性未成熟雌性小鼠孕前砷暴露导致植入前胚胎体外发育阻滞

目前研究发现妊娠期环境砷暴露可以导致其后代发育异常如不孕不育、流产、早产、胎儿生长受限、子代先天畸形及性别比例失调等生殖健康问题,而对孕前砷暴露对植入前胚胎发育的影响的研究还不充分.我们选用3～5周龄性未成熟雌性小鼠,按8mg/kg亚砷酸钠(NaAsO2)剂量隔日腹腔注射1次,共注射8次.结果显示:孕前砷暴露导致小鼠植入前胚胎大部分阻滞在1-2细胞期.同时发现,这些阻滞的胚胎活性氧(ROS)水平明显升高,细胞色素C明显释放,细胞凋亡率明显升高.这些结果说明,孕前砷暴露通过氧化应激诱发胚胎凋亡导致植入前胚胎的发育阻滞,这也预示着孕前砷暴露将有可能导致育龄妇女受孕困难.     

小鼠植入前胚胎及几种组织中IFRG15的差异表达研究

为进一步研究干扰素α应答基因IFRG15（Interferon responsive gene 15）在小鼠整个发育过程中的表达规律,从植入前胚胎及2、5、16周龄的雌、雄昆明小白鼠心、肝、脾、肺、肾、肌肉、卵巢或睾丸等组织中提取总RNA,以HPRT1（Hypoxanthine phosphoribosyltransferase 1）为内参基因,利用RT-PCR的方法进行目的片段的扩增及差异性分析。结果表明,IFRG15在植入前胚胎8-细胞期,桑葚胚期开始显著高表达于受精卵、2-细胞期、4-细胞期（p〈0.05）,在囊胚期表达量达到最高,且显著高于其他各期（p〈0.05）;在雌雄小鼠几个组织体外发育过程中均检测到表达,但表达量有所不同,在雄性小鼠各组织中的表达无显著规律性差异;在5周龄雌性小鼠组织中达到最高（p〈0.05）,卵巢组织尤为明显,推测该基因对卵巢的成熟有重要的促进作用;本实验成功获得IFRG15在小鼠植入前各期胚胎及体外发育过程中的表达模式,为进一步探究该基因在小鼠克隆胚发育过程中的作用奠定基础。     

p-CREB在小鼠植入前胚的表达及其与2-细胞阻滞的关系

目的观察p-CREB在小鼠植入前胚以及阻滞品系(昆明小鼠)与非阻滞品系(B6C3F1小鼠)2-细胞胚的分布与表达,初步探讨p-CREB在小鼠植入前胚中的作用以及与小鼠2-细胞阻滞的关系。方法利用激光扫描共聚焦显微镜检测p-CREB在B6C3F1小鼠植入前胚中的定位,比较不同品系小鼠体外培养以及B6C3F1小鼠体外培养与体内发育2-细胞胚内p-CREB的表达变化。结果 p-CREB的免疫阳性反应在小鼠1-细胞胚中主要分布于细胞质中;2-细胞胚及其后期植入前胚主要定位于细胞核内;昆明小鼠体外培养2-细胞胚核内荧光强度显著低于同一条件发育的B6C3F1小鼠,B6C3F1小鼠体外培养2-细胞胚核内荧光强度显著高于体内发育。结论 p-CREB在小鼠植入前胚发育中起重要作用,p-CREB在昆明小鼠2-细胞胚核内表达较低可能与小鼠2-细胞阻滞有关。     

小鼠体内外受精植入前胚胎全基因组甲基化模式比较

为考察体外受精、操作及培养环境对体外受精的小鼠植入前胚胎全基因组DNA甲基化模式的影响,本研究以体内受精的植入前胚胎作为对照,采用间接免疫荧光法检测小鼠体内外受精植入前胚胎基因组DNA甲基化模式.实验结果表明,体外受精各期植入前胚胎呈现出与之相应时期的体内受精植入前胚胎不同的DNA甲基化模式和水平,原核期甲基化水平较高,2-4-、8-细胞期明显降低,而桑葚胚和囊胚期又略有升高.各期体外受精植入前胚胎的基因组DNA甲基化水平都比同时期体内受精胚胎的甲基化水平低.本实验结果部分显示了体外受精、操作及培养环境可能对正常的DNA甲基化模式产生影响,造成体外受精植入前胚胎甲基化模式异常.     

怀孕前后酒精摄入对雌鼠植入前胚胎DNA甲基化模式建立的影响

女性怀孕前后饮酒会对胎儿的发育及神经系统造成不利影响,称为“胎儿酒精综合征”（fetal alcohol spectrum disorders,FASD）。小鼠通常作为研究该病的动物模型。该实验采用体外培养技术及体内冲胚法研究雌鼠怀孕前后酒精摄入对各期植入前胚胎全基因组DNAT基化模式建立的影响。小鼠植入前胚胎体外培养实验发现,体外实验组I（怀孕前酒精处理组1,除8-cell外,其他各期胚胎的DNA甲基化水平明显低于体外对照组;体外实验组II（正常胚胎在含乙醇的培养基中培养）,各期植入前胚胎DNA甲基化水平均明显低于体外对照组。体内实验发现,体内实验组I（怀孕前酒精处理组）与体内的实验组II（怀孕后酒精处理组）,各期植入前胚胎DNA甲基化水平明显低于体内对照组。体内、外实验结果表明：受精前后酒精对各期植入前胚胎DNA甲基化模式的正确建立造成紊乱,该结果可为进一步揭示FSAD发病机制提供一定的实验基础。     

小鼠胚胎致密化起始的调控机制

植入前小鼠胚胎的发育事件包括第一次卵裂、胚胎基因组激活、桑椹胚致密、囊胚形成。小鼠受精卵胚胎的致密化发生在8-细胞阶段晚期, 致密过程中, 胚胎卵裂球本身以及卵裂球之间发生了一系列的变化。这些变化包括卵裂球微绒毛以及胞质成分的极性化分布, 卵裂球之间形成特殊的胞间连接。致密化是哺乳动物胚胎发育过程中的第一个细胞分化事件, 即导致了内细胞团以及滋养外胚层的产生。植入后, 内细胞团将发育成为胚体, 滋养外胚层将发育成为胎盘等胚外组织。细胞粘附分子E-cadherin介导的胞间粘附起始了致密化。卵裂球发生粘附所需的组分在致密前已经存在, 但是直至8-细胞阶段晚期连接复合体才表现出明显的粘附活性。敲除E-cadherin基因, 发现母源性的E-cadherin足以介导致密。E-cadherin介导的胞间粘附是细胞粘附的第一步。文章综述了E-cadherin介导胞间粘附的具体过程以及蛋白激酶C(Protein kinase C, PKC)调控该过程的相关 机制。     

H3K27乙酰化模式在孤雌胚与正常胚中的差异及其对胚胎发育的影响

目的考察小鼠孤雌胚胎H3K27乙酰化模式与体内胚胎的差异,探究表观遗传模式对孤雌胚发育的影响。方法利用SrCl2激活卵母细胞,获得植入前各时期孤雌胚胎,并统计胚胎发育率;小鼠注射孕马血清激素(Pregnant Mare Serum Gonadotrophin,PMSG)和人绒毛膜促性腺激素(Human Chorionic Gonadotropin,hCG)超排后合笼,在不同发育时间采用体内冲胚的方法获得体内各时期胚胎;将获得的各期各类胚胎用H3K27乙酰化抗体与特异性位点结合,与连接有FITC荧光基团的二抗共同孵育,利用激光共聚焦显微镜检测荧光强度,获得小鼠植入前各时期孤雌胚和体内胚组蛋白H3K27乙酰化模式。结果用SrCl2激活成熟卵母细胞得到的孤雌胚的激活率和囊胚率分别为96.39%和69.54%,处于正常发育水平;孤雌胚H3K27乙酰化荧光强度从原核期相对较高的水平逐渐降低,2-细胞、4-细胞和8-细胞时期荧光强度都处于较低水平,到桑葚胚时期又突然升高,总体变化趋势和体内组先降低后升高的整体趋势一样,且原核期至8-细胞时期的荧光值孤雌胚高于体内胚,桑囊胚时期则相反;两组的H3K27乙酰化荧光强度值在原核期和桑葚胚时期差异不显著(P>0.05),在2-细胞、4-细胞、8-细胞和囊胚期差异显著(P<0.01)。结论本研究表明小鼠孤雌胚H3K27乙酰化模式与体内胚的模式存在差异,可能是影响孤雌胚发育能力的重要原因之一。进一步的深入研究将对纠正小鼠孤雌胚乙酰化模式和提高孤雌胚发育能力具有重要意义。     

密闭培养条件下小鼠早期胚胎Igf2/H19印迹调控区甲基化状态分析

胚胎密闭培养是空间胚胎发育研究的基本条件.本文主要研究密闭培养条件对小鼠早期胚胎发育过程中印迹基因Igf2/H19的印迹调控区(ICR)甲基化水平的影响.应用亚硫酸氢盐测序法(BSP)分析小鼠2-细胞胚胎在密闭条件下分别培养24h、48h和72h后,相对应的发育阶段胚胎Igf2/H19的ICR甲基化水平,以常规体外培养和体内发育的各阶段胚胎为对照.结果显示,密闭培养条件下,小鼠8-细胞胚胎、桑葚胚和囊胚的Igf2/H19的ICR甲基化水平都低于常规体外培养的结果,且更明显低于体内发育的结果;同时发现,小鼠8-细胞胚胎密闭培养时,Igf2/H19的ICR甲基化水平最低.由此可见,密闭培养会引起小鼠植入前各发育阶段胚胎Igf2/H19的ICR甲基化水平降低,并证明Igf2/H19的ICR甲基化水平可以作为监测哺乳动物早期胚胎发育状况的分子指标.     

葡萄糖对小鼠胚胎体外发育的影响

通过在CZB培养液中添加不同浓度葡萄糖及在胚胎发育的不同阶段加入葡萄糖,对小鼠胚胎进行体外培养,以探讨葡萄糖在小鼠早期胚胎体外发育中的作用。其结果表明,小鼠胚胎在含糖CZB与在无糖CZB中培养比较,4-细胞发育率无差异;各浓度葡萄糖组囊胚率显著高于无糖组,其中3.0mmol/L浓度组囊胚细胞数显著高于其余组;实验二：2-细胞至4-细胞、4-细胞至桑椹胚前添加葡萄糖囊胚率显著提高。上述结果证明,在小鼠胚胎体外培养中加入葡萄糖不会导致2-细胞阻滞;葡萄糖浓度增加至10mmol/L对小鼠胚胎无毒性作用,其最适浓度为3.0mmol/L;2-细胞至4-细胞、4-细胞至桑椹胚前添加葡萄糖是必要的。关键词 葡萄糖;小鼠;2-细胞阻滞;胚胎;体外发育     

Cdc25B蛋白过表达可使小鼠胚胎突破2-细胞期阻滞

目的：探讨Cdc25B蛋白过表达对小鼠2-细胞期胚胎发育的影响。方法：利用体外转录试剂盒将Cdc25B转录成mRNA,将mRNA显微注射入小鼠2-细胞期胚胎中,观察胚胎发育情况和卵裂率。用蛋白激酶活性测定方法和Western印迹分别检测Cdc25B蛋白过表达小鼠胚胎MPF的活性及Cdc2-Tyr15的磷酸化状态。结果：hCG后48 h,mRNA注射组有超过40%的2-细胞期胚胎分裂到4-细胞期而对照组仍停留在2-细胞期;激酶活性测定显示注射Cdc25B mRNA后,MPF的活性显著升高;Cdc2-Tyr15的磷酸化状态变化与激酶活性测定结果一致。结论：Cdc25B蛋白过表达可以激活有丝分裂促进因子（MPF）,从而使小鼠2-细胞期胚胎突破2-细胞期阻滞,发育到4-细胞期。     

Cyclooxygenase-2-derived endogenous prostacyclin reduces apoptosis and enhances embryo viability in mouse

The role of prostaglandins (PGs) in apoptosis in preimplantation mice embryo development is reported in this study. It is known that apoptosis plays a very important role in normal mice embryo development. Very few reports are available on this subject. Embryos (6-8 cells) were cultured in the presence of a selective cyclooxygenase (COX)1 inhibitor (SC560), a selective COX2 inhibitor (NS398) and a selective prostacyclin synthase (PGIS) inhibitor (U51605) in a 48-h culture. In another experiment, culture media were supplemented with prostaglandin E2 (PGE2) and prostaglandin I2 (PGI2 or prostacyclin) analogues. The apoptosis was evaluated by detection of active caspase-3. It was strongly detected in the presence of selective COX-2 and PGIS inhibitors, which can be decreased by a PGI2 analogue. In our embryo transfer experiment, the implantation rate decreased with exposure to either the COX2 or the PGIS inhibitor which is increased further after PGI2 supplementation. The level of PGI2 is also higher at the 8-16-cell stage, compaction and blastocyst stage than PGE2. All these results indicate that COX2-derived PGI2 plays an important role in preimplantation embryo development and acts as an antiapopetic factor in in vitro culture.     

Interleukin-1 beta induces autophagy of mouse preimplantation embryos and improves blastocyst quality

Autophagy is one of the basic cellular mechanism during preimplantation development of mammalian embryos, and it plays crucial role in several physiological processes. It is induced by interleukin (IL)-1β in mammalian cells. Our present study shows that IL-1β is important for autophagy activation in embryo development. Our in vitro culture system analysis shows effect of IL-1β in medium on the development of mouse embryos and it was found to be concentration dependent. A preimplantation embryo culture using medium containing IL-1β did not improve cleavage and blastocyst development rates of mouse embryos; however, blastocyst quality was significantly improved by increasing total cell number, especially in supplementary 20 ng/mL IL-1β. Furthermore, autophagy activation mainly occurs in 2 to 4 cell embryo and blastocyst, 20 ng/mL IL-1β into culture medium can effectively enhance levels of messenger RNA and protein of autophagy-related-factors in 2 to 4 cell embryos and blastocyst, while these factors reduce in VGX-1027 (IL-1β inhibitor) groups that also reduce the quality of blastocyst. Effects of IL-1β on the development of embryo reduced in 20 ng/mL IL-1β supplemented group when 5 mM 3-methyladenine (3-MA) was also added, which used to inhibit autophagy activation in endogenous PtdIns3Ks signal pathway. Our current results show that exogenous IL-1β can effectively induce autophagy in mouse embryos at stages of 2 to 8 cell and blastocyst, that also help to improve the quality of blastocyst.     

Hypotaurine requirement for in vitro development of golden hamster one-cell embryos into morulae and blastocysts, and production of term offspring from in vitro-fertilized ova.

Almost 30 years after the first successful in vitro fertilization (IVF) in golden hamsters (Mesocricetus auratus), we report that IVF hamster embryos can develop in a chemically defined, protein-free culture medium into morulae and blastocysts, and produce normal offspring after transfer to recipients. When examined 96 h post-insemination, 82% (160/200) of IVF ova had cleaved to at least 2 cells, 55% (97/200) had developed beyond the 4-cell stage, and 22% (38/200) had developed into morulae/blastocysts. In vitro development of IVF embryos to greater than or equal to 8 cells was absolutely dependent on hypotaurine. Twenty living offspring were produced from transfer of IVF embryos to recipients, with an overall success rate of 5% and 17% for oviductal (2-cell) and uterine (8-cell/morulae) transfers, respectively. In vivo-fertilized pronucleate embryos collected 3 h after egg activation were less able to develop in vitro than embryos collected only 6 h later, revealing a critical influence of the oviduct within the first hours of embryo development. Hypotaurine partly compensated for the decreased oviductal exposure of early 1-cell embryos. Establishment of a key role for hypotaurine in hamster embryo development, support of IVF embryos to morula/blastocyst stages in vitro, and production of living offspring after IVF embryo transfer are significant steps towards the goal of obtaining comparative data on preimplantation embryogenesis.     

Intracellular redox imbalance and extracellular amino acid metabolic abnormality contribute to arsenic‐induced developmental retardation in mouse preimplantation embryos

Inorganic arsenic, an environmental contaminant, is known to cause cancer, developmental retardation, and many other serious diseases. Previous researches have shown that arsenic exerts its toxicity partially through generating reactive oxygen species (ROS). However, it is still not well understood how ROS links arsenic exposure to developmental retardation of preimplantation embryo. Here we demonstrate that high‐level arsenite induces severe redox imbalance by decreasing the levels of glutathione and increasing the levels of ROS through the oxidative stress adaptor p66Shc, which induces apoptosis by activating the cytochrome c‐caspase. In addition, low‐level arsenite seriously perturbs the metabolism of extracellular amino acid, especially that of the cytotoxic and antioxidative amino acids in preimplantation embryos, may also be the reason for developmental delay. Furthermore, An antioxidant, N‐acetyl‐L ‐cysteine, improves the development of arsenite‐exposed embryos by reducing intracellular ROS and adjusting amino acid metabolism, suggesting that increasing the intracellular antioxidant level may have preventive or therapeutic effects on arsenic‐induced embryonic toxicity. In conclusion, we suggest that p66Shc‐linked redox imbalance and abnormal extracellular amino acid metabolism mediate arsenite‐induced embryonic retardation. J. Cell. Physiol. 222: 444–455, 2010. © 2009 Wiley‐Liss, Inc.     

Insulin and branched-chain amino acid depletion during mouse preimplantation embryo culture programmes body weight gain and raised blood pressure during early postnatal life

Mouse maternal low protein diet exclusively during preimplantation development (Emb-LPD) is sufficient to programme altered growth and cardiovascular dysfunction in offspring. Here, we use an in vitro model comprising preimplantation culture in medium depleted in insulin and branched-chain amino acids (BCAA), two proposed embryo programming inductive factors from Emb-LPD studies, to examine the consequences for blastocyst organisation and, after embryo transfer (ET), postnatal disease origin. Two-cell embryos were cultured to blastocyst stage in defined KSOM medium supplemented with four combinations of insulin and BCAA concentrations. Control medium contained serum insulin and uterine luminal fluid amino acid concentrations (including BCAA) found in control mothers from the maternal diet model (N-insulin + N-bcaa). Experimental medium (three groups) contained 50% reduction in insulin and/or BCAA (L-insulin + N-bcaa, N-insulin + L-bcaa, and L-insulin + N-bcaa). Lineage-specific cell numbers of resultant blastocysts were not affected by treatment. Following ET, a combined depletion of insulin and BCAA during embryo culture induced a non sex-specific increase in birth weight and weight gain during early postnatal life. Furthermore, male offspring displayed relative hypertension and female offspring reduced heart/body weight, both characteristics of Emb-LPD offspring. Combined depletion of metabolites also resulted in a strong positive correlation between body weight and glucose metabolism that was absent in the control group. Our results support the notion that composition of preimplantation culture medium can programme development and associate with disease origin affecting postnatal growth and cardiovascular phenotypes and implicate two important nutritional mediators in the inductive mechanism. Our data also have implications for human assisted reproductive treatment (ART) practice.     

Adaptive responses by mouse early embryos to maternal diet protect fetal growth but predispose to adult onset disease

Poor maternal nutrition during pregnancy can alter postnatal phenotype and increase susceptibility to adult cardiovascular and metabolic diseases. However, underlying mechanisms are largely unknown. Here, we show that maternal low protein diet (LPD), fed exclusively during mouse preimplantation development, leads to offspring with increased weight from birth, sustained hypertension, and abnormal anxiety-related behavior, especially in females. These adverse outcomes were interrelated with increased perinatal weight being predictive of later adult overweight and hypertension. Embryo transfer experiments revealed that the increase in perinatal weight was induced within blastocysts responding to preimplantation LPD, independent of subsequent maternal environment during later pregnancy. We further identified the embryo-derived visceral yolk sac endoderm (VYSE) as one mediator of this response. VYSE contributes to fetal growth through endocytosis of maternal proteins, mainly via the multiligand megalin (LRP2) receptor and supply of liberated amino acids. Thus, LPD maintained throughout gestation stimulated VYSE nutrient transport capacity and megalin expression in late pregnancy, with enhanced megalin expression evident even when LPD was limited to the preimplantation period. Our results demonstrate that in a nutrient-restricted environment, the preimplantation embryo activates physiological mechanisms of developmental plasticity to stablize conceptus growth and enhance postnatal fitness. However, activation of such responses may also lead to adult excess growth and cardiovascular and behavioral diseases.     

Inhibition of hsp70–1 and hsp70–3 expression disrupts preimplantation embryogenesis and heightens embryo sensitivity to arsenic

Mouse 70-kDa heat shock proteins Hsp70–1 and Hsp70–3 (Hsp70–1/3) are stress-inducible protein chaperones thought to protect embryonic cells and tissues from the effects of a wide range of environmental exposures. Hsp70–1/3 are expressed constitutively, and at times are stress-inducible during various stages of preimplantation embryogenesis. In order to elucidate the functions of constitutive and stress-inducible Hsp70 expression in mouse preimplantation embryos, the consequences of inhibiting expression with antisense oligonucleotides complementary to the mRNAs of hsp70–1 and hsp70–3 (AO70–1/3) were evaluated. Transfection of preimplantation embryos (four-cell stage) with 2.5 μM AO70–1/3 had no effect on in vitro blastocoel formation. However, transfection with 5 or 10 μM AO70–1/3 reduced in vitro blastocyst development to 30% and 0%, respectively (approximately 90% control embryos developed to blastocyst). Thus constitutive expression of Hsp70–1/3 appears significant to preimplantation embryogenesis. Limiting expression of Hsp70–1/3 with 5 μM AO70–1/3 also heightened embryo sensitivity to arsenic, resulting in less than 5% in vitro development to blastocyst in the presence of the subtoxic dose of 0.4 μM sodium arsenite. Whether the combined effect of AO70–1/3 and arsenic is due to blocking inducible expression of the Hsp70s, or due to further reducing the amount of constitutively expressed Hsp70s available to the embryo is not known at this time. However, these results clearly indicate that some minimal amount of Hsp70–1 and/or Hsp70–3 is required for preimplantation embryogenesis, and that increasing the demand for Hsp70s by arsenic exposure heightens this requirement. Mol. Reprod. Dev. 51:373–380, 1998. © 1998 Wiley-Liss, Inc.     

TGFalpha and EGFR in ovine preimplantation embryos and effects on development

The present study aimed to assess location and relative amounts of transforming growth factor alpha (TGFalpha) and its receptor (EGFR) in ovine oocytes and preimplantation embryos by using immunohistochemical technique that was graded on a relative scale of 0-3, with 0 representing absence of staining, and 3 exhibiting prominent staining, and to evaluate the effects of TGFalpha/EGF on in vitro development of preimplantation embryos by adding different concentrations of EGF and TGFalpha to culture medium. The results showed that EGFR was abundant in cell plasma membranes in immature and mature oocytes, cumulus cells of immature cumulus-oocyte complexes (COC), fertilized oocytes and at different stages of embryo development. However, the relative amounts in inner cell mass (ICM) (1+) was less than that in trophectoderm (TE) cells (2+) at the blastocysts stage. The staining pattern for TGFalpha was a similar to EGFR. However, the staining for TGFalpha slightly increased in the fertilized oocytes (1-2+) as compared to immature and mature oocytes (1+). TGFalpha was mainly detected in the cytoplasm close to the membrane in both ICM and trophectoderm (TE) cells. The developmental rate of 8-cell stage embryos cultured with 5 ng/ml TGFalpha was increased as compared to other treatments (P<0.05). There was no significant difference in the rate of development of blastocysts cultured with 5 ng/ml TGFalpha, 20 ng/ml EGF, 20 ng/ml EGF+5 ng/ml TGFalpha or the control treatment (P>0.05). In addition, there was no significant difference in the number of cells in blastocyst stage as compared with different treatments (P>0.05). However, TGFalpha alone enhanced cell survival rated (P<0.01) and reduced apoptosis. We concluded that TGFalpha can improve development of ovine preimplantation embryos at the 8-cell and blastocyst stages in vitro.     

Protein kinase Akt2/PKBβ is involved in blastomere proliferation of preimplantation mouse embryos

Activation of Akt/Protein Kinase B (PKB) by phosphatidylinositol-3-kinase (PI3K) controls several cellular functions largely studied in mammalian cells, including preimplantation embryos. We previously showed that early mouse embryos inherit active Akt from oocytes and that the intracellular localization of this enzyme at the two-cell stage depends on the T-cell leukemia/lymphoma 1 oncogenic protein, Tcl1. We have now investigated whether Akt isoforms, namely Akt1, Akt2 and Akt3, exert a specific role in blastomere proliferation during preimplantation embryo development. We show that, in contrast to other Akt family members, Akt2 enters male and female pronuclei of mouse preimplantation embryos at the late one-cell stage and thereafter maintains a nuclear localization during later embryo cleavage stages. Depleting one-cell embryos of single Akt family members by microinjecting Akt isoform-specific antibodies into wild-type zygotes, we observed that: (a) Akt2 is necessary for normal embryo progression through cleavage stages; and (b) the specific nuclear targeting of Akt2 in two-cell embryos depends on Tcl1. Our results indicate that preimplantation mouse embryos have a peculiar regulation of blastomere proliferation based on the activity of the Akt/PKB family member Akt2, which is mediated by the oncogenic protein Tcl1. Both Akt2 and Tcl1 are essential for early blastomere proliferation and embryo development.