XB-ART-12135Mech Dev October 1, 1999; 88 (1): 67-72.
A novel guanine exchange factor increases the competence of early ectoderm to respond to neural induction.
Inductive interactions between different cell layers have an extremely important role in early embryogenesis. One of the most intensively studied and best characterised of these is the induction of neural tissue from ectodermal cells by the dorsal mesoderm. The competence of ectodermal cells to respond to neural induction varies according to dorsal-ventral position; with dorsal ectoderm (much of which forms the neural plate) having a far higher competence. Here we show that overexpression of the nucleotide exchange factor lfc increases ectodermal competence for neural induction as well as the amount of neural tissue in the whole embryo. Lfc is expressed pan ectodermally soon after gastrulation and may respond to an early determinant of dorsal ectoderm.
PubMed ID: 10525189
Article link: Mech Dev
Genes referenced: akt1 arhgef2 bmp4 eef1a2 eif4a2 en2 hoxb1 hoxb4 hoxb9 krt12.4 msi1 ncam1 nog nrp1 odc1 prkca prkcb rac1 snai2
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|Fig. 1. Whole mount in situ analysis of the expression of Xlfc (blue/purple staining). (A,B) Stage 10 (early gastrula) embryos. (A) View of blastopore end, dorsal side lower most. (B) Lateral view, blastopore end to right. (C,D) Stage 12 (late gastrula) embryos. (C) View of blastopore end (posterior). Note even distribution of staining ventral and dorsal. (D) Anterior view. (E,F) Stage 14 (neurula) embryos. (E) Dorsal view, anterior top right; posterior bottom left. Note staining becoming concentrated in the dorsal (neural) ectoderm. (F) Ventral view. (G,H) Stage 18 (late neurula) stage. (G) Dorsal view, anterior top. Staining is now predominantly in the neural tube. (H) Lateral view, dorsal to right. (I) A 10-mm central transversal section through a late gastrula stage (12) albino embryo. The dorsal side is uppermost. Note that only the outer (ectodermal) cells are stained (brown). The section has been counter-stained red.|
|Fig. 2. (A) Xlfc expression is activated by ectopic noggin expression and repressed by ectopic BMP4 expression. Zygotes were injected with 500 pg of noggin or BMP4 RNA as shown. The expression of Xlfc in whole embryos was, subsequently, examined at the gastrula and neurula stages (12 and 18, respectively) by RT-PCR. ODC is included as a loading control. (B) Overexpression of lfc in whole embryos causes an expansion of the neural plate at the expense of the presumptive neural crest and epidermis. An RT-PCR analysis of RNA extracted from late neurula embryos injected with either lfc or lfcD as shown. NIC, non-injected control embryos. -RT, control without reverse transcription. ef1a is included as a loading control.|
|Fig. 3. Lfc increases the competence of ectodermal explants to respond to neural induction. RT-PCR analysis of caps taken from embryos injected with 500 pg lfc RNA, 500 pg lfcD RNA, 10 pg noggin RNA (nogL), 500 pg noggin RNA (nogH) or a combination, as shown. NIC, non-injected control. WE, whole embryos at the late neurula stage. ef1a is included as a loading control.|
|arhgef2 (Rho/Rac guanine nucleotide exchange factor (GEF) 2) gene expression in Xenopus laevis embryos, NF stage 18, as assayed by in situ hybridization. Dorsal view: anterior up (and right).|