A multigene locus containing the Manx and bobcat genes is required for development of chordate features in the ascidian tadpole larva

The Manx gene is required for the development of the tail and other chordat e features in the ascidian tadpole larva. To determine the structure of the Manx gene, we isolated and sequenced genomic clones from the tailed ascidi an Molgula oculata, The Manx gene contains 9 exons and encodes both major a nd minor Manx mRNAs, which differ in the length of their 5' untranslated re gions. The coding region of the single-copy bobcat gene, which encodes a DE AD-box RNA helicase, is embedded within the first Manx intron, The organiza tion of the bobcat and Manx transcription units was determined by comparing genomic and cDNA clones. The Manx-bobcat gene locus has an unusual organiz ation in which a non-coding first exon is alternatively spliced at the 5' e nd of two different mRNAs, The bobcat and Manx genes are expressed coordina tely during oogenesis and embryogenesis, but not during spermatogenesis, in which bobcat mRNA accumulates independently of Manx mRNA, Similar to Manx, zygotic bobcat transcripts accumulate in the embryonic primordia responsib le for generating chordate features, including the dorsal neural tube and n otochord, are downregulated during embryogenesis in the tailless species Mo lgula occulta and are upregulated in M, occulta x M. oculata hybrids, which restore these chordate features. Antisense experiments indicate that zygot ic bobcat expression is required for development of the same suite of chord ate features as Manx, The results show that the Manx-bobcat gene complex ha s a role in the development of chordate features in ascidian tadpole larvae .