Casares, F. | Search bioRxiv

bioRxiv2018

Dynamic Hh signaling can generate temporal information during tissue patterning

The differentiation of tissues and organs requires that cells exchange information in space and time. Spatial information is often conveyed by morphogens, molecules that disperse across receiving cells generating signaling gradients. Cells translate such concentration gradients into space-dependent patterns of gene expression and cellular behavior [1, 2]. But could morphogen gradients also convey developmental time? Here, investigating the developmental role of Hh on a component of the Drosophila visual system, the ocellar retina, we discovered that ocellar cells use the non-linear gradient of Hh as a temporal cue, collectively performing the biological equivalent of a mathematical logarithmic transformation. In this way, a morphogen diffusing from a non-moving source is decoded as a wave of differentiating photoreceptors that travels at constant speed throughout the retinal epithelium.

developmental biology↗

bioRxiv2016

Specific expression and function of the Six3 optix in serially homologous organs

Organ size and pattern results from the integration of two positional information systems. One global, encoded by the Hox genes, links organ type with position along the main body axis. Within specific organs, local information is conveyed by signaling molecules that regulate organ growth and pattern. The mesothoracic (T2) wing and the metathoracic (T3) haltere of Drosophila represent a paradigmatic example of this coordination. The Hox gene Ultrabithorax (Ubx), expressed in the developing T3, selects haltere identity by, among other processes, modulating the production and signaling efficiency of Dpp, a BMP2-like molecule that acts as a major regulator of size and pattern. Still, the mechanisms of the Hox-signal integration even in this well-studied system, are incomplete. Here we have investigated this issue by studying the expression and function of the Six3 transcription factor optix during the development of the Drosophila wing and haltere development. We find that in both organs Dpp defines the expression domain of optix through repression, and that the specific position of this domain in wing and haltere seems to reflect the differential signaling profile among these organs. We show that optix expression in wing and haltere primordia is conserved beyond Drosophila in other higher diptera. Despite the similar expression pattern, optix plays different roles in wing and haltere. In the wing, optix is required for the growth of the most anterior/proximal region (the \"marginal cell\") and for the correct formation of sensory structures along the proximal anterior wing margin. In contrast, in the haltere optix is necessary for the suppression of sensory bristles without any noticeable effect on organ growth. Therefore, optix shows an organ-specific function. Beyond dipterans, optix expression in the anterior wing has been shown also in butterflies. We propose that the ancestral role of optix might have been structural in the anterior wing. Once expressed in the wing, optix expression had been re-deployed for wing spot formation in other parts of the wing of Heliconius butterflies.

developmental biology↗