Identification and expression of a transforming growth factor beta (TGF-β) homologue in the tropical liver fluke Fasciola gigantica

Receptor-regulated smads (R-Smads) in the liver fluke Fasciola gigantica: Characterization, comparative sequence analysis, and life stage-specific expression

The transforming growth factor-beta (TGF-β) signaling pathway is a key conserved developmental pathway, demonstrating remarkable conservation in its components, structures, and functions across diverse animal species. This study presents a comprehensive characterization and comparative analysis of receptor-regulated Smads (R-Smads) in Fasciola gigantica, a major parasite affecting cattle, buffalo, and ruminants in tropical regions. Four R-Smads were identified: FgSmad1/5, FgSmad2, FgSmad3, and FgSmad8. Full-length cDNAs for these R-Smads, isolated using the rapid amplification of cDNA ends (RACE) approach, were 3348, 3010, 5172, and 1991 bp in length, encoding proteins of 464, 506, 678, and 404 amino acids, respectively. FgSmad1/5 and FgSmad8 were classified as bone morphogenetic protein (BMP)-specific R-Smads (BR-Smads) due to their conserved signature motifs and similarity to those found in parasitic platyhelminths and mammalian hosts. Conversely, FgSmad2 and FgSmad3 were identified as TGF-β/activin-specific R-Smads (AR-Smads), displaying a distinctive pattern of conserved motifs commonly observed among trematode parasites. Notably, FgSmad2 exhibited an atypical feature for R-Smads, as it lacked the MH1 domain. The expressions of F. gigantica R-Smad genes were observed across all developmental stages, with the highest levels of most R-Smads occurring in the unembryonated egg stage (primarily BR-Smads) and the metacercaria stage (predominantly AR-Smads), underscoring a significant shift in TGF-β and BMP signaling dynamics during development. These findings greatly advance our understanding of R-Smad proteins within the TGF-β signaling pathway of F. gigantica and provide a solid foundation for future research into their roles and regulatory mechanisms.

Detailed characterisation of the Co-Smad protein in liver fluke Fasciola gigantica

Fasciolosis, caused by the liver flukes Fasciola hepatica and Fasciola gigantica, is a zoonotic parasitic disease associated with substantial economic losses in livestock. The transforming growth factor-beta signalling pathway is implicated in developmental processes and biological functions throughout the animal kingdom, including the Fasciola spp. It may also mediate host-helminth interactions during infection. In this work, we present an exploration of FgSmad4, the sole member of the Co-Smad protein family in F. gigantica. The isolated FgSmad4 cDNA was 4,014 bp in length encoding for a protein comprising 771 amino acids. FgSmad4 exhibited typical Co-Smad protein features, including Mad Homology 1 (MH1) and Mad Homology 2 (MH2) domains, a Nuclear Localisation Signal, a DNA-Binding Motif, and a Nuclear Export Signal. Sequence and phylogenetic analyses of FgSmad4 revealed that its MH1 and MH2 sequences are most similar to those of other trematode species. The MH1 domain, in particular, closely resembles the Co-Smad protein in mammalian hosts more than those in cestodes and nematodes. The expression patterns of FgSmad4 during the liver fluke's developmental stages showed significant variation. Transcript levels were highest at the newly excysted juvenile stage, followed by unembryonated egg, redia, and metacercaria, with the lowest expression in the adult fluke, embryonated egg, and cercaria stages. Our results underscore the conservation and suggest the potential role of FgSmad4, a key transforming growth factor-beta signalling molecule within the liver fluke F. gigantica. As Co-Smad is typically involved in several biological pathways, the precise functions and mechanisms of this identified FgSmad4 necessitate further exploration.

Reconstruction of the TGF-β signaling pathway of Fasciola gigantica

In the present study, we reconstructed the transforming growth factor beta (TGF-β) signaling pathway for Fasciola gigantica, which is a neglected tropical pathogen. We defined the components involved in the TGF-β signaling pathway and investigated the transcription profiles of these genes for all developmental stages of F. gigantica. In addition, the presence of these components in excretory and secretory products (FgESP) was predicted via signal peptide annotation. The core components of the TGF-β signaling pathway have been detected in F. gigantica; classical and nonclassical single transduction pathways were constructed. Four ligands have been detected, which may mediate the TGF-β signaling pathway and BMP signaling pathway. Two ligand-binding type II receptors were detected, and inhibitory Smad7 was not detected. TLP, BMP-3, BMP-1, and ActRIb showed higher transcription in 42-day juvenile and 70-day juvenile, while ActRIIa, Smad1, ActRIIb, Smad8, KAT2B, and PP2A showed higher transcription in egg. TLM, Ski, Smad6, BMPRI, p70S6K, Smad2, Smad3, TgfβRI, Smad4, and p300 showed higher transcription in metacercariae. Four ligands, 2 receptors and 3 Smads are predicted to be present in the FgESP, suggesting their potential extrinsic function. This study should help to understand signal transduction in the TGF-β signaling pathway in F. gigantica. In addition, this study helps to illustrate the complex mechanisms involved in developmental processes and F. gigantica - host interaction and paves the way for further characterization of the signaling pathway in trematodes.