Maternal methylosome protein 50 is essential for embryonic development in medaka Oryzias latipes

• Published in: Journal of experimental zoology. Part A, Ecological and integrative physiology Ecological and integrative physiology, 2024-08, Vol.341 (7), p.798-810
• Main Authors: Duan, Shi, Yang, Qing, Wu, Fan, Li, Zhenyu, Hong, Wentao, Cao, Mengxi, Chen, Xinhua, Zhong, Xueping, Zhou, Qingchun, Zhao, Haobin
• Format: Article
• Language: English
• Subjects: Animal embryos; Animals; Apoptosis; Cell cycle; Cell death; Chromosomes; Deoxyribonucleic acid; DNA; DNA biosynthesis; DNA replication; DNA sequencing; Embryo, Nonmammalian - metabolism; Embryogenesis; Embryonic Development; Embryonic growth stage; Embryos; Extracellular matrix; Female; Fish; Fish Proteins - genetics; Fish Proteins - metabolism; Freshwater fishes; Gastrulation; Gene expression; Gene Expression Regulation, Developmental; Gene regulation; Gene sequencing; Genes; Histones; Mep50; Myc protein; Nucleic acids; Nucleotide sequence; Oryzias - embryology; Oryzias - genetics; Oryzias latipes; PCR; Proteins; Replication; Ribonucleic acid; RNA; RNA processing; RNA sequencing; Transcription factors; Transcriptomes; Wnt protein; Zygotes
• ISSN: 2471-5638; 2471-5646; 2471-5646
• DOI: 10.1002/jez.2824

Methylosome protein 50 (Mep50) is a protein that is rich in WD40 domains, which mediate and regulate a variety of physiological processes in organisms. Previous studies indicated the necessity of Mep50 in embryogenesis in mice Mus musculus and fish. This study aimed to further understand the roles of maternal Mep50 in early embryogenesis using medaka Oryzias latipes as a model. Without maternal Mep50, medaka zygotes developed to the pre‐early gastrula stage but died later. The transcriptome of the embryos at the pre‐early gastrula stage was analyzed by RNA sequencing. The results indicated that 1572 genes were significantly upregulated and 741 genes were significantly downregulated in the embryos without maternal Mep50. In the differentially expressed genes (DEGs), the DNA‐binding proteins, such as histones and members of the small chromosome maintenance complex, were enriched. The major interfered regulatory networks in the embryos losing maternal Mep50 included DNA replication and cell cycle regulation, AP‐1 transcription factors such as Jun and Fos, the Wnt pathway, RNA processing, and the extracellular matrix. Quantitative RT‐PCR verified 16 DEGs, including prmt5, H2A, cpsf, jun, mcm4, myc, p21, ccne2, cdk6, and col1, among others. It was speculated that the absence of maternal Mep50 could potentially lead to errors in DNA replication and cell cycle arrest, ultimately resulting in cell apoptosis. This eventually resulted in the failure of gastrulation and embryonic death. The results indicate the importance of maternal Mep50 in early embryonic development, particularly in medaka fish. The embryos produced from the homozygous female mutant mating with a wild‐type male developed to stage 12 but ultimately died. The RNA‐seq was performed to analyze the effect of maternal Mep50 loss on gene expression in stage 12. The results indicated that without maternal Mep50, the genes involved in DNA replication and chromosome maintenance were downregulated. This includes members of the Mcm complex, Mcmbp, and histones, which may cause interference in DNA replication and chromosome formation. Upregulation of the gene Gadd45a and downregulation of the cyclins and Cdk2/6 may result in cell cycle arrest. Downregulation of Myc may decrease its repression of p21 and p15. Upregulation of p21 and p15 may cause repression of cyclins/Cdks, prompting cell apoptosis. Cell cycle arrest may result in the repression of cell proliferation and cell apoptosis, leading to embryonic de