Kaune Heidy, Peyrache Emeline, Williams Suzannah A
Nuffield Department of Obstetrics and Gynaecology, Women's Centre, Level 3, John Radcliffe Hospital, University of Oxford, Oxford, UK; Faculty of Medicine, Diego Portales University, Santiago, Chile.
Nuffield Department of Obstetrics and Gynaecology, Women's Centre, Level 3, John Radcliffe Hospital, University of Oxford, Oxford, UK.
Theriogenology. 2015 Mar 15;83(5):897-903. doi: 10.1016/j.theriogenology.2014.11.024. Epub 2014 Dec 1.
The generation of a competent egg requires complex molecular interactions between the oocyte and the ovary, and transforming growth factor β (TGF-β) is a major signaling pathway. Smad4 is a central regulator of the TGF-β signaling pathway as it mediates gene expression triggered by activation of TGF-β receptors. Deletion of Smad4 in granulosa cells disrupts follicle development; however, the role of Smad4 in the oocyte has not been confirmed. Furthermore, the role of Smad4 in embryo development has not been confirmed because previous studies of Smad4(del/del) embryos were generated from heterozygous parents, and thus it is possible that maternal transcripts rescue development before embryonic day 6.5 (E6.5) when Smad4(del/del) embryos die. To determine the role of TGF-β signaling in oocyte and embryo development, mice with oocyte-specific deletion of Smad4 were studied. Fertility was evaluated in Mutant (Smad4(F/F):ZP3Cre) and CONTROL (Smad4(F/F)) females mated continuously with control males during a 6-month period. Surprisingly, Mutant females were fertile with the same litter size (Mutants, 9.23 ± 0.4; CONTROLs, 9.42 ± 0.4) and interlitter period as CONTROLs. Ovulation rate induced using a superovulation regime did not differ between CONTROLs and Mutants at both 6 weeks and 6 months. Embryo development was assessed at E6.5 using CONTROL and Mutant females mated with heterozygous males. Development of Smad4(del/del) embryos at E6.5 was retarded consistent with previous studies of embryos generated from heterozygous parents indicating that there is no rescue of preimplantation development by maternal transcripts. The numbers of implanted embryos at 6.5 dpc also did not differ (
9.1 ± 0.4; Mutant: 7.0 ± 0.9). However, only 26.3% of E6.5 embryos carried by Mutant females were Smad4(del/del) compared with the expected ratio of 50%. Since litter size was not decreased, this indicates that either the number of Smad4(del) sperm fertilizing the oocytes is reduced or implantation of Smad4(del/del) embryos is suboptimal. In summary, we have shown that Smad4 in the oocyte, and thus TGF-β signaling, is not required for oocyte or follicle development, ovulation, fertilization, preimplantation development, or implantation.
生成有功能的卵子需要卵母细胞与卵巢之间复杂的分子相互作用，而转化生长因子β（TGF-β）是主要的信号通路。Smad4是TGF-β信号通路的核心调节因子，因为它介导由TGF-β受体激活引发的基因表达。颗粒细胞中Smad4的缺失会破坏卵泡发育；然而，Smad4在卵母细胞中的作用尚未得到证实。此外，Smad4在胚胎发育中的作用也未得到证实，因为之前对Smad4（del/del）胚胎的研究是由杂合子亲本产生的，因此有可能在胚胎第6.5天（E6.5）之前，当Smad4（del/del）胚胎死亡时，母源转录本挽救了发育。为了确定TGF-β信号在卵母细胞和胚胎发育中的作用，研究了卵母细胞特异性缺失Smad4的小鼠。在6个月期间，将突变体（Smad4（F/F）：ZP3Cre）和对照（Smad4（F/F））雌性小鼠与对照雄性小鼠连续交配，评估其生育能力。令人惊讶的是，突变体雌性小鼠具有生育能力，产仔数（突变体为9.23±0.4；对照为9.42±0.4）和产仔间隔与对照相同。在6周和6个月时，使用超排卵方案诱导的排卵率在对照和突变体之间没有差异。在E6.5时，使用与杂合子雄性交配的对照和突变体雌性小鼠评估胚胎发育。E6.5时Smad4（del/del）胚胎的发育受到阻碍，这与之前对由杂合子亲本产生的胚胎的研究一致，表明母源转录本不能挽救植入前的发育。在6.5天胚龄时植入胚胎的数量也没有差异（对照：9.1±0.4；突变体：7.0±0.9）。然而，与预期比例50%相比，突变体雌性小鼠携带的E6.5胚胎中只有26.3%是Smad4（del/del）。由于产仔数没有减少，这表明要么使卵母细胞受精的Smad4（del）精子数量减少，要么Smad4（del/del）胚胎的植入不理想。总之，我们已经表明，卵母细胞中的Smad4，以及因此的TGF-β信号，对于卵母细胞或卵泡发育、排卵、受精、植入前发育或植入不是必需的。
