Multiple Dlk1 splice variants are expressed during early mouse embryogenesis.

Delta-like homologue 1 (Dlk1), an atypical Notch ligand, is known to have roles in growth and development, stem cell maintenance, and cancer. Evidence suggests that Dlk1 expression patterns are more complex than previously appreciated, with multiple isoforms expressed in various tissues in both the embryo and adult. However, the early embryonic expression of Dlk1 has not been well examined. Given that tissue specific Dlk1 knockouts have to date failed to recapitulate phenotypes associated with the conventional Dlk1 loss of function model, a better understanding of early Dlk1 expression is important. To address this question, we have examined Dlk1 expression during the early stages of mouse embryogenesis. Dlk1 expression was first detected at Theiler Stage 14 (TS14), and its expression pattern persisted in specific tissues through TS20. Further, we found that all known Dlk1 splice isoforms were expressed in early embryogenesis, with Dlk1-A and Dlk1-C/C2 isoforms being expressed at the highest levels. The broad co-expression of multiple Dlk1 isoforms corroborates recent work suggesting that Dlk1-mediated signaling may act through multiple DLK1 isoforms to balance differentiation.