Asymmetric Transcript Discovery by RNA-seq in C. elegans Blastomeres Identifies neg-1, a Gene Important for Anterior Morphogenesis

After fertilization but prior to the onset of zygotic transcription, the C. elegans zygote cleaves asymmetrically to create the anterior AB and posterior P(1) 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 P(1) 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 P(1)-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.