Department of Biology, University of New Brunswick, Fredericton, Canada E3B 5A3.
Proc Biol Sci. 2020 Dec 9;287(1940):20201414. doi: 10.1098/rspb.2020.1414. Epub 2020 Dec 2.
In multicellular organisms with specialized cells, the most significant distinction among cell types is between reproductive (germ) cells and non-reproductive/somatic cells (soma). Although soma contributed to the marked increase in complexity of many multicellular lineages, little is known about its evolutionary origins. We have previously suggested that the evolution of genes responsible for the differentiation of somatic cells involved the co-option of life history trade-off genes that in unicellular organisms enhanced survival at a cost to immediate reproduction. In the multicellular green alga, , cell fate is established early in development by the differential expression of a master regulatory gene known as . A closely related -Like Sequence () is present in its single-celled relative, . is expressed in response to stress, and we proposed that an environmentally induced -like gene was co-opted into a developmental pathway in the lineage leading to . However, the exact evolutionary scenario responsible for the postulated co-option event remains to be determined. Here, we show that in addition to being developmentally regulated, can also be induced by environmental cues, indicating that has maintained its ancestral regulation. We also found that the absence of a functional RegA protein confers increased sensitivity to stress, consistent with RegA having a direct or indirect role in stress responses. Overall, this study (i) provides mechanistic evidence for the co-option of an environmentally induced gene into a major developmental regulator, (ii) supports the view that major morphological innovations can evolve via regulatory changes and (iii) argues for the role of stress in the evolution of multicellular complexity.
在具有专门细胞的多细胞生物中，细胞类型之间最重要的区别是生殖（生殖）细胞和非生殖/体细胞（体细胞）之间的区别。尽管体细胞为许多多细胞谱系的显著复杂性增加做出了贡献，但对其进化起源知之甚少。我们之前曾提出，负责体细胞分化的基因的进化涉及到对生活史权衡基因的共同选择，这些基因在单细胞生物中以牺牲立即繁殖为代价提高了生存能力。在单细胞绿藻中，细胞命运在发育早期通过称为的主调控基因的差异表达来建立。其单细胞近亲中存在一个密切相关的序列（）。对胁迫作出反应，我们提出了一种环境诱导的样基因被共同选择到导致的发育途径中。然而，导致所假设的共同选择事件的精确进化情景仍有待确定。在这里，我们表明，除了受发育调控外，还可以被环境线索诱导，表明其维持了其祖先的调控。我们还发现，功能缺失的 RegA 蛋白赋予对胁迫的敏感性增加，这与 RegA 在应激反应中具有直接或间接作用一致。总的来说，这项研究（i）提供了将环境诱导基因共同选择为主要发育调节剂的机制证据，（ii）支持了主要形态创新可以通过调节变化进化的观点，以及（iii）认为应激在多细胞复杂性的进化中起作用。
