Meiotic catastrophe and retrotransposon reactivation in male germ cells lacking Dnmt3L

Mammalian genomes employ heritable cytosine methylation in the long-term silencing of retrotransposons and genes subject to genomic imprinting and X chromosome inactivation. Little is known of the mechanisms that direct cytosine methylation to specific sequences. Here we show that DNA methyltransferase 3-like (Dnmt3L (ref. 1)) is expressed in testes during a brief perinatal period in the non-dividing precursors of spermatogonial stem cells at a stage where retrotransposons undergo de novo methylation. Deletion of the Dnmt3L gene prevented the de novo methylation of both long-terminal-repeat (LTR) and non-LTR retrotransposons, which were transcribed at high levels in spermatogonia and spermatocytes. Loss of Dnmt3L from early germ cells also caused meiotic failure in spermatocytes, which do not express Dnmt3L. Whereas dispersed repeated sequences were demethylated in mutant germ cells, tandem repeats in pericentric regions were methylated normally. This result indicates that the Dnmt3L protein might have a function in the de novo methylation of dispersed repeated sequences in a premeiotic genome scanning process that occurs in male germ cells at about the time of birth.     

塔形马蹄螺雄性生殖系统的组织学研究

塔形马蹄螺为雌雄异体,其雄性生殖系统主要由精巢和输精管组成,没有交接器,也没有其他的附属腺体．精巢由许多精小管组成;生精小管内有处于不同发育时期的精原细胞,初级精母细胞,次级精母细胞,精子细胞和精子;输精管壁的上皮细胞游离面具有纤毛;精巢的发育具有季节性．     

黄胫小车蝗配子发生时c-kit蛋白特异性表达

应用组织学、免疫组织化学和生物统计分析相结合的方法,对黄胫小车蝗(Oedaleus infernalisSauss.)配子发生期间原癌基因c-kit的特异表达进行了研究.结果表明:精子发生过程中,精原细胞、初级精母细胞、次级精母细胞和成熟精子中均有不同程度的c-kit蛋白表达,精巢末端还有较粗大的阳性颗粒分布;卵子发生过程中,第1~6阶段卵母细胞中有不同程度的c-kit蛋白特异性表达,但随着卵黄的发生逐渐消失.     

蟋蟀雄性生殖系统的结构和精子发生

研究了蟋蟀雄性生殖系统的结构和精子发生的动态过程 .成熟的雄性生殖系统主要由一对精巢 ,一对输精管 ,一对附腺 ,一对储精囊和一根射精管组成 .精巢乳白色由许多精巢管盘曲组成 ,精巢管包括原精区、生长区、成熟区和变形区四个区域 .其主要特点是处于不同发育时期的精母细胞呈放射状密集排列在圆球形的育精囊中 .精子发生的动态是 :一龄期 ,精巢小管仅具一些精原细胞 ;二～三龄期 ,精原细胞不断通过有丝分裂增殖 ;四龄期 ,初级精母细胞形成 ,并由减数分裂形成次级精母细胞 ;五龄期 ,精细胞大量形成 ,并变形成为精子 .其主要特点是成虫期的精巢管中存在所有各期生殖细胞 ,当下端的精子成熟时 ,上端部分的精母细胞再发育形成精子 ,表明从五龄开始蟋蟀便能连续不断地产生精子     

盐酸吗啉胍对蚕豆根尖细胞的遗传毒性效应

以不同浓度的盐酸吗啉胍为诱变剂，运用蚕豆根尖微核检测技术和染色体畸变实验方法，测定蚕豆根尖细胞的有丝分裂指数、微核率和染色体畸变率．结果表明：盐酸吗啉胍能够降低蚕豆根尖细胞有丝分裂指数，能诱发较高频率的微核和染色体畸变，产生染色体断片、滞后染色体和染色体桥．随着盐酸吗啉胍处理浓度的增加，有丝分裂指数降低，而微核率和染色体畸变率均升高；随着盐酸吗啉胍浓度的进一步增加，染色体畸变率却下降，但仍明显高于对照组．     

鳜精巢的组织学和超微结构观察

对鳜精巢的组织学结构和超微结构进行观察．鳜精巢呈叶型结构,由精原细胞、初级精母细胞、次级精母细胞、精细胞、成熟精子等生殖细胞和支持细胞、间质细胞、边界细胞、类肌细胞、成纤维细胞、内皮细胞等非生殖细胞组成．鳜精子形成过程,精细胞大致经历了鞭毛发生,核质凝缩及核位置的改变,线粒体迁移等过程．鳜成熟精子无顶体结构,头短而圆,主要为核占据,核凹窝发达,尾细长,具侧鳍,尾部轴丝为“9 2”结构．     

碳离子不同入射深度上番茄种子的发芽率和染色体畸变

作者用碳离子束辐照多层重叠番茄种子的方法,研究了离子的入射深度与种子的发芽率和根尖细胞染色体畸变水平之间的关系,结果表明:置于离子束通道部位的种子发芽率较高,染色体畸变水平则较低;置于离子射程末端Bragg峰区的种子发芽率较低,染色体畸变水平则较高。这些趋势与离子在入射深度上的物理剂量分布特点相一致。     

Mutagenic effects of chromium trioxide on root tip cells of Vicia faba

In this study on the mutagenic effects of different concentrations of chromium trioxide (CrO3) on Vicia faba root tip, micronucleus assay and chromosome aberration assay were used to determine the mitotic indexes, micronucleus rate and chromosome aberration rate of Vicia faba root tip cells. The results showed that the effects of CrO3 concentration on the mitotic indexes were complicated. CrO3 increases the micronucleus rate of Vicia faba root tip cells. It was found that within certain range of CrO3 concentration the micronucleus rate increased systematically with increased concentration of CrO3, but that the micronucleus rate decreased at higher level of CrO3 and that CrO3 also caused various types of chromosome aberration at a rate which increased systematically with increased concentration of CrO3. We concluded that CrO3 has significant mutagenic effect on Vicia faba root tip cells.     

低温贮藏对栽培大麦染色体的影响

本文对国家种质自然库中低温下不同贮存年限的３４份栽培大麦种质资源的染色体及其变异进行了探讨。结果显示，种子贮存越久，其染色体的畸变率越高。根尖细胞有丝分裂中期染色体畸变以加倍及断裂为主，有丝分裂后期染色体出现单桥、双桥现象。染色体畸变与种子发芽主之间呈极显著负相关。     

蚯蚓浸膏对环磷酰胺诱发的蚕豆根尖细胞变异的保护作用

以蚕豆根尖为材料，研究了赤子爱胜蚓浸膏对环磷酰胺诱变的保护作用．结果表明，用赤子爱胜蚓浸膏处理后，可以降低由环磷酰胺诱发的蚕豆根尖细胞微核率和染色体畸变率．１％蚯蚓浸膏处理组与阳性对照组相比，微核率和染色体畸变率分别降低７０２１％和４５３６％；０５％蚯蚓浸膏处理组，微核率和染色体畸变率分别降低４６３９％和３８３９％；０１％蚯蚓浸膏处理组，微核率和染色体畸变率分别降低２９８８％和２６８６％．