Expression of the genes Emx1, Tbr1, and Eomes (Tbr2) in the telencephalon of Xenopus laevis confirms the existence of a ventral pallial division in all tetrapods.
To investigate the pallial organization and the exact location and extension of the ventral pallium in amphibians, we cloned a fragment of the homeobox XenopusTbr1 (xTbr1) gene and analyzed its expression compared with that of the genes xEomes (Tbr2) and xEmx1 in the telencephalon of the frog Xenopus laevis during embryonic and larval development. The expression of xEmx1 was also analyzed in the adult frog. We compared the expression patterns of these pallial marker genes with that of the subpallial gene xDistal-less-4 (xDll4). Our results indicate that the whole pallium of Xenopus expresses the T-box genes xTbr1 and xEomes (in proliferating cells and/or mantle) during embryonic and larval development, and the expression of these genes is topographically complementary to that of xDll4 in the subpallium. In addition to their massive expression in the pallium, both xTbr1 and xEomes are expressed in a few dispersed cells in the subpallium, which may represent immigrant cells of pallial origin, because these genes are not found in the subpallial proliferating cells. On the other hand, during development xEmx1 is expressed in a large part of the pallium (proliferating and postmitotic cells) except for an area adjacent to the pallio-subpallial boundary, where xEmx1 is observed only in some mantle cells. This pallial area poor in xEmx1 expression and poor in expression of the subpallial gene xDll4, but expressing the pallial marker genes xTbr1 and xEomes, appears to represent the amphibian ventral pallium, comparable to that described in other vertebrates (Puelles et al. [2000] J. Comp. Neurol. 424:409-438). In the adult frog, the ventral pallium appears to include the rostral part of the lateral amygdalar nucleus as well as a large part of the medial amygdalar nucleus (as defined by Marín et al. [1998] J. Comp. Neurol. 392:285-312). In contrast, the caudal part of the previously termed lateral amygdalar nucleus shows strong xEmx1 expression and may be a lateral pallial derivative. The possible homology of these amphibian amygdalar nuclei is discussed. Finally, expression of xTbr1, xEomes, and xEmx1 is observed in the mitral cell layer of the olfactory bulb from early developmental stages, further supporting that this structure is a pallial derivative.
Brox
Aurora
A
Department of Human Anatomy, Faculty of Medicine, University of Murcia, 30100 Murcia, Spain.
Puelles
Luis
L
Ferreiro
Beatriz
B
Medina
Loreta
L
D000818:Animals; D004268:DNA-Binding Proteins / Q000096:biosynthesis*; D004625:Embryo, Nonmammalian; D018507:Gene Expression Regulation, Developmental; D018398:Homeodomain Proteins / Q000096:biosynthesis*; D017403:In Situ Hybridization; D007814:Larva; D020133:Reverse Transcriptase Polymerase Chain Reaction; D020825:T-Box Domain Proteins / Q000096:biosynthesis*; D013687:Telencephalon / Q000196:embryology*; D014157:Transcription Factors; D029867:Xenopus Proteins; D014982:Xenopus laevis; D000099260:Empty Spiracles Homeobox Proteins
D004268:DNA-Binding Proteins; D018398:Homeodomain Proteins; D020825:T-Box Domain Proteins; D014157:Transcription Factors; D029867:Xenopus Proteins; D000099260:Empty Spiracles Homeobox Proteins; C103223:EOMES protein, Xenopus; C492270:Tbr1 protein, Xenopus