The full-length unprocessed hedgehog protein is an active signaling molecule

Prior research has shown that hedgehog (HH) proteins are cleaved and cholesterol-modified to generate signaling molecules. It was already known that the amino-terminal cleavage product (HH-Np) is responsible for HH-dependent signaling. No prior work had resolved whether full-length HH proteins could also signal. This gap motivated investigations into alternative HH signaling mechanisms. The field has long accepted that only processed HH-Np is active. That uncertainty drove studies to test full-length HH function. Researchers have not previously demonstrated full-length HH signaling in vivo. This paper introduces a new model for HH signaling.

This study aimed to test whether full-length HH proteins can signal without cleavage. The specific problem was whether HH signaling requires HH-Np. The motivation was to address a gap in HH signaling models. The researchers proposed to test full-length HH activity in cell culture and in Drosophila. They hypothesized that full-length HH might have signaling roles. The study sought to determine if full-length HH could rescue HH loss of function. The goal was to assess the evolutionary conservation of this activity. The authors aimed to challenge the current model of HH signaling.

The researchers used in vitro assays to assess HH signaling activity. They tested full-length HH proteins in cultured cells. They also used in vivo experiments in Drosophila. The study included a loss-of-function eye phenotype rescue. The team expressed a full-length hh variant that cannot be cleaved. They monitored plasma membrane trafficking of full-length HH proteins. The experiments combined biochemical and genetic approaches. The methods included both functional assays and morphological analysis.

Full-length HH proteins trafficked to the plasma membrane and signaled in vitro. The study found that full-length HH could rescue a hh loss-of-function phenotype. The expressed full-length hh variant could not be processed into HH-Np. Despite this, the variant rescued eye development in Drosophila. The results suggest full-length HH can signal independently of cleavage. The findings support a novel signaling mechanism for HH proteins. The study shows that full-length HH activity is evolutionarily conserved. These results challenge the established model of HH signaling.

The authors propose that full-length HH proteins may signal in some contexts. They suggest that HH signaling is not exclusive to the cleaved HH-Np form. The study supports a role for full-length HH in cell-cell communication. The findings imply that HH signaling has multiple mechanisms. The results suggest evolutionary conservation of full-length HH activity. The authors state that their findings challenge prior assumptions. They suggest that HH signaling is more complex than previously thought. The study opens new questions about HH signaling diversity.