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Cloning and developmental expression of LFB3/HNF1 beta transcription factor in Xenopus laevis.
De Simone V
We have cloned the Xenopus laevis homologue of the LFB3/HNF1 beta transcription factor. RNase protection and in situ hybridisation experiments show that XLFB3 transcription starts in the gastrulating endoderm at stage 10.5 (mid-gastrula). At later stages, XLFB3 transcripts within the endoderm are restricted to mid- and hindgut and to their derivative organs and tissues. XLFB3 is also expressed in the neuroectoderm and in the pronephros anlage. XLFB3 is not expressed in the rostral part of all three germ layers, with coincident anterior borders that are shifted anteriorly by treatment of developing embryos with retinoic acid. XLFB3 is a useful marker of early endoderm differentiation and its expression pattern along the antero-posterior axis, as well as the response to retinoic acid treatment, suggests a role in early morphogenesis.
Fig. 4 (a) In situ hybridisation showing XLFB3 mRNA distribution
on a saginal section of a st. 10.5 embryo of X. laevis. Positive signal
is detectable only in the invaginated endoderm. (b and c) In situ
hybridisation of sagittal sections of a st. 12 and a st. 18 X. laevis em-
bryos, respectively. Neuroectoderm and endoderm are labelled, except
for the most anterior part. A strong signal is present on the hepatic
diverticle, i.e. = invaginated endoderm; imz = involuting marginal
zone; bl = blastopore; ym = yolk mass; ne = neuroectoderm; ar = ar-
chenteron roof; eym = endodermal yolk mass; ba = brain anlage;
Id = liver diverticulum.
Fig. 5. Bright (a) and dark (b) fields of a transversal section of a st.
16 X. laevis embryo. Labelling is visible on the neuroectoderm, inter-
mediate mesoderm and endoderm, im = intermediate mesoderm;
np= neural plate; ar = archenteron roof; eym -- endodermal yolk
Fig. 6 (a) In situ hybridisation showing XLFB3 mRNA distribution on a transversal section of a st. 23 X. laevis embryo. A strong positive signal is present in the two pronephric regions and in the endoderm. A signal is also present in the roof plate of the neural tube. (b and c) Parasagittal and sagittal sections, respectively, of st. 23 embryos. (d and e) Two parasagittal sections (at different levels) of st. 29-30 embryos, rp = roof plate; p = pronephros; eym = endodermal yolk mass; wd = Wolffian duct.
Fig. 7. Bright (a) and dark (b) fields of a saginal section of a st. 48 X. laevis embryo. Positive signal is present in developing mesonephric vesicles and in several tissues derived by the digestive tract, me = mesonephric vesicles; s = stomach; i = intestine; li = liver; p = pancreas; wd = Wolffian duct.