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We have utilized the differential display PCR method to isolate transcripts expressed during early embryogenesis of Xenopus laevis. Among many transcripts that have been found to be expressed differentially during the development, one transcript which was expressed predominantly in the unfertilized egg, was isolated as a full-length cDNA and the sequence was determined. This cDNA contained a predicted size of 198 amino acids. A search of the GenBank database revealed that the predicted amino acid sequence of the cDNA is highly homologous-87.8% identical-to the recently identified human protein, HsYKT6, a prenylated vesicle associated-SNARE ((soluble NSF (N-ethylmaleimide-sensitive fusion protein) attachment protein receptor)). Thus we have named the gene as Xsnare1. RT-PCR analysis showed that the Xsnare1 mRNA expressed throughout the oogenesis, in egg and in the early phase of embryogenesis and the level of expression declined after gastrulation. These results suggest that the Xsnare1, a maternally active, putative Xenopus homologue of prenylated v-SNARE, is a developmentally regulatory gene and may be play a role in the process of the early development of Xenopus laevis.
FIG. 1. Nucleotide and deduced amino acid sequence of Xsnare1. Amino acid sequence is underneath of nucleotide sequence with
numbers in bold. Leucine zipper is double underlined (heptad leucine residues are bolded) and CAAX-like motif at the C-terminal is boxed.
Polyadenylation site following by poly (A) track at 3* end of nucleotide is underlined. Stop codon is represented as an asterisk.
FIG. 2. Comparison of Xsnare1 with a novel prenylated v-SNAREs from other species. (A) The abbreviation are: Hs, Homo sapiens; Rn,
R. norvegicus; Sc, S. cerevisiae; Sp, S. pombe; Ce, C. elegans; At, A. thaliana. All except Arabidopsis are full-length gene. Identical and
conserved amino acid is boxed with black and gray, respectively. (B) The numbers above the diagonal are absolute amino acid similarities,
and the numbers below the diagonal are conserved amino acid substitutions.
FIG. 3. Expression and distribution of Xsnare1 transcript. (A)
The temporal expression of Xsnare1 was analyzed by RT-PCR. The
numbers 1 to 4 indicate oocytes stage I/II/III, IV, V, and VI, respec-
tively; the number 5 represents unfertilized egg; the numbers 6 to
11 indicate embryos at stage 8 (mid-blastula), 10.5 (early gastrula),
12.5 (late gastrula), 17 (neurula), 23 (tailbud), 31 (tadpole), respec-
tively. Elongation factor-1a (EF-1a) was coamplified as an internal
control. (B) Fully grown oocytes (stage VI) were frozen and cut to
animal and vegetal halves to determine localization of Xsnare1
mRNA along the animal and vegetal axis. No apparent differences
in the amount of the Xsnare1 mRNA was detected in the animal
(A) and vegetal (V) halves. To verify that the dissection was made
correctly, localization of Vg1 mRNA (known vegetal pole maker) in
the vegetal halves was determined.
