XB-ART-42932Front Neuroanat January 1, 2011; 5 11.
Ontogenetic distribution of the transcription factor nkx2.2 in the developing forebrain of Xenopus laevis.
The expression of the Nkx2.2 gene is involved in the organization of the alar-basal boundary in the forebrain of vertebrates. Its expression in different diencephalic and telencephalic regions, helped to define distinct progenitor domains in mouse and chick. Here we investigated the pattern of Nkx2.2 protein distribution throughout the development of the forebrain of the anuran amphibian, Xenopus laevis. We used immunohistochemical and in situ hybridization techniques for its detection in combination with other essential territorial markers in the forebrain. No expression was observed in the telencephalon. In the alar hypothalamus, Nkx2.2 positive cells were scattered in the suprachiasmatic territory, but also in the supraopto-paraventricular area, as defined by the expression of the transcription factor Orthopedia (Otp) and the lack of xDll4. In the basal hypothalamus Nkx2.2 expressing cells were localized in the tuberal region, with the exception of the arcuate nucleus, rich in Otp expressing cells. In the diencephalon it was expressed in all three prosomeres (P1-P3) and not in the zona limitans intrathalamica. The presence of Nkx2.2 expressing cells in P3 was restricted to the alar portion, as well as in prosomere P2, whereas in P1 the Nkx2.2 expressing cells were located in the basal plate and identified the alar/basal boundary. These results showed that Nkx2.2 and Sonic hedgehog are expressed in parallel adjacent stripes along the anterior-posterior axis. The results of this study showed a conserved distribution pattern of Nkx2.2 among vertebrates, crucial to recognize subdivisions that are otherwise indistinct, and supported the relevance of this transcription factor in the organization of the forebrain, particularly in the delineation of the alar/basal boundary of the forebrain.
PubMed ID: 21415915
PMC ID: PMC3049246
Article link: Front Neuroanat
Species referenced: Xenopus
Genes referenced: dll4 dlx2 nkx2-1 nkx2-2 otp pax6 pth shh sst.1 tbr1 tff3.7 trhd tub
Article Images: [+] show captions
|Figure 1. Photomicrographs of sagittal (A–D) and transverse (E–P) sections through the Xenopus forebrain subdivisions along the different representative developmental stages. The sagittal sections show the almost continuous Nkx2.2 expression from anterior hypothalamic areas to the most caudal regions of the forebrain (A–D). Nkx2.2 is not expressed in telencephalic areas, from embryonic stages through the adult. Nkx2.2 expression starts in the SPV territory of the alar hypothalamus (E–H). In the basal hypothalamus Nkx2.2 expression is restricted to the tuberal hypothalamus (I–L). In the diencephalon, Nkx2.2 is observed in the three prosomeres (P1–P3) and the Zli lacks Nkx2.2 expressing cells (I–P). Abbreviations: Arc, nucleus arcuatus; BH, basal hypothalamus; MB, mammillary band; MDB, midbrain-diencephalic boundary; OB, olfactory bulb; oc, optic chiasm; OT, optic tectum; P1-P3, diencephalic prosomeres 1–3; Pa, pallium; POC, preoptic commissural area/commissural septo-preoptic area; PO, preoptic area; PT, pretectum; PTh, prethalamus; PThE, prethalamic eminence; PV, paraventricular nucleus; SC, suprachiasmatic nucleus; SPa, subpallium; SPV, supraopto-paraventricular area; Tel, telencephalon; Th, thalamus; TP, posterior tubercle; Tub, tuberal area; ZI, zona incerta; Zli, zona limitans intrathalamica. Scale bars: 500 μm (D,L), 200 μm (C,G,H,K,O,P), 100 μm (A,B), and 50 μm (E,F,I,J,M,N).|
|Figure 2. Photomicrographs of sagittal (A,D–G,I) and transverse (B,C,E′,H) sections through the alar hypothalamus illustrating the Nkx2. 2 expression in combination with several hypothalamic markers. The most anterior Nkx2.2 expressing cells are observed in the SPV (the Otp expressing territory) during development (A,B,E,E′), in the region where it colocalizes with mesotocin (C,F,F′) and somatostatin (D), but only a subpopulation of the SPV cells coexpress Nkx2.2 and Otp [see arrow in (B,E,E′)]. At suprachiasmatic levels, the Nkx2.2 positive cells are located in the catecholaminergic (G,G′,H) and xDll4 (I) expressing region, constituting an independent territory within this domain (G–I). The yellow lines in (A,E,G) indicate the level of the sections of (B,E′,H), respectively. Yellow boxes in (F,G) indicate the higher magnifications shown in (F′,G′), respectively. Abbreviations as in Figure 1. Scale bars: 500 μm (F), 200 μm (E,E′,G), 100 μm (D,H) and 50 μm (A,B,C,F′,G′,I).|
|Figure 3. Photomicrographs of transverse (A,C,D) and sagittal (B,E) sections through the basal hypothalamus illustrating the Nkx2. 2 expression in combination with several hypothalamic markers. The Nkx2.1 expression confirms that the limited Nkx2.2 expression found in the basal hypothalamic territory is situated in the tuberal region (A), restricted to the anterior part [asterisk in (B)] and avoiding the nucleus arcuatus, labeled for Otp (B,C), and the mammillary band, defined by TH (D) and xDll4 (E,E′). Yellow box in e indicates the area shown in higher magnification in e′. Abbreviations as in Figure 1. Scale bars: 100 μm (B,E), 50 μm (A,C,D,E′).|
|Figure 4. Photomicrographs of transverse (A,E,F,G) and sagittal (B,C,D) sections through the diencephalon illustrating the Nkx2. 2 expression in combination with diverse diencephalic markers. The prethalamic eminence, rich in Tbr1 (A), was devoid of Nkx2.2 expression, in contrast to the prethalamus, defined by the Pax6 (B) and xDll4 expressions (C). The yellow box in d shows a higher magnification of the Nkx2.2/GABA double labeled cells found in the thalamus [see arrowheads in (D,D′)]. The double labeling Nkx2.2/Nkx2.1 (E) and Nkx2.2/TH (F) define the position of the Nkx2.2 cells in the zona incerta of the prethalamus. The xShh diencephalic expression defines the lack of Nkx2.2 expression in the Zli (zona limitans intrathalamica) (G). Abbreviations as in Figure 1. Scale bars: 100 μm (B,C,D), 50 μm (A,E,F,G), 25 μm (D′).|
|Figure 5. Photomicrographs of transverse (A,B) and horizontal (C) sections through the forebrain illustrating Nkx2. 2 expression in combination with xShh. The expressions of Nkx2.2 and xShh extend along the anterior–posterior axis in parallel adjacent stripes, forming longitudinal columns along the forebrain. Abbreviations as in Figure 1. Scale bars: 50 μm.|
|Figure 6. Schematic drawings of sagittal and coronal sections through a premetamorphic brain of Xenopus laevis illustrating the distribution of Nkx2. 2 expressing zones (green regions in the sagittal view) and cells (green dots in the coronal view) along the forebrain. The appropriated levels of the coronal sections are indicated in the sagittal view. Abbreviations as in Figure 1.|
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