Fernandes Jorge M O, MacKenzie Matthew G, Kinghorn James R, Johnston Ian A
School of Biology, University of St Andrews, St Andrews, Fife KY16 8LB, UK.
J Exp Biol. 2007 Oct;210(Pt 19):3461-72. doi: 10.1242/jeb.009183.
FoxK1 is a member of the highly conserved forkhead/winged helix (Fox) family of transcription factors and it is known to play a key role in mammalian muscle development and myogenic stem cell function. The tiger pufferfish (Takifugu rubripes) orthologue of mammalian FoxK1 (TFoxK1) has seven exons and is located in a region of conserved synteny between pufferfish and mouse. TFoxK1 is expressed as three alternative transcripts: TFoxK1-alpha, TFoxK1-gamma and TFoxK1-delta. TFoxK1-alpha is the orthologue of mouse FoxK1-alpha, coding for a putative protein of 558 residues that contains the forkhead and forkhead-associated domains typical of Fox proteins and shares 53% global identity with its mammalian homologue. TFoxK1-gamma and TFoxK1-delta arise from intron retention events and these transcripts translate into the same 344-amino acid protein with a truncated forkhead domain. Neither are orthologues of mouse FoxK1-beta. In adult fish, the TFoxK1 splice variants were differentially expressed between fast and slow myotomal muscle, as well as other tissues, and the FoxK1-alpha protein was expressed in myogenic progenitor cells of fast myotomal muscle. During embryonic development, TFoxK1 was transiently expressed in the developing somites, heart, brain and eye. The relative expression of TFoxK1-alpha and the other two alternative transcripts varied with the incubation temperature regime for equivalent embryonic stages and the differences were particularly marked at later developmental stages. The developmental expression pattern of TFoxK1 and its localisation to mononuclear myogenic progenitor cells in adult fast muscle indicate that it may play an essential role in myogenesis in T. rubripes.
FoxK1是转录因子中高度保守的叉头框/翼状螺旋（Fox）家族的成员，已知其在哺乳动物肌肉发育和肌源性干细胞功能中起关键作用。哺乳动物FoxK1的虎河豚（Takifugu rubripes）直系同源物（TFoxK1）有七个外显子，位于河豚和小鼠之间保守的同线区域。TFoxK1以三种可变转录本形式表达：TFoxK1-α、TFoxK1-γ和TFoxK1-δ。TFoxK1-α是小鼠FoxK1-α的直系同源物，编码一种推定的含558个残基的蛋白质，该蛋白质含有Fox蛋白典型的叉头框和叉头框相关结构域，与其哺乳动物同源物的整体一致性为53%。TFoxK1-γ和TFoxK1-δ由内含子保留事件产生，这些转录本翻译成具有截短叉头框结构域的相同的344个氨基酸的蛋白质。它们都不是小鼠FoxK1-β的直系同源物。在成年鱼中，TFoxK1剪接变体在快、慢肌节肌以及其他组织之间差异表达，并且FoxK1-α蛋白在快肌节肌的肌源性祖细胞中表达。在胚胎发育过程中，TFoxK1在发育中的体节、心脏、大脑和眼睛中短暂表达。对于相同的胚胎阶段，TFoxK1-α与其他两种可变转录本的相对表达随孵化温度条件而变化，并且在发育后期差异尤为明显。TFoxK1的发育表达模式及其在成年快肌中定位于单核肌源性祖细胞表明它可能在虎河豚的肌生成中起重要作用。
