Rappleye Chad A, Tagawa Akiko, Le Bot Nathalie, Ahringer Julie, Aroian Raffi V
Section of Cell and Developmental Biology, Univ, of California, San Diego, La Jolla, CA 92093, USA.
BMC Dev Biol. 2003 Oct 3;3:8. doi: 10.1186/1471-213X-3-8.
Cell polarity is essential for many decisions made during development. While investigation of polarity-specific factors has yielded great insights into the polarization process, little is known on how these polarity-specific factors link to the basic cellular mechanisms that function in non-polarity aspects of the cell. To better understand the mechanisms that establish embryonic polarity, we investigated genes required for polarity in the one-cell C. elegans embryo that are also required for other non-polarity functions. This has led to the identification of the Pod-class of mutants that are characterized by osmosensitive embryos and defects in anterior-posterior polarity.
Mutation in either of two loci of this class, emb-8 and pod-2, disrupts embryonic polarization and results in osmotically-sensitive embryos. Loss of emb-8, a previously uncharacterized polarity gene, causes mislocalization of PAR-3 and PAR-2 that molecularly mark the anterior and posterior cortices. emb-8 encodes NADPH-cytochrome P450 reductase, a protein supplying electrons to cytochrome P450-family enzymes, some of which catalyze fatty acid modifications. Cloning of the previously characterized polarity gene pod-2 reveals it encodes acetyl-CoA carboxylase, an enzyme that catalyzes the first step in de novo fatty acid synthesis. Depletion of fatty acid synthase, the next enzyme in the biosynthetic pathway, by RNA-interference (RNAi) also causes similar loss of one-cell polarity. Furthermore, pod-2 polarity defects can be rescued by addition of exogenous fatty acids. By following the behavior of the pronucleus in emb-8 and pod-2 mutant embryos, we demonstrate that loss of polarity correlates with impaired interaction between the pronucleus-centrosome complex and the posterior cortex.
The characterization of emb-8 and pod-2 mutant embryos suggests that the pronucleus-centrosome complex interaction with the cortex plays a direct role in establishing polarity and that fatty acid pathways are important for this polarizing event.
细胞极性对于发育过程中做出的许多决定至关重要。虽然对极性特异性因子的研究已经为极化过程带来了深刻见解，但对于这些极性特异性因子如何与细胞非极性方面起作用的基本细胞机制相联系却知之甚少。为了更好地理解建立胚胎极性的机制，我们研究了单细胞秀丽隐杆线虫胚胎中极性所需的基因，这些基因也是其他非极性功能所必需的。这导致了Pod类突变体的鉴定，其特征是对渗透压敏感的胚胎和前后极性缺陷。
该类别的两个基因座emb-8和pod-2中的任何一个发生突变都会破坏胚胎极化，并导致对渗透压敏感的胚胎。emb-8是一个先前未表征的极性基因，其缺失会导致分子标记前后皮质的PAR-3和PAR-2定位错误。emb-8编码NADPH-细胞色素P450还原酶，一种为细胞色素P450家族酶提供电子的蛋白质，其中一些酶催化脂肪酸修饰。先前表征的极性基因pod-2的克隆表明它编码乙酰辅酶A羧化酶，一种催化从头脂肪酸合成第一步的酶。通过RNA干扰（RNAi）耗尽生物合成途径中的下一种酶脂肪酸合酶，也会导致单细胞极性的类似丧失。此外，添加外源脂肪酸可以挽救pod-2的极性缺陷。通过追踪emb-8和pod-2突变体胚胎中前核的行为，我们证明极性丧失与前核-中心体复合物和后皮质之间的相互作用受损相关。
emb-8和pod-2突变体胚胎的表征表明，前核-中心体复合物与皮质的相互作用在建立极性中起直接作用，并且脂肪酸途径对于这一极化事件很重要。
