家蚕微孢子虫CQ1分离株侵染家蚕的组织病理学观察

Histopathological Observation of Silkworm Infected by Nosema bombycis CQ1 Isolate

运用扫描电子显微镜以及组织切片、超薄切片结合透射电子显微镜观察家蚕微孢子虫CQ1分离株感染家蚕后的增殖与蚕体重要组织的病理变化,为利用CQ1分离株开展家蚕微孢子虫在宿主体内增殖和传播的分子机制研究提供较为详细的病理学依据。用扫描电子显微镜观察发现家蚕微孢子虫CQ1分离株添食侵染3龄起蚕后6 d,可在幼虫中肠中观察到增殖的孢子,并且发现孢子从围食膜穿出进入肠腔后留下的痕迹;感染后7 d发现中肠破损细胞内充满孢子;感染后8 d观察到中肠内有发芽的孢子空壳存在,说明从中肠释放出的孢子进入肠腔后,会部分发芽造成中肠再次感染。病理切片和超薄切片观察表明,3龄起蚕添食感染CQ1分离株孢子液后9 d,在中肠、脂肪体、丝腺的组织细胞内都存在大量的孢子,被感染的组织细胞肿大,同一细胞内充满不同发育时期的孢子,其裂殖体体积大于孢子体,大部分孢子在细胞内游离存在,脂肪体、丝腺的病理切片中无寄生泡结构;但在中肠组织切片以及脂肪体超薄切片中,发现有疑似寄生泡结构,特别是在透射电子显微镜下观察到感染的脂肪体细胞中这种疑似寄生泡结构呈椭圆形,大小为17μm×12μm,膜的结构清晰可辨,并可观察到泡内有10余个孢子。无寄生泡是微粒子属(Nosema)的主要特征之一,所以观察到的这种类似寄生泡的结构还需要进一步确证。

In order to provide detailed pathological basis for studies on molecular mechanism of reproduction and transmission of Nosema bombycis in host silkworm(Bombyx mori) cells,here we adopted scanning electron microscopy(SEM),histological sectioning and ultrathin sectioning in combination with transmission electron microscopy(TEM) to observe the spore reproduction and the pathological changes in major tissues of silkworm infected by Nosema bombycis CQ1 isolate.Through scanning electron microscopic observation,we found progeny spores in midgut of the newly exuviated silkworm larvae of the 3rd instar at 6 d after infection by spores of Nosema bombycis CQ1 isolate.Notably,we discovered the pores on peritrophic membrane,which were left by microsporidian spores penetrating from the midgut cells into the coelenteron of midgut.At 7 d after infection,the ruptured midgut cells were filled by microsporidian spores.At 8 d after infection,the empty shells of germinated spores were seen in midgut,indicating that,after entering coelenteron,some of the microsporidian spores released from midgut into coelenterons had germinated and re-infected the midgut.Observation to histological slices and ultrathin sections showed that,at 9 d after infection,there were a lot of spores in the cells of midgut,fat body and silk gland.The infected tissues and cells swelled,and there were spores at different developmental stages in the same cell.The size of schizonts was bigger than that of the sporeblasts.Most of the spores were free in cytoplasm.No parasitophorous vacuole was observed in histological slices of fat body and silk gland.However,parasitophorous vacuole-like structures were observed in the histological slices of midgut and ultra-thin sections of fat body.Especially,under transmission electron microscope,the parasitophorous vacuole-like structure was oval shaped in the infected fat body cells.It was 17 μm×12 μm in size and had clear membrane structure inside which more than a dozen of spores were visible.One of the major characteristics of genus Nosema is without parasitophorous vacuole,so the parasitophorous vacuole-like structure observed in present study needs to be further verified.