Structural and functional characterisation of the fork head transcription factor-encoding gene, Hc-daf-16, from the parasitic nematode Haemonchus contortus (Strongylida).
Structural and functional characterisation of the fork head transcription factor-encoding gene, Hc-daf-16, from the parasitic nematode Haemonchus contortus (Strongylida).
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DOI：
10.1016/j.ijpara.2009.09.005
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发表时间：
2010-03-15
影响因子：
4
通讯作者：
Gasser RB
中科院分区：
文献类型：
--
作者：
Hu M;Lok JB;Ranjit N;Massey HC Jr;Sternberg PW;Gasser RB
尽管寄生线虫的系统发育具有多样性，但它们与自由生活的线虫在其生活史的关键时刻，特别是在负责在宿主中建立感染的幼虫阶段，具有共同的长寿和发育停滞(=低生物)的属性。胰岛素样信号在调节自由生活线虫的寿命和滞留(=Dauer形成)中起着至关重要的作用。线虫中的胰岛素样信号负性调节daf-16编码的叉头盒O(FoxO)转录因子，这与启动Dauer特异的基因表达模式有关。已经在几种寄生线虫中发现了daf-16的同源基因。虽然已经证明了来自寄生线虫Strongyloids stercoralis(Rhabditida)的同源物的功能，但囊状线虫(Strongylida)的同源物/直系物的功能功能尚不清楚。在本研究中，我们使用基因组学方法确定了两个完整的daf-16同源基因(分别命名为HC-daf-16.1和HC-daf-16.2)及其转录本的结构，并以线虫为遗传替代物评估了它们的功能(S)。与Ce-DAF-16和SS-DAF-16的多种异构体不同，Ce-DAF-16和SS-DAF-16由单个基因编码，并通过交替剪接产生，而编码蛋白质HC-DAF-16.1和HC-DAF-16.2的mRNAs是从不同的不同座位转录而来的。这两个同源基因在螺旋藻的所有发育阶段和性别中都有转录，推测的蛋白质(603和556个氨基酸)都包含一个特征的高度保守的叉头区。尽管与线虫和斯特氏线虫的同源基因相比，基因组组织有明显的差异，但遗传互补研究表明，HC-daf-16.2，而不是HC-daf-16.1，可以恢复该位点零突变的线虫株的daf-16功能。这些发现与之前对S stercoris的结果一致，并证明了来自两个不同分类目的关键寄生线虫和线虫之间的daf-16b同源基因的功能保守。我们从这些实验中得出结论，叉头转录因子DAF-16以及由此推断的其他胰岛素样信号元件在螺旋线虫中保守，这是一种具有重要经济意义的寄生线虫。我们证明了HC-DAF-16.2的功能是足够保守的，可以取代Ce-DAF-16在促进线虫的达尔捕获方面。
Despite their phylogenetic diversity, parasitic nematodes share attributes of longevity and developmental arrest (=hypobiosis) with free-living nematodes at key points in their life cycles, particularly in larval stages responsible for establishing infection in the host. Insulin-like signalling plays crucial roles in the regulation of life span and arrest (=dauer formation) in the free-living nematode, Caenorhabditis elegans. Insulin-like signalling in C. elegans negatively regulates the fork head boxO (FoxO) transcription factor encoded by daf-16, which is linked to initiating a dauer-specific pattern of gene expression. Orthologues of daf-16 have been identified in several species of parasitic nematode. Although function has been demonstrated for an orthologue from the parasitic nematode Strongyloides stercoralis (Rhabditida), the functional capabilities of homologues/orthologues in bursate nematodes (Strongylida) are unknown. In the present study, we used a genomic approach to determine the structures of two complete daf-16 orthologues (designated Hc-daf-16.1 and Hc-daf-16.2) and their transcripts in the parasitic nematode Haemonchus contortus, and assessed their function(s) using C. elegans as a genetic surrogate. Unlike the multiple isoforms of Ce-DAF-16 and Ss-DAF-16, which are encoded by a single gene and produced by alternative splicing, mRNAs encoding the proteins Hc-DAF-16.1 and Hc-DAF-16.2 are transcribed from separate and distinct loci. Both orthologues are transcribed in all developmental stages and both sexes of H. contortus, and the inferred proteins (603 and 556 amino acids) each contain a characteristic, highly conserved fork head domain. In spite of distinct differences in genomic organisation compared with orthologues in C. elegans and S. stercoralis, genetic complementation studies demonstrated here that Hc-daf-16.2, but not Hc-daf-16.1, could restore daf-16 function to a C. elegans strain carrying a null mutation at this locus. These findings are consistent with previous results for S. stercoralis and demonstrate functional conservation of the daf-16b orthologue between key parasitic nematodes from two different taxonomic orders and C. elegans. We conclude from these experiments that the fork head transcription factor DAF-16 and, by inference, other insulin-like signalling elements, are conserved in H. contortus, a parasitic nematode of paramount economic importance. We demonstrate that functionality is sufficiently conserved in Hc-DAF-16.2 that it can replace Ce-DAF-16 in promoting dauer arrest in C. elegans.
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