Developmental Expression of Transcription Factors and Wnt Ligands in Sponge Halisarca Dujardinii

Understanding the molecular mechanisms that guided early animal evolution is a central challenge of evolutionary developmental biology. Sponges (Porifera), as one of the earliest-branching metazoan lineages, are crucial for reconstructing the ancestral genetic toolkit for development. Here, we present the first transcriptomic analysis of embryogenesis in the demosponge Halisarca dujardinii, characterizing gene expression across three key stages: cleavage, blastula, and prelarva. We identified significant transcriptional shifts, including upregulation of cadherins during blastula formation, suggesting the establishment of adherens junctions, and a wave of kinase expression in the prelarva. Furthermore, we phylogenetically classified and analyzed the developmental expression of 186 transcription factors from the zinc finger, homeobox, Forkhead, and T-box families. Strikingly, spatial expression analysis revealed that Wnt ligands and T-box genes are expressed in complementary domains along the embryonic anterior-posterior axis, with HduWntL specifically marking the future posterior pole from the blastula stage. Our results demonstrate that despite its morphological simplicity, H. dujardinii employs a complex repertoire of developmental transcription factors and signaling molecules, and provides evidence for the early specification of the primary body axis, offering new insights into the evolution of developmental mechanisms in metazoans.