Ligand for the serine/threonine-protein kinase receptor type-1 sma-6 which activates a TGF-beta-like signaling pathway (PubMed:24004951). Multifunctional protein that is involved in body size, male ectodermal patterning, innate immunity, lipid metabolism and neural plasticity (PubMed:10021351, PubMed:9847238, PubMed:12176330, PubMed:29162682, PubMed:23019581). Dose-dependent regulator of body size, probably influencing the sizes of some or all cells rather than their number (PubMed:10021351, PubMed:9847238, PubMed:22189608). Plays a role in patterning of male-specific genital sensilla (simple sense organs), known as rays, and mating-associated structures, spicules (PubMed:10021351, PubMed:9847238). Plays a protective role in response to infection by the Gram-negative bacterium S.marcescens, by activating expression of genes involved in innate immunity (PubMed:12176330). Regulator of lipid homeostasis, acting non cell-autonomously in the hypodermis; partly dependent on the Insulin/IGF-1-like signaling (IIS) mediated pathway (PubMed:29162682). Required for aversive olfactory learning of pathogenic bacteria in adults (PubMed:23019581). Involved in gland cell morphology, possibly via activation of a Smad-independent TGF-beta signaling pathway (PubMed:24690231). Required to oppose the autoregulation of expression of Runt-related transcription factor rnt-1. Homodimer; disulfide-linked (By similarity). Interacts with drag-1 (PubMed:24004951). Expressed in embryos just prior to hatching and remains constant in most cells throughout the larval and adult stages (PubMed:9847238). Expressed by AVA command interneurons (PubMed:23019581). Expressed in L4 larval stage primarily in neurons, including ventral cord neurons DA, DB, VA and VB; the lateral excretory canal associated CAN cells; and anterior neurons AVK, DVA, I5, M1, M2, M4 and M5. Reduced body size (PubMed:10021351). Abnormalities in the male tail (PubMed:10021351). Disrupted aversive learning (PubMed:23019581). Belongs to the TGF-beta family.