model, which gives new insights about comparative analysis of claustral and cortical evolution.
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    • "In neocortical development, Emx2, Pax6 and FGFs act in counterbalance . Pax6 deficiency results in an areal expansion of visual cortex, a reduction of frontal areas, and dysgenesis of limbic structures (Stoykova et al., 2000; Tole et al., 2005). On the other hand, Emx2 deficiency produces an expansion of frontal regions and a reduction of occipital regions (visual cortex; Bishop et al., 2000). "
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    • "In mouse embryos, the amygdalar derivatives of the ventral pallium are characterized by expression of Tbr1, Lhx2, and Lhx9 (Puelles et al., 2000; Medina et al., 2004; Tole et al., 2005; Garc ıa-L opez et al., 2008). These include part of the basal amygdalar complex, and the anterior and posteromedial cortical amygdalar areas. "
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