Meiotic chromosome configurations in triploid and heteroploid mosaic males of Crassostrea gigas and Crassostrea ariakensis

Reversion from triploids to diploids or heteroploid mosaics may make the revertants recover reproductive ability and lose their aquacultural advantages. Meiotic chromosomes in triploids and mosaics of Crassostrea gigas and Crassostrea ariakensis were studied. Pachytene spermatocytes showed incomplete trivalent formation, varying 64–72% in C. gigas and 62–69% in C. ariakensis. At metaphase I, trivalents, bivalents and univalents occurred in various combinations. Trivalents occurred in all spermatocytes, ranged 6–10 per spermatocyte and averaged 8.53–8.97 in C. gigas and 8.49–8.95 in C. ariakensis. Univalents and bivalents appeared in 59.2–72.1% of the spermatocytes in C. gigas, and ranged 0.77–1.39 and 1.01–1.51 per spermatocyte respectively. In C. ariakensis, they occurred in 57.5–81% of the spermatocytes, and ranged 0.9–1.32 and 1.03–1.35 respectively. The most common trivalent was formed by a bivalent with the third chromosome attaching to its side to form ‘long‐tail‐cross’ or ‘t’ or ‘frying‐pan’‐shaped configurations that constituted 65.7% and 59.9% of the trivalents in C. gigas and C. ariakensis respectively. Other kinds of trivalent associations included tandem chains (14.7%, 16.5%), closed circles or triangles (5.3%, 9.8%), convergent ‘T’ or ‘Y’ (5.8%, 7.4%) and unclassified configurations (8.5%, 6.4%). Diploid spermatocytes were not observed from mosaics, although they showed considerable proportions of ‘diploid’ cells in their gills.     

芸薹属二倍体种的基因组结构及细胞遗传学研究进展

本文综合分析了细胞遗传学及比较基因组学在芸薹属栽培种基因组结构及进化方面的研究进展。测序物种的DNA序列比较分析显示，芸薹族特有的六倍体祖先基因组的进化途径为，先由芸薹科x=8的祖先核型衍生出染色体数减少的x=7的核型，然后该核型经过三倍化事件产生古老的六倍体基因组，最后才分化产生3个芸薹属栽培二倍体种。根据3个二倍体种测序基因组的比较分析，构建了具有9条染色体的芸薹属祖先基因组及所形成的二倍体的染色体组成。传统及分子细胞遗传学研究为二倍体种基因组的多倍体性质及部分同源性关系提供了直观的证据，特别是二倍体间的异源染色体附加系的减数分裂配对行为揭示了单条染色体间的同源性程度。最后，对依据近缘物种的基因组结构进行芸薹属作物种质资源的创建与利用提出建议。     

视黄酸信号通路在青鳉精原干细胞体外增殖与分化中的作用

为探究视黄酸(Retinoic acid, RA)在鱼类精原干细胞(Spermatogonial stem cells, SSC)增殖与分化中的作用,本研究首先以三荧光报告载体pGRY(延伸因子1α启动子驱动组蛋白H2B-绿色荧光融合蛋白、减数分裂联会复合体蛋白3(Scp3)启动子驱动嘌呤霉素红色荧光融合蛋白、精蛋白启动子驱动黄色荧光蛋白)转染青鳉精原干细胞系SG3,获得稳转细胞SG3-pGRY,然后分别在2D与3D培养条件下检测RA信号对其增殖与分化的影响。结果显示,稳转细胞SG3-pGRY的红色荧光可监测细胞内源性Scp3的表达,且细胞仍保持干性及分化潜能,表明其可用于监测细胞分化状态。在2D培养条件下,即在细胞培养板中待细胞生长密度约90%就进行传代培养,RA可显著抑制细胞增殖,其受体α、β、γ泛抑制剂BMS493可促进细胞增殖；第48 h,RA处理可下调细胞多能性相关基因pou5f3、klf4表达,上调减数分裂相关基因dazl表达,但对其他减数分裂相关基因如scp3表达无明显影响；第8 d,处理组及对照组均未能观察到红色荧光,这与已有报道RA处理体外培养小鼠SSC可显著促进Scp3表达,并进入减数分裂I期偶线期的研究结果明显不同。在3D培养条件下,即用96孔球形低吸附微量培养板进行培养,48 h后细胞成球状体聚集生长,RA、 BMS493处理组、对照组在48 h后均观察到明显红色荧光,减数分裂相关基因表达与2D相比显著上调；第8 d与34 d,RA处理组减数分裂相关基因表达均显著高于对照组,而BMS493处理组低于对照组。综上,RA信号可抑制SG3增殖,促进其分化,但不是诱导细胞发生减数分裂的关键分子。本研究不仅为鱼类SSC分化相关研究提供了良好研究模型,而且促进了我们对于RA信号在鱼类SSC增殖与分化中作用的深入认识。