Department of Zoology, University of Melbourne, 3010 Victoria, Australia.
Development. 2013 Mar;140(5):965-75. doi: 10.1242/dev.091629. Epub 2013 Jan 23.
Early cell lineage specification in eutherian mammals results in the formation of a pluripotent inner cell mass (ICM) and trophoblast. By contrast, marsupials have no ICM. Here, we present the first molecular analysis of mechanisms of early cell lineage specification in a marsupial, the tammar wallaby. There was no overt differential localisation of key lineage-specific transcription factors in cleavage and early unilaminar blastocyst stages. Pluriblast cells (equivalent to the ICM) became distinguishable from trophoblast cells by differential expression of POU5F1 and, to a greater extent, POU2, a paralogue of POU5F1. Unlike in the mouse, pluriblast-trophoblast differentiation coincided with a global nuclear-to-cytoplasmic transition of CDX2 localisation. Also unlike in the mouse, Hippo pathway factors YAP and WWTR1 showed mutually distinct localisation patterns that suggest non-redundant roles. NANOG and GATA6 were conserved as markers of epiblast and hypoblast, respectively, but some differences to the mouse were found in their mode of differentiation. Our results suggest that there is considerable evolutionary plasticity in the mechanisms regulating early lineage specification in mammals.
真兽类哺乳动物的早期细胞谱系特化导致多能性内细胞团（ICM）和滋养层的形成。相比之下，有袋动物没有 ICM。在这里，我们首次对有袋动物——塔马尔袋鼠的早期细胞谱系特化机制进行了分子分析。在卵裂和早期单层囊胚阶段，关键谱系特异性转录因子没有明显的差异定位。多能性胚细胞（相当于 ICM）通过 POU5F1 的差异表达，以及更广泛的 POU2（POU5F1 的同源物）的差异表达，与滋养层细胞区分开来。与小鼠不同的是，多能性-滋养层分化与 CDX2 定位的全局核质转移同时发生。与小鼠不同的是，Hippo 通路因子 YAP 和 WWTR1 显示出相互不同的定位模式，表明它们具有非冗余的作用。NANOG 和 GATA6 分别作为上胚层和下胚层的标志物被保守下来，但在它们的分化方式上与小鼠存在一些差异。我们的研究结果表明，在调控哺乳动物早期谱系特化的机制方面，存在着相当大的进化可塑性。
