Mouse Tabby (Ta) and X chromosome-linked human EDA share the features of hypoplastic hair, teeth, and eccrine sweat glands. We have cloned the Ta gene and find it to be homologous to the EDA gene. The gene is altered in two Ta alleles with a point mutation or a deletion. The gene is expressed in developing teeth and epidermis; no expression is seen in corresponding tissues from Ta mice. Ta and EDA genes both encode alternatively spliced forms; novel exons now extend the 3 end of the EDA gene. All transcripts recovered have the same 5 exon. The longest Ta cDNA encodes a 391-residue transmembrane protein, ectodysplasin-A, containing 19 Gly-Xaa-Yaa repeats. The isoforms of ectodysplasin-A may correlate with differential roles during embryonic development.
Anhidrotic ectodermal dysplasia (EDA) is an X-linked recessive disorder which affects ectodermal structures. A cDNA encoding a 135 amino acid protein with mutations in 5-10% of EDA patients has been reported. We have built up a complete splicing map of the EDA gene and characterized the longest and what most probably represents the full-length EDA transcript, EDA-A. It encodes a 391 amino acid transmembrane protein with a short collagenous domain, (Gly-X-Y)19, and is highly homologous to the protein mutated in Tabby mice (Ta-A). Four new transcripts that code for truncated proteins lacking the collagenous domain were also detected. The splice variants show different expression patterns in eight tissues analyzed, suggesting a regulatory mechanism for gene expression. The EDA-A form of the protein is transported to the cell membrane and induces rounding of the cells, properties also associated with the 135 amino acid isoform. We have determined the genomic organization and the exon-intron boundaries of the EDA gene. SSCP analysis of the nine exons corresponding to EDA-A allowed the identification of mutations in 12 out of 15 EDA patients. Interestingly, three mutations removed either two or four of the Gly-X-Y repeats without interrupting the reading frame, thus suggesting a functional role for the collagenous domain. Our results will allow mutation diagnostics in the majority of patients.
Mutations in the human ectodysplasin-A (EDA) are responsible for the most common form of the ectodermal dysplasia and the defective orthologous gene in mice produces the tabby phenotype, suggesting its vital role in the development of hair, sweat glands and teeth. Among several EDA splice isoforms, the most common and the longest EDA splice isoforms, EDA-A1 and EDA-A2, differing by only two amino acids, activate NF-κB-promoted transcription by binding to distinct receptors, EDAR and XEDAR. The extent to which any particular isoform is sufficient for the formation of hair, sweat glands or teeth has remained unclear. Here we report that transgenic expression of the mouse EDA-A1 isoform in tabby (EDA-less) males rescued development of several skin appendages. The transgenic tabby mice showed almost complete restoration of hair growth, dermal ridges, sweat glands and molars. The number of hair follicles in the transgenic mice is the same as in wildtype; though the development of follicles and associated glands varies from indistinguishable from wild-type to smaller and/or only partially formed. These results suggest that the other EDA isoforms may not be absolutely required for skin appendage formation, but consistent with distinctive temporal and spatial expression of the EDA-A2 isoform, are likely required for appropriate timing and completeness of development. Our data provide the first direct physiological evidence that EDA-A1 is a key regulator of hair follicle and sweat gland initiation; its soluble ligand form could aid in deriving therapeutic reagents for conditions affecting hair and sweat gland formation.
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