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The expression of both epidermal and nonepidermal keratins has been detected in the cement gland of Xenopus laevis by antibody staining. Northern blot and in situ hybridizations with gene-specific probes indicated the expression of the nonepidermal keratin, XK endo B, and the embryonic epidermal keratin, XK70, in the cement gland. Furthermore, since explanted animal pole cells can be induced to differentiate into cement gland cells in vitro by incubation in NH4Cl, we have demonstrated the in vitro induction of XK endo B, maintenance of XK70, and repression of another embryonic epidermal keratin, XK81. This is the first report of keratin gene expression in the cement gland.
FIG. 1. Keratin expression in the cement gland at late neurula as visualized by immunocytochemistry. (A) The plane of sections in B and C is
indicated by the hatched line. (B) Cross section through the head stained with antibodies to XK endo B. (C) Cross section through the head
stained with antibodies to a common epitope in XK81 and XK70. Staining is visualized by indirect immunofluorescence. The brain cavity (BC),
eye vesicles (EV), outer ectoderm (OE), inner ectoerm (IE), pituitary rudiment (PR), and cement gland (CG) are indicated.
FIG. 2. Keratin RNA expression as localized by dissection. Tissue
dissections are shown schematically in A. (B, C, D) Northern blots of
RNAs from dissected epidermis (lane l), dissected endoderm (lane 2),
and dissected cement gland (lane 3). The blots were hybridized to a
nick-translated probe specific for XK endo B RNA (B), for XKâ70 (C),
and for XK81 (D). Ethidium bromide staining of the gel indicated that
all lanes contained about equal amounts of RNA.
FIG. 3. In situ hybridization analysis of epidermal keratin expression
in the cement gland. Sections through the head of a stage 28
(tailbud) embryo (see Fig. 1 for the plane of section) were hybridized
to either a XKâiâO-specific probe (A) or a XKSl-specific probe (B). The
region of the section containing the cement gland is shown. The cement
gland (CG), the outer ectoderm (OE), and the inner ectoderm
(IE) are indicated.
FIG. 4. Keratin RNA expression in NH&l-induced animal caps. For dissection and induction protocol see Materials and Methods. Northern
blots were hybridized to probes specific for XK endo B RNA (A), XK81 RNA (B), or XK70 RNA (C). (A) Equal amounts of total RNA from
uninduced (lanes l-4) and NH&l-induced (lanes 5-8) animal caps were analyzed, after the explants were cultured to different equivalent
stages: stage 20 (lanes 1 and 5); stage 23 (lanes 2 and 6); stage 28 (lanes 3 and â7); stage 34 (lanes 4 and 8). (B, C) Equal amounts of total RNA from
uninduced (lanes l-5) and NH&l-induced (lanes 6-10) animal caps, culture for different times to equivalent stage 17 (lanes 1 and 6), stage 20
(lanes 2 and 7), stage 25 (lanes 3 and 8), stage 28 (lanes 4 and 9), and stage 34 (lanes 5 and 10). Ethidium bromide staining of the gels indicated
that all lanes contained about equal amounts of RNA, except lane A4 which contained about half as much RNA as the other lanes.
