PDF(Pubmed)
Abstract：
Development of the mammalian oocyte requires physical contact with the surrounding granulosa cells of the follicle, which provide it with essential nutrients and regulatory signals. This contact is achieved through specialized filopodia, termed transzonal projections (TZPs), that extend from the granulosa cells to the oocyte surface. Transforming growth factor (TGFβ) family ligands produced by the oocyte increase the number of TZPs, but how they do so is unknown. Using an inducible Cre recombinase strategy together with expression of green fluorescent protein to verify Cre activity in individual cells, we examined the effect of depleting the canonical TGFβ mediator, SMAD4, in mouse granulosa cells. We observed a 20-50% decrease in the total number of TZPs in SMAD4-depleted granulosa cell-oocyte complexes, and a 50% decrease in the number of newly generated TZPs when the granulosa cells were reaggregated with wild-type oocytes. Three-dimensional image analysis revealed that TZPs of SMAD4-depleted cells were longer than controls and more frequently oriented towards the oocyte. Strikingly, the transmembrane proteins, N-cadherin and Notch2, were reduced by 50% in SMAD4-depleted cells. SMAD4 may thus modulate a network of cell adhesion proteins that stabilize the attachment of TZPs to the oocyte, thereby amplifying signalling between the two cell types.
摘要：
哺乳动物卵母细胞的发育需要与卵泡周围的颗粒细胞物理接触，为它提供必需的营养和调节信号。这种联系是通过专门的足印实现的，称为跨区域投影(TZP)，从颗粒细胞延伸到卵母细胞表面。卵母细胞产生的转化生长因子（TGFβ）家族配体增加了TZP的数量，但他们是如何做到的还不得而知。使用诱导型Cre重组酶策略以及绿色荧光蛋白的表达来验证Cre在单个细胞中的活性，我们检查了消耗典型TGFβ介体的效果，SMAD4，在小鼠颗粒细胞中。我们观察到SMAD4耗尽的颗粒细胞-卵母细胞复合物中TZP的总数减少了20-50％，当颗粒细胞与野生型卵母细胞重新聚集时，新产生的TZP的数量减少了50％。三维图像分析显示，SMAD4耗尽细胞的TZP比对照更长，并且更频繁地朝向卵母细胞。引人注目的是，跨膜蛋白，N-cadherin和Notch2在SMAD4耗尽的细胞中减少了50%。因此，SMAD4可能会调节细胞粘附蛋白网络，从而稳定TZP与卵母细胞的附着，从而放大两种细胞类型之间的信号传导。
