Trophectoderm Transcriptome Analysis in LIN28 Knockdown Ovine Conceptuses Suggests Diverse Roles of the LIN28-let-7 Axis in Placental and Fetal Development

Abstract

The proper conceptus elongation in ruminants is critical for the successful placentation and establishment of pregnancy. We have previously shown that the trophectoderm-specific knockdown of LIN28A/B in day 9 ovine blastocysts resulted in increased let-7 miRNAs and reduced conceptus elongation at day 16 of gestation. In this current study, by transcriptome analysis of LIN28A knockdown (AKD) or LIN28B knockdown (BKD) trophectoderm (TE), we explored the downstream target genes of the LIN28-let-7 axis and their roles in the placental and fetal development. We identified 449 differentially expressed genes (DEGs) in AKD TE and 1214 DEGs in BKD TE compared to non-targeting control (NTC). Our analysis further revealed that 210 downregulated genes in AKD TE and 562 downregulated genes in BKD TE were the potential targets of let-7 miRNAs. Moreover, 16 downregulated genes in AKD TE and 57 downregulated and 7 upregulated genes in BKD TE were transcription factors. The DEGs in AKD and BKD TE showed enrichment in the biological processes and pathways critical for placental development and function, and fetal development and growth. The results of this study suggest the potential roles of the LIN28-let-7 axis in placental and fetal development beyond its involvement in trophoblast proliferation and conceptus elongation.

Prediction of Early- and Late-Onset Pre-Eclampsia in the Preclinical Stage via Placenta-Specific Extracellular miRNA Profiling

“…It is well known that the let-7 family plays a key role in placental and fetal development [38,39], and its levels are controlled by the RNA-binding protein Lin28, which is a natural inhibitor of let-7 processing in both the pri-and pre-miRNA steps [40]. In turn, Lin28 is directly up-regulated via Wnt/β-catenin signaling, responsible for TE lineage specification through transcription factor Cdx2 [41].…”

“…At the same time, via the targeting of Tead4, let-7 miRNAs have an impact on the expression level of Cdx2, a clue transcription factor of the Hippo signaling pathway, which causes the development of trophectoderm through the interaction with unphosphorylated YAP1 in the nucleus of the outer cells of the blastocyst [42]. It was demonstrated that a trophectoderm-specific LIN28A/B knockdown increased the let-7 miRNA levels in blastocysts and resulted in a decrease in the expression levels of certain target genes responsible for trophoblast proliferation, invasion, migration, syncytialization, immune tolerance, angiogenesis, and vascular integrity, including the collagen genes COL1A1, COL1A2, COL3A1, COL5A1, and COL5A2; together with RAMP2, all of these genes were shown to be involved in the positive regulation of the ERK1/2 cascade, canonical Wnt-and TGF-beta signaling, and the genes of the PPAR-, PI3K-AKT-, and Hippo signaling pathways [39]. It was found that let-7 miRNA levels impacted the migration and invasion of extravillous trophoblast cells via the influence on the expression level of their common gene target MDM4 [43].…”

New Roles for EVs, miRNA and lncRNA in Bovine Embryo Implantation

“…Sheep conceptuses treated with morpholino antisense oligonucleotide against PPARs or HSD11B1 also result in severely growth-retarded conceptuses or conceptus fragments on day 14 (57,58). Furthermore, trophectoderm-specific knockdown of LIN28A/B in day 9 ovine blastocysts results in increased let-7 mRNA and reduced conceptus elongation on day 16 (59). It should be noted that while these three molecules play a role during the conceptus elongation in utero, sufficient conceptus elongation in vitro has not been demonstrated.…”