Inhibition of stored Ca2+ release disrupts convergence-related cell movements in the lateral intermediate mesoderm resulting in abnormal positioning and morphology of the pronephric anlagen in intact zebrafish embryos.

Ca(2+) is a highly versatile intra- and intercellular signal that has been reported to regulate a variety of different pattern-forming processes during early development. To investigate the potential role of Ca(2+) signaling in regulating convergence-related cell movements, and the positioning and morphology of the pronephric anlagen, we treated zebrafish embryos from 11.5 h postfertilization (hpf; i.e. just before the pronephric anlagen are morphologically distinguishable in the lateral intermediate mesoderm; LIM) to 16 hpf, with a variety of membrane permeable pharmacological reagents known to modulate [Ca(2+)](i). The effect of these treatments on pronephric anlagen positioning and morphology was determined in both fixed and live embryos via in situ hybridization using the pronephic-specific probes, cdh17, pax2.1 and sim1, and confocal imaging of BODIPY FL C(5)-ceramide-labeled embryos, respectively. We report that Ca(2+) released from intracellular stores via inositol 1,4,5-trisphosphate receptors plays a significant role in the positioning and morphology of the pronephric anlagen, but does not affect the fate determination of the LIM cells that form these primordia. Our data suggest that when Ca(2+) release is inhibited, the resulting effects on the pronephric anlagen are a consequence of the disruption of normal convergence-related movements of LIM cells toward the embryonic midline.