title: POPK-1/Sad-1 kinase is required for the proper translocation of maternal mRNAs and putative germ plasm at the posterior pole of the ascidian embryo.
abstract: Maternal mRNAs localized to specific regions in eggs play important roles in the establishment of embryonic axes and germ layers in various species. Type I postplasmic/PEM mRNAs, which are localized to the posterior-vegetal cortex (PVC) of fertilized ascidian eggs, such as the muscle determinant macho-1 mRNA, play key roles in embryonic development. In the present study, we analyzed the function of the postplasmic/PEM RNA Hr-POPK-1, which encodes a kinase of Halocynthia roretzi. When the function of POPK-1 was suppressed by morpholino antisense oligonucleotides, the resulting malformed larvae did not form muscle or mesenchyme, as in macho-1-deficient embryos. Epistatic analysis indicated that POPK-1 acts upstream of macho-1. When POPK-1 was knocked down, localization of every Type I postplasmic/PEM mRNA examined, including macho-1, was perturbed, showing diffuse early distribution and eventual concentration into a smaller area. This is the probable reason for the macho-1 dysfunction. The postplasmic/PEM mRNAs such as macho-1 and Hr-PEM1 are co-localized with the cortical endoplasmic reticulum (cER) and move with it after fertilization. Eventually they become highly concentrated into a subcellular structure, the centrosome-attracting body (CAB), at the posterior pole of the cleaving embryos. The suppression of POPK-1 function reduced the size of the domain of concentrated cER at the posterior pole, indicating that POPK-1 is involved in the movement of postplasmic/PEM RNAs via relocalization of cER. The CAB also shrank. These results suggest that Hr-POPK-1 plays roles in concentration and positioning of the cER, as well as in the concentration of CAB materials, such as putative germ plasm, in the posterior blastomeres.
authors.affiliation: Department of Biological Sciences, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan. yorinaka@bio.sci.osaka-u.ac.jp
authors.forename: Yoriko
authors.initials: Y
authors.lastname: Nakamura
authors.forename: Kazuhiro W
authors.initials: KW
authors.lastname: Makabe
authors.forename: Hiroki
authors.initials: H
authors.lastname: Nishida
mesh_terms: D000818:Animals; D001692:Biological Transport; D001757:Blastomeres / Q000166:cytology; D019521:Body Patterning; D004625:Embryo, Nonmammalian; D004721:Endoplasmic Reticulum / Q000378:metabolism; D005855:Germ Layers; D047908:Intracellular Signaling Peptides and Proteins; D017346:Protein Serine-Threonine Kinases / Q000502:physiology*; D023121:RNA, Messenger, Stored / Q000378:metabolism*; D014561:Urochordata; D015053:Zygote
chemical_list: D047908:Intracellular Signaling Peptides and Proteins; D023121:RNA, Messenger, Stored; C421165:sad-1 protein, C elegans; D017346:Protein Serine-Threonine Kinases