A novel proteolytic event controls Hedgehog intracellular sorting and distribution to receptive fields

Morphogens like Hedgehog (Hh) are critical for tissue patterning during development. Their activity depends on how they are secreted and distributed across a receptive field. In Drosophila, Hh is released from photoreceptor neurons at two distinct locations: the retina and axon termini. This dual release influences eye and brain development separately. However, the mechanisms that control this partitioning remain poorly understood. Prior research has shown that Hh is essential for developmental signaling, but the specific process that determines its localization has been unclear. This gap motivated the current investigation into how Hh is targeted to different regions of photoreceptor neurons. No prior work had resolved whether proteolysis might influence Hh localization. The study addresses this by examining the role of C-terminal proteolysis in Hh sorting. This work provides new insights into the molecular basis of morphogen distribution.

This study aims to uncover the mechanism that controls the dual release of Hedgehog (Hh) in photoreceptor neurons of the developing Drosophila visual system. The specific problem is to determine how Hh is targeted to either the retina or axon termini. The motivation stems from the need to understand how morphogens are spatially regulated during development. The study focuses on the C-terminal region of Hh as a potential determinant of its localization. By investigating proteolytic events, the researchers seek to clarify how Hh is partitioned for release at different sites. The goal is to define a novel mechanism that governs intracellular sorting of Hh. This work could help explain how morphogens achieve precise spatial signaling. The findings may also have broader implications for related signaling proteins.

The researchers used Drosophila photoreceptor neurons as a model system to study Hedgehog (Hh) localization. They examined the role of C-terminal proteolysis in Hh sorting by analyzing mutant and wild-type Hh proteins. Fluorescent labeling techniques were employed to track Hh distribution in neurons. Axonal transport was assessed using live imaging and immunostaining methods. The study also involved genetic manipulations to disrupt proteolytic events. By comparing the localization of intact versus cleaved Hh proteins, the researchers identified the role of C-terminal proteolysis. The analysis included both axonal and retinal compartments of photoreceptor neurons. These approaches allowed the team to determine how proteolysis influences Hh targeting.

The study found that C-terminal proteolysis of Hedgehog (Hh) controls its intracellular sorting. Hh with an intact C-terminus is transported along axons to the termini. In contrast, Hh that undergoes C-terminal cleavage remains in the retina. This cleavage event determines the balance between eye and brain development. The results suggest that proteolysis acts as a molecular switch for Hh localization. The researchers observed that cleaved Hh is retained in the retina, while uncleaved Hh is transported axonally. This finding provides a mechanistic explanation for Hh’s dual release pattern. The study also shows that proteolysis enables Hh to reach its two target fields. These results support a novel model of morphogen sorting.

The authors conclude that C-terminal proteolysis of Hedgehog (Hh) is a key regulatory event in its intracellular sorting. This mechanism allows Hh to be directed to either the retina or axon termini. The cleavage event creates a balance between eye and brain development. The findings suggest that post-translational modifications can control morphogen distribution. The study supports the idea that proteolysis may regulate the polarity of related signaling proteins. The authors propose that similar mechanisms could apply to other morphogens. Their conclusions are based on the observed effects of C-terminal cleavage on Hh localization. The study does not claim that proteolysis is the only factor in Hh sorting.