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J Invest Dermatol
2012 Aug 01;1328:1977-87. doi: 10.1038/jid.2012.110.
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Exons 5-15 of kazrin are dispensable for murine epidermal morphogenesis and homeostasis.
Chhatriwala MK
,
Cipolat S
,
Sevilla LM
,
Nachat R
,
Watt FM
.
???displayArticle.abstract??? Kazrin binds to periplakin and ARVCF catenin, and regulates adhesion and differentiation of cultured human keratinocytes. To explore kazrin function in vivo, we generated a kazrin gene-trap mouse in which only exons 1-4 were expressed, fused to β-galactosidase. On transient transfection, the protein encoded by exons 1-4 did not enter the nucleus, but did cause keratinocyte shape changes. The mice had no obvious defects in skin development or homeostasis, and periplakin and desmoplakin localization was normal. Expression of the kazrin-β-galactosidase fusion protein faithfully reported endogenous kazrin expression. Kazrin was not expressed in embryonic epidermis and was first detected at postnatal day 1. In adult mice, epidermal kazrin expression was less widespread than in humans and Xenopus, being confined to the bulb of anagen hair follicles, the infundibulum, and parakeratotic tailepidermis. In anagen bulbs, kazrin was expressed by a band of cells with elongated morphology and low desmoplakin levels, suggesting a role in morphogenetic cell movements. We conclude that exons 5-15 of kazrin, encoding the nuclear localization signal and C-terminal domain, are not required for epidermal development and function. The previously reported role of kazrin in regulating cell shape appears to reside within the N-terminal coiled-coil domain encoded by exons 1-4.
Figure 1. Generation of kazrin β-galactosidase (β-gal) gene-trap (gt/gt) mouse and conditional knockout (flx/flx) mice. (a) Exon structure of mouse kazrin. Blue box represents insertion of the neomycin resistance gene (β-geo) cassette in the kazrin β-gal gt/gt mouse. Red triangles indicate loxP sites for removing exon 5 in the kazrin flx/flx mice. (b) Predicted domain architecture of kazrin-β-geo fusion protein in the kazrin β-gal (top) gt/gt mouse and kazrin fragment expressed in the (bottom) kazrin flx/flx mouse. (c) RT-PCR amplification of transcripts upstream (exons 2–3) or downstream (exons 4–5) of the gene trap. RNA in each lane is from a single representative litter-matched mouse of the genotype indicated. (d) Quantitative RT-PCR of transcripts upstream (exons 2–3) and downstream (exons 6–7) of the gene trap. Top: Expression values relative to glyceraldehyde 3-phosphate dehydrogenase (GAPDH). Each bar shows the mean and standard deviation of at least three mice per genotype. Bottom: Ratio (%) of upstream and downstream transcripts from the top panel. Primer positions upstream and downstream of the β-geo cassette are indicated by the orange and green brackets, respectively, in a. (e) Alignment of predicted amino-acid sequences encoded by exons 1 and 2 of human kazrinA and mouse kazrin. (f) RT-PCR amplification of exons 1–4, 1–5, 2–4, or 2–5 of mouse kazrinA. Positive (GAPDH) and negative (water) controls are shown. β-geo, β-galactosidase fused to a neomycin resistance gene; Ex, exon.
Figure 2. Analysis of kazrin protein expression. (a) Domain architecture of kazrinA and kazrinE. The N terminus of kazrinE is identical to kazrinA. (b) Purification of recombinant human kazrinA overexpressed in Escherichia coli as a glutathione-S-transferase (GST) fusion protein. (c) Lysates of normal human keratinocytes transfected with scrambled small interfering RNA (siControl) or pooled siRNAs specific for all isoforms of kazrin (siKazrinAll) were blotted with pan-kazrin antibody, rabbit pre-immune serum, or rabbit secondary antibody alone. (d) Pan-kazrin antibody crosslinked to protein G agarose beads was used to immunoprecipitate endogenous kazrin from lysates of normal human keratinocytes. (e, f) Pan-kazrin antibody detection of endogenous kazrin, kazrin β-galactosidase (β-gal) fusion protein, and the 28-kDa fragment encoded by kazrin exons 1–4 in lysates of wild-type (wt) mice or litter-matched gene trap (gt/gt) and conditional knockout (flx/flx) mice. simKazrinAll: wt/wt keratinocytes transfected with two pooled siRNAs (see also Supplementary Figure S1c online). Glyceraldehyde 3-phosphate dehydrogenase (GAPDH) was used as a loading control for c–f.
Figure 3. Transient expression of full-length kazrin or exons 1–4 in cultured human keratinocytes. (a–e) Immunolabeling of kazrin (green) with 4′,6-diamidino-2-phenylindole (DAPI) nuclear counterstain (blue). (f) Quantification of effect of kazrin exons 1–4 on cell morphology. Cells were scored as having altered cell shape (elongation/prominent filopodia/prominent lamellipodia), cytoplasmic kazrin puncta, or both. Data are mean±SEM of three experiments. The numbers of cells scored per experiment were 128, 245, or 180. Bars=25 μm. Ex, exon.
Figure 4. Comparison of skin of wild-type (wt/wt) and kazrin gene trap (gt/gt) and conditional knockout (flx/flx) mice. Sections of adult back (anagen or telogen) and tail skin from litter-matched wt/wt, gt/gt, or flx/flx mice were (a, b) stained with hematoxylin and eosin or (c, d) labeled with antibodies to Ki67, (e, f) desmoplakin, or (e, f) periplakin. Bars: 100 μm in all panels.
Figure 5. β-Galactosidase expression in the epidermis of gene-trap mice. Epidermal whole mounts of back (a, c, e) and tail (b, d, f–i) from the ages indicated were stained for X-gal. Bars: 200 μm in all panels. E17.5, embryonic day 17.5; P1, postnatal day 1.
Figure 6. Kazrin expression in adult mice. (a) Epidermal tail whole mount of kazrin gene-trap (gt/gt) mouse stained for X-gal to visualize endogenous kazrin in hair during anagen. Inf, infundibulum; IRS, inner root sheath. (b) Quantitative RT-PCR of mRNA from anagen back skin, telogen back skin, or telogen tail skin using primers to detect all forms of kazrin (exons 6 and 7) or specific for kazrinE (KazE) (exons 10 and 11). The unpaired Student's t-test was used to determine whether differences in transcript levels were statistically significant. (c–e) Paraffin sections of tail-scale interfollicular epidermis from kazrin gt/gt mouse co-stained with antibodies to (c, d; red) K14 and (c, e; green) kazrin or (d; green) non-immune serum with (blue) 4′,6-diamidino-2-phenylindole (DAPI) nuclear counterstain. Field shown in (e) partially overlaps with the field shown in c. (f, g) Frozen section of tail skin from kazrin gt/gt mice stained for (blue) X-gal and counterstained (with nuclear fast red). (g) Higher-magnification view of the area demarcated by the black box in f. (h–t) Tail epidermal whole mounts stained with (h) non-immune serum, or the antibodies indicated. (j) Higher-magnification view of the area demarcated with white dashed line in i. (c–e, h–n) Blue staining is the DAPI nuclear counterstain. (j–t) The epidermis from wt/wt mice, except (l), which is from gt/gt mouse. Bars: (a, c, d, f, j–r) 100 μm; (e) 40 μm; (h, i) 200 μm; and (s, t) 50 μm.
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