中国学者两项成果同登PLoS Genetics

　　生物通报道：来自中科院遗传与发育生物学研究所程祝宽课题组发表了题为“The Role of Rice HEI10 in the Formation of Meiotic Crossovers”的文章，在水稻中鉴定出了HEI10基因，这是水稻中分离的第一个可以用于指示重组位置的标记蛋白，相关研究为在水稻中进一步深入研究重组机制提供了坚实基础。

减数分裂是维持生物体染色体数恒定，导致遗传重组产生的基础。减数分裂缺陷是导致不孕、不育和出生障碍的主要原因。绝大多数减数分裂基因在不同物种中有着高度保守的功能。HEI10基因最初在人类体细胞中分离，并证明有调控细胞周期的功能。在小鼠中的研究表明，HEI10基因的突变会导致减数分裂异常并最终导致不育，但是HEI10在减数分裂过程中的具体生物学功能目前仍然不清楚。

在这篇文章中，程祝宽实验室王克剑、王莫和唐丁等人在水稻中鉴定出了HEI10基因，研究分析发现，HEI10基因突变导致交叉结的数目显著减少，而剩余交叉随机分布于不同染色体上。但是HEI10的突变并不影响重组早期蛋白的定位以及联会复合体的形成。

令人惊奇的是，HEI10蛋白在染色体上呈现一种动态的定位：最初呈现为明显的点状而且与重组蛋白MER3高度共定位，随着减数分裂联会的进行，HEI10沿着染色体轴逐渐连成线状信号，在联会复合体解体之后，线状信号逐渐消失，只有大的点状信号维持在染色体上，而这些点状信号恰好对应于交叉结的位置。

HEI10是水稻中分离的第一个可以用于指示重组位置的标记蛋白，相关研究为在水稻中进一步深入研究重组机制提供了坚实基础。

除此之外，来自中国农业大学，瑞典乌普萨拉大学的研究人员发表文章，取得了鸡冠形态遗传作用机制的研究新成果。

农业动物因其丰富的表型变异和特殊的驯化、育种历史，成为遗传学中基因定位研究的独特资源。基因定位方法发展较快，农业动物中大量影响表型的基因和位点得到了初步定位，但是仅有少数表型的功能基因和功能突变得到了分离和证实。鸡冠具有丰富的表型，其中多种形态是由遗传因素决定的，是一种非常理想的研究对象，早在1902年，鸡玫瑰冠等性状就被作为研究对像，第一次在动物中阐明了孟德尔遗传定律。鸡玫瑰冠性状是一个单基因控制的显性性状，相对于野生型的单冠而言，可以显著改变鸡冠的形态，但是其遗传基础尚未研究清楚。

在这篇文章中，研究人员发现玫瑰冠是由7号染色体一个7.4Mb的染色体倒位所造成的，同时存在第二个玫瑰冠等位基因，该等位基因是由倒位型玫瑰冠染色体和野生型单冠染色体之间发生非对等重组产生的一种基因组结构重排。

进一步发现，玫瑰冠表型是由MNR2基因位置的改变导致其在鸡冠发育过程中异常表达造成的。104年前，Bateson和Punnett等提出玫瑰冠等位基因和豆冠等位基因之间的上位效应导致了胡桃冠表型，这也是第一个上位效应的例子，在此，该研究在分子水平对其进行了解释。

玫瑰冠突变位点的MNR2基因和豆冠突变位点的SOX5基因在相同的间充质细胞中异常表达，至少在鸡冠原基的部分细胞中共同表达，导致了胡桃冠的形成。玫瑰冠突变位点同时在纯合公鸡中引起了精子活力下降，该研究推测是因为CCDC108基因结构被染色体倒位突变破坏所导致的。

这项研究结果说明了农业动物中遗传多样性的部分特征，包括两个或多个突变的进化，以及结构突变如何加速了表型的进化。这些研究结果拓展了我们对这些基因新功能的认识，丰富了我们对基因型-表型关系的理解，也可以作为分子标记应用到动物育种和保种中。

（生物通：万纹）

原文摘要：

The Role of Rice HEI10 in the Formation of Meiotic Crossovers

HEI10 was first described in human as a RING domain-containing protein that regulates cell cycle and cell invasion. Mice HEI10mei4 mutant displays no obvious defect other than meiotic failure from an absence of chiasmata. In this study, we characterize rice HEI10 by map-based cloning and explore its function during meiotic recombination. In the rice hei10 mutant, chiasma frequency is markedly reduced, and those remaining chiasmata exhibit a random distribution among cells, suggesting possible involvement of HEI10 in the formation of interference-sensitive crossovers (COs). However, mutation of HEI10 does not affect early recombination events and synaptonemal complex (SC) formation. HEI10 protein displays a highly dynamic localization on the meiotic chromosomes. It initially appears as distinct foci and co-localizes with MER3. Thereafter, HEI10 signals elongate along the chromosomes and finally restrict to prominent foci that specially localize to chiasma sites. The linear HEI10 signals always localize on ZEP1 signals, indicating that HEI10 extends along the chromosome in the wake of synapsis. Together our results suggest that HEI10 is the homolog of budding yeast Zip3 and Caenorhabditis elegans ZHP-3, and may specifically promote class I CO formation through modification of various meiotic components.

The Rose-comb Mutation in Chickens Constitutes a Structural Rearrangement Causing Both Altered Comb Morphology and Defective Sperm Motility

Rose-comb, a classical monogenic trait of chickens, is characterized by a drastically altered comb morphology compared to the single-combed wild-type. Here we show that Rose-comb is caused by a 7.4 Mb inversion on chromosome 7 and that a second Rose-comb allele arose by unequal crossing over between a Rose-comb and wild-type chromosome. The comb phenotype is caused by the relocalization of the MNR2 homeodomain protein gene leading to transient ectopic expression of MNR2 during comb development. We also provide a molecular explanation for the first example of epistatic interaction reported by Bateson and Punnett 104 years ago, namely that walnut-comb is caused by the combined effects of the Rose-comb and Pea-comb alleles. Transient ectopic expression of MNR2 and SOX5 (causing the Pea-comb phenotype) occurs in the same population of mesenchymal cells and with at least partially overlapping expression in individual cells in the comb primordium. Rose-comb has pleiotropic effects, as homozygosity in males has been associated with poor sperm motility. We postulate that this is caused by the disruption of the CCDC108 gene located at one of the inversion breakpoints. CCDC108 is a poorly characterized protein, but it contains a MSP (major sperm protein) domain and is expressed in testis. The study illustrates several characteristic features of the genetic diversity present in domestic animals, including the evolution of alleles by two or more consecutive mutations and the fact that structural changes have contributed to fast phenotypic evolution.