胰岛素样生长因子2基因印迹状态及其启动子活性在巨大儿胎盘组织中的变化

Insulinllike growth factor 2 imprinting status and promoter usage in the placenta of macrosomia

目的通过检测巨大儿的胎盘组织中胰岛素样生长因子2(IGF_2)基因印迹状态及其mRNA 表达水平和不同启动子活性,探讨巨大儿的发生机理。方法根据 IGF_2基因第9外显子Apa Ⅰ酶切位点多态性,应用 RT-PCR 结合限制性片段长度多态性技术,对83例分娩巨大儿产妇的胎盘组织(巨大儿组)和同期分娩正常体重儿的85例产妇的胎盘组织(正常体重儿组)进行杂合子筛选,对筛选出的杂合子进行 IGF_2基因印迹状态分析,用 RT-PCR 半定量检测两组胎盘组织 IGF_2mRNA 表达水平及不同启动子的活性。结果两组胎盘组织中各有30例杂合子。在这些杂合子中,IGF_2基因均为单等位基因表达,呈维持印迹状态。巨大儿组胎盘组织中 IGF_2 mRNA 表达水平为2.2±1.2,明显高于正常体重儿组的1.6±0.6,两组比较,差异有统计学意义(P<0.05);IGF_2 4个启动子(P1、P2、P3、P4)在两组胎盘组织中均表现为:P4活性最强,P3次之,P2较弱,P1最弱,仅在两例(巨大儿组和正常体重儿组各1例)中检测到 P1起始的转录本;两组胎盘组织 IGF_2不同启动子活性检测分别为:正常体重儿组P2:0.19±0.17、P3:0.98±0.80、P4:2.05±1.27;巨大儿组P2:0.20±0.20、P3:0.99±0.72、P4:2.06±1.26,两组分别比较,差异均无统计学意义(P>0.05)。结论胎盘组织中 IGF_2 mRNA 表达水平的增加可能与巨大儿的形成有关,而 IGF_2基因印迹状态和启动子活性与巨大儿的形成无明显关系。

Objective To study the mechanism of marcosomia by investigating insulin-like growth factor 2 （ IGF2 ） imprinting status, expression level and the promoter usage in the placenta of macrosomia, Methods We selected heterozygous cases for Apa Ⅰ polymorphism in exon 9 of IGF2 gene and then analyzed its imprinting status in 168 placentas of macrosomia and normal pregnancies. IGF2 transcription levels and promoter usages in macrosomic and normal placenta were evaluated by using semi-quantitative RT-PCR assay. Results Thirty specimens of maerosomic placenta and 30 of normal placenta were identified as heterozygnus for IGF2. All of the heterozygous specimens showed maintenance of imprinting. The expression of placental IGF2 mRNA（2.2 ± 1.2）was significantly higher in macrosomia than that of normal weight group （1.6 ± 0. 6 ,P 〈 0. 05 ）. Of four promoters, P4 was the most powerful, P3 was the second, and P2 was weakest. Transcripts from P1 were the fewest, and they were only detected in two specimens. The value of P4 was 2.06 ± 1.26, P3 0. 99 ± 0. 72, P2 0. 20 ± 0. 20 in macrosomia group and P4 2.05 ± 1.27, P3 0. 98 ±0. 80, P2 0. 19±0. 17 in normal group. There were no significant differences between two groups （P 〉 0. 05 ）. Conclusion It is possible that over expression of IGF2 in placenta contributes to macrosomia while the promoter usage and imprinting status are not associated with maerosomia.