THOMBOSPONDINS IN EARLY XENOPUS EMBRYOS - DYNAMIC PATTERNS OF EXPRESSION SUGGEST DIVERSE ROLES IN NERVOUS-SYSTEM, NOTOCHORD, AND MUSCLE DEVELOPMENT

The thrombospondins (TSPs) are a family of extracellular matrix (ECM) glycoproteins that modulate many cell behaviors including adhesion, mi gration, and proliferation. Here we report the molecular cloning of th e Xenopus homologs of TSP-1 and TSP-3, and the developmental patterns of expression of Xenopus TSP-1, TSP-3, and TSP-4 mRNAs. Xenopus TSP-1 and TSP-3 protein sequences each share approximately 80% amino acid id entity with their mammalian counterparts. TSP-1 mRNAs are detectable a t low levels in fertilized eggs indicating that this TSP is a maternal ly deposited transcript. Zygotic expression of TSP-1, TSP-3, and TSP-4 begins at the end of gastrulation and transcripts encoding each prote in accumulate through the tadpole stages of development, Whole mount i n situ hybridizations reveal that each TSP mRNA is localized in the em bryo with distinct, developmentally regulated patterns of expression, TSP-1 mRNAs are detected in a wide range of tissues including the floo r plate of the neural tube, epidermis, somites, notochord and, most no tably, alternating rhombomeres. Transcripts encoding TSP-3 are express ed in the notochord, floor plate, sensorial layer of the epidermis and sensory epithelia, TSP-4 mRNAs are restricted to semitic mesoderm and skeletal muscle, These data suggest that the TSPs represent a functio nally diverse family of ECM proteins with tissue-specific functions du ring embryogenesis. (C) 1998 Wiley-Liss, Inc.