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XK endo B is a type I keratin that was originally identified by its preferential expression in the embryonic notochord of the amphibian Xenopus laevis. A peptide identical to a short region of its predicted amino acid sequence was used to generate antibodies against the XK endo B protein. This paper reports an immunocytochemical study of the spatial expression pattern of XK endo B during development. The protein was observed in the notochord and endoderm as predicted from previous RNA analysis. In addition, XK endo B was detected in the cement gland, in the pituitary, olfactory and pharyngeal pouch rudiments, and in a nonuniform distribution in the neural tube as well as the inner sensorial layer of the ectoderm. XK endo B expression is not limited to any germ layer or any particular cell type, but is nevertheless highly restricted in its distribution in the embryo. Its expression in several different embryonic tissues requiring inductive interactions for differentiation makes XK endo B a valuable tool with which to study the regulation of induced gene expression during embryogenesis.
Fig. 1. Detection of XK endo B by Western-blot analysis. Equal
embryo equivalents were loaded per lane from either total Trixon
X 100-soluble protein preparations (lanes 1 and 2) or cytoskeletal
protein preparations (lanes 3 and4). Filters were stained with either
untreated antibody (lanes 1 and 3) or antobidy preabsorbed with
HPLC-purified peptide. The positions of the polypeptide markers
are indicated an the lefr by their sizes in kDa
Fig. 2A-D. Expression of XK endo B in the endoderm and notochord.
A The planes o j section are indicated for B-D. B Crosssection
of a stage-28 (tailbud) embryo. C, D Longitudinal sections
through a stage-28 embryo and stage-41 tadpole, respectively. The
endoderm (E), neural tube (NT), notochord (N) and the somites
(9 are indicated. All staining was visualized by indirect immunofluorescence
Fig. 3A-F. Expression of XK endo B protein in the head at tailbud. of a stage-30 embryo. The brain cavity (BC), olfactory placodes
A-D Cross-sections through the head of a stage-28 embryo. B (OP), stomodeal-hypophyseal rudiment (S-HR), eye vesicles (EV),
Neighboring section to that shown in A stained with antibody inner ectoderm (I@, cement gland (CC) and pharyngeal cavity
preabsorbed with high-performance liquid chromatography ( P o are indicated. F The planes of section are indicated for
(HPLC)-purified peptide. E Longitudinal section through the head Fig. 3A-E and Fig. 4A-C
Fig. 4A-D. Expression of XK endo
B in the inner ectoderm including the
pharyngeal pouch rudiments. A
Cross-section through the posterior
region of the head of a stage-28
embryo. B Neighboring section
stained with antibody preabsorbed
with HPLC-purified peptide. C
Cross-section through the anterior
portion of the trunk. D The boxed
area in C enlarged. The notochord
(N), neural tube (NT), eye vesicles
(EV), pharyngeal cavity (Pc),
pharyngeal pouch rudiments (PPR),
and inner ectoderm (ZE) are indicnted
Fig. SA, B. XK endo B expression in a wholemount of a stage30
embryo. A The notochord (N), neural tube (NT), and cement gland
(CG ) are indicated. B The ventral half of the embryo shown in
A. The plane of focus differs to highlight the staining in the pharyngeal
pouches (PP)
