The Xenopus primordial germ cell transcriptome identifies sox7: a novel role in early PGC development

Abstract

Xenopus primordial germ cells (PGCs) are determined by the presence of maternally derived germ plasm. Germ plasm components both protect PGCs from somatic differentiation and begin a unique gene expression program. Segregation of the germline from the endodermal lineage occurs during gastrulation, and PGCs subsequently initiate zygotic transcription. However, the gene-network(s) that operate to both preserve and promote germline differentiation are poorly understood. Here, we utilized RNA-sequencing analysis to comprehensively interrogate PGC and neighboring endoderm cell mRNAs after lineage segregation. We identified 1,865 transcripts enriched in PGCs compared to endoderm cells. We next compared the PGC-enriched transcripts to previously identified maternal, vegetally-enriched transcripts, and found that >50% of maternal transcripts were enriched in PGCs, including sox7. PGC-directed sox7 knockdown and over-expression studies revealed an early requirement for sox7 in germ plasm localization, zygotic transcription, and PGC number. We identified oct60 as the most highly expressed and enriched OCT3/4 homologue in PGCs. We compared the Xenopus PGC transcriptome with human PGC transcripts and showed that 80% of genes are conserved, underscoring the usefulness of Xenopus for human based studies.