Vellutini Bruno C, Martín-Durán José M, Hejnol Andreas
Sars International Centre for Marine Molecular Biology, University of Bergen, Thormøhlensgate 55, 5006, Bergen, Norway.
BMC Biol. 2017 Apr 28;15(1):33. doi: 10.1186/s12915-017-0371-9.
Stereotypic cleavage patterns play a crucial role in cell fate determination by precisely positioning early embryonic blastomeres. Although misplaced cell divisions can alter blastomere fates and cause embryonic defects, cleavage patterns have been modified several times during animal evolution. However, it remains unclear how evolutionary changes in cleavage impact the specification of blastomere fates. Here, we analyze the transition from spiral cleavage - a stereotypic pattern remarkably conserved in many protostomes - to a biradial cleavage pattern, which occurred during the evolution of bryozoans.
Using 3D-live imaging time-lapse microscopy (4D-microscopy), we characterize the cell lineage, MAPK signaling, and the expression of 16 developmental genes in the bryozoan Membranipora membranacea. We found that the molecular identity and the fates of early bryozoan blastomeres are similar to the putative homologous blastomeres in spiral-cleaving embryos.
Our work suggests that bryozoans have retained traits of spiral development, such as the early embryonic fate map, despite the evolution of a novel cleavage geometry. These findings provide additional support that stereotypic cleavage patterns can be modified during evolution without major changes to the molecular identity and fate of embryonic blastomeres.
定型分裂模式通过精确定位早期胚胎卵裂球在细胞命运决定中起关键作用。尽管错位的细胞分裂会改变卵裂球命运并导致胚胎缺陷，但在动物进化过程中分裂模式已多次改变。然而，尚不清楚分裂的进化变化如何影响卵裂球命运的特化。在此，我们分析了在苔藓虫进化过程中发生的从螺旋分裂（一种在许多原口动物中显著保守的定型模式）到双辐射分裂模式的转变。
使用三维实时成像延时显微镜（四维显微镜），我们对苔藓虫膜孔苔虫的细胞谱系、丝裂原活化蛋白激酶（MAPK）信号传导以及16个发育基因的表达进行了表征。我们发现早期苔藓虫卵裂球的分子特性和命运与螺旋分裂胚胎中假定的同源卵裂球相似。
我们的研究表明，尽管进化出了新的分裂几何形状，但苔藓虫保留了螺旋发育的特征，如早期胚胎命运图谱。这些发现进一步支持了在进化过程中定型分裂模式可以被改变，而胚胎卵裂球的分子特性和命运不会发生重大变化。
