Intercellular calcium signaling is regulated by morphogens duringDrosophilawing development

Abstract

Organ development is driven by a set of patterned inductive signals. However, how these signals are integrated to coordinate tissue patterning is still poorly understood. Calcium ions (Ca 2+ ) are critical signaling components involved in signal integration and are regulated by a core Ca 2+ signaling toolkit. Ca 2+ signaling encodes a significant fraction of information in cells through both amplitude and frequency-dependent regulation of transcription factors and key regulatory enzymes. A range of intercellular Ca 2+ transients, including coordinated oscillations, recently have been reported in Drosophila wing discs. In an accompanying paper, we show that impaired Ca 2+ signaling impacts the final size and shape of the wing. Here, we discover specific spatiotemporal signatures of Ca 2+ transients during wing disc development. To do so, we developed a new neural-network-based approach for registration of oscillatory signals in organs that frequently move during imaging, and a pipeline for spatiotemporal analysis of intercellular Ca 2+ oscillations. As a specific test case, we further demonstrated that the morphogen pathway, Hedgehog, controls frequencies of Ca 2+ oscillations uniformly in the tissue and is required for spatial patterning of oscillation amplitudes. Thus, the time-averaged dynamics of spontaneous intercellular Ca 2+ transients reflect the morphogenetic signaling state of the tissue during development. This suggests a general mechanism of physiological signaling that provides a memory of morphogenetic patterns. Additionally, our study provides a powerful approach for registering and quantifying oscillatory dynamics in developing organs.

Calcium as a signal integrator in developing epithelial tissues

“…Ca 2+ signaling dynamics can also be spatially patterned in tissues, mirroring the patterns of morphogen signaling pathways. Spontaneous intercellular Ca 2+ transients have recently been discovered in the developing butterfly and fly wing in vivo [78,143,144], and ex vivo in the presence of fly extract, a growth serum that contains a large range of active proteins [76,78,81,144,145]. Perturbation of Ca 2+ signaling in the wing leads to a range of adult wing defects [78,144,146].…”

“…Hh is secreted from the posterior compartment, but Hh signaling is not active in the posterior compartment (Figure 4D, [145,147]). Inhibition of the primary transducer of Hh signaling, Smoothened, in the pouch not only leads to an increase in oscillation frequency in the whole tissue, but also led to an increase in amplitude in the anterior compartment, leading to a uniform amplitude across the entire pouch [145]. These findings indicate that Ca 2+ signaling exhibits spatial asymmetries downstream of morphogen signaling.…”

“…The amplitudes of the Ca 2+ oscillations ex vivo are higher in the posterior compartment of the pouch. Hh is secreted from the posterior compartment, but Hh signaling is not active in the posterior compartment (figure 4(D) [145,147]). Inhibition of the primary transducer of Hh signaling, Smoothened, in the pouch not only leads to an increase in oscillation frequency in the whole tissue, but also led to an increase in amplitude in the anterior compartment, leading to a uniform amplitude across the entire pouch [145].…”