Abstract
After fertilization but prior to the onset of zygotic transcription, the C. elegans zygote cleaves asymmetrically to create the anterior AB and posterior P1 blastomeres, each of which goes on to generate distinct cell lineages. To understand how patterns of RNA inheritance and abundance arise after this first asymmetric cell division, we pooled hand-dissected AB and P1 blastomeres and performed RNA-seq. Our approach identified over 200 asymmetrically abundant mRNA transcripts. We confirmed symmetric or asymmetric abundance patterns for a subset of these transcripts using smFISH. smFISH also revealed heterogeneous subcellular patterning of the P1-enriched transcripts chs-1 and bpl-1. We screened transcripts enriched in a given blastomere for embryonic defects using RNAi. The gene neg-1 (F32D1.6) encoded an AB-enriched (anterior) transcript and was required for proper morphology of anterior tissues. In addition, analysis of the asymmetric transcripts yielded clues regarding the post-transcriptional mechanisms that control cellular mRNA abundance during asymmetric cell divisions, which are common in developing organisms.
Highlights
Asymmetric cell divisions produce daughter cells of different size, molecular content, or developmental potential
At key moments in development, asymmetric cell divisions give rise to daughter cells of differing characteristics, a process that promotes cell-type diversity in complex organisms
The first cell division of the C. elegans early embryo is a powerful model for understanding asymmetric cell division because the timing of divisions and the placement of their division planes are precise and reproducible
Summary
Asymmetric cell divisions produce daughter cells of different size, molecular content, or developmental potential. These events promote tissue-type diversity in developing embryos, specify terminal differentiation, and allow for the maintenance of adult tissues [1, 2]. Asymmetric cell divisions trigger divergent cell fates through the unequal distribution of cell fate determinants or by moving daughter cells into different morphogen fields [3, 4]. Searches to identify intrinsic cell fate determinants and the mechanisms that guide their asymmetric distribution have been difficult to adapt to high-throughput strategies. A key challenge is separating daughter cells with sufficient purity and yield for genome-wide and proteome-wide assays. We sought to overcome this challenge in Caenorhabditis elegans by coupling a low-input RNA-seq protocol [5, 6] with hand-dissection of blastomeres, which ensures absolute purity in each pool of isolated cells (Fig 1A)
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