A new study led by Prof. LIU Xinguo from the Guangzhou Institutes of Biomedicine and Health of the Chinese Academy of Sciences, has revealed that the selective translation of an upstream open reading frame (uORF) located in the 5′ untranslated region (5′UTR) of the pluripotency-associated metabolic factor Lin28b produces an 85-amino acid microprotein, which has been named PLUM (Pluripotency-associated Lin28b uORF-encoded Microprotein). The study was recently published in Nature Communications.

Deleting PLUM drives mouse primed pluripotent stem cells (PSCs) to convert to the naïve state with nearly 100% efficiency, while also causing severe implantation defects in embryos. This study identifies PLUM as the first functional microprotein encoded by a non-canonical ORF in pluripotent stem cells and establishes it as a key link connecting RNA regulation and metabolic remodeling during pluripotency and early embryonic development.

Metabolic regulation and mRNA translation are tightly coordinated processes, both of which are essential for cellular plasticity. During the transition of pluripotent states, metabolic rewiring is accompanied by dynamic changes in ribosome biogenesis and protein synthesis. Although global translation activity is relatively low in PSCs, widespread selective translation occurs in non-coding regions, including numerous non-canonical ORFs. These ORFs are often regarded as cis-regulatory elements that control downstream translation; however, whether they encode functional proteins that actively participate in pluripotency regulation has remained largely unexamined.

Using PSC and mouse models, the research team demonstrated that the loss of PLUM almost completely induces the transition of primed PSCs into the naïve state and impairs embryo implantation, highlighting PLUM's decisive role in cell-fate control. Mechanistically, PLUM directly interacts with the RNA-binding protein L1td1, regulating the formation of L1td1's cytoplasmic condensates and its phase-separation behavior. Deleting PLUM reshapes L1td1's RNA-binding profile, enhancing the stability of transcripts associated with naïve pluripotency (such as Tfcp2l1 and Zfp42) and promoting the activation of genes related to oxidative phosphorylation.

In addition, the loss of PLUM disrupts P-bodies—cellular structures responsible for mRNA decay. These P-bodies are enriched with transcripts that encode subunits of mitochondrial complex I and V, suggesting that PLUM modulates mitochondrial function through its role in P-body assembly.

This study uncovers a previously unrecognized function of a microprotein derived from a non-canonical ORF in pluripotency control and embryonic development. It also reveals a mechanism that integrates RNA regulation, biomolecular condensates, and mitochondrial metabolic remodeling—providing new conceptual insights into PSC fate determination and potential targets for optimizing pluripotent states and improving embryo quality in assisted reproductive technology.

The study was a collaborative effort involving researchers from multiple institutions: the Guangzhou Institutes of Biomedicine and Health (CAS), the CAS Hong Kong Institute of Innovation, Tianfu Jincheng Laboratory, Guangzhou Medical University, and The Chinese University of Hong Kong.