Zebrafish Bmp4 regulates left–right asymmetry at two distinct developmental time points

Abstract

Left-right (LR) asymmetry is regulated by early asymmetric signals within the embryo. Even though the role of the bone morphogenetic protein (BMP) pathway in this process has been reported extensively in various model organisms, opposing models for the mechanism by which BMP signaling operates still prevail. Here we show that in zebrafish embryos there are two distinct phases during LR patterning in which BMP signaling is required. Using transgenic lines that ectopically express either noggin3 or bmp2b, we show a requirement for BMP signaling during early segmentation to repress southpaw expression in the right lateral plate mesoderm and regulate both visceral and heart laterality. A second phase was identified during late segmentation, when BMP signaling is required in the left lateral plate mesoderm to regulate left-sided gene expression and heart laterality. Using morpholino knock down experiments, we identified Bmp4 as the ligand responsible for both phases of BMP signaling. In addition, we detected bmp4 expression in Kupffer's vesicle and show that restricted knock down of bmp4 in this structure results in LR patterning defects. The identification of these two distinct and opposing activities of BMP signaling provides new insight into how BMP signaling can regulate LR patterning.

Suppression of Alk8-mediated Bmp signaling cell-autonomously induces pancreatic β-cells in zebrafish

“…Embryos and adult fish were raised and maintained under standard laboratory conditions. We used the following mutant and transgenic lines: laf/alk8 tm110 (23), Tg(ins:GFP) zf5 (38), Tg(ins:dsRed) m1018 (from W. Driever, Freiburg), Tg(HSE:caAlk6, eGFP) w64 (19), Tg(gutGFP) s854 (also known as Tg(XlEef1a1:GFP) s854 ) (15), Tg(hsp70l:bmp2b) f13 (39), Tg(ptf1a:GFP) jh1 (40), and Tg(-3.5nkx2.2a:GFP) ia3/ia3 (41).…”

“…To further test this model, we treated Tg(ins:GFP);Tg(ins:dsRed) embryos with dorsomorphin (a selective inhibitor of the BMP type I receptors Alk3, Alk6, and Alk8, see ref. 39) between 44 and 72 hpf to inhibit Bmp signaling specifically during the formation of ventral bud-derived endocrine cells (this time period was chosen to allow budding of the ventral pancreas, but inhibit Bmp signaling during subsequent ventral bud development). We found that the number of GFP-only-positive β-cells adjacent to the extrapancreatic duct was increased in the dorsomorphin-treated embryos ( Fig.…”

Loss of plakophilin 2 disrupts heart development in zebrafish

“…6B). This reflects the requirement of bmp4 for left-sided expression of spaw, which in turn induces left-sided expression of bmp4 and lefty1, whereas lefty1 and lefty2 negatively regulate each other (Bisgrove et al, 1999;Chocron et al, 2007;Bakkers et al, 2009). To examine if these effects are early or late events in cardiogenesis, we examined bmp4 expression at sphere, shield and 48 hpf in addition to the 18-somite stage by qRTPCR.…”

BMP/SMAD1 signaling sets a threshold for the left/right pathway in lateral plate mesoderm and limits availability of SMAD4

“…BMPs have been implicated in LR patterning, but data on their precise roles have been highly contradictory, with results varying both within and between developmental models Yokouchi et al 1999;Monsoro-Burq and Le Douarin 2001;Fujiwara et al 2002;Piedra and Ros 2002;Schlange et al 2002;Kishigami et al 2004;Zhu and Scott 2004;Chocron et al 2007;Mine et al 2008). This is in part because BMPs act at distinct times and in distinct spatial domains to influence laterality (Kishigami et al 2004).…”