Scuola Normale Superiore, Pisa, Italy.
Scuola Normale Superiore, Pisa, Italy ; Fritz Lipmann Institute for Age Research, Leibniz Institute, Leibniz, Germany.
Evodevo. 2014 Sep 22;5:32. doi: 10.1186/2041-9139-5-32. eCollection 2014.
Annual killifishes inhabit temporary ponds and their embryos survive the dry season encased in the mud by entering diapause, a process that arrests embryonic development during hostile conditions. Annual killifishes are present within three clades distributed in Africa (one East and one West of the Dahomey gap) and South America. Within each of these phylogenetic clades, a non-annual clade is sister taxon to a annual clade and therefore represent an example of convergent evolution. Early cleavage of teleost embryos is characterized by a very fast cell cycle (15-30 minutes) and lack of G1 and G2 phases. Here, we decided to investigate rates of early cleavage in annual killifishes. In addition, we specifically tested whether also annual killifish embryos lack G1 and G2 phases.
We used time lapse brightfield microscopy to investigate cell division kinetics during the first developmental stages of annual- and non-annual species belonging to the three different phylogenetic clades. Annual killifishes of all three clades showed cleavage times significantly longer when compared to their non-annual sister taxa (average 35 min vs. average 75 min). Using FUCCI fluorescent imaging of the cell cycle after microinjection in the annual species Nothobranchius furzeri, we demonstrate that the first 5 division are synchronous and do not show a G1 phase. Cell cycle synchronization is lost after the 5th cleavage division.
Our results show, for the first time, that cell cycle rate during cleavage, a trait thought to be rather evolutionary conserved can undergo convergent evolutionary change in response to variations in life-history.
一年生的弹涂鱼栖息在季节性池塘中，其胚胎通过进入休眠来在泥中度过干旱季节，这一过程在恶劣条件下阻止胚胎发育。一年生弹涂鱼分布在三个分支中，分别位于非洲（达荷美缺口以东和以西各一个）和南美洲。在这些系统发育分支中的每一个中，非一年生分支是一年生分支的姐妹分类群，因此代表了趋同进化的一个例子。硬骨鱼胚胎的早期卵裂以非常快的细胞周期（15-30 分钟）和缺乏 G1 和 G2 期为特征。在这里，我们决定研究一年生弹涂鱼的早期卵裂速度。此外，我们特别测试了一年生弹涂鱼胚胎是否也缺乏 G1 和 G2 期。
我们使用延时明场显微镜来研究属于三个不同系统发育分支的一年生和非一年生物种在第一个发育阶段的细胞分裂动力学。与非一年生姐妹类群相比，所有三个分支的一年生弹涂鱼的卵裂时间明显更长（平均 35 分钟对平均 75 分钟）。通过对一年生物种 Nothobranchius furzeri 进行微注射后的细胞周期 FUCCI 荧光成像，我们证明前 5 次分裂是同步的，并且没有 G1 期。第 5 次卵裂后，细胞周期同步性丧失。
我们的结果首次表明，在卵裂过程中的细胞周期率，这一被认为是相当进化保守的特征，可以在生活史的变化下发生趋同进化的改变。
