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Neural induction in Xenopus requires the activation of new sets of genes that are necessary for cellular and regional specification of the neural tube. It has been reported earlier that members of the Distal-less homeobox gene family are specifically activated in distinct regions of the central nervous system (CNS) of Xenopus embryos (Dirksen et al., 1993; Papalopulu and Kintner, 1993). In this paper we describe in detail a Xenopus homeobox containing gene Xdll-2, which belongs to the Distal-less gene family. In contrast to other previously described Xenopus family members, Xdll-2 is expressed in the embryonic ectoderm and is specifically repressed in the CNS. This repression can be mimicked in isolated animal caps by treatment with activin. Expression of Xdll-2 persists in the epidermis and some neural crest cells. Because of its spatial and temporal expression pattern this gene is a good candidate to have a regulatory function in the initial formation of the epidermis. Its high level of expression in adult skin indicates that its function is continuously required in this tissue.
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7915132
???displayArticle.link???Mech Dev
Fig 2 Developmental express,on of Xdll-2 (A) Northern blot analysis of 2 5µg of total RNA from different stages of embryos (Stage E) egg, (stage 10, 12) gastrula, (stages 15, 20) neurula, (stages 30-40) tadpoles The positions of 18S and 28S mRNAs are indicated by arrows We estimate that the Xdll-2 RNA is about 19 kb long (B) Northern blot analysis of RNA from dissected animal and vegetal half of stage 10 embryos Equal amounts of RNA (2 5 t~g) were loaded per lane Ecto-ectoderm, Endo-endoderm (C) Ethidium bromide staining of the gel in (B) (D) Northern blot of RNA from microdissected regions of stage 14 embryos Equal amounts of RNA were loaded per lane A-anterior, P-posterior, D-dorsal, V-ventral (E) Ethidium bromide staining of the gel m (D) (F) Northern blot hybridization of RNA from dissected ventralectoderm and mesendoderm of stage 14 embryos E-ectoderm, M-combined ventralmesoderm and endoderm Equal amounts of RNA (1 0 /~g) were loaded (G) Ethidium bromide staining of the gel m (G) (H) Northern blot hybridizatlon of RNA from microdissected regions of stage 18 embryo A-anterior, P-posterior, D-dorsal, V-ventral (1) Ethidium bromide staining of the gel m (H)
Fig 3 Analysis of spatial expression of Xdll-2 by whole-mount in situ hybridizatlon (A) In Situ hybridization of Xdll-2 to a stage 14 embryo. This lateral view shows the presence of hybridization in the ventral half of the embryo, but absence in the dorsal Anterior is right Dorsal is on top (B) In Situ hybridization of Xdll-2 to stage 18 embryos anterior view Note the lack of hybridizatlon m the neural fold (arrow) and underlying mesoderm (C) In Situ hybridization to stage 30 embryo visualizing the late expression of Xdll-2 in the branchial arches (arrows) and otic vesicle (triangle) Lateral view (D) Anterior view of the same embryos in (C) Arrows point to the hybridization in the olfactory placodes CG-cement gland.
Northern blot analysis of RNA from adult tissues The positions of 18S and 28S mRNAs are indicated by arrows. The lower RNA band has the correct size, the upper band is probably an unprocessed RNA.
In situ hybridization of a section of Xenopus adult skin with 35S-labeled Xdll-2 cRNA The epidermal layers show hybrldizatlon (A) Autoradlography (B) Neutral red staining of the same section
Fig 6 (A) Effect of activin on the expression of Xdll-2 Northern blot analysis of RNA (25µg) from reduced and uninduced ectoderm. Prior to induction, ectoderm was separated into inside and outside ectoderm. Each layer was then separately incubated in activin. (B) Same Northern blot rehybridized with a cardiac muscle actin probe Lane 1- Inside ectoderm, activin Lane 2-Inside ectoderm, no activin Lane 3- Outside ectoderm, activin Lane 4-Outside ectoderm, no activin (C) Effect of ammonium chloride on the expression of Xdll-2 Northern blot analysis of RNA (2 5/~g) from reduced and uninduced ectoderm 1-uninduced, 2-reduced (D) Ethidium bromide staining of the gel in (c)
