A DnaA-dependent riboswitch for transcription attenuation of the his operon

Transcription attenuation in response to the availability of a specific amino acid is believed to be controlled by alternative configurations of RNA secondary structures that lead to the arrest of translation or the release of the arrested ribosome from the leader mRNA molecule.In this study,we first report a possible example of the DnaA‐dependent riboswitch for transcription attenuation in Escherichia coli.We show that(i)DnaA regulates the transcription of the structural genes but not that of the leader hisL gene;(ii)DnaA might bind to rDnaA boxes present in the HisL‐SL RNA,and subsequently attenuate the transcription of the operon;(iii)the HisL‐SL RNA and rDnaA boxes are phylogenetically conserved and evolutionarily important;and(iv)the translating ribosome is required for deattenuation of the his operon,whereas tRNA^(His) strengthens attenuation.This mechanism seems to be phylogenetically conserved in Gram‐negative bacteria and evolutionarily important.

精子线粒体早老素相关菱形样蛋白及精子DNA碎片指数与体外受精-胚胎移植妊娠结局的相关性分析

目的观察行体外受精-胚胎移植的不孕夫妇中男性患者精子DNA碎片指数(DNA fragmentation index, DFI)和精子线粒体早老素相关菱形样蛋白(presenilin associated rhomboid like protein, PARL)水平变化,探讨其与体外受精-胚胎移植妊娠结局的关系。方法行体外受精-胚胎移植的不孕夫妇中男性患者140例,根据临床妊娠情况分为妊娠成功组57例和妊娠失败组83例。2组行体外受精-胚胎移植前,采用精子染色质扩散法检测精子DFI,采用ELISA法检测精子线粒体PARL水平,比较2组年龄、精子密度、精子活力、精子DFI、精子线粒体PARL水平及优质胚胎率等临床资料。以精子DFI、精子线粒体PARL水平的平均值25%、5.86μg/L为临界值,将140例患者分为高DFI组62例(DFI≥25%)和低DFI组78例(DFI<25%),高PARL组71例(PARL≥5.86μg/L)和低PARL组69例(PARL<5.86μg/L);比较高、低DFI、PARL组精子密度、精子活力、精子畸形率、优质胚胎率、种植率、卵裂率、受精率、临床妊娠率;采用Pearson或Spearman相关性分析精子线粒体PARL水平、精子DFI分别与精子密度、精子活力、优质胚胎率、临床妊娠率、精子畸形率的相关性;采用多因素logistic回归分析体外受精-胚胎移植妊娠失败的影响因素。结果妊娠成功组优质胚胎率(47.30%)、精子密度[(27.42±4.13)×10^(6)/mL]、精子活力[(51.84±13.02)%]、精子线粒体PARL水平[(13.54±2.01)μg/L]均高于妊娠失败组[31.82%、(22.09±3.26)×10^(6)/mL、(32.28±8.12)%、(4.51±1.07)μg/L](P<0.05),精子畸形率[(16.80±4.82)%]、精子DFI[(10.98±3.06)%]均低于妊娠失败组[(26.83±6.94)%、(30.46±6.18)%](P<0.05)。高DFI组优质胚胎率(30.00%)、临床妊娠率(30.65%)、精子密度[(20.14±4.36)×10^(6)/mL]、精子活力[(24.45±8.73)%]均低于低DFI组[46.89%、48.72%、(27.54±4.12)×10^(6)/mL、(52.81±13.04)%](P<0.05),精子畸形率[(30.12±7.93)%]高于低DFI组[(16.87±5.94)%](P<0.05);高PARL组优质胚胎率(47.96%)、临床妊娠率(53.52%)、精子密度[(27.25±4.12)×10^(6)/mL]、精子活力[(50.66±12.95)%]均高于低PARL组[28.68%、27.54%、(21.04±4.23)×10^(6)/mL、(24.76±8.87)%](P<0.05),精子畸形率[(16.72±5.63)%]低于低PARL组[(30.75±7.81)%](P<0.05);精子线粒体PARL与精子密度(r=0.507,P=0.007)、精子活力(r=0.514,P=0.009)、优质胚胎率(r=0.470,P<0.001)、临床妊娠率(r=0.564,P=0.002)均呈正相关,与精子畸形率呈负相关(r=-0.489,P=0.007);精子DFI与精子密度(r=-0.496,P=0.008)、精子活力(r=-0.503,P=0.006)、优质胚胎率(r=-0.520,P=0.006)、临床妊娠率(r=-0.483,P=0.031)呈均负相关,与精子畸形率呈正相关(r=0.512,P=0.004)。精子线粒体PARL(OR=0.842,95%CI:0.759~0.934,P=0.001)、精子DFI(OR=2.426,95%CI:1.334~4.411,P=0.004)是体外受精-胚胎移植后妊娠失败的影响因素。结论体外受精-胚胎移植妊娠失败的不孕夫妇中男性患者精子DFI升高、精子线粒体PARL水平降低,二者是体外受精-胚胎移植妊娠失败的影响因素。