Importance of the pluripotency factor LIN28 in the mammalian nucleolus during early embryonic development

Abstract

The maternal nucleolus is required for proper activation of the embryonic genome (EGA) and early embryonic development. Nucleologenesis is characterized by the transformation of a nucleolar precursor body (NPB) to a mature nucleolus during preimplantation development. However, the function of NPBs and the involved molecular factors are unknown. We uncover a novel role for the pluripotency factor LIN28, the biological significance of which was previously demonstrated in the reprogramming of human somatic cells to induced pluripotent stem (iPS) cells. Here, we show that LIN28 accumulates at the NPB and the mature nucleolus in mouse preimplantation embryos and embryonic stem cells (ESCs), where it colocalizes with the nucleolar marker B23 (nucleophosmin 1). LIN28 has nucleolar localization in non-human primate (NHP) preimplantation embryos, but is cytoplasmic in NHP ESCs. Lin28 transcripts show a striking decline before mouse EGA, whereas LIN28 protein localizes to NPBs at the time of EGA. Following knockdown with a Lin28 morpholino, the majority of embryos arrest between the 2- and 4-cell stages and never develop to morula or blastocyst. Lin28 morpholino-injected embryos arrested at the 2-cell stage were not enriched with nucleophosmin at presumptive NPB sites, indicating that functional NPBs were not assembled. Based on these results, we propose that LIN28 is an essential factor of nucleologenesis during early embryonic development.

Lin28a Is Dormant, Functional, and Dispensable During Mouse Oocyte-to-Embryo Transition1

“…Lin28a mRNA expression analysis is in agreement with previous microarray analyses [53,54] and RT-PCR profiling [39]. Altogether, these data demonstrate that Lin28a transcript is abundant in the oocyte and becomes degraded after fertilization, and zygotic transcripts start to accumulate after the 8-cell stage.…”

“…Consequently, Lin28a À/À female mice have smaller ovaries, produce smaller numbers of mature oocytes, and have reduced fertility (;30% smaller litter size) [38]. In contrast, postzygotic morpholino-based knockdown of Lin28a resulted in most early embryos arresting between 2-and 4-cell stages, and LIN28A has been implicated in nucleogenesis during early development [39]. Here we report results of LIN28A expression analysis during OET and functional analysis of Lin28a and Lin28b, using oocyte-specific transgenic RNA interference (RNAi) [40].…”

LIN28: roles and regulation in development and beyond

“…LIN28 is expressed early in development, with the protein showing accumulation in mouse nucleolar precursor bodies during the twocell stage of embryogenesis (Vogt et al, 2012). Expression is seen throughout the developing embryo by E6.5, and extends to the extra-embryonic tissue as well (Yang and Moss, 2003).…”

How cells build totipotency and pluripotency: nuclear, chromatin and transcriptional architecture

“…However, since NLBs also contain a large amount of RNAs it is expected that RNA-binding proteins also accumulate at NLBs. Vogt et al showed [27 ] that whereas LIN28 protein, an RNA-binding protein with roles in maintaining pluripotency in ES cells [28], predominantly accumulates in NLBs, it mostly localizes in the cytoplasm in ES cells. Knockdown of LIN28 by microinjection of LIN28-mophorlino into zygotes leads to a developmental arrest at the transition between the 2-cell to the 4-cell stage although no abnormalities in chromocenter formation in LIN28-depleted embryos were observed [27 ] ( Figure 1b).…”

“…Vogt et al showed [27 ] that whereas LIN28 protein, an RNA-binding protein with roles in maintaining pluripotency in ES cells [28], predominantly accumulates in NLBs, it mostly localizes in the cytoplasm in ES cells. Knockdown of LIN28 by microinjection of LIN28-mophorlino into zygotes leads to a developmental arrest at the transition between the 2-cell to the 4-cell stage although no abnormalities in chromocenter formation in LIN28-depleted embryos were observed [27 ] ( Figure 1b). Together, these studies suggest that the presence of the NLBs themselves and the proteins associated with NLBs in the first and second cell cycles in embryos are essential for normal development.…”