The Ionian School, Genetic Code and tRNA Origin Laboratory, Via Roma 19, 67030, Alfedena (L'Aquila), Italy.
Biosystems. 2021 Dec;210:104563. doi: 10.1016/j.biosystems.2021.104563. Epub 2021 Oct 13.
The stage reached by the evolution of cellularity in the Last Universal Common Ancestor (LUCA) has not yet been identified. In actual fact, it has not been clarified whether the LUCA was a cell (genote) or a protocell (progenote). Recently, Pende et al. (2021) analysed the phylogenetic distribution of the cell division system present in bacteria and archaea reaching the conclusion that LUCA was a cell and not a progenote. I find this conclusion unreasonable with respect to the observations they presented. One of the points is that the presence in the domains of life of many genes - some paralogs - which would define the membrane-remodeling superfamily would seem to imply a tempo and a mode of evolution for the LUCA more typical of the progenote than the genote. Indeed, the simultaneous presence of different genes - in a given evolutionary stage and with functions that are also partially correlated - would seem to define a heterogeneity that would appear to be the expression of a rapid and progressive evolution precisely because this evolution would have taken place in the diversification of all these genes. Furthermore, the presence of different genes coding for the function of cell division and related functions could reflect a progenotic status in LUCA, precisely because these functions might have originated from a single ancestral gene instead coding for a protein (or proteins) with multiple functions, and therefore an expression of a rapid and progressive evolution typical of the progenote. I also criticize other aspects of considerations made by Pende at al. (2021). The arguments presented here together with those existing in the literature make the hypothesis of a cellular LUCA favoured by Pende et al. (2021) unlikely.
真核生物最后共同祖先（LUCA）中细胞进化所达到的阶段尚未确定。事实上，LUCA 究竟是一个细胞（基因种）还是一个原细胞（原基因种）还没有得到澄清。最近，Pende 等人（2021）分析了细菌和古菌中存在的细胞分裂系统的系统发育分布，得出结论认为 LUCA 是一个细胞，而不是一个原细胞。我认为他们提出的观察结果得出这个结论是不合理的。其中一个观点是，生命领域中许多基因（有些是旁系同源基因）的存在，这些基因定义了膜重塑超家族，这似乎意味着 LUCA 的进化时间和模式更类似于原基因种，而不是基因种。事实上，在给定的进化阶段，同时存在不同的基因——具有部分相关功能的基因——似乎定义了一种异质性，这种异质性似乎是快速和渐进进化的表现，正是因为这种进化发生在所有这些基因的多样化过程中。此外，不同的基因编码细胞分裂和相关功能的存在可能反映了 LUCA 中的原细胞状态，正是因为这些功能可能起源于单个祖先基因，而不是编码具有多种功能的蛋白质（或蛋白质），因此是快速和渐进进化的典型表现，而这种进化典型存在于原细胞中。我还批评了 Pende 等人（2021）提出的其他考虑因素。这里提出的论点以及文献中存在的论点，使得 Pende 等人（2021）提出的具有细胞的 LUCA 的假设不太可能成立。
