Requirement for a localized, IP₃R-generated Ca²⁺transient during the furrow positioning process in zebrafish zygotes

Abstract

We report that the first localized Ca(2+) transient visualized in the blastodisc cortex of post-mitotic zebrafish zygotes has unique features. We confirm that this initial 'furrow positioning' Ca(2+) transient precedes the physical appearance of the first cleavage furrow at the blastodisc surface and that it has unique dynamics, which distinguish it from the subsequent furrow propagation transients that develop from it. This initial transient displays a distinct rising phase that peaks prior to the initiation of the two linear, subsurface, self-propagating Ca(2+) waves that constitute the subsequent furrow propagation transient. Through the carefully timed introduction of the Ca(2+) buffer, dibromo-BAPTA, we also demonstrate the absolute requirement of this initial rising phase Ca(2+) transient in positioning the furrow at the blastodisc surface: no rising phase transient, no cleavage furrow. Likewise, the introduction of the inositol 1,4,5-trisphosphate receptor (IP3R) antagonist, 2-aminoethoxydiphenyl borate, eliminates both the rising phase transient and the appearance of the furrow at the cell surface. On the other hand, antagonists of the ryanodine receptor and NAADP-sensitive channels, or simply bathing the zygote in Ca(2+)-free medium, have no effect on the generation of the rising phase positioning transient or the appearance of the furrow at the surface. This suggests that like the subsequent propagation and deepening/zipping Ca(2+) transients, the rising phase furrow positioning transient is also generated specifically by Ca(2+) released via IP3Rs. We propose, however, that despite being generated by a similar Ca(2+) release mechanism, the unique features of this initial transient suggest that it might be a distinct signal with a specific function associated with positioning the cleavage furrow at the blastodisc surface.

A Novel Role for MAPKAPK2 in Morphogenesis during Zebrafish Development

“…Calcium levels are low during early epiboly [24]–[26],[43], but increase and become dynamic from 50 to 100% epiboly. Spikes of calcium are evident in the yolk cell beginning at 50% epiboly, followed by waves of calcium that traverse the blastoderm margin from 65% epiboly to blastopore closure [16],[24].…”

Calcium signalling during the cleavage period of zebrafish development

“…2C FOR CYTOKINESIS In addition to direct visualization, there is also good indirect evidence (for example, from injecting Ca 2C chelators such as BAPTA-type buffers; Pethig et al 1989) at various times during the cell cycle to unambiguously indicate that Ca 2C signalling plays a required and necessary role in the cleavage of both medaka (Fluck et al 1994) and zebrafish (Chang & Meng 1995;Webb et al 1997;Créton et al 1998;Lee et al 2003Lee et al , 2006 embryos.…”

Biphasic assembly of the contractile apparatus during the first two cell division cycles in zebrafish embryos

“…With regards to the appearance of a cleavage furrow on the outer, external surface of the zebrafish blastodisc, it has been proposed that there may be up to four sequential phases with respect to early divisions. These are: A furrow positioning phase; followed by a furrow propagation phase (with little furrow deepening); followed by a furrow deepening phase; then finally once the daughter cells have been separated, a furrow zipping or apposition phase (Lee et al, 2004(Lee et al, , 2006Li et al, 2008).…”