Stickler Eva, Avella Matteo
Department of Biological Science, University of Tulsa, Tulsa, Oklahoma, USA.
Research Branch, Sidra Medicine, Doha, Qatar.
J Transl Med. 2024 Dec 20;22(1):1134. doi: 10.1186/s12967-024-05948-4.
The mechanisms enabling sperm to locate unfertilized eggs within the fallopian tubes remain a subject of debate in reproductive biology. Previous studies using polytocous mammals observed a 1:1 sperm-egg ratio within the ampulla at the time of fertilization. From these observations, it is hypothesized that this mechanism could be linked to sperm-egg fusion, such that unfertilized eggs may attract sperm until fusion occurs, whereupon the attraction ceases.
To test this, fertile male mice were mated with infertile homozygous Cd9 females, whose eggs cannot fuse with sperm, leading to the accumulation of supernumerary sperm in the perivitelline space. Fertile heterozygous Cd9 females, were used as controls.
The results revealed that both Cd9 and Cd9 females ovulated similar numbers of eggs (6.53 ± 0.61 vs. 5.50 ± 0.53 eggs/ampulla). The majority of eggs produced by Cd9 females were fertilized by one single sperm, without any additional sperm found bound to the zona or within the perivitelline space. In contrast, most of the eggs ovulated by Cd9 females either showed an accumulation of supernumerary sperm within in the perivitelline space or showed no sperm bound to the zona nor present within the perivitelline space.
These findings indicate that genetic ablation of Cd9 leads to an imbalance in the 1:1 sperm-egg ratio observed within the ampulla. This information may set the foundation for future studies with the aim to identify the specific mechanisms that sperm use to locate unfertilized eggs and whether they become ineffective when gamete fusion is prevented.
在生殖生物学领域，精子如何在输卵管内定位未受精卵子的机制仍是一个存在争议的话题。以往对多胎哺乳动物的研究发现，受精时壶腹部的精子与卵子比例为1:1。基于这些观察结果，推测这种机制可能与精卵融合有关，即未受精的卵子可能会吸引精子，直到融合发生，此时吸引力停止。
为了验证这一点，将可育雄性小鼠与不育的纯合Cd9雌性小鼠交配，后者的卵子无法与精子融合，导致卵周隙中出现多余精子的积累。可育的杂合Cd9雌性小鼠用作对照。
结果显示，Cd9和Cd9雌性小鼠排出的卵子数量相似（分别为6.53±0.61个/壶腹和5.50±0.53个/壶腹）。Cd9雌性小鼠产生的大多数卵子由单个精子受精，在透明带或卵周隙中未发现其他附着的精子。相比之下，Cd9雌性小鼠排出的大多数卵子要么在卵周隙中出现多余精子的积累，要么在透明带上未发现精子附着，卵周隙中也没有精子。
这些发现表明，Cd9基因缺失导致壶腹部观察到的1:1精卵比例失衡。这一信息可能为未来的研究奠定基础，旨在确定精子用于定位未受精卵子的具体机制，以及当配子融合被阻止时它们是否失效。
