Abstract
The newly identified liver-enriched gene 1 (LEG1) encodes a protein with a characteristic domain of unknown function 781 (DUF781/LEG1), constituting a protein family with only one member in mammals. A functional study in zebrafish suggested that LEG1 genes are involved in liver development, while the platypus LEG1 homolog, Monotreme Lactation Protein (MLP), which is enriched in the mammary gland and milk, acts as an antibacterial substance. However, no functional studies on eutherian LEG1s have been published to date. Thus, we here report the first functional prediction study at the cellular level. As previously reported, eutherian LEG1s can be classified into three paralogous groups. Pigs have all three LEG1 genes (pLEG1s), while humans and mice have retained only LEG1a. Hence, pLEG1s might represent an ideal model for studying LEG1 gene functions. RNA-seq was performed by the overexpression of pLEG1s and platypus MLP in HepG2 cells. Enrichment analysis showed that pLEG1a and pLEG1b might exhibit little function in liver cells; however, pLEG1c is probably involved in the endoplasmic reticulum (ER) stress response and protein folding. Additionally, gene set enrichment analysis revealed that platypus MLP shows antibacterial activity, confirming the functional study in platypus. Therefore, our study showed from the transcriptomic perspective that mammalian LEG1s have different functions in liver cells due to the subfunctionalization of paralogous genes.
Highlights
Limited information is currently available concerning the biological functions of liver-enriched gene 1 (LEG1 or C6orf58 homolog), which encodes a protein with the characteristic domain of unknown function 781 (DUF781 or LEG1 domain)
We show here that pLEG1a and pLEG1b play few roles in hepatic cells, while pLEG1c might be involved in misfolded protein processing and endoplasmic reticulum stress responses
Predicted that pLEG1a, pLEG1b, pLEG1c, and platypus Monotreme Lactation Protein (MLP) are all secreted proteins involved in multicellular organism development, while pLEG1c and MLP play additional roles in the liver and digestive system development (Table S1)
Summary
Limited information is currently available concerning the biological functions of liver-enriched gene 1 (LEG1 or C6orf homolog), which encodes a protein with the characteristic domain of unknown function 781 (DUF781 or LEG1 domain). The encoded LEG1 proteins are glycosylated secreted proteins, as indicated by several potential N-glycosylated sites and a signal peptide preceding the LEG1 domain. These features have been validated in numerous proteomic studies in mammals, in which glycosylated LEG1 proteins are present in the saliva, milk, and seminal plasma [3,4,5,6,7]. The only functional study of mammalian LEG1 far was carried out in platypus, in which the mammary gland- and milk-enriched LEG1 homolog Monotreme Lactation Protein (MLP) plays a role
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