title: The maternal transcriptome of the crustacean Parhyale hawaiensis is inherited asymmetrically to invariant cell lineages of the ectoderm and mesoderm.
abstract: BACKGROUND
  The embryo of the crustacean Parhyale hawaiensis has a total, unequal and invariant early cleavage pattern. It specifies cell fates earlier than other arthropods, including Drosophila, as individual blastomeres of the 8-cell stage are allocated to the germ layers and the germline. Furthermore, the 8-cell stage is amenable to embryological manipulations. These unique features make Parhyale a suitable system for elucidating germ layer specification in arthropods. Since asymmetric localization of maternally provided RNA is a widespread mechanism to specify early cell fates, we asked whether this is also true for Parhyale. A candidate gene approach did not find RNAs that are asymmetrically distributed at the 8-cell stage. Therefore, we designed a high-density microarray from 9400 recently sequenced ESTs (1) to identify maternally provided RNAs and (2) to find RNAs that are differentially distributed among cells of the 8-cell stage.
  
  
  RESULTS
  Maternal-zygotic transition takes place around the 32-cell stage, i.e. after the specification of germ layers. By comparing a pool of RNAs from early embryos without zygotic transcription to zygotic RNAs of the germband, we found that more than 10% of the targets on the array were enriched in the maternal transcript pool. A screen for asymmetrically distributed RNAs at the 8-cell stage revealed 129 transcripts, from which 50% are predominantly expressed in the early embryonic stages. Finally, we performed knockdown experiments for two of these genes and observed cell-fate-related defects of embryonic development.
  
  
  CONCLUSIONS
  In contrast to Drosophila, the four primary germ layer cell lineages in Parhyale are specified during the maternal control phase of the embryo. A key step in this process is the asymmetric distribution of a large number of maternal RNAs to the germ layer progenitor cells.
authors: Max Planck Institut für Entwicklungsbiologie, Tübingen, Germany.
authors: Peter
authors: P
authors: Nestorov
authors: Florian
authors: F
authors: Battke
authors: Mitchell P
authors: MP
authors: Levesque
authors: Matthias
authors: M
authors: Gerberding
mesh_terms: D033304:Amphipoda / Q000196:embryology / Q000235:genetics* / Q000378:metabolism; D000818:Animals; D019070:Cell Lineage / Q000235:genetics*; D004475:Ectoderm / Q000166:cytology / Q000196:embryology / Q000378:metabolism*; D005260:Female; D008648:Mesoderm / Q000166:cytology / Q000196:embryology / Q000378:metabolism*; D011247:Pregnancy; D059467:Transcriptome / Q000235:genetics*