RAPID AND SLOW MECHANISMS FOR LOSS OF CELL ADHESIVENESS DURING FERTILIZATION IN CHLAMYDOMONAS
RAPID AND SLOW MECHANISMS FOR LOSS OF CELL ADHESIVENESS DURING FERTILIZATION IN CHLAMYDOMONAS
复制标题
DOI：
10.1016/s0012-1606(05)80019-3
复制
发表时间：
1991-09-01
影响因子：
2.7
通讯作者：
SNELL, WJ
中科院分区：
文献类型：
--
作者：
HUNNICUTT, GR;SNELL, WJ
虽然双鞭毛藻的营养细胞、配子和受精卵都有鞭毛，但只有mt+和mt −配子的鞭毛是粘附的。引起线粒体凝集的分子mt+和mt −凝集素是长杆状的糖蛋白，位于鞭毛膜上。这些鞭毛凝集素在受精的早期事件中用作粘附和信号分子，在粘附过程中从鞭毛中丢失。然而，鞭毛凝集素可以通过从细胞体的质膜募集和激活预先存在的无活性凝集素来维持（Hunnicuttet al.，111，1605-1616），除非相反交配类型的配子融合形成合子。在细胞融合时，鞭毛细胞丧失。在这里介绍的研究中，我们采用了一种体外生物测定法来测量在配子发生过程中，在受精过程中，和受精卵形成后的细胞体和鞭毛中的凝集素。利用生物测定法，可以检测出在体内功能上无活性的凝集素，我们发现营养细胞缺乏凝集素。这些粘附分子仅在配子发生后出现，首先出现细胞体凝集素，然后是鞭毛凝集素。令人惊讶的是，受精卵形成后30分钟，当受精卵的鞭毛不再粘附时，用生物测定法可检测到的鞭毛凝集素活性仍然很高。对这些结果的一种解释是，受精卵继续从细胞体向鞭毛募集凝集素，但细胞融合废除了凝集素的激活。在融合后45-90分钟内，细胞体和鞭毛凝集素都丢失，并且可以在培养基中检测到。这些机制使受精卵与其他受精卵和未交配的配子不粘连，从而导致衣原体相当于多精受精的障碍。
Although vegetative cells, gametes, and zygotes of the biflagellated algaChlamydomonasbear flagella, only the flagella ofmt+andmt−gametes are adhesive. The molecules responsible for adhesiveness,mt+andmt−agglutinins, are long rod-shaped glycoproteins displayed on the flagellar membrane. These flagellar agglutinins, which gametes use both as adhesion and signaling molecules during the early events of fertilization, are lost from the flagella during adhesion. Flagellar adhesiveness can be maintained, however, by recruitment and activation of preexisting, inactive agglutinins from the plasma membrane of the cell body (Hunnicuttet al., 1990.J. Cell Biol.111, 1605–1616) unless the gametes of opposite mating types fuse to form zygotes. Upon cell fusion, flagellar adhesiveness is lost. In the studies presented here, we have employed anin vitrobioassay to measure agglutinins in both cell bodies and flagella at various times during gametogenesis, during fertilization, and after zygote formation. By use of the bioassay, which can detect agglutinins that are functionally inactivein vivo, we found that vegetative cells are devoid of agglutinins. These adhesion molecules appear only after gametogenesis is underway with the cell body agglutinins appearing first and then the flagellar agglutinins. Surprisingly, 30 min after zygote formation, when the zygotes' flagella are no longer adhesive, the flagellar agglutinin activity detectable with the bioassay remains high. One interpretation of these results is that zygotes continue to recruit agglutinins from the cell body to the flagella, but cell fusion abrogates activation of the agglutinins. Within 45–90 min after fusion both the cell body and flagellar agglutinins are lost and can be detected in the medium. These mechanisms, which render the zygotes nonadhesive to other zygotes and unmated gametes, contribute to theChlamydomonasequivalent of a block to polyspermy.