小白鼠精子成形過程中微管角色的探討

Abstract

本研究以超薄切片方法、 Osmium-DMSO-Osmium (O-D-O）冷凍斷裂以及體外組織培養等技術觀察正常小白鼠精細胞與經過秋水仙素處理後之精細胞間的差異。微管系統的破壞常會造成高基氏體瓦解成小囊泡狀，分泌小泡的釋出亦會受到影響；頂體冠在細胞核上的延展與核膜貼近速度不一致，且頂體常呈現不規則的形狀，甚至有多個精細胞共頂體的現象。至於細胞核的濃縮變形，雖然不論核周平行微管束（manchette ) 存在與否均會照常進行，但其形變多呈不規則狀。此外，細胞質橋常無法正常維持，因而易形成多核精細胞；內質網有排列成多層環狀構造的趨努；粒線體亦可能失去原有立體球狀構造而變為雙凹圓盤狀或不規則的形狀；核周平行微管束及外質特化（ectoplasmic specialization）的結構也會發生變異。因此，我們認為頂體的發育可能是由內質網及高基氏體提供原料，以形成外被小泡的分泌方式將內含物運送到頂體的特定區域，造成頂體的生長，整個過程中，微管除了可能與外被小泡的運送有關外，在頂體形狀的維持上亦扮演重要的角色。而細胞質橋的結構以及內質網、粒線體等胞器的立體形狀與彼此在空間上的位置均應與微管有關。另外，細胞核的形變過程則需要在染色質絲濃縮模式正常下，配合微管系統與賽氏細胞的協調作用，才能產生正確的形變。本研究同時利用 O-D-O 冷凍斷裂掃描式電子顯微鏡技術及立體顯像圖對觀察精細胞中各胞器之三度空間結構，發現高基氏體具有比出芽分泌更複雜的分泌模式，而粒線體則在精子尾部中片上以頭尾相接之方式纏繞成規則的單股左螺旋構造。

Thin-sectioning, Osmium-DMSO-Osmium (O-D-O) method and in vitro tissue culture have been applied in this study to compare the ultrastructural differences between normal and colchicine-treated mouse testis. Microtubule depolymerization in colchicine-treated spermatids resulted in both decomposition of Golgi apparatus and retardation of vesicle transportation. Discordance of spreading acrosome over the nucleus with the modified nuclear envelope as well as abnormality of the shape of acrosomal cap were frequently observed. Sometimes, numerous synacrosomes can also be seen. With regard to nuclear shaping, although it seemed disregard of the manchette existance, the shape changes of nuclei were always appeared abnormal while the microtubule system were affected by colchicine. Besides, many spermatids fused together to form a symplast due to the intercellular bridges disintegration. Endoplasmic reticulum tended to rearrange into multi-layered circular structure. Mitochondria may lose their normal spherical shape to become biconcave disk or irregular form. The structures of manchette and ectoplasmic specialization also appeared disordered. Accordingly, we suggest that acrosome formation is achieved by fusion of coated vesicles, which secreted from Golgi apparatus, at the particular region of acrosome. During this acrosome developmental process, microtubules may play important roles in transportation of coated vesicles and maintainance of acrosomal shape. Furthermore, the structure or spatial distribution of intercellular bridges, endoplasmic reticulum and mitochondria may all have some relation to microtubules. In addition, the correct structure of manchette and endoplasmic specialization as well as condensation of chromatin are basic requirements to insure normal shape change of nucleus during spermiogenesis. Three-dimensional organization of organelles in spermatids were also carefully examined by stereoscopy under scanning electron microscope. A different secretory pattern of Golgi apparatus and a single sinistral helix structure of mitochondrial sheath in the middle piece have been proposed in this study.