Transcriptomic insights into the molecular basis of brachyurization of the mud crab Scylla paramamosain.

The development of megalopa into the first juvenile crab (C1) in brachyuran species involves a key morphological event known as brachyurization metamorphosis. To date, the molecular mechanism underling brachyurization in crabs remains poorly understood. To shed new light on this process, this study performed comparative transcriptomic analysis of intact individuals and abdominal tissues from the mud crab Scylla paramamosain at the megalopa and C1 stages. It revealed 2317 DEGs in the intact individuals and 4864 DEGs in the abdominal tissues during brachyurization, in which 3514 DEGs were unique to the abdomen. Gene Ontology (GO) and KEGG enrichment analyses further elucidated distinctly functional preferences in different tissues during larval development. DEGs in the intact individuals were enriched in the pathways related to exoskeleton development, such as chitin metabolism and cuticle structure. In contrast, DEGs in the abdominal tissues showed significant enrichment in proteasomes, membrane components, cell junctions, and various signaling pathways (e.g., MAPK, mTOR, Hippo, Wnt), suggesting active roles in cellular remodeling, apoptosis, and signal transduction. In addition, the up-regulated transcription factor genes in the abdominal tissues, including zf-C2H2, Homeobox, and bHLH, are involed in the regulation of developmental processes. The expression profiles of 16 tissue-specific DEGs were further validated by qPCR, confirming the reliability of the transcriptomic data. Our study provides new insights into the molecular basis of brachyurization, revealing that this synergistic process-comprising exoskeleton remodeling, abdominal tissue degradation, and metabolic reprogramming-is precisely regulated by an intricate molecular network.