Large-scale proteomic analysis of T. spiralis muscle-stage ESPs identifies a novel upstream motif for in silico prediction of secreted products

The Trichinella genus contains parasitic nematodes capable of infecting a wide range of hosts including mammals, birds and reptiles. Like other helminths, T. spiralis secretes a complex mixture of bioactive molecules capable of modulating its immediate surroundings and creating a hospitable environment for growth, survival and ultimately transmission. The constitution of these excretory-secretory products (ESPs) changes depending on the tissue niche and the specific stage of parasite development. Unique to T. spiralis is a true intracellular stage wherein larvae develop inside striated myotubes. Remarkably, the parasite larvae do not destroy the host cell but rather reprogram it to support their presence and growth. This transformation is largely mediated through stage-specific secretions released into the host cell cytoplasm. In this study, we apply state of the art proteomics and computational approaches to elucidate the composition and functions of muscle-stage T. spiralis ESPs. Moreover, we define a commonly-occurring, upstream motif that we believe is associated with the stichosome, the main secretory organ of this worm, and can thus be used to predict secreted proteins across experimentally less tractable T. spiralis life cycle stages. Author Summary Trichinella spiralis is the only helminth parasite with a true intracellular stage. Newborn larvae penetrate the intestinal wall of the host, enter the circulation and preferentially infect muscle cells. Remarkably, they do not destroy the host cell but rather initiate a series of modulatory events that transform it into a ‘nurse cell complex’, a collagenated cyst that can persist for years. Each stage of T. spiralis development is guided by host-targeted secretions released by the worm directly into its immediate environment, mediating events such as immunoregulation, cell cycle control and angiogenesis. As such, these worm effectors hold therapeutic potential for chronic and autoimmune diseases. The composition of excretory-secretory products (ESPs) changes according to what the worm needs to accomplish and what tissue niche it is occupying at the time, with many deriving from the stichosome, the worm’s dedicated secretory organ. In this study, we characterise ESPs of muscle-stage T. spiralis larvae using proteomic and bioinformatic approaches and we define a regulatory motif associated with stichosome-derived proteins. ### Competing Interest Statement The authors have declared no competing interest.