哺乳动物精子发生中减数分裂的起始

生殖细胞的发生、增殖和分化是生命科学领域研究的重要课题之一. 生殖是所有动物赖以生存的基础,精子发生是完成繁殖所必须经历的过程,其最终目的是源源不断地产生单倍体精子.精子发生过程本身是一个复杂特殊的细胞增殖与分化过程,其中减数分裂是精子发生最重要的步骤,但关于减数分裂如何精确起始的分子机制仍知之甚少.已有报道发现,维甲酸（RA）调控Stra8可能是哺乳动物减数分裂起始的机制之一,Nanos2、Boule对RA-Stra8通路具有重要的调控作用. 本文对哺乳动物精子发生中减数分裂起始的相关研究进展进行综述.     

Constant expression of mouse calpastatin isoforms during differentiation in myoblast cell line, C2C12

C2C12 is a myoblast cell line which is used to studydifferentiation into multinucleated cells in vitro. Addition of calpain inhibitors, calpeptin orE-64d, to the culture medium prevented the myoblasticfusion of C2C12 cells. Immunoblot studies usingaffinity-purified antibody, revealed that the expressedlevels of mouse calpastatin remained unaltered duringC2C12 cell fusion. The detected calpastatin migratedas a protein of 130 kDa on SDS-polyacrylamide gelelectrophoresis. The estimated molecular mass wassomewhat greater than that in mouse liver anderythrocytes, and much greater than that reported inrat myoblasts. The 130 kDa isoform may contain anadditional N-terminal region designated XL domainfound in bovine calpastatin.     

Sexual development of mouse germ cells: Nanos2 promotes the male germ cell fate by suppressing the female pathway

Much research has been conducted in recent years to elucidate the mechanisms underlying the crucial developmental process of sex determination. It has now been shown that somatic sex is principally determined by the chromosomal sex and the molecular mechanisms involved in this process have become relatively well understood in both human and mouse. However, the pathways involved in the sex determination of the germ cells remain largely unknown except for the fact that the somatic cues surrounding these cells play a significant role. Moreover, which sexual pathway of the germ cells is induced or suppressed has long been a subject of some dispute. Recent findings indicate that the key molecule that influences this choice is retinoic acid. In addition, the Nanos protein has been shown to play a critical role in promoting male germ cell differentiation. In this review, the possible mechanisms underlying these events, which have been brought to light by recent findings, are summarized to provide a better and more precise understanding of our current knowledge of the sex determination and subsequent differentiation of germ cells.     

Regeneration of the gut requires retinoic acid in the budding ascidian Polyandrocarpa misakiensis

The protochordate ascidian Polyandrocarpa misakiensis has a striking ability to regenerate. When the posterior half of the adult body is amputated, the anterior half completely loses the esophagus, stomach and intestine. These organs are reconstituted in a week. Histological observation revealed that the regeneration involves transdifferentiation of the atrial epithelium near the cut surface. The morphological features of the gut primordium were similar to those observed in the developing bud of this species. Inhibitors of the synthesis of retinoic acid (RA) suppressed the formation of the gut. 13‐cis RA rescued the regenerates from the inhibitor‐induced hypoplasia. These results suggest that RA is required for the regeneration of the gut. A gene encoding the RA receptor (Pm‐RAR) and its target gene, TRAMP, were expressed in and around the regenerating gut. Pm‐RAR‐specific and TRAMP‐specific double‐stranded RNA molecules inhibited the regeneration of the gut, indicating that the RA signal is mediated at least in part by Pm‐RAR and TRAMP. These results suggested that RA triggers the transdifferentiation of the atrial epithelium into the gut in regenerating animals, as it does during asexual reproduction.     

C2C12成肌细胞诱导肌性分化过程中miR-101a的表达

以C2C12成肌细胞为模型,在分化培养基中诱导C2C12建立体外肌性细胞分化模型.以poly (A)3′-端加尾和实时定量PCR方法研究miR-101a在C2C12细胞分化过程中的表达情况.结果发现,在细胞转入分化培养基进行肌性分化的1-5 d中,miR-101a的表达量逐渐增加,提示miR-101a可能在肌肉发生中发挥调控作用.     

AdipoRon对小鼠骨骼肌细胞胰岛素敏感性的影响及其机制

目的：观察脂联素受体激动剂AdipoRon对小鼠成肌细胞株（C2C12）胰岛素敏感性的影响,并探讨其作用机制。方法：使用马血清将C2C12诱导分化为成肌细胞,分为6组（9个复孔）：空白对照组、AdipoRon （脂联素受体激动剂）高剂量组、AdipoRon低剂量组、胰岛素组以及AdipoRon低剂量+PI3K （磷脂酰肌醇3激酶）抑制剂组和胰岛素+PI3K抑制剂组,作用12 h,收集上清检测葡萄糖消耗量,使用CCK8测定细胞增殖。六孔板中将C2C12诱导分化为肌管细胞,加入药物作用12 h,并用RT-PCR法检测GLUT4的mRNA水平。结果：与空白对照组相比,AdipoRon高剂量组、AdipoRon低剂量组、胰岛素组耗糖量均有所增加,具有统计学意义（P<0.05）。加入PI3K抑制剂组后,耗糖量与空白对照组无统计学意义。与空白对照组相比,AdipoRon高剂量组、AdipoRon低剂量组、胰岛素组细胞均有增殖,但只有胰岛素组具有统计学意义（P<0.05）。与对照空白组相比,AdipoRon高剂量组、AdipoRon低剂量组、胰岛素组GLUT4mRNA水平均有所提高,具有统计学意义（P<0.05）。加入PI3K抑制剂组后,GLUT4mRNA水平与空白对照组无统计学意义。结论：AdipoRon能够不影响细胞增殖的情况下增加葡萄糖的消耗量,这可能是通过提高胰岛素敏感性发挥作用的,但具体机制尚待进一步的研究。     

Teratocarcinoma F9 cells induced to differentiate with sodium butyrate produce both tissue-type and urokinase-type plasminogen activators.

Sodium butyrate (NaB) can induce teratocarcinoma cell differentiation as retinoic acid (RA). However, the function of these two agents seems to be a little different [Kosaka et al., Exp Cell Res, 192:46-51, 1991]. F9 cells treated with NaB synthesize both tissue-type (tPA) and urokinase-type (uPA) plasminogen activator, though RA induces only tPA production. Urokinase-type PA is demonstrated to exist in association with membrane and to localize its activity to the close environment of the cell surface. This may cause the specific cell morphology and characteristics of differentiated F9 cells induced with NaB.     

MiR-34c在奶山羊雄性生殖干细胞增殖分化过程中的作用

microRNA (miRNA)在奶山羊雄性生殖细胞和精子发生过程有重要的调控功能。为研究miR-34c对雄性生殖干细胞增殖与分化中的作用,本文利用视黄酸效应基因8（Stra8）在雄性生殖细胞中随年龄增长,以其表达量上调的表达特征为指针,使用实时定量PCR技术筛选分析miRNAs。结果发现,miR-34c与Stra8的表达规律基本一致。在无精症奶山羊的睾丸组织中,发现miR-34c在无精症奶山羊睾丸组织中表达缺失。利用miR-34c模拟物及抑制剂转染奶山羊雄性生殖干细胞,体外转染miR-34c模拟物及其抑制剂,发现miR-34c能够下调Rarg、Stra8与c-Myc基因的表达,减缓奶山羊雄性生殖干细胞的增殖。结果提示,miR-34c可能具有调控奶山羊雄性生殖干细胞的减数分裂的作用,同时抑制其增殖。     

干扰Sema7A抑制C2C12成肌细胞的增殖和分化

为研究脑信号蛋白家族（Semaphorins）成员Sema7A对成肌细胞增殖和分化的影响,本文设计并合成了Sema7A基因的小干扰RNA（small interfering RNA,siRNA）,用此siRNA转染C2C12成肌细胞．通过Hoechst核染和流式细胞术检测细胞增殖情况,免疫荧光检测肌管的形成情况,real-time qPCR和Western印迹技术检测成肌标记基因的变化.结果显示,干扰Sema7A后,C2C12成肌细胞增殖减慢,处在G2和S期的细胞所占的比例明显下降,而G1期细胞的比例升高．免疫荧光检测结果显示,干扰Sema7A后,肌管的直径及MyHC+细胞所占比例均显著降低．Real-time qPCR和Western印迹结果也显示,肌肉分化标志基因MyoD、MyoG、MyHC的mRNA及蛋白质表达均下降．进一步检测Sema7A受体下游信号通路发现,干扰Sema7A后,其下游信号分子PI3K和AKT的磷酸化水平被下调．以上结果表明,Sema7A可以调节C2C12成肌细胞的增殖和分化,可能是通过其受体作用于PI3K/AKT信号通路实现的,这为进一步研究Sema7A在骨骼肌发育中的作用提供实验基础.