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General Comment |
DDC-4 is related to the secreted frizzled-related proteins (sFRPs), originally defined as tissue-polarity genes in Drosophila (Wolf et al., 1997). sFRPs are approximately 30 kDa in size, and contain a putative signal sequence, a frizzled-like cysteine-rich domain, and a conserved hydrophilic carboxy-terminal domain (Rattner et al., 1997). The frizzled gene family is originally defined in Drosophila as a tissue-polarity gene. Secreted frizzled-related proteins (sFRP's) are approximately 30kDa in size, and contain a putative signal sequence, a cysteine-rich domain, and a conserved hydrophilic carboxy-terminal domain. The cysteine-rich domain is followed by seven putative membrane-spanning segments, a structure suggesting that frizzled is a receptor for one or more ligands that carry tissue polarity information. Recently, a large number of frizzled-related genes have been identified in diverse animals, including mammals, birds, fish, sea urchins, and nematodes. A second frizzled-related gene, Dfz2, was also identified in Drosophila. Dfz2 functions as a receptor for Wingless, one member of the Wnt family of extracellular signaling molecules.
In Drosophila, the DDC cluster of genes has been extensively characterized; at least 12 of these genes have been linked to roles in female fertility. Hemizygous female flies with DDC band deficiency crossed with wild type males; of the 18 alleles available, amdH149, l(2)37Bb1, Bb9, Bb11, Bd6, Be1, Bd7, Be2, Be3, Ce4, and Cg1 did not allow enough growth to form transplantable ovaries; l(2)37Bg1, Bg2, and Cgts1 prevented development of transplanted ovaries in their hosts; l(2)37Ce5 allowed implanted ovaries to attach to oviducts and grow, but
insufficiently for production of eggs; and DdcN27, amd29, and l(2)37Bd4 appeared not to restrict ovary development (McCrady et al.,1994).
With a differential display method, (Wolf et al., 1997) used DDC-4 as a probe to screen a rat ovarian cDNA library; Y81 clone 40 was found as a full length isolate. Y81 clone 40 showed high homology with the cysteine-rich (ligand binding) domain of the frizzled gene family.
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