Deciphering the cellular basis of heterosis in pigs through single-cell transcriptomics of growth axis-related tissues

Heterosis, also known as hybrid vigour, is widespread in animals. It is complex and primarily regulated by a variety of tissues related to the growth axis, but the molecular bases for this phenomenon remain elusive. To define the cellular and molecular mechanisms driving pig heterosis, we used single-cell RNA sequencing to analyze the tissue-resident cell types in the pituitary, liver, growth plate, and longissimus dorsi muscle of both small-ear spotted pigs and their hybrids, with a particular focus on the GH/IGF1 axis. In pituitary, somatotrophs, producing growth hormone, increased in hybrids with GH1 gene enrichment, and POU1F1, ITPR1, and GHRHR were highly expressed in response to hybridization, regulating growth hormone synthesis and secretion. In liver, GHR, IGFBP1, and IGFBP2 decreased in hybrids, but JAKs and STATs increased, boosting IGF1 levels for growth potential. In growth plate, GHR is exclusively enriched in ossification-related cells and significantly activates the upregulation of IGF2 in hybrids, contributing to chondrogenesis and osteocytogenesis. In skeletal muscle, PDGFA enriched in hybrid IMF cells binds to the PDGF receptor in FAP cells, inhibiting adipogenesis through paracrine action, while in MuSCs, GHR activates FOXO3 and BMP6, significantly upregulated in hybrids and contributing to myogenesis. The findings characterize resident cells in growth-related tissues and offer new insights into pig heterosis that enhance animal production.