Analysis of the Expression Pattern of Cajal-Retzius Cell Markers in the <b><i>Xenopus laevis</i></b> Forebrain

Abstract

Cajal-Retzius cells are essential for cortical development in mammals, and their involvement in the evolution of this structure has been widely postulated, but very little is known about their progenitor domains in non-mammalian vertebrates. Using in situhybridization and immunofluorescence techniques we analyzed the expression of some of the main Cajal-Retzius cell markers such as Dbx1, Ebf3, ER81, Lhx1, Lhx5, p73, Reelin, Wnt3a, Zic1, and Zic2 in the forebrain of the anuran Xenopus laevis, because amphibians are the only class of anamniote tetrapods and show a tetrapartite evaginated pallium, but no layered or nuclear organization. Our results suggested that the Cajal-Retzius cell progenitor domains were comparable to those previously described in amniotes. Thus, at dorsomedial telencephalic portions a region comparable to the cortical hem was defined in Xenopus based on the expression of Wnt3a, p73, Reelin, Zic1, and Zic2. In the septum, two different domains were observed: a periventricular dorsal septum, at the limit between the pallium and the subpallium, expressing Reelin, Zic1, and Zic2, and a related septal domain, expressing Ebf3, Zic1, and Zic2. In the lateral telencephalon, the ventral pallium next to the pallio-subpallial boundary, the lack of Dbx1 and the unique expression of Reelin during development defined this territory as the most divergent with respect to mammals. Finally, we also analyzed the expression of these markers at the prethalamic eminence region, suggested as Cajal-Retzius progenitor domain in amniotes, observing there Zic1, Zic2, ER81, and Lhx1 expression. Our data show that in anurans there are different subtypes and progenitor domains of Cajal-Retzius cells, which probably contribute to the cortical regional specification and territory-specific properties. This supports the notion that the basic organization of pallial derivatives in vertebrates follows a comparable fundamental arrangement, even in those that do not have a sophisticated stratified cortical structure like the mammalian cerebral cortex.

Development of subdomains in the medial pallium of Xenopus laevis and Trachemys scripta: Insights into the anamniote-amniote transition

“…Moreover, in mammals it has been demonstrated the involvement of the Wnt signaling pathway in the Prox1 + granule cells regulation (Liu et al, 2000;Pleasure et al, 2000;Gao et al, 2009;Kuwabara et al, 2009;Karalay et al, 2011). Therefore, the Wnt3a expression in the Xenopus laevis CH (Jiménez and Moreno, 2021), together with the Prox1 expression in the MP (present results), suggest that the molecular developing specification process in both models could be comparable. In reptiles, a basic and small CH has been described [(Cabrera-Socorro et al, 2007;Nomura et al, 2013), as well as the Lhx2 and Pax6 expressions in MP (Moreno et al, 2010;Desfilis et al, 2018;Tosches et al, 2018); present results].…”

“…Furthermore, in mammals together with Lhx2, Pax6 expression is essential in the anatomical localization of CH ( Godbole et al, 2017 ) and thus of the hippocampus. In Xenopus laevis , the presence of a CH has recently been defined based on the expression of different conserved genes, including Wnt3a ( Jiménez and Moreno, 2021 ), as well as the Lhx2 and Pax6 pallial expressions [( Bachy et al, 2001 , 2002b ; Moreno et al, 2004 , 2008 ); present results]. Moreover, in mammals it has been demonstrated the involvement of the Wnt signaling pathway in the Prox1 + granule cells regulation ( Liu et al, 2000 ; Pleasure et al, 2000 ; Gao et al, 2009 ; Kuwabara et al, 2009 ; Karalay et al, 2011 ).…”

Persistence of Cajal-Retzius cells in the postnatal hippocampus is required for development of dendritic spines of CA1 pyramidal cells

“…(C) Sample clustering using Manhattan method for distance and average agglomeration method for height mapping. (D) Table of commonly acknowledged CR cells markers extracted from literature including Lhx1, Trp73, Ebf3, Erc2, Zic1, Cnr1, Erbb4, Fam196a , and Cacna2d2 (Jiménez & Moreno, 2021). Log2FC differences generated by the following equation: [ Gene ] P15 Pde1c-Cre+/-;DTA – [ Gene ] P15 Pde1c-Cre-/-;DTA .…”

Glutamatergic neuron types in the amygdala of the urodele amphibian Pleurodeles waltl

“…According to our scRNAseq data, neurons in clusters TEGLU37 and TEGLU38 express Zic1 and Lhx5 , markers that are also found in the frog medial amygdala (Fig. 3A)(Jiménez and Moreno 2021). Furthermore, these neurons express Foxg1 but not Tbr1 (Fig.…”

“…However, these neurons do not coexpress Etv1 , according to our scRNAseq and in situ hybridization data. In reptiles, neurons co-expressing Etv1 and Fezf2 have been identified in the pDVR of turtles and lizards (Tosches et al 2018; Norimoto et al 2020), suggesting that the gene regulatory program that establishes the co-expression of these two transcription factors exists only in amniotes, but not in amphibians (or at least not in salamanders; see (Jiménez and Moreno 2021)). Additional cellular transcriptomics data in mammals, birds, reptiles, and other amphibians are needed to understand the evolutionary relationships of neuron types in the amphibian lateral amygdala, reptilian and avian pDVR, and mammalian cortical amygdala and basolateral complex.…”