两种淡水鱼类的Sox基因

ＴＨＥＳＯＸＧＥＮＥＳＩＮＴＷＯＳＰＥＣＩＥＳＯＦＦＲＥＳＨＷＡＴＥＲＦＩＳＨＥＳ两种淡水鱼类的Ｓｏｘ基因ＫｅｙｗｏｒｄｓＳｅｘ,Ｉｎｔｒｏｎ,Ｆｒｅｓｈｗａｔｅｒｆｉｓｈ关键词性别内含子淡水鱼类ＴｈｅＳｒｙｉｓｔｈｅｓｅｘｄｅｔｅｒｍｉｎｉ...     

The SOX gene family: function and regulation in testis determination and male fertility maintenance

The Sox (Sry-type HMG box) genes encode a group of proteins characterized by the existence of an SRY (sex-determining region on Y chromosome) box, a 79 amino acid motif that encodes an HMG (high mobility group) domain which can bind and bend DNA, which is the only part in SRY that is conserved between species. The Sox gene family functions in many aspects in embryogenesis, including testis development, CNS neurogenesis, oligodendrocyte development, chondrogenesis, neural crest cell development and other respects. The Sox gene family was originally identified through homology with Sry. The Sry gene is the mammalian testis-determining gene. It functions to open the testis determination pathway directly and close the ovary pathway indirectly. Sry and Sox9 are the most important two genes expressed during testis determination. Besides, researchers have found that Sox8 and Sox9 have functions in the male fertility maintenance after birth. In this review, information was evaluated from mouse or from human if not mentioned otherwise.     

SOX9 regulates prostaglandin D synthase gene transcription in vivo to ensure testis development

In mammals, male sex is determined by the Y-chromosomal gene Sry (sex-determining region of Y chromosome). The expression of Sry and subsequently Sox9 (SRY box containing gene 9) in precursors of the supporting cell lineage results in the differentiation of these cells into Sertoli cells. Sertoli cells in turn orchestrate the development of all other male-specific cell types. To ensure that Sertoli cells differentiate in sufficient numbers to induce normal testis development, the early testis produces prostaglandin D(2) (PGD(2)), which recruits cells of the supporting cell lineage to a Sertoli cell fate. Here we show that the gene encoding prostaglandin D synthase (Pgds), the enzyme that produces PGD(2), is expressed in Sertoli cells immediately after the onset of Sox9 expression. Promoter analysis in silico and in vitro identified a paired SOX/SRY binding site. Interestingly, only SOX9, and not SRY, was able to bind as a dimer to this site and transactivate the Pgds promoter. In line with this, a transgenic mouse model showed that Pgds expression is not affected by ectopic Sry expression. Finally, chromatin immunoprecipitation proved that SOX9 but not SRY binds to the Pgds promoter in vivo.     

Diversification Pattern of the HMG and SOX Family Members During Evolution

From a database containing the published HMG protein sequences, we constructed an alignment of the HMG box functional domain based on sequence identity. Due to the large number of sequences (more than 250) and the short size of this domain, several data sets were used. This analysis reveals that the HMG box superfamily can be separated into two clearly defined subfamilies: (i) the SOX/MATA/TCF family, which clusters proteins able to bind to specific DNA sequences; and (ii) the HMG/UBF family, which clusters members which bind non specifically to DNA. The appearance and diversification of these subfamilies largely predate the split between the yeast and the metazoan lineages. Particular emphasis was placed on the analysis of the SOX subfamily. For the first time our analysis clearly identified the SOX subfamily as structured in six groups of genes named SOX5/6, SRY, SOX2/3, SOX14, SOX4/22, and SOX9/18. The validity of these gene clusters is confirmed by their functional characteristics and their sequences outside the HMG box. In sharp contrast, there are only a few robust branching patterns inside the UBF/HMG family, probably because of the much more ancient diversification of this family than the diversification of the SOX family. The only consistent groups that can be detected by our analysis are HMG box 1, vertebrate HMG box 2, insect SSRP, and plant HMG. The various UBF boxes cannot be clustered together and their diversification appears to be extremely ancient, probably before the appearance of metazoans. Received: 20 July 1998 / Accepted: 19 October 1998     

池蝶蚌Sox2 基因在不同组织及不同月龄精巢中的表达

Sox 基因家族在胚胎发育过程和性别分化中起重要作用, 为研究池蝶蚌中Sox 基因的功能, 以人SRY基因HMG-box 保守区的序列设计简并引物, 以雌、雄池蝶蚌基因组DNA 和精巢cDNA 为模板进行扩增, 获得了2 个不完全相同的序列, 分别为DNA-HMG1、DNA-HMG2 和cDNA-HMG, 长度均为220 bp, 编码73个氨基酸。与人等物种Sox1、Sox2、Sox3 及Sox14 有很高的同源性, 雌雄个体之间没有序列差异性。采用RACE-PCR 扩增获得了池蝶蚌性腺Sox2 部分cDNA 片段, 长度为1774 bp, 该序列核苷酸与欧洲帽贝的SoxB和人类的Sox2 的同源性最高; 在部分开放阅读框249 个氨基酸残基中, 具有Sox 家族典型的HMG-box 结构域, 与人类、小鼠、原鸡和斑马鱼等Sox2 的HMG-box 同源性为98%。为了解该基因在各组织中的表达情况,采用实时荧光定量PCR 方法分析了外套膜、闭壳肌、鳃、肠、肝、肾、精巢和卵巢在内的8 种组织hs-Sox2的表达情况, 结果显示, hs-Sox2 基因在8 种组织中均有表达, 其中在肾脏中的表达量最高, 其次是肠与闭壳肌, 在雄性性腺中的表达量明显高于雌性性腺, 在肝脏中的表达量最低; 为了解hs-Sox2 在不同性腺发育时期的表达情况, 采用实时荧光定量PCR 方法分析了5 个不同月龄的精巢组织中hs-Sox2 的表达情况, 结果显示在39 月龄性腺的表达量最高, 其次是16 月龄性腺, 63 月龄蚌中的表达量最少。以上结果表明, hs-Sox2 基因可能参与了池蝶蚌精巢的发育及功能的维持。       

Mechanism of Regulatory Target Selection by the SOX High-Mobility-Group Domain Proteins as Revealed by Comparison of SOX1/2/3 and SOX9

SOX proteins bind similar DNA motifs through their high-mobility-group (HMG) domains, but their action is highly specific with respect to target genes and cell type. We investigated the mechanism of target selection by comparing SOX1/2/3, which activate δ-crystallin minimal enhancer DC5, with SOX9, which activates Col2a1 minimal enhancer COL2C2. These enhancers depend on both the SOX binding site and the binding site of a putative partner factor. The DC5 site was equally bound and bent by the HMG domains of SOX1/2 and SOX9. The activation domains of these SOX proteins mapped at the distal portions of the C-terminal domains were not cell specific and were independent of the partner factor. Chimeric proteins produced between SOX1 and SOX9 showed that to activate the DC5 enhancer, the C-terminal domain must be that of SOX1, although the HMG domains were replaceable. The SOX2-VP16 fusion protein, in which the activation domain of SOX2 was replaced by that of VP16, activated the DC5 enhancer still in a partner factor-dependent manner. The results argue that the proximal portion of the C-terminal domain of SOX1/2 specifically interacts with the partner factor, and this interaction determines the specificity of the SOX1/2 action. Essentially the same results were obtained in the converse experiments in which COL2C2 activation by SOX9 was analyzed, except that specificity of SOX9-partner factor interaction also involved the SOX9 HMG domain. The highly selective SOX-partner factor interactions presumably stabilize the DNA binding of the SOX proteins and provide the mechanism for regulatory target selection.     

Shuttling of SOX proteins

The control of access of SOX proteins to their nuclear target genes is a powerful strategy to activate or repress complex genetic programs. The sub-cellular targeting sequences of SOX proteins are concentrated within the DNA binding motif, the HMG (for high mobility group) domain. Each SOX protein displays two different nuclear localization signals located at the N-terminal and C-terminal part of their highly conserved DNA binding domain. The N-terminal nuclear localization signal binds calmodulin and is potentially regulated by intracellular calcium signalling, while the C-terminal nuclear localization signal, which binds importin-β, responds to other signalling pathways such as cyclic AMP/protein kinase A. Mutations inducing developmental disorders like sex reversal have been reported in both NLSs of SRY, interfering with its nuclear localization and suggesting that both functional nuclear localization signal are required for its nuclear activity. A nuclear export signal is also present in the HMG box of SOX proteins. Group E SOX proteins harbour a perfect consensus nuclear export signal sequence in contrast to all other SOX proteins, which display only imperfect ones. However, observations made during mouse embryonic development suggest that non-group E SOX proteins could also be regulated by a nuclear export mechanism. The presence of nuclear localization and nuclear export signal sequences confers nucleocytoplasmic shuttling properties to SOX proteins, and suggests that cellular events regulated by SOX proteins are highly dynamic.     

Sry-negative XX sex reversal in the American cocker spaniel dog

The Sry gene product serves an important function in male sex determination through testis induction. However, testicular development has been reported in SRY-negative XX sex reversed humans. XX sex reversal of the American cocker spaniel, inherited as an autosomal recessive trait, may be a homolog of this disorder. The purpose of this study was to determine whether the Sry high mobility group (HMG) box is present in genomic DNA of affected dogs. Conserved Sry HMG box and hypoxanthine phosphoribosyltransferase (HPRT) sequences were used as primers in polymerase chain reactions. A 167 bp Y-specific canine Sry HMG box sequence was cloned from genomic DNA of normal male dogs. Internal primers generated a 104 bp Sry HMG box product from normal males, but not from females or XX sex reversed dogs. Parallel reactions generated an HPRT product from all dogs. Results indicate that the Sry HMG box is absent in genomic DNA of XX sex reversed dogs. We speculate that activation of the testis differentiation cascade in the absence of Sry in this model is due to a mutant autosomal gene. © 1995 Wiley-Liss, Inc.     

Cloning and functional analysis of the Sry-related HMG box gene, Sox18

The Sox gene family (Sry like HMG box gene) is characterised by a conserved DNA sequence encoding a domain of approximately 80 amino acids which is responsible for sequence specific DNA binding. We initially published the identification and partial cDNA sequence of murine Sox18, a new member of this gene family, isolated from a cardiac cDNA library. This sequence allowed us to classify Sox18 into the F sub-group of Sox proteins, along with Sox7 and Sox17. Recently, we demonstrated that mutations in the Sox18 activation domain underlie cardiovascular and hair follicle defects in the mouse mutation, ragged (Ra) (Pennisi et al., 2000. Mutations in Sox18 underlie cardiovascular and hair follicle defecs in ragged mice. Nat. Genet. 24, 434-437). Ra homozygotes lack vibrissae and coat hairs, have generalised oedema and an accumulation of chyle in the peritoneum. Here we have investigated the genomic sequences encoding Sox18. Screening of a mouse genomic phage library identified four overlapping clones, we sequenced a 3.25 kb XbaI fragment that defined the entire coding region and approximately 1.5 kb of 5' flanking sequences. This identified (i) an additional 91 amino acids upstream of the previously designated methionine start codon in the original cDNA, and (ii) an intron encoded within the HMG box/DNA binding domain in exactly the same position as that found in the Sox5, -13 and -17 genes. The Sox18 gene encodes a protein of 468 aa. We present evidence that suggests HAF-2, the human HMG-box activating factor -2 protein, is the orthologue of murine Sox18. HAF-2 has been implicated in the regulation of the Human IgH enhancer in a B cell context. Random mutagenesis coupled with GAL4 hybrid analysis in the activation domain between amino acids 252 and 346, of Sox18, implicated the phosphorylation motif, SARS, and the region between amino acid residues 313 and 346 as critical components of Sox18 mediated transactivation. Finally, we examined the expression of Sox18 in multiple adult mouse tissues using RT-PCR. Low-moderate expression was observed in spleen, stomach, kidney, intestine, skeletal muscle and heart. Very abundant expression was detected in lung tissue.     

From SRY to SOX9: mammalian testis differentiation

Sry (sex-determining region on the Y chromosome) is a master gene that initiates testis differentiation of the bipotential indifferent gonad in mammals. In mice, Sry expression is transiently activated in a center-to-pole wave along the anteroposterior (AP) axis of developing XY gonads. Shortly after the onset of Sry activation, Sox9 (Sry-related HMG box-9), a fundamental testis-differentiation gene common to all vertebrates, is also activated in a center-to-pole pattern similar to the initial Sry expression profile. Several male-specific cellular events, such as glycogenesis, coelomic epithelium proliferation, mesonephric migration and vasculogenesis, are induced in XY gonads following the onset of Sry and Sox9 expression. This paper mainly focuses on recent advances in elucidating the regulatory mechanisms of Sry and Sox9 expression and male-specific cellular events immediately downstream of SRY action during the initial phases of testis differentiation.