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The origin and elaboration of the central nervous system played an important role in chordate and vertebrate history. All chordates possess a dorsal tubular central nervous system, but elaboration of dorsoventral and segmental pattern is far more pronounced in cephalochordates and vertebrates than in the more basal urochordates. Analysis of the urochordates, therefore, should allow deduction of the neural organization and neuronal patterning mechanisms that predated overt dorsoventral and segmental complexity. Here we report functional studies of the ascidian Pax gene (HrPax-37). The spatiotemporal expression pattern of HrPax-37 has suggested involvement in two distinct developmental processes: specification of dorsal cell fates of ectoderm during neurulation, and regional differentiation of the neural tube in later stages. Here we show that HrPax-37 is descendent from the precursor of the Pax-3 and Pax-7 genes implicated in specification of dorsal fate in the vertebrate neural tube. We also demonstrate that injection of HrPax-37 RNA into fertilized eggs causes ectopic expression of the dorsal neural marker tyrosinase gene in neurulae, confirming a regulatory role in dorsal patterning of the neural tube comparable to its vertebrate homologues. These results suggest that dorsal specification in the neural tube by Pax-3/7 subfamily genes was established in the ancestors of extant chordates during emergence of the dorsal tubular nervous system.

Original publication




Journal article


Dev Biol

Publication Date





240 - 252


Amino Acid Sequence, Animals, Antigens, Differentiation, Base Sequence, Body Patterning, Cell Differentiation, Central Nervous System, Cloning, Molecular, DNA, Complementary, DNA-Binding Proteins, Epidermis, Evolution, Molecular, Histocytochemistry, Homeodomain Proteins, In Situ Hybridization, Models, Genetic, Molecular Sequence Data, Multigene Family, Muscle Proteins, Nerve Tissue Proteins, PAX3 Transcription Factor, PAX7 Transcription Factor, Paired Box Transcription Factors, Sequence Analysis, DNA, Sequence Homology, Amino Acid, Time Factors, Tissue Distribution, Transcription Factors, Urochordata