Comparative genome mapping reveals evidence of gene conversion between Sox9 paralogs of rainbow trout (Oncorhynchus mykiss)

Considerable evidence suggests that one genome duplication event preceded the divergence of teleost fishes and a second genome duplication event occurred before the radiation of teleosts of the family Salmonidae. Two Sox9 genes have been isolated from a number of teleosts and are called Sox9a and Sox9b. Two Sox9 gene copies have also been isolated from rainbow trout, a salmonid fish and are called Sox9 and Sox9α2. Previous evaluations of the evolutionary history of rainbow trout Sox9 gene copies using phylogenetic reconstructions of their coding regions indicated that they both belong to the Sox9b clade. In this study, we determine the true evolutionary history of Sox9 gene copies in rainbow trout. We show that the locus referred to as Sox9 in rainbow trout is itself duplicated. Mapping of the duplicated Sox9 gene copies indicates that they are co-orthologs of Sox9b while mapping of Sox9α2 indicates that it is an ortholog of Sox9a. This relationship is supported by phylogenetic reconstruction of Sox9 gene copies in teleosts using their 3′ untranslated regions. The conflicting phylogenetic topology of Sox9 genes in rainbow trout indicates the occurrence of gene conversion events between Sox9 and Sox9α2 which is supported by a number of recombination analyses.     

A Drosophila group E Sox gene is dynamically expressed in the embryonic alimentary canal

We have identified a novel Drosophila Sox-domain gene, Sox100B, related to the vertebrate group E genes Sox9 and Sox10. In vertebrates, group E Sox genes are expressed in the developing gonad, adult kidney and gut as well as other tissues. During embryogenesis in Drosophila, Sox100B is expressed in two rows of large intestinal cells, in midgut basophilic cells, in the Malpighian tubules and at the posterior cap of gonadal mesoderm. Our observations indicate that aspects of tissue-specific expression, as well as sequence, are conserved between vertebrate and invertebrate group E Sox proteins.     

Isolation and sequence analysis of sox genes from lizard Eremias multiocellata

The Sox (SRY-related high-mobility-group box) family of genes shares a conserved HMG box and is involved in a diverse range of developmental processes and sex determination in vertebrates. Twenty Sox genes are present in the genomes of humans and mice, but far less is known about the Sox gene family in reptiles. Using two pairs of highly degenerate primers designed from a multiple alignment of Sox amino acid sequences in several species, different positive clones were obtained from male and female Eremias multiocellata, a viviparous lizard which is subject to TSD (temperature-dependent sex determination). These clones were sequenced and identified. They are members of the SoxB (Sox2, Sox14), SoxC (Sox11, Sox12) and SoxE (Sox9a, Sox9b, Sox10) groups. No sex-specific differences were observed. Based on the amino acid sequence similarities, the phylogenetic analysis was carried out and these genes clustered with their orthologues. In addition, we found the gene duplication in E. multiocellata, it may be a mechanism to produce new functional genes.     

VegT activation of Sox17 at the midblastula transition alters the response to nodal signals in the vegetal endoderm domain

In Xenopus, the prospective endoderm and mesoderm are localized to discrete, adjacent domains at the beginning of gastrulation, and this is made evident by the expression of Sox17 in vegetal blastomeres and Brachyury (Xbra) in marginal blastomeres. Here, we examine the regulation of Sox17alpha expression and the role of Sox17alpha in establishing the vegetal endodermal gene expression domain. Injection of specific inhibitors of VegT or Nodal resulted in a loss of Sox17alpha expression in the gastrula. However, the onset of Sox17alpha expression at the midblastula transition was dependent on VegT, but not on Nodal function, indicating that Sox17alpha expression is initiated by VegT and then maintained by Nodal signals. Consistent with these results, VegT, but not Xenopus Nodal-related-1 (Xnr1), can activate Sox17alpha expression at the midblastula stage in animal explants. In addition, VegT activates Sox17alpha in the presence of cycloheximide or a Nodal antagonist, suggesting that Sox17alpha is an immediate-early target of VegT in vegetal blastomeres. Given that Nodal signals are necessary and sufficient for both mesodermal and endodermal gene expression, we propose that VegT activation of Sox17alpha at the midblastula transition prevents mesodermal gene expression in response to Nodal signals, thus establishing the vegetal endodermal gene expression domain. Supporting this idea, Sox17alpha misexpression in the marginal zone inhibits the expression of multiple mesodermal genes. Furthermore, in animal explants, Sox17alpha prevents the induction of Xbra and MyoD, but not Sox17beta or Mixer, in response to Xnr1. Therefore, VegT activation of Sox17alpha plays an important role in establishing a region of endoderm-specific gene expression in vegetal blastomeres.     

大绿蛙6个Sox基因的克隆及进化讨论

Sox基因家族编码一类转录调控因子,他们参与到个体发育的许多过程,如中枢神经系统的形成、性别分化、骨和淋巴细胞的发育等.许多动物体内都检测到Sox基因,基于序列及其结构特点,Bowles等将其划分为10个族.本文采用简并PCR技术,扩增了大绿蛙Sox基因的HMG-box保守区,经SSCP及序列分析,获得6个基因并分别命名为:RlSox3a、RlSox3b、RlSox3c、RlSox11、RlSox14 和RlSox21.所获序列无性别差异,经系统发生分析发现分属于大绿蛙Sox家族的B 和C 亚族.其中RlSox3基因出现多拷贝,为Sox基因家族进化的DDC(duplication-degeneration-complementation)模式提供了一定的分子证据.结合GenBank中已登录的31个Sox基因氨基酸序列,使用MEGA 3.0软件构建NJ (neighbor-joining) 系统发生树,讨论了Sox基因的系统发生历程.     

Functional analysis of Sox8 and Sox9 during sex determination in the mouse

Sex determination in mammals directs an initially bipotential gonad to differentiate into either a testis or an ovary. This decision is triggered by the expression of the sex-determining gene Sry, which leads to the activation of male-specific genes including the HMG-box containing gene Sox9. From transgenic studies in mice it is clear that Sox9 is sufficient to induce testis formation. However, there is no direct confirmation for an essential role for Sox9 in testis determination. The studies presented here are the first experimental proof for an essential role for Sox9 in mediating a switch from the ovarian pathway to the testicular pathway. Using conditional gene targeting, we show that homozygous deletion of Sox9 in XY gonads interferes with sex cord development and the activation of the male-specific markers Mis and P450scc, and leads to the expression of the female-specific markers Bmp2 and follistatin. Moreover, using a tissue specific knock-out approach, we show that Sox9 is involved in Sertoli cell differentiation, the activation of Mis and Sox8, and the inactivation of Sry. Finally, double knock-out analyses suggest that Sox8 reinforces Sox9 function in testis differentiation of mice.     

鳙Sox基因克隆及序列进化分析

利用简并引物SoxN和Sox9在鳙基因组DNA中进行PCR扩增和产物克隆测序,并对序列进行同源性比较和系统进化分析。结果表明本文鉴定出鳙15个Sox基因HMG盒序列,分别属于SoxB、SoxC和SoxE组,依据斑马鱼同源基因将其分别命名为Sox1a、Sox1b、Sox2、Sox3、Sox4a、Sox4b、Sox9a、Sox9b、Sox10、Sox11b、Sox12、Sox14a、Sox14b、Sox19和Sox21a。基于鳙和斑马鱼 Sox1、Sox4和Sox9 基因核苷酸序列构建的系统进化树显示这3个Sox基因的复制时间发生在鳙和斑马鱼的分化之前,结果支持了鱼类特异的基因组复制假说。以Sox1a、Sox1b和Sox4基因为分子钟标记构建系统进化树探讨鳙和斑马鱼的分化时间,结果显示,同属于鲤科鱼类的鳙（鲤亚科）和斑马鱼（鱼丹亚科）在原始的鱼丹亚科鱼类中存在一个共同祖先,大约出现在63.7百万年前。研究结果为进一步研究鱼类Sox基因复制和基因组进化等问题提供了重要参考资料。