A model of early molecular regionalization in the chicken embryonic pretectum

Abstract

The pretectal region of the brain is visualized as a dorsal region of prosomere 1 in the caudal diencephalon, including derivatives from both the roof and alar plates. Its neuronal derivatives in the adult brain are known as pretectal nuclei. The literature is inconsistent about the precise anteroposterior delimitation of this region and on the number of specific histogenetic domains and subdomains that it contains. We performed a cross-correlated gene-expression map of this brain area in chicken embryos, with the aim of identifying differently fated pretectal domains on the basis of combinatorial gene expression patterns. We examined in detail Pax3, Pax6, Pax7, Tcf4, Meis1, Meis2, Nkx2.2, Lim1, Dmbx1, Dbx1, Six3, FoxP2, Zic1, Ebf1, and Shh mRNA expression, as well as PAX3 and PAX7 immunoreaction, between stages HH11 and HH28. The patterns analyzed serve to fix the cephalic and caudal boundaries of the pretectum and to define three molecularly distinct anteroposterior pretectal domains (precommissural, juxtacommissural, and commissural) and several dorsoventral subdomains. These molecular specification patterns are established step by step between stages HH10 and HH18, largely before neurogenesis begins. This set of gene-architectonic data constitutes a useful scaffold for correlations with fate maps and other experimental embryologic results and may serve as well for inquiries on homologies in this part of the brain.

Expression analysis of Sulf1 in the chick forebrain at early and late stages of development

“…Thus, to adequately localize the DTgp1 band, we carried out double in situ hybridization for Sulf1 and Nkx2.2, plp/dm20, or Pax6. Pretectal Pax6 transcripts appeared in the entire alar plate adjacent to the alar-basal boundary, while an additional positive strip appeared separated in the basal mantle layer ( Fig.1H; Ferran et al, 2007). Double in situ hybridization with Sulf1 (labeled in blue) and Pax6 (labeled in red) showed that the basal Pax6 ϩ cell band appeared ventral to the DTgp1 Sulf1-positive band (between DTgp1 and VTgp1; arrow in Fig.…”

“…1E-J). At these early stages of development, the alar/basal boundary in p1 is underlined by the ventral edge of Pax6 expression in the alar plate; and the dorsal border of Nkx2.2 expression in the parabasal band of the basal plate Ferran et al, 2007). Thus, to adequately localize the DTgp1 band, we carried out double in situ hybridization for Sulf1 and Nkx2.2, plp/dm20, or Pax6.…”

“…The alar pretectum appears anteroposteriorly divided into three main radial histogenetic areas called commissural (PTc), juxtacommissural (PTj), and precommissural domains (PTp; Yoon et al, 2000;Redies et al, 2000;Puelles et al, 2007;Ferran et al, 2007). These terms refer to their positions relative to the posterior commissure.…”

“…In this work, we compared the expression of Sulf1 with that of Nkx2.2, plp/dm20, and Pax6, by double in situ hybridization to precisely locate Sulf1-positive bands in prosomere 1 according to recent studies on pretectal regionalization (Ferran et al, 2007). The issue of molecularly defining the alar-basal boundary at diencephalic levels is still open for discussion.…”

Architect genes of the brain: A look at brain evolution through genoarchitecture

“…That is, this tool allows grouping cells with common identities, thus allowing us to have an anatomical characterization of the brain much more elaborated than the one we previously had (Figures 3 and 4). That is, using the genoarchitecture we can observe with fine detail how the anatomical characterization of this area is throughout all embryonic development and during the postnatal life of a species (ontogeny) (Ferran et al, 2009;Ferran, Sánchez-Arrones, Sandoval, & Puelles, 2007).…”