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Expression of thymosin beta 4 gene during Xenopus laevis embryogenesis.
Yamamoto M
,
Shoda A
,
Minamino N
,
Matsuo H
,
Nishimatsu S
,
Ueno N
,
Murakami K
.
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In order to investigate the molecular events which take place during gastrulation, extracts from developing Xenopus embryos were analyzed for temporal peptide distribution by high performance liquid chromatography. One peptide peak which became increasingly dominant after gastrulation was purified and partially characterized. The amino acid sequence of enzymic digests showed the peptide is extremely similar to mammalian thymosin beta 4. The peptide was capable of binding actin monomers like mammalian counterparts. Cloning of the Xenopus thymosin beta 4 cDNA showed that only three amino acid substitutions occurred between amphibian and bovine. Northern blot analysis revealed the mRNA is maternally present at a low level and the transcript becomes abundant after gastrulation, supporting the distribution of the peptide.
w Biochemical properties of the gastrulation-associated peptide from Xenopus laevis.
(A) Reversed-phase HPLC profile of extracts from developing embryos on an analytical C4
column. (B) Amino acid sequence of the Xenopus peptide and comparison with bovine
thymosin p4. Amino acids are indicated by one-letter symbols. Identical amino acid
residues are indicated by dots. “X†denotes amino acid not determined. (C) Cross-linking
of Xenopus peptide to Cl-actin. G-actin was incubated with increasing concentrations
(lane 1, control without peptide, lane 2,0.025 t.tg, lane 3, 0.25 l.tg, lane 4, 2.5 l.tg) of the
Xenopus thymosin p4, chemically cross-linked, and analyzed by 10% SDS-PAGE under
reducing condition. Molecular weight markers were run on lane 5.
m Structure and sequence of Xenopus thymosin j34. (A) Restriction enzyme map and
sequencing strategy for Xenopus thymosin p4 cDNA. The arrows indicate the direction
of sequence analysis. The open box represents peptide coding region and the hatched box
denotes the sequence used as a probe to detect embryonic mRNA in Fig.3. (B) Nucleotide
sequence of the cDNA, pXTP4A encoding Xenopus thymosin p4. The deduced amino
acid sequence was indicated by one-letter symbols. Polyadenylation signal sequences are
underlined.
Fig. Detectiono f Xenopust hymosinm RNA in developinge mbryos. Total RNA was
purified and separatedo n a 1.2% agaroseg el. The RNA wast ransferredt o a nylon
membranea ndh ybridized with the Xenopust hymosinp 4 cDNA fragment( seeF ig. 2A)
Iabeledw ith t3âP].
