以線蟲為模型探討肌動凝蛋白在雄性減數分裂的細胞膜動態以及染色體分離的角色

The role of actomyosin dynamics in membrane activities and chromosome segregation during male meiotic divisions in C. elegans

蕭孟生(Meng-Sheng Xiao)

指導教授 ： 吳瑞菁

國立臺灣大學/醫學院/醫學檢驗暨生物技術學研究所/碩士(2020年)

https://doi.org/10.6342/NTU202002566

摘要

在雄性生殖細胞的發展過程中，源自同一精母細胞發展出來的精細胞會在共享的細胞質中完成減數分裂。這個特殊分裂過程存在許多的物種當中，從線蟲、小鼠乃至人類都能夠發現類似模式。目前對於精子是如何調控細胞膜結構去維持細胞相連的機制仍不清楚。我們首先觀察線蟲的雄性減數分裂過程中肌動球蛋白所形成的動態結構。在第一次減數分裂末期，連接兩個次級精母細胞的細胞間橋有著很強的肌動蛋白以及肌球蛋白的信號。 接著在第二次減數分裂要開始的時候，肌動球蛋白的信號會集中聚集在兩個單套精細胞間形成假裂溝的位置。 在第二次減數分裂要結束的時候，兩次減數分裂所產生的細胞膜凹陷都會鬆開形成殘餘體，肌動球蛋白的信號會展開在殘餘體的成形的周圍，在四個正在產生的精細胞與殘餘體連接處可以看到較強的肌動球蛋白信號。 利用肌動蛋白抑制劑去影響肌動蛋白的功能，會發現兩次減數分裂都無法產生細胞膜的凹陷。 有趣的是在剛完成第一次分裂的精母細胞中，抑制肌動蛋白的功能會導致兩個次級精母細胞之間的膜完全分裂。 這些結果顯示出肌動蛋白能夠在雄性減數分裂的過程中支撐細胞間橋的結構。
在抑制肌動蛋白的實驗當中，我們還發現到染色體的分離也受到了肌動蛋白的影響。雖然在紡錘絲型態與染色體分離調控蛋白定位都沒有受到明顯地影響，兩次減數分裂染色體的分離速率卻明顯的降低，甚至染色體也會出現分離後合併的現象。
我們的研究結果顯示的雄性減數分裂過程中，肌動蛋白能夠在分離細胞質成分的同時，藉由維持細胞膜的結構讓精母細胞在減數分裂分裂期間保持合胞體的型態。 而肌動蛋白結構對於雄性減數分裂染色體的分離也相當重要。

關鍵字

肌動蛋白 ； 雄性減數分裂 ； 細胞裂溝 ； 細胞間橋 ； 染色體分離 ； 微管

並列摘要

In the male reproductive system, spermatids derived from the same spermatocyte share the cytoplasm pool before maturation. This unique process is conserved in most species from nematode to mammals. It is unclear how these syncytial morphologies are regulated. We examined the dynamics of actomyosin network during male meiotic divisions in C. elegans. At the end of meiosis I, two secondary spermatocytes remain connected through an intercellular bridge that is highly enriched with actin and myosin. Such structure is relaxed when the anaphase II begins, as the actomyosin enriches at the position between two haploid spermatids and forms pseudo-cleavage furrow. At the end of meiosis II, all the furrows generated in the two division events would be released, and strong actomyosin signal can be observed at the base of four growing spermatids. After the spermatids are budded off, the remaining cytoplasm is enclosed as the residual body. Inhibition of actin dynamics showed failure of the furrow ingression in both meiosis I and meiosis II spermatocytes. Interestingly, in spermatocytes that have just complete first division, inhibition of actin dynamics causes bisection of the membrane between the two secondary spermatocytes. These results suggest actin maintains the structure of intracellular bridge during male meiotic divisions. Additionally, we found inhibition of actin dynamics perturbed chromosome segregation during male meiotic divisions. Although spindle morphology and key chromosome segregation regulators were properly localized, inhibition of membrane activities causes significantly reduced chromosome segregation rate in both division events, and separating chromosomes tend to collapse back. Taken together, our data reveal that actin plays crucial roles in maintaining membrane structure for separating cytoplasmic components and yet remain syncytium during male meiotic divisions. Such structures are important for proper segregation of chromosomes during the two separation events.

並列關鍵字

actin ； male meiotic division ； cleavage furrow ； intercellular bridge ； chromosome segregation ； microtubule

參考文獻

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