Holloway Beth A, Gomez de la Torre Canny Sol, Ye Ying, Slusarski Diane C, Freisinger Christina M, Dosch Roland, Chou Margaret M, Wagner Daniel S, Mullins Mary C
Department of Cell and Developmental Biology, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania, United States of America.
PLoS Genet. 2009 Mar;5(3):e1000413. doi: 10.1371/journal.pgen.1000413. Epub 2009 Mar 13.
One of the earliest morphogenetic processes in the development of many animals is epiboly. In the zebrafish, epiboly ensues when the animally localized blastoderm cells spread, thin over, and enclose the vegetally localized yolk. Only a few factors are known to function in this fundamental process. We identified a maternal-effect mutant, betty boop (bbp), which displays a novel defect in epiboly, wherein the blastoderm margin constricts dramatically, precisely when half of the yolk cell is covered by the blastoderm, causing the yolk cell to burst. Whole-blastoderm transplants and mRNA microinjection rescue demonstrate that Bbp functions in the yolk cell to regulate epiboly. We positionally cloned the maternal-effect bbp mutant gene and identified it as the zebrafish homolog of the serine-threonine kinase Mitogen Activated Protein Kinase Activated Protein Kinase 2, or MAPKAPK2, which was not previously known to function in embryonic development. We show that the regulation of MAPKAPK2 is conserved and p38 MAP kinase functions upstream of MAPKAPK2 in regulating epiboly in the zebrafish embryo. Dramatic alterations in calcium dynamics, together with the massive marginal constrictive force observed in bbp mutants, indicate precocious constriction of an F-actin network within the yolk cell, which first forms at 50% epiboly and regulates epiboly progression. We show that MAPKAPK2 activity and its regulator p38 MAPK function in the yolk cell to regulate the process of epiboly, identifying a new pathway regulating this cell movement process. We postulate that a p38 MAPKAPK2 kinase cascade modulates the activity of F-actin at the yolk cell margin circumference allowing the gradual closure of the blastopore as epiboly progresses.
许多动物发育过程中最早出现的形态发生过程之一是外包。在斑马鱼中，当位于动物极的胚盘细胞扩散、变薄并包围位于植物极的卵黄时，外包过程就开始了。已知只有少数几个因子在这个基本过程中发挥作用。我们鉴定出一个母性效应突变体，名为贝蒂·布普（bbp），它在外包过程中表现出一种新的缺陷，即当卵黄细胞的一半被胚盘覆盖时，胚盘边缘会急剧收缩，导致卵黄细胞破裂。全胚盘移植和mRNA显微注射拯救实验表明，Bbp在卵黄细胞中发挥作用以调节外包过程。我们通过定位克隆了母性效应bbp突变基因，并确定它是丝氨酸 - 苏氨酸激酶丝裂原活化蛋白激酶激活蛋白激酶2（MAPKAPK2）的斑马鱼同源物，此前并不知晓该基因在胚胎发育中发挥作用。我们发现，MAPKAPK2的调控机制是保守的，并且在斑马鱼胚胎中，p38丝裂原活化蛋白激酶在调节外包过程中位于MAPKAPK2的上游发挥作用。钙动力学的显著变化，以及在bbp突变体中观察到的巨大边缘收缩力，表明卵黄细胞内的F - 肌动蛋白网络过早收缩，该网络在50%外包时首次形成并调节外包进程。我们证明，MAPKAPK2活性及其调节因子p38 MAPK在卵黄细胞中发挥作用以调节外包过程，从而确定了一条调节这一细胞运动过程的新途径。我们推测，一个p38 MAPKAPK2激酶级联反应调节卵黄细胞边缘周围F - 肌动蛋白的活性，使得随着外包进程胚孔逐渐关闭。
