Int. J. Dev. Biol. 61: 465 - 470 (2017)

https://doi.org/10.1387/ijdb.170037af

Vol 61, Issue 6-7

Expression of the ALK1 family of type I BMP/ADMP receptors during gastrula stages in Xenopus embryos

Developmental Expression Pattern | Published: 24 May 2017

Avi Leibovich¹, Herbert Steinbeißer² and Abraham Fainsod*^,1

¹Department of Developmental Biology and Cancer Research, Institute for Medical Research Israel-Canada, Faculty of Medicine, Hebrew University, Jerusalem, Israel and ²Institute of Human Genetics, University Hospital Heidelberg, Heidelberg, Germany

Abstract

Multiple members of the transforming growth factor beta (TGFβ) family of secreted factors play central inductive and patterning roles during embryogenesis. During gastrulation in vertebrates, the bone morphogenetic protein (BMP) sub-family is linked to formation of the embryonic organizer, Spemann’s organizer in Xenopus, and dorsal-ventral mesoderm patterning. Our knowledge regarding the BMP receptors mediating this signaling is still very incomplete. The BMPR1A (ALK3) and BMPR1B (ALK6) receptors are known to mediate the BMP4 signal. These receptors belong to the ALK1 subfamily of type I receptors that also includes ACVR1 (ALK2), and ACVRL1 (ALK1). We studied by qPCR and in situ hybridization the spatio-temporal expression patterns of ALK2 and ALK1 and compared them to ALK3 and ALK6, and to the main BMPs expressed during gastrulation, i.e., BMP4, BMP7, BMP2, and ADMP, in an attempt to establish a link between ligands and receptors. There is extensive overlap between BMP4, and ALk3 and Alk6 expression, supporting their functional interaction. Robust Alk6 expression was observed from mid-gastrula. Animal region expression of both receptors shows co-expression with BMP4 and BMP7. Alk2 transcripts were detected within the organizer, overlapping with its proposed ligand, ADMP, suggesting a probable function within the organizer. Alk1 is very weakly expressed during gastrula, but its transcripts were localized to the lateral marginal zone flanking the organizer domain. No receptor closely matched the maternal BMP2 expression, although Alk2, Alk3, and Alk6, have transcripts of maternal origin. Our analysis shows that the BMP ligands and their receptors exhibit dynamic expression patterns during gastrula stages.

Keywords

TGFβ receptor, ALK receptor, BMP signaling, Xenopus embryo, anti-dorsalizing morphogenetic protein