The Anhidrotic Ectodermal Dysplasia Gene (EDA) Undergoes Alternative Splicing and Encodes Ectodysplasin-A with Deletion Mutations in Collagenous Repeats

Abstract

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 within a furin consensus sequence block proteolytic release of ectodysplasin-A and cause X-linked hypohidrotic ectodermal dysplasia

“…Finally mutations of the basic amino acids at positions P1, P2, and P4, key to the activity of furin (40), blocked cleavage of corresponding peptides by furin and proteolytic processing of recombinant EDA in cell culture. The fact that these P2 and P4 mutations are ones identified in patients with XLHED (5,6,23,54) further implicates furin in the biological processing of EDA.…”

“…When this condition goes unrecognized, there is a 30% mortality rate due to hypothermia during the first 2 years of life (2). The XLHED locus, ED-1, encodes a multidomain transmembrane protein, ectodysplasin-A (EDA) (1,(3)(4)(5)(6). A similar X-linked disorder also exists in mice and is due to spontaneous mutations of the murine ortholog of EDA (3,4).…”

“…The triple helical domain and EC1 compose a stalk region separating the TNF ligand domain from the cell surface. EDA shows extensive alternative splicing, but only the two largest forms, EDA-A1 (391 aa) and EDA-A2 (389 aa), contain the EC2 domain with its TNF motif (6). Although the presence of a collagen domain in the stalk region of EDA is unusual in the context of TNF cytokines, this overall structure is similar to that of the adipocyte protein ACRP30 and characteristic of the structure of C1q family proteins, which together form a TNF-C1q superfamily (11,19).…”

“…A role for furin processing in the function of EDA is suggested by the detection of mutations involving four of five basic amino acids in the EDA compound consensus furin site of XLHED patients (5,6,23,54) as shown in Fig. 1 A.…”

Traf6 is essential for murine tooth cusp morphogenesis

“…There are only two amino acid differences between EdaA1 and EdaA2, but EdaA1 and EdaA2 bind to different receptors (Bayes et al, 1998). EdaA1 binds to Edar, whereas EdaA2 binds to a novel TNF receptor Xedar (Yan et al, 2000).…”