Time‐sequenced transcriptomes of developing distal mouse limb buds: A comparative tissue layer analysis

Background The development of the amniote limb has been an important model system to study patterning mechanisms and morphogenesis. For proper growth and patterning, it requires the interaction between the distal sub‐apical mesenchyme and the apical ectodermal ridge (AER) that involve the separate implementation of coordinated and tissue‐specific genetic programs. Results Here, we produce and analyze the transcriptomes of both distal limb mesenchymal progenitors and the overlying ectodermal cells, following time‐coursed dissections that cover from limb bud initiation to fully patterned limbs. The comparison of transcriptomes within each layer as well as between layers over time, allowed the identification of specific transcriptional signatures for each of the developmental stages. Special attention was given to the identification of genes whose transcription dynamics suggest a previously unnoticed role in the context of limb development and also to signaling pathways enriched between layers. Conclusion We interpret the transcriptomic data in light of the known development pattern and we conclude that a major transcriptional transition occurs in distal limb buds between E9.5 and E10.5, coincident with the switch from an early phase continuation of the signature of trunk progenitors, related to the initial proximo distal specification, to a late intrinsic phase of development. Key Findings We generate temporal series of transcriptomes of the AER and the micro‐dissected underlying limb progenitor cells, separately and simultaneously, during critical stages of limb development. We identify a major transition in transcriptional activity occurring between E9.5 and E10.5 in both limb components. We also report the parallel trajectories of the ectoderm and mesoderm limb components, reflecting the strong connection between these two tissue layers. We provide some novel insights into the expression changes associated with the morphogenetic capacity of the limb progenitors and the interaction with the distal ectoderm.