Bone morphogenetic protein 2 in the early development of Xenopus laevis

Abstract

The temporal and spatial transcription patterns of the Xenopus laevis Bone morphogenetic protein 2 (BMP-2) gene have been investigated. Unlike the closely related BMP-4 gene, the BMP-2 gene is strongly transcribed during oogenesis. Besides some enrichment within the animal half, maternal BMP-2 transcripts are ubiquitously distributed in the early cleavage stage embryos but rapidly decline during gastrulation. Zygotic transcription of this gene starts during early neurulation and transcripts are subsequently localized to neural crest cells, olfactory placodes, pineal body and heart anlage. Microinjection of BMP-2 RNA into the two dorsal blastomeres of 4-cell stage embryos leads to ventralization of developing embryos. This coincides with a decrease of transcripts from dorsal marker genes (beta-tubulin, alpha-actin) but not from ventral marker genes (alpha-globin). BMP-2 overexpression inhibits transcription of the early response gene XFD-1, a fork head/HNF-3 related transcription factor expressed in the dorsal lip, but stimulates transcription of the posterior/ventral marker gene Xhox3, a member of the helix-turn-helix family. Activin A incubated animal caps from BMP-2 RNA injected embryos show transcription of ventral but an inhibition of dorsal marker genes; thus, BMP-2 overrides the dorsalizing activity of activin A. The results demonstrate that BMP-2 overexpression exerts very similar effects as have previously been described for BMP-4, and they suggest that BMP-2 may act already as a maternal factor in ventral mesoderm formation.

Signaling pathways and tissue interactions in neural plate border formation

“…31,32 The source of BMP ligands is likely the non-neural ectoderm or the prospective NPB ectoderm itself, which expresses BMP ligands in zebrafish, frog, chick and mouse embryos. 28,[33][34][35] Consistently, the potential of epidermis to induce NPB or NC is supposedly attributable to the expression of BMP ligands. The endogenous or experimental juxtaposition of epidermis and prospective or definitive neuroectoderm, which is essentially devoid of BMP activity, results in moderate activation of BMP signaling in the contact area and induces NPB and NC.…”

Mechanisms driving neural crest induction and migration in the zebrafish andXenopus laevis

“…71,72 More to the point, during neural crest specification (early during gastrulation) a plethora of secreted factors are expressed. In the dorsal region these include the BMP antagonists Chordin, 73 BMP2, 80 and IGFBP5, 81 and the multifunctional antagonists Cerberus (anti-Wnt, BMP, Nodal) 82 and Shisa-1 and Shisa-2 (anti-FGF, anti-Wnt). 83,84 Similarly, the ventral organizing center has been found to secrete the anti-chordin Xolliod, 85-87 the anti-Wnt and anti-Xolloid Sizzled, 88 BMPs, [89][90][91][92] the BMP signaling modulator Crossveinless-2 (CV2), 93 and the BMP antagonist Twisted Gastrulation (Tsg).…”

Wnt antagonism initiates cardiogenesis in Xenopus laevis

“…First, inhibition of endogenous BMP signaling with a dominant negative type I receptor blocked maintenance but not initial expression of Nkx2.5, a homolog of the Drosophila tinman gene and an early marker of heart field specification (Shi et al 2000). Second, mRNAs encoding BMP isoforms are not expressed by either of the tissues known to have heart-inducing activity, the dorsoanterior endoderm or the Spemann organizer (Isaacs et al , 1995Tannahill et al 1992;Suzuki et al 1993;Song and Slack 1994;Clement et al 1995;Yamagishi et al 1995;Jones et al 1996). In avians, fibroblast growth factor (FGF) family members have been proposed to work in conjunction with BMPs, but in Xenopus, their mRNAs are also not expressed in heart-inducing tissues, again suggesting the participation of additional factors in cardiogenesis.…”