Neurotrophin which may function as a ligand to the Toll-related receptor Tollo. Involved in a Tollo and JNK signaling pathway that positively regulates neuromuscular junction (NMJ) growth in presynaptic motorneurons. May function by activating Tollo to promote the phosphorylation of JNK. Homodimer; disulfide-linked. Expressed in larval muscles. RNAi-mediated knockdown has no effect on neuromuscular junction (NMJ) growth. However, conditional knockdown in the muscles results in a decrease in bouton number at the NMJs. 'Spaetzle' means 'noodles' in German.