The activated form, spaetzle C-106, acts as a ligand for the Toll receptor (PubMed:12872120). Binding to Toll activates the Toll signaling pathway and induces expression of the antifungal peptide drosomycin (PubMed:8808632). Component of the extracellular signaling pathway that establishes dorsal-ventral polarity in the embryo (PubMed:8124709, PubMed:11212919). Homodimer; disulfide-linked (PubMed:12872120, PubMed:9533958). In the presence of Tl, crystal structures show one Tl molecule bound to a spaetzle C-106 homodimer (PubMed:24733933, PubMed:24282309). However, the active complex probably consists of two Tl molecules bound to a spaetzle C-106 homodimer (PubMed:24282309, PubMed:24733933). This is supported by in vitro experiments which also show binding of the spaetzle C-106 dimer to 2 Tl receptors (PubMed:12872120). Ligand binding induces conformational changes in the extracellular domain of Tl (PubMed:24282309). This may enable a secondary homodimerization interface at the C-terminus of the Tl extracellular domain (PubMed:24282309). Secreted in a cell culture system. Secreted in a cell culture system. Secreted in a cell culture system. Secreted in a cell culture system. Secreted in a cell culture system. Expressed both maternally and zygotically. All isoforms, except isoform 8.20, are rapidly degraded on cellularisation of the blastoderm embryo. During embryonic development, easter cleaves the signal peptide and also generates the C-terminal 12 kDa active fragment, C-106 (except for isoform 8.24 and isoform 11.27 as they do not contain the cleavage site) (PubMed:9533958). During the immune response, cleaved in the same manner by SPE (PubMed:16399077). Extracellular forms of isoform 8.19 and isoform 11.7 are glycosylated. 'Spaetzle' means 'noodles' in German.