(last modified March 10, 2004)
Human and mouse contain two homologous dystrobrevin genes, alpha- (DTNA) and beta-dystrobrevin (DTNB). The alpha-dystrobrevin gene encodes several mRNA transcripts and protein isoforms that are expressed in different tissues, including brain and muscle. Different nomenclatures have been used to describe the different isoforms (Blake, Sadoulet-Puccio, Ambrose). To facilitate a clear distinction with beta-dystrobrevin, we use the nomenclature proposed by Ambrose, i.e. DTNA-1, DTNA-2, DTNA-3, etc.
When dystrophin is isolated from the electric organ of Torpedo californica, it is associated with two proteins of 58 kDa (homologous to the syntrophins) and 87 kDa (Butler (1992) J.Biol.Chem. 267:6213-6218). Khurana et al. cloned the human homologue of the Torpedo 87 kDa protein, starting from a human EST-sequence (EST00891) which showed homology with dystrophin. Later, Sadoulet-Puccio et al. named the protein "Dystrobrevin". The human alpha-dystrobrevin gene (Gene Symbol DTNA) contains 24 coding exons, spans at least 180 kb (Sadoulet-Puccio) and maps to the long arm of chromosome 18 (18q12.1-q12.2). The murine gene maps to the proximal part of chromosome 18. Many distinct alpha-dystrobrevin mRNAs have been detected. These are expressed in different tissues, generated by three different promoters, using different sets of 5'UTR exons, extensive alternative splicing and three different 3'-terminal exons. Dystrobrevin transcripts are strongly expressed in brain, skeletal and cardiac muscle, while lower levels are found in liver, lung and pancreas. No transcript could be detected in kidney or placenta.
DTNA is hydrophylic protein which is highly similar to the Cysteine-rich C-terminal end of dystrophin containing an additional 148 amino acid C-terminal end with four potential tyrosine phosphorylation sites. Different numbers of DTNA isoforms have been found on Western blots (types 1 to 3), generated by alternative splicing, truncated at the C-terminus. In addition to dystrophin and syntrophin, DTNA is able to bind with the sarcoglycan–sarcospan complex (Yoshida et al., 2000), syncoilin (Newey et al., 2001), dysbindin (Benson et al., 2001), and desmuslin (Mizuno et al., 2001). Yoshida et al. (2000). found that the N-terminal half of dystrobrevin participates in an association with the sarcoglycan-sarcospan complex. The authors hypothesized that the sarcoglycan-sarcospan complex is linked to the signaling protein neuronal nitric oxide synthase via alpha-syntrophin associated with dystrobrevin.
Blake found that the composition of the dystrophin-associated protein complex in the brain differs from that in muscle. Because beta-dystrobrevin and dystrophin are expressed in similar populations of neurons in the hippocampus and cortex, it is possible that beta-dystrobrevin interacts directly with dystrophin. If this is the case, then beta-dystrobrevin levels may be reduced in DMD patients similar to the reduction in sarcolemmal staining seen with other components of the DGC in dystrophic muscle. The findings may be relevant to the cognitive dysfunction affecting DMD/BMD patients.
In a Japanese family in which members of four generations were affected, five with LVNC associated with congenital heart defects and one with isolated LVNC Ichida et al. (2001) found a missense mutation (Pro121Leu) in the DTNA-gene.
Links to other databases:
Gene
Symbol nomenclature LocusLink
OMIM Gene Map
When dystrophin is isolated from the electric organ of Torpedo californica, it is associated with two proteins of 58 kDa (homologous to the syntrophins) and 87 kDa (Butler et al. [1992]). The Torpedo 87 kDa protein was recently cloned and found to encode a 726 amino acid 82,037 Dalton protein (Wagner (1993) Neuron 10:511-522). Khurana et al. cloned the human homologue of this protein, starting from a human EST-sequence (EST00891) which showed homology with dystrophin. Later, Sadoulet-Puccio et al. named the protein "Dystrobrevin". Thus, dystrobrevin is the mammalian homologue of a 87 kDa post-synaptic phosphoprotein of Torpedo californica, showing a moderate but significant homology to the cysteine-rich C-terminal domain of dystrophin.
The human alpha-dystrobrevin (Gene Symbol DTNA, aliases DRP3 DTN DTN-1 DTN-2 DTN-3) gene contains 24 coding exons spanning at least 180 kb (Sadoulet-Puccio). FISH-analysis showed that the gene maps to the long arm of chromosome 18 (18q12.1-q12.2, Khurana). The murine dystrobrevin gene was isolated on murine YACs (ICRFy902L2418Q and ICRFy902M0312Q) and spans about 170 kb (Ambrose). The murine DTNA gene contains a CA-repeat in its 3'UTR (95/HA/001, Blake) which could be mapped to the D18Mit62-D18Mit23 interval at the proximal part of murine chromosome 18 (Ambrose).
A comparison of the genomic organization of dystrophin and dystrobrevin showed that the two genes have significant similarities in their genomic structure, implying an ancestral or evolutionary relationship.
| Exon | Exon size (bp) | Intron size (kb) | 5' cDNA position | Splice after | Remarks |
|---|---|---|---|---|---|
| B | 23 | -352 | - | 1st exon / 5'UTR | |
| F | 93 | - | 5'UTR exon | ||
| E | 128 | - | 5'UTR exon | ||
| G | 53 | - | 5'UTR exon | ||
| C | 209 | -338 | - | 1st exon / 5'UTR | |
| D | 127 | -128 | - | 5'UTR exon | |
| A | 242 | -243 | - | 1st exon / 5'UTR | |
| 1 | 68 | 10 | -1 | 1 | |
| 2 | 81 | 20 | 68 | 1 | |
| 3 | 214 | 13 | 149 | 2 | encodes calcium-binding EF-hand 1, part of 2 |
| 4 | 86 | >15 | 363 | 1 | encodes rest of calcium-binding EF-hand 2 |
| 5 | 155 | 2.8 | 449 | 0 | |
| 6 | 106 | 2.7 | 604 | 1 | encodes ZZ-domain |
| 7 | 167 | 1.8 | 710 | 0 | |
| 8 | 125 | 2.9 | 877 | 2 | |
| 9 | 9 | 2.1 | 1002 | 2 | alternative splicing, encoding DTW |
| 10 | 84 | 1.4 | 1011 | 2 | |
| 11 | 6.1 | 1095 | - | .. bp coding / 3'UTR DTNA-3 transcripts | |
| 12 | 78 | 0.5 | 1095 | 2 | cardiac and skeletal muscle transcripts; present both / brain transcripts; contain neither exon, rarely 12 or 13 and even rarer both exons (Ambrose) |
| 13 | 93 | 9.5 | 1173 | 2 | |
| 14 | 88 | 0.6 | 1266 | 0 | |
| 15 | 98 | 3.1 | 1354 | 2 | encode coiled coil regions helix I |
| 16 | 114 | 6.2 | 1452 | 2 | |
| 17 | 97 | 1.8 | 1566 | 0 | encodes coiled coil region helix II |
| 18 | >15 | 1663 | - | 48 bp coding / 3'UTR DTNA-2 transcripts | |
| 18a | (21...) | ? | (1662+1) | mouse: major transcript skip exons 18 and 19, alternative transcripts include exon 18a, exon 19 (4 bp gtgggaACCAgtataa) and exon 20a (with GG splice acceptor site) (Ambrose) | |
| 19 | 4 | ? | (1662+22) | (2) | |
| 20a | 151 | - | (1672) | 1 | |
| 20 | 160 | 3.0 | 1663 | 1 | |
| 21 | 90 | 0.8 | 1823 | 1 | |
| 22 | 166 | 4.6 | 1913 | 2 | encode tyrosine kinase substrate domain |
| 23 | 133 | 1.8 | 2079 | 0 | |
| 24 | 49 | 2.6 | 2212 | - | .. bp coding / 3'UTR |
| 25 | 3.6 x 103 | - | 2261 | - | 3'UTR DTNA-1 transcripts/ two polyA-addition sites |
Legend:
Exon: numbering of exons and intron/exon boundaries are according to Ambrose,
with the first base of the Met-codon counted as position 1 (see Reference Sequence). Exon size: size of exon
indicated in basepairs. Intron size: size of intron indicated in kilobasepairs. 5'
cDNA position: first base of the exon (according to cDNA sequence Ambrose).
Splice after: splicing occurs in between of two coding triplets (0), after the
first (1) or the second (2) base of a triplet. Remarks: 5'UTR = 5' untranslated
region, 3'UTR = 3' untranslated region.
Links to other databases: RefSeq: NM_001390 UniGene: Hs.110708
Five distinct dystrobrevin mRNAs, generated by differential splicing, have been detected in human, measuring 6.5, 5.1, 4.0, 3.4 and 2.2 kb resp. Dystrobrevin expression closely parallels that of dystrophin. Transcripts are strongly expressed in brain, skeletal and cardiac muscle, while lower levels are found in liver, lung and pancreas. No transcript could be detected in kidney or placenta (Sadoulet-Puccio). Different dystrobrevin mRNA isoforms are predominant in different tissue types. The 6.5 and 5.1 kb transcripts are found in brain, liver, lung, pancreas and skeletal muscle, the 4.0 kb transcript is expressed in skeletal muscle only, and the 3.4 and 2.2 kb transcripts are found in cardiac muscle as well as brain, liver, lung, pancreas and skeletal muscle (Sadoulet-Puccio). No transcript was detected in kidney and placenta.
In mouse, Ambrose et al. analysed expression in brain, muscle (cardiac and skeletal) and lung. They identified four different 5'UTR-exons (A to D) indicating transcriptional regulation by multiple different promoters. Furthermore, three different 3'UTR (exons 11, 18 and 24+25) were identified and alternative splicing, partially tissue-specific, was observed in three regions (exons 9, 12-13 and 18-20). Exons 12 and 13 are utilized specifically in striated muscle. The sequence encoded by exon 9 has no equivalent in the Torpedo 87K protein.
| Transcript | Alternative name | Size (in kb) |
Expresion (Northern) |
Remarks |
|---|---|---|---|---|
| alpha-dystrobrevin-1 | DTNA-alpha, DTNA-epsilon | 7.5 | H: brain, lung L: skeletal muscle |
3'UTR in exon 25, alternative splicing exons 12 and 13 |
| alpha-dystrobrevin-2 | 5.0 | H: brain L: skeletal muscle, cardiac muslce |
3'UTR in exon 18, alternative splicing exons 12 and 13 | |
| alpha-dystrobrevin-1 | 4.0 | L: brain, muscle | 3'UTR in exon 25 (spliced 3'UTR), alternative splicing exons 12 and 13 | |
| alpha-dystrobrevin-? | 3.8 | lung | ||
| alpha-dystrobrevin-2 | DTNA-gamma | 3.6 | H: brain, skeletal muscle, cardiac muscle | 3'UTR in exon 18 (early polyA-addition site), alternative splicing exons 12 and 13 |
| alpha-dystrobrevin-3 | DTNA-delta | 1.8 | skeletal muscle, cardiac muscle | 3'UTR in exon 11 |
Legend:
Transcript: mRNA ranscript with designated name (Ambrose).
Alternative name: other name which has also been used to characterize the isoform. Size
(in kb): size of the mRNA, in kilo basepairs. Expression: expression detected
on Northern blot (H: = high, L: = low; Ambrose).
Remarks: additional remarks regarding the structure of the transcript.
Links to other databases: RefSeq: NP_001381 OMIM: 601239
Dystrobrevin is a 686 amino acid hydrophylic phosphoprotein with an calculated molecular weigth of 77,572 Daltons. DTNA is highly similar to the Cysteine-rich C-terminal end of dystrophin. DTNA does not contain a WW-domain but does have two calcium-binding EF-hands (exons 3-4), a ZZ-domain (exon 7, a postulated binding site for calmodulin) and a Leucine zipper motif (exons 15-17, overlapping the alpha- and beta1-syntrophin binding sites of dystrophin). The position of the Cys-residues (12) is not conserved exactly. In addition, like Torpedo 87K protein, DTNA-1 isoforms contain four potential tyrosine phosphorylation sites in its C-terminal 148 amino acids. Dystrobrevins-2 and -3 are truncated at the C-terminus and do not contain this domain.
Three major murine dystrobrevin isoforms, types 1, 2 and 3, have been reported by Ambrose (see above). In human, Sadoulet-Puccio et al. report six forms (dystrobrevin-alpha, -beta, -gamma, -delta, -epsilon and -zeta) varying in size from 80-22 kDa (see Table) and transcribed from mRNAs of 6.5, 5.1, 3.4 and 2.2 kb. At least three and possibly four of the isoforms, i.e. alpha, beta/gamma (probably comigrating) and delta, could be detected on Western blot. Using anti-A0 antibodies in rabbit, Yoshida et al. (1995, FEBS Lett. 367:311-314) observed two isoforms of 94 and 62 kD respectively.
| Isoform | MW | ORF | mRNA | Remarks |
|---|---|---|---|---|
| alpha | 80 | 686 | 6.5 | without exon 12/13 |
| beta | 65 | 577 | 5.1 or 3.4 | 3'UTR after exon 17 |
| gamma | 59 | 513 | 5.1 or 3.4 | without exon 12/13 and 3'UTR after exon 17 |
| delta | 42 | 374 | 2.2 | 3'UTR after exon 10 |
| epsilon | 44 | 391 | 2.2 | new 5'UTR 5' of exon 8 and without exon 13 |
| zeta | 22 | 192 | 2.2 | new 5'UTR 5' of exon 8 and without exon 12/13 |
Legend:
Isoform: dystrobrevin isoform. MW: calculated molecular weigth of the
protein. ORF: length of the open reading frame. mRNA: mRNA shown to ecode
this isoform Sadoulet-Puccio.
Structure: structure of the isoform in relation dystrophin.
Human alpha-dystrobrevin shows 84% similarity / ..% identity (amino acid level) to the Torpedo 87 kDa protein. Similarity to the cysteine-rich and carboxy-terminal domains of dystrophin (exon 63-78) starts after the unique 23 amino acid N-terminus of dystrobrevin and is about 50% (27% identity, exons 1-22). Conservation of the gene structure is striking. Not only have e.g. DTNA exons 1-8 (dystrophin exons 63-69) a similar size but the intron/exon junctions are also conserved along with the codon phase of the splice sites.
Dystrophin-related and dystrophin-associated proteins are believed to play an important role in membrane stability and membrane maintenance during muscle contraction and relaxation. Dystrobrevin-alpha is believed to link the DGC to the signaling protein neuronal nitric oxide synthase (nNOS). In vitro, dystrobrevin has been shown to interact with synthropin.
Links to other databases: OMIM: 606617
Ichida et al. (2001) analysed patients with left ventricular noncompaction (LVNC) and patients with Barth syndrome (BTHS) for mutations in the tafazzin gene (TAZ or G4.5) and several 'candidate disease genes'. One of the candidate genes scanned for mutations was the DTNA-gene. In a Japanese family in which members of four generations were affected, five with LVNC associated with congenital heart defects and one with isolated LVNC they found a missense mutation (Pro121Leu) in the DTNA-gene. This missense change is predicted to reduce an alpha-helix by 2 amino acids and the removal of a loop in this portion of the protein.
The murine DTNA gene contains a CA-repeat in its 3'UTR (95/HA/001, Blake et al. JBC 1996). This can be amplified using primers 5'-GTGACTACTGTAATTTGACCTC-3' and 5'-ATCACTTCAAAATATAACAGTCC-3' (Blake, Ambrose).
| Amplified | Length | Reference | forward primer | reverse primer | Name |
|---|---|---|---|---|---|
| exon 1 |
Legend:
Exonic sequences are in upper case, intronic and gene flanking sequences in lower case and
added primer tails in italics. Amplified: region amplified. Numbering of exons is
according to Ambrose.
Length: length of PCR-product in basepairs. Reference: publication
describing the primer(s). Forward primer: sequence of forward primer. Reverse
primer: sequence of reverse primer. Name: name of the primers.
Some primers to amplify dystrobrevin mRNA are given by Sadoulet-Puccio.
| Amplified | Length | Reference | Forward primer | Reverse primer | Name |
|---|---|---|---|---|---|
Legend:
Exonic sequences are in upper case, intronic and gene flanking sequences in lower case and
added primer tails in italics. Amplified: region amplified. Numbering of exons is
according to Ambrose.
Length: length of PCR-product in basepairs. Reference: publication
describing the primer(s). Forward primer: sequence of forward primer. Reverse
primer: sequence of reverse primer. Name: name of the primers.
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