Subdivisions of the turtle Pseudemys scripta hypothalamus based on the expression of regulatory genes and neuronal markers

Abstract

The patterns of distribution of a set of conserved brain developmental regulatory transcription factors and neuronal markers were analyzed in the hypothalamus of the juvenile turtle, Pseudemys scripta. Combined immunohistochemical techniques were used for the identification of the main boundaries and subdivisions in the optic, paraventricular, tuberal, and mammillary hypothalamic regions. The combination of Tbr1 and Pax6 with Nkx2.1 allowed identification of the boundary between the telencephalic preoptic area, rich in Nkx2.1 expression, and the prethalamic eminence, rich in Tbr1 expression. In addition, at this level Nkx2.2 expression defined the boundary between the telencephalon and the hypothalamus. The dorsalmost hypothalamic domain was the supraoptoparaventricular region that was defined by the expression of Otp/Pax6 and the lack of Nkx2.1/Isl1. It is subdivided into rostral, rich in Otp and Nkx2.2, and caudal, only Otp-positive, portions. Ventrally, the suprachiasmatic area was identified by its catecholaminergic groups and the lack of Otp, and could be further divided into a rostral portion, rich in Nkx2.1 and Nkx2.2, and a caudal portion, rich in Isl1 and devoid of Nkx2.1 expression. The expressions of Nkx2.1 and Isl1 defined the tuberal hypothalamus, whereas only the rostral portion expressed Otp. Its caudal boundary was evident by the lack of Isl1 in the adjacent mammillary area, which expressed Nkx2.1 and Otp. All these results provide an important set of data on the interpretation of the hypothalamic organization in a reptile, and hence make a useful contribution to the understanding of hypothalamic evolution.

Embryonic Origin of the Islet1 and Pax6 Neurons of the Chicken Central Extended Amygdala Using Cell Migration Assays and Relation to Different Neuropeptide-Containing Cells

“…4a in Moreno et al, 2012a]. Consistent with this proposal, in the present study, we found that the chicken Ceov is populated by cells derived from the Stv, and some of these cells were found to express Islet1 ( fig.…”

“…A similar group has also been identified in reptiles [Martínez-García et al, 2007Moreno et al, 2012a]. Based on their relation to distinct embryonic Pa subdomains, we proposed the existence of dorsal and ventral subdivisions of the chicken BSTL, with the BSTLd being related to the Pad and being part of the EAce, and the ventral BSTL being related to the Pavc and, as such, being part of the medial extended amygdala or EAme [Abellán and Medina, 2009].…”

“…Based on the expression of transcription factors during embryonic development and/or after hatching, it appears that at least the Std-derived Pax6 cells, Stv-derived Islet1 cells, the Pa-derived Nkx2.1 cells and the EMT-derived Pax6 cells are present in the EAce of turtles [Moreno et al, , 2012a, and were likely present in the EAce of ancestral amniotes. Similarly to the mouse and the chicken (see above), the EAce subdivisions of different reptiles appear to include neuronal subpopulations expressing pro-ENK [Reiner, 1987], which may derive from distinct subpallial subdivisions, as suggested for the mouse and chicken.…”

“…Therefore, the aim of this study was to investigate whether this proposal is true using migration assays. Our data from migration assays demonstrate that many neurons of the chicken EAce, including subpopulations of the BSTL, derive from the Stv (expressing Islet1) and Std (expressing Pax6), resembling the EAce of the mouse [Waclaw et al, 2010;Bupesh et al, 2011a] and turtle [Moreno et al, , 2012a.…”

“…Finally, the knowledge on the embryonic origin and molecular profile of the different neuronal subpopulations of the EAce in mice and chicken, together with available data in turtles [Moreno et al, , 2012a and amphibians [Moreno et al, 2009; more references below], is also extremely useful to study the evolution of the different neuronal subpopulations of the EAce, elucidate how cells with different origin/phenotype distribute along the EAce subdivisions in the different species and to understand the adaptive value of each subtype by analyzing species with different ecological niches and specializations. Based on the expression of transcription factors during embryonic development and/or after hatching, it appears that at least the Std-derived Pax6 cells, Stv-derived Islet1 cells, the Pa-derived Nkx2.1 cells and the EMT-derived Pax6 cells are present in the EAce of turtles [Moreno et al, , 2012a, and were likely present in the EAce of ancestral amniotes.…”