Abstract
BackgroundIn most multicellular organisms, the transforming growth factor-β (TGF-β) signalling pathway is involved in regulating the growth and stem cell differentiation. Previous studies have demonstrated the importance of three key molecules in this pathway in the parasitic nematode Haemonchus contortus, including one TGF-β type I receptor (Hc-tgfbr1), one TGF-β type II receptor (Hc-tgfbr2), and one co-Smad (Hc-daf-3), which regulated the developmental transition from the free-living to the parasitic stages of this parasite. However, almost nothing is known about the function of the TGF-β ligand (Hc-tgh-2) of H. contortus.MethodsHere, the temporal transcription profiles of Hc-tgh-2 at eight different developmental stages and spatial expression patterns of Hc-TGH-2 in adult female and male worms of H. contortus have been examined by real-time PCR and immunohistochemistry, respectively. In addition, RNA interference (RNAi) by soaking was employed to assess the importance of Hc-tgh-2 in the development from exsheathed third-stage larvae (xL3s) to fourth-stage larvae (L4s) in H. contortus.ResultsHc-tgh-2 was continuously transcribed in all eight developmental stages of H. contortus studied with the highest level in the infective third-stage larvae (iL3) and Hc-TGH-2 was located in the muscle of the body wall, intestine, ovary of adult females and testes of adult males. Silencing Hc-tgh-2 by the specific double-stranded RNA (dsRNA), decreased the transcript level of Hc-tgh-2 and resulted in fewer xL3s developing to L4s in vitro.ConclusionsThese results suggested that the TGF-β ligand, Hc-TGH-2, could play important roles in the developmental transition from the free-living (L3s) to the parasitic stage (L4s). Furthermore, it may also take part in the processes such as digestion, absorption, host immune response and reproductive development in H. contortus adults.
Highlights
IntroductionThe transforming growth factor-β (TGF-β) signalling pathway is involved in regulating the growth and stem cell differentiation
In most multicellular organisms, the transforming growth factor-β (TGF-β) signalling pathway is involved in regulating the growth and stem cell differentiation
One TGF-β ligand homologue from Trichinella spiralis formed a cluster (82%) with four TGF-β ligand homologues from four metazoans (Capra hircus, Danio rerio, Homo sapiens and Mus musculus), which grouped together with 10 selected TGF-β ligand homologues from strongylid, ascarid and filarial nematodes by 83% nodal support, to the exclusion of TGF-β ligand homologues of three parasitic nematodes (Parastrongyloides trichosuri, Strongyloides stercoralis and Strongyloides ratti) that have an alternative free-living life-cycle (Fig. 1)
Summary
The transforming growth factor-β (TGF-β) signalling pathway is involved in regulating the growth and stem cell differentiation. According to the structural motifs, members of He et al Parasites Vectors (2020) 13:326 the TGF-β family are divided into five groups including TGFβs, activins/inhibin, growth and differentiation factors (GDFs), bone morphogenetic proteins (BMPs) and mullerian inhibitory factor (MIF) [2, 5]. In the free-living nematode Caenorhabditis elegans, there are five TGF-β ligands (Ce-DBL-1, Ce-DAF-7, CeUNC-129, Ce-TIG-2 and Ce-TIG-3) involved in regulating essential development including dauer formation, body-size determination and male tail morphology [6, 7]. Ce-DAF-7 is involved in the regulation of longevity, reproduction and fat metabolism [16,17,18]
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