In mammals, around fertilization, the nucleolus of embryos transforms into the nucleolus precursor bodies (NPBs), which continue to mature until the blastocyst stage, leading to distinct morphological changes. In our study, we observed two types of nucleolar morphology in mouse in vitro fertilized embryos at the four-cell stage, which we refer to single nucleolus (SN) and multiple nucleoli (MN). To visualize nucleolar morphology, four-cell embryos were immunostained with anti-NOPP140 antibody. These embryos were categorized into five types based on the number of blastomeres carrying SN: SN4/MN0, SN3/MN1, SN2/MN2, SN1/MN3, and SN0/MN4, with percentages of 13, 27, 21, 23 and 9, respectively. Next, using a light microscope, we divided the four-cell in vitro fertilized embryos without fixation into two groups: those with at least two blastomeres displaying SN (SN embryos) and those without (MN embryos). Notably, significantly more SN embryos developed into blastocysts and offspring at 18.5 dpc compared with MN embryos. Furthermore, SN embryos displayed a higher NANOG-positive cell number at the blastocyst stage, significantly lower body and placental weights, resulting in a higher fetal/placental ratio. These findings suggest a close association between nucleolar state at the four-cell stage and subsequent developmental potential.

中文翻译：

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体外受精后四细胞小鼠胚胎核仁形态的异质性：与发育潜力的关联

在哺乳动物中，受精前后，胚胎的核仁转变为核仁前体（NPB），并继续成熟直至囊胚阶段，从而导致明显的形态变化。在我们的研究中，我们在四细胞阶段的小鼠体外受精胚胎中观察到两种类型的核仁形态，我们将其称为单核仁（SN）和多核仁（MN）。为了观察核仁形态，用抗 NOPP140 抗体对四细胞胚胎进行免疫染色。根据携带SN的卵裂球数量将这些胚胎分为五种类型：SN4/MN0、SN3/MN1、SN2/MN2、SN1/MN3和SN0/MN4，百分比分别为13、27、21、23和9，分别。接下来，使用光学显微镜，我们将未经固定的四细胞体外受精胚胎分为两组：具有至少两个卵裂球显示SN的胚胎（SN胚胎）和没有显示SN的胚胎（MN胚胎）。值得注意的是，与 MN 胚胎相比，在 18.5 dpc 时，SN 胚胎明显更多地发育成囊胚和后代。此外，SN胚胎在囊胚阶段表现出更高的NANOG阳性细胞数量，显着降低体重和胎盘重量，从而导致更高的胎儿/胎盘比率。这些发现表明四细胞阶段的核仁状态与随后的发育潜力之间存在密切关联。