A NOVEL MEMBER OF THE TRANSFORMING-GROWTH-FACTOR-BETA (TGF-BETA) SUPERFAMILY FROM THE FILARIAL NEMATODES BRUGIA-MALAYI AND BRUGIA-PAHANGI

Transforming growth factor-beta (TGF-beta) superfamily genes encode pr oducts controlling pattern formation, cell differentiation, and immune -mediated inflammation. Members of this superfamily are known in multi cellular organisms from mammals to the model nematode Caenorhabditis e legans. Using PCR with oligonucleotides complementary to highly conser ved motifs in the TGF-beta superfamiIy, we first isolated a genomic cl one from the filarial nematode Brugia malayi. This gene, termed Bm-tgh -1 (TGF-beta) homolog-1), spans 2.5 kb of genomic DNA and contains sev en exons. Transcripts of this gene art: poorly represented in cDNA lib raries, bur a full-length cDNA was isolated by RACE from B. pahangi (B p-tgh-1). The tgh-1 genes from the two species are >98% identical at t he nucleotide and amino acid levels, differing at 18/1576 base pairs a nd 5/428 amino acids; all nonsynonymous substitutions are in the long N-terminal propeptide. They show a high level of similarity throughout all seven exons to a C. elegans gene on cosmid T25F10. Homology to ot her members of the TGF-beta superfamily is restricted to the C-termina l domain which contains the mature active protein. Key features shared with other members of the superfamily include the tetrabasic proteoly tic cleavage site to release an active C-terminal peptide, seven cyste ines arrayed in identical fashion, and conserved sequence motifs. tgh- 1 is most similar to the BMP-1 subfamily involved in developmental sig naling in nematodes, insects, and vertebrates. RT-PCR on first-strand cDNA from both Brugia species, with primers specific to the 3' end, sh owed that tgh-1 is not expressed in the microfilarial stage, but is de tectable in the mosquito-derived infective larvae and is maximal in ma turing parasites around the time of molting in the mammalian host. Adu lt parasites show a relatively low level of expression. The identifica tion of tgh-1, and its preferential expression in developing parasites , suggests that it may be involved in key developmental events in the complex filarial life cycle. (C) 1998 Academic Press.