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A cDNA encoding Xenopus type I collagen alpha 1 (Xenopus COL1A1) has been isolated from an ovary cDNA library. The COL1A1 cDNA is approximately 5.7 kb pairs and encodes 1447 amino acids. The putative COL1A1 polypeptide shares high identities of amino acid sequence with other vertebrate COL1A1 proteins. The level of Xenopus COL1A1 transcripts was increased markedly in the posterior region of the embryo at the tail-bud stage, then gradually spread to the anterior region. Histological observations of the tail-bud embryos showed that COL1A1 was mainly expressed in the inner layer of the posterior dorsal epidermis exposed to the somitemesoderm, except for in the dorsal fin. Less intense signals were also detected in the outer layer of the dorsal epidermis and dermatome. The expression of COL1A1 was increased in posteriorized embryos resulting from treatment with retinoic acid but decreased in hyper-dorsalized embryos resulting from lithium chloride treatment. These results suggest that COL1A1 is a major component of the dorsal dermis exposed to the somite in Xenopus embryos, but its expression is not related to the temporal sequence of somite segregation.
Fig. 3. Spatial expression pattern of Xenopus COL1A1 shown by whole-mount in situ hybridization. (A) Stage 25 embryo. Weak expres- sion of Xenopus COL1A1 was detected in the posterior dorsal region. (B) Stage 28 embryo. Expression of Xenopus COL1A1 gradu- ally spread to the anterior region. (C) Stage 30 embryo. Expression of Xenopus COL1A1 was extended to the head region. (D) Transverse sections of the stage 30 embryo at the levels indicated by the white bars in (C). (D,F) A section at the head region (bar 1). The transcripts were detected in the inner layer of epidermis. Note that the signals extended to the ventral region (arrowheads). (E,G) A section at the trunk region (bar 2). Intense staining was detected in the inner layer of the dorsal epidermis. Less intense sig- nals were detected in the outer layer of the dorsal epidermis and dermatome. COL1A1 was not detected in the ventralepidermis. Bars, 1 mm (A), 150 μm (D), 75 μm (G)
Fig. 5. Effects of retinoic acid and lithium chloride on the expres- sion of Xenopus COL1A1. (A) Quantitative reverse transcriptionpolymerase chain reaction (RT-PCR) was performed using 1 μg of total RNA extracted from the normal, retinoic acid-treated, or lithium chloride-treated embryos. The expression of Xenopus COL1A1 was increased by retinoic acid and decreased by lithium chloride. (B) Whole-mount in situ hybridization of the retinoic acid- treated embryo (stage 28). Expression of Xenopus COL1A1 was increased not only in the anterior region, which was posteriorized by retinoic acid, but also in the original posterior region.
A section at the head region (bar 1). The transcripts were detected in the inner layer of epidermis.
A section at the trunk region (bar 2). Intense staining was detected in the inner layer of the dorsal epidermis. Less intense signals were detected in the outer layer of the dorsal epidermis and dermatome. Stage 30.
