Zorn AM and Mason J (2001), Gene expression in the embryonic Xenopus liver.

XB-ART-9081

Mech Dev 2001 May 01;1031-2:153-7. doi: 10.1016/s0925-4773(01)00341-0.

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Gene expression in the embryonic Xenopus liver.

Zorn AM , Mason J .

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In recent years, significant progress has been made in uncovering the molecular basis of endoderm specification in Xenopus. Much less is understood, however, about endodermal patterning and how endoderm-derived organs such as the liver are formed. Progress has been hampered by the lack of good molecular markers of presumptive liver tissue. Here, we have examined the embryonic expression of a number of marker genes during liver organogenesis, including the transcription factors hex, sox17alpha, and hnf3beta, as well as a number of proteins specific to the adult liver. Interestingly, sox17alpha appears to specifically mark the gall bladder precursors. At 7 days of development expression of the liver differentiation markers albumin, alpha1-microglobulin/bikunin precursor, fibrinogen, transferrin and transthyretin is restricted to the differentiating liver bud. Surprisingly, however, at 3 days of development most of these genes have a more widespread endodermal expression pattern. In addition to expression in the undifferentiated liver bud they were expressed extensively throughout the presumptive intestinal tissue, which may reflect some general feature of how the hepatic gene program is developmentally regulated.

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Species referenced: Xenopus
Genes referenced: a2m alb ambp fga fgg foxa2 hhex sox13 sox17a tf ttr

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	Fig. 2. Embryonic expression of liver markers by in situ hybridization. Each indicated probe was tested on three stages: day 7 (stage 46/47) gut tubes in the left column, day 3 (stage 41/42) gut tubes in the centre column and whole tail bud embryos (stages 30â€“35) in the right column. Light blue 5-bromo-4-chloro-3-indolyl-phosphate colour reactions were used to visualize the specific expression in the day 7 gut tubes. The pancreas tissue is bright white in these preparations. Brown, blue or black colour substrates indicate the specific staining in day 3 gut tubes. All preparations are shown with anterior to the left. lv, liver bud; p, pancreatic bud; gb, gall bladder bud; lu, lung bud.
	Fig. 3. Expression of markers in the liver diverticulum endoderm. (A) Schematic of a tail bud embryo (stage 33) with the line indicating the plane of section through the liver diverticulum (left). The right side shows a typical resulting section with the endoderm indicated in grey. ot, otic vesicle; nt, neural tube; endo, endoderm; ecto, ectoderm; meso, mesoderm; lvd, liver diverticulum. (B) Representative vibritome sections (as illustrated above) of whole-mount embryos hybridized with the indicated probes. Sections from the hex, hnf3Î², AMBP, endodermin, fibrinogen and transferrin stained embryos are through the anterior portion of the liver diverticulum at the level of the otic vesicle. Sox17Î± and transthyretin sections are from the posterior end of the liver diverticulum. All of the markers are expressed in the endodermal layer and excluded from the mesoderm. Note that the dark colour of the outer ectoderm is pigment and not staining.



	sox17a (SRY (sex determining region Y)-box 17 alpha ) gene expression in Xenopus laevis embryo, isolated gut tube, assayed via in situ hybridization, NF stage 41-42, anterior left, dorsal up.
	a2m (alpha-2-macroglobulin) gene expression in Xenopus laevis embryo, assayed via in situ hybridization, NF stage 30, lateral view, anterior left, dorsal up.
	a2m (alpha-2-macroglobulin) gene expression in Xenopus laevis embryo, isolated gut tube, assayed via in situ hybridization, NF stage 41-42, anterior left, dorsal up.
	a2m (alpha-2-macroglobulin) gene expression in Xenopus laevis embryo, visualised via light blue 5-bromo-4-chloro-3- indolyl-phosphate color reactions, in NF stage 46/47 isolated gut tubes, anterior left.



	fgg (fibrinogen gamma chain) gene expression in Xenopus laevis embryo, isolated gut tube, assayed via in situ hybridization, NF stage 41-42, anterior left, dorsal up.
	fgg (fibrinogen gamma chain) gene expression in Xenopus laevis embryo, liver visualised via light blue 5-bromo-4-chloro-3- indolyl-phosphate color reactions, in NF stage 46/47 isolated gut tubes, anterior left.
	alb (albumin) gene expression in Xenopus laevis embryo, visualised via light blue 5-bromo-4-chloro-3- indolyl-phosphate color reactions, in NF stage 46/47 isolated gut tubes, anterior left.


	tf (transferrin) gene expression in Xenopus laevis embryo, isolated gut tube, assayed via in situ hybridization, NF stage 41-42, anterior left, dorsal up.
	tf (transferrin) gene expression in Xenopus laevis embryo, visualised via light blue 5-bromo-4-chloro-3- indolyl-phosphate color reactions, in NF stage 46/47 isolated gut tubes, anterior left.


	ttr (transthyretin) gene expression in Xenopus laevis embryo, isolated gut tube, assayed via in situ hybridization, NF stage 41-42, anterior left, dorsal up.
	ttr (transthyretin) gene expression in Xenopus laevis embryo, visualised via light blue 5-bromo-4-chloro-3- indolyl-phosphate color reactions, in NF stage 46/47, in isolated gut tubes, anterior left.

	alb (albumin) gene expression in Xenopus laevis embryo, visualised via light blue 5-bromo-4-chloro-3- indolyl-phosphate color reactions, in NF stage 46/47, in isolated gut tubes, anterior left.