Objective: To investigate whether genes required for synaptogenesis and synaptic function are also involved in fat storage control in Caenorhabditis elegans.
Methods: Fat storage was examined in mutants of genes affecting the synaptogenesis and synaptic function. In addition, the genetic interactions of SNAREs syntaxin/unc-64 and SNAP-25/ric-4 with daf-2, daf-7, nhr-49, sbp-1 and mdt-15 in regulating fat storage were further investigated. The tissue-specific activities of unc-64 and ric-4 were investigated to study the roles of unc-64 and ric-4 in regulating fat storage in the nervous system and/or the intestine.
Results: Mutations of genes required for the formation of presynaptic neurotransmission site did not obviously influence fat storage. However, among the genes required for synaptic function, the plasma membrane-associated SNAREs syntaxin/unc-64 and SNAP-25/ric-4 genes were involved in the fat storage control. Fat storage in the intestinal cells was dramatically increased in unc-64 and ric-4 mutants as revealed by Sudan Black and Nile Red strainings, although the fat droplet size was not significantly changed. Moreover, in both the nervous system and the intestine, expression of unc-64 significantly inhibited the increase in fat storage observed in unc-64 mutant. And expression of ric-4 in the nervous system completely restored fat storage in ric-4 mutant. Genetic interaction assay further indicated that both unc-64 and ric-4 regulated fat storage independently of daf-2 [encoding an insulin-like growth factor-I (IGF-I) receptor], daf-7 [encoding a transforming growth factor-beta (TGF-beta) ligand], and nhr-49 (encoding a nuclear hormone receptor). Besides, mutation of daf-16 did not obviously affect the phenotype of increased fat storage in unc-64 or ric-4 mutant. Furthermore, unc-64 and ric-4 regulated fat storage probably through the ARC105/mdt-15- and SREBP/sbp-1-mediated signaling pathways. In addition, fat storage in unc-64; ric-4 was higher than that in either unc-64 or ric-4 single mutant nematodes, suggesting that unc-64 functions in parallel with ric-4 in regulating fat storage.
Conclusion: The plasma membrane-associated SNAREs syntaxin/unc-64 and SNAP-25/ric-4 function in parallel in regulating fat storage in C. elegans, probably through the ARC105/mdt-15- and SREBP/sbp-1-mediated signaling pathways.
目的: 研究神经突触组装与功能调控相关基因是否参与秀丽线虫的脂肪积累调节。
方法: 分析神经突触组装与功能调控相关基因突变体的脂肪积累变化, 进而观察SNAREs syntaxin/unc-64和SNAP-25/ric-4基因与daf-2、 daf-7、 nhr-49、 sbp-1 及mdt-15所介导的信号通路在调控脂肪积累上的遗传关系。 对unc-64 与ric-4基因进行组织特异性活性分析, 以确定它们在神经系统与肠道内对脂肪积累的影响。
结果: 突触前为神经突触组装所必需的基因的突变并未明显影响脂肪积累。 对调控神经突触功能的基因进行分析的结果显示, SNAREs syntaxin/unc-64与SNAP-25/ric-4基因均参与了脂肪积累的调节。 利用苏丹黑染色与尼罗红标记法观察到unc-64与ric-4突变体肠道中脂肪积累显著增加, 而unc-64与ric-4突变体中积累的脂肪颗粒并未出现尺寸的显著变化。 在神经系统与肠道中, unc-64基因的表达均能显著降低unc-64突变体动物的脂肪积累, 而基因ric-4在神经系统的表达则可以完全恢复ric-4突变体动物的脂肪积累。 遗传分析表明, unc-64 与ric-4对脂肪积累的调控独立于daf-2 (IGF-I受体基因)、 daf-7 (TGF-β配体基因)和nhr-49(核激素受体基因), 且不受daf-16基因突变的影响。 进一步的研究结果显示, unc-64 与ric-4可能经由ARC105/mdt-15与SREBP/sbp-1介导的信号通路来调节动物的脂肪积累进程。 此外, unc-64; ric-4双突变体的脂肪积累水平要显著高于unc-64或ric-4单突变体的脂肪积累水平, 提示这两个基因通过平行的遗传通路调控脂肪积累。
结论: 质膜相关的SNAREs syntaxin/unc-64和SNAP-25/ric-4基因通过平行的遗传通路并经由ARC105/mdt-15与SREBP/sbp-1介导的信号通路来调控秀丽线虫的脂肪积累。