Hook Jeff, Lemckert Frances, Schevzov Galina, Fath Thomas, Gunning Peter
Department of Pharmacology The School of Medical Sciences; The University of New South Wales; Sydney, Australia.
Bioarchitecture. 2011 Jan;1(1):49-59. doi: 10.4161/bioa.1.1.15172.
The actin filament system is fundamental to cellular functions including regulation of shape, motility, cytokinesis, intracellular trafficking and tissue organization. Tropomyosins (Tm) are highly conserved components of actin filaments which differentially regulate filament stability and function. The mammalian Tm family consists of four genes; αTm, βTm, γTm and δTm. Multiple Tm isoforms (>40) are generated by alternative splicing and expression of these isoforms is highly regulated during development. In order to further identify the role of Tm isoforms during development, we tested the specificity of function of products from the γTm gene family in mice using a series of gene knockouts. Ablation of all γTm gene cytoskeletal products results in embryonic lethality. Elimination of just two cytoskeletal products from the γTm gene (NM1,2) resulted in a 50% reduction in embryo viability. It was also not possible to generate homozygous knockout ES cells for the targets which eliminated or reduced embryo viability in mice. In contrast, homozygous knockout ES cells were generated for a different set of isoforms (NM3,5,6,8,9,11) which were not required for embryogenesis. We also observed that males hemizygous for the knockout of all cytoskeletal products from the γTm gene preferentially transmitted the minus allele with 80-100% transmission. Since all four Tm genes are expressed in early embryos, ES cells and sperm, we conclude that isoforms of the γTm gene are functionally unique in their role in embryogenesis, ES cell viability and sperm function.
肌动蛋白丝系统对于细胞功能至关重要，这些功能包括形状调节、运动性、胞质分裂、细胞内运输和组织构建。原肌球蛋白（Tm）是肌动蛋白丝的高度保守成分，可差异性地调节丝的稳定性和功能。哺乳动物的Tm家族由四个基因组成；αTm、βTm、γTm和δTm。通过可变剪接产生多种Tm异构体（>40种），并且这些异构体的表达在发育过程中受到高度调控。为了进一步确定Tm异构体在发育过程中的作用，我们使用一系列基因敲除实验在小鼠中测试了γTm基因家族产物的功能特异性。所有γTm基因细胞骨架产物的缺失导致胚胎致死。仅从γTm基因中去除两种细胞骨架产物（NM1,2）就导致胚胎存活率降低50%。对于那些在小鼠中消除或降低胚胎存活率的靶点，也无法产生纯合敲除的胚胎干细胞。相比之下，针对一组不同的异构体（NM3,5,6,8,9,11）产生了纯合敲除的胚胎干细胞，这些异构体对于胚胎发生并非必需。我们还观察到，对于γTm基因所有细胞骨架产物敲除的半合子雄性小鼠，优先传递负等位基因，传递率为80 - 100%。由于所有四个Tm基因都在早期胚胎、胚胎干细胞和精子中表达，我们得出结论，γTm基因的异构体在胚胎发生、胚胎干细胞活力和精子功能中具有独特的功能作用。
