Figure 1.
Characterization and expression analysis of Vsig1 splice variants.
(A) Schematic diagram of the Vsig1 gene. Boxes and lines represent the exons and introns, respectively. Positions of both polyA signals and probes used in Northern blot analysis are shown. (B) Schematic representation of exonic sequences present in the different Vsig1 mRNA isoforms. Black boxes represent the coding exon, while white boxes represent the 5′ and 3′UTRs of the Vsig1 splice variants. (C) Northern blot with total RNA from different tissues of 3-month-old mice was hybridized with probe 1 (top panel) and probe 2 (middle panel). Integrity and variation of loaded RNA samples were assessed by rehybridization with a probe for human elongation factor 2 (EF-2). (D) Restricted expression of Vsig1C isoform in testis was confirmed by RT-PCR analysis using primers containing the sequence of exons 1b and 4. The used primers only amplify the 396-bp cDNA fragment in testis RNA. Production of the control Hprt products was observed throughout tissues, demonstrating the presence of intact loaded RNA. (E) Immunoblot with cellular extracts from different tissues was probed using polyclonal anti-VSIG1 antibodies and subsequently reprobed with monoclonal anti- α-tubulin antibodies (α-Tub). (F) Immunoblot with untreated and N-glycosidase F-treated stomach extracts was probed with anti-VSIG1 antibodies.
Figure 2.
Expression analysis of VSIG1 during stomach development.
(A) RNA blot of total RNA isolated from the stomach of different stages of pre- (E) and postnatal (P) development was hybridized with Vsig1 (probe 2 in Fig. 1A) and the hEF-2 cDNA probe. (B) Immunohistochemistry of paraffin sections with anti-VSIG1 antibody shows the restricted expression of VSIG1 in the glandular epithelium of the stomach at E12.5 (B), E13.5 (C) and E17.5 (D). (E) Expression of GATA4 in glandular epithelia of the stomach at E17.5. Arrows in C–E mark the transitional junction between the glandular and squamous epithelia. In 3-month-old stomachs, VSIG1 is located at the adhesion junctions between epithelial cells of the gastric unit (F). The box in F is magnified in G and shows restricted localization of VSIG1 to the basolateral membrane of pit cells (G). Scale bar (B–E) = 500 µm; (F) = 100 µm; (G) = 20 µm.
Figure 3.
Subcellular localization of VSIG1 to adherens junctions of glandular epithelia.
Double immunostaining of embryonic stomach (E17.5) with rabbit polyclonal anti-VSIG1 (A and D), mouse monoclonal anti-α-catenin (B) and mouse monoclonal anti-ZO1 (E) antibodies. The immunoreactivity for VSIG1 is distributed across the basolateral membranes of luminal epithelia and cell-cell adhesion sites, and overlap with that of α-catenin (C). Immunostaining signals of ZO1 are restricted to tight junctions of luminal epithelia (E) and do not show co-localization with VSIG1 (F). Nuclei (C and F) are visualized with DAPI (blue). Scale bar = 20 µm.
Figure 4.
Generation and expression analysis of the Vsig1-EGFP transgenic allele.
(A) Schematic representation of the Vsig1-EGFP transgenic construct. The Vsig1-EGFP construct consists of the 4.5-kb genomic fragment located upstream of exon 1a of the Vsig1 gene (black box) and the EGFP gene (green box). (B) Expression of the Vsig1-EGFP transgenic allele in adult stomachs and testes of different transgenic lines and wild-type (WT) mice was determined by Northern-blot hybridization using the EGFP probe. Integrity of RNA samples was documented by images of the corresponding agarose gel. (C) Immunoblot of EGFP expression in cellular extracts from different tissues of 3-month-old transgenic mouse. The protein blot was subsequently probed with anti-α-tubulin antibody. (D) Expression of the Vsig1-EGFP transgenic allele during pre- and postnatal stomach development was examined by immunoblotting using total lysates obtained from transgenic stomachs of embryos at E15.5 and E18.5, and from P10, P20 and P60 mice. Protein extract from wild-type stomach (WT) was used as controls. (E) Temporal expression of VSIG1 during prenatal and postnatal development of stomach was examined by immunoblotting. (F) Fluorescent micrographs of stomachs from transgenic embryos at E18.5 and 60-day-old mice show EGFP epifluorescence in the posterior stomach (P) but not in the anterior stomach (A). (G) Expression of Vsig1-EGFP in the glandular epithelium was confirmed by immunofluorescence in paraffin sections of E15.5, P0.5, P10 and P20 with anti-EGFP (green fluorescence) and anti-VSIG1 (red fluorescence) antibodies. DAPI (blue fluorescence) was used for nuclear staining. Scale bar (F) = 500 µm; (G) = 200 µm.
Figure 5.
Targeting disruption of the Vsig1.
(A) Structure of the wild-type, targeting vector and recombinant allele are shown together with the relevant restriction sites. A 2.5-kb genomic fragment containing exon 1a was replaced by a pgk-neo selection cassette (NEO). The probe used and predicted length of the EcoRI restriction fragment in Southern blot analysis are shown. TK, thymidine kinase cassette; E, EcoRI; X, XbaI; X*, disrupted XbaI site; Xh, XhoI. (B) Blot with EcoRI-digested genomic DNA of recombinant ESC clones was probed with the 3′ probe shown in panel A. The external probe recognized only a 10.7-kb fragment of recombinant allele in Vsig1−/Y ESCs and a 12.2-kb fragment of the wild-type allele in Vsig1+/Y ESCs. (C) PCR assay using microsatellite markers was performed to determine the degree of chimerism in the stomachs of chimeric male mice. The 129- and C57-specific fragments were amplified using DNA of the 129/Sv and C57BL/6J mouse strains, and stomach isolated from different chimeric males (Ch).
Figure 6.
Transdifferentiation of the Vsig1−/Y cells into squamous epithelia inside the gastric corpus of chimeric Vsig1−/Y↔Vsig1+/Y stomachs.
(A–F) Serial sections of stomach prepared from 5-month-old chimeric mice were stained with H&E (A and B) or immunohistologically analyzed for expression of glandular and squamous epithelia-specific markers (C–F). The bracket in H&E-stained sections (A) marks the area containing squamous epithelia, which are present inside the glandular epithelia of the gastric corpus and is magnified in B. Cells of this lesion do not express VSIG1 (C) or glandular epithelium-specific markers H+,K+-ATPase (D) and GATA4 (E), but do express cytokeratin K5 (F), which is normally expressed in squamous epithelia of the forestomach (G). Inserts show higher magnification. (H and I) Dissected stomachs from Vsig1−/Y↔Vsig1+/Y chimeras at E17.5 were longitudinally sectioned and immunological stained with anti-VSIG1 antibody. The transition zone between glandular mucosa and stratified squamous epithelia of the forestomach is indicated by an arrow. The box in H is magnified in I and denotes a patch of atypical squamous epithelium that lacks the primordial gastric units of the glandular epithelium as well as cells that express VSIG1. Scale bar (A and C–H) = 500 µm; (B and I) = 100 µm; inserts = 200 µm.