Kosinski Mary, McDonald Kent, Schwartz Joel, Yamamoto Ikuko, Greenstein David
Department of Cell and Developmental Biology, Vanderbilt University School of Medicine, 465 21st Avenue South, Nashville, TN 37232, USA.
Development. 2005 Aug;132(15):3357-69. doi: 10.1242/dev.01916. Epub 2005 Jun 23.
The major sperm protein (MSP) is the central cytoskeletal element required for actin-independent motility of nematode spermatozoa. MSP has a dual role in Caenorhabditis elegans reproduction, functioning as a hormone for both oocyte meiotic maturation and ovarian muscle contraction. The identification of the signaling function of MSP raised the question, how do spermatozoa, which are devoid of ribosomes, ER and Golgi, release a cytoplasmic protein lacking a signal sequence? Here, we provide evidence that MSP export occurs by the budding of novel vesicles that have both inner and outer membranes with MSP sandwiched in between. MSP vesicles are apparently labile structures that generate long-range MSP gradients for signaling at the oocyte cell surface. Both spermatozoa and non-motile spermatids bud MSP vesicles, but their stability and signaling properties differ. Budding protrusions from the cell body contain MSP, but not the MSD proteins, which counteract MSP filament assembly. We propose that MSP generates the protrusive force for its own vesicular export.
主要精子蛋白（MSP）是线虫精子肌动蛋白非依赖性运动所需的核心细胞骨架成分。MSP在秀丽隐杆线虫的繁殖中具有双重作用，作为卵母细胞减数分裂成熟和卵巢肌肉收缩的激素发挥作用。MSP信号功能的确定引发了一个问题，即没有核糖体、内质网和高尔基体的精子如何释放一种缺乏信号序列的细胞质蛋白？在这里，我们提供证据表明，MSP通过新型囊泡的出芽进行输出，这些囊泡具有内膜和外膜，MSP夹在两者之间。MSP囊泡显然是不稳定的结构，它们产生长距离的MSP梯度以在卵母细胞表面进行信号传递。精子和不活动的精子细胞都会产生MSP囊泡，但它们的稳定性和信号特性有所不同。从细胞体伸出的芽状突起含有MSP，但不含有抑制MSP细丝组装的MSD蛋白。我们提出，MSP为其自身囊泡输出产生突出力。
