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52-kD SS-A/Ro: genomic structure and identification of an alternatively spliced transcript encoding a novel leucine zipper-minus autoantigen expressed in fetal and adult heart.

ABSTRACT: The 52-kD SS-A/Ro protein is one of the antigenic targets strongly associated with the autoimmune response in mothers whose children have manifestations of neonatal lupus. In addition to the cDNA clone we previously reported for the full-length 52-kD SS-A/Ro protein, an interesting MOLT-4 cDNA clone, p52-2, was found to have an internal deletion of 231 nucleotides including the domain encoding the leucine zipper motif. To further investigate the nature of this deletion, genomic DNA clones were isolated from a lambda FIXII library. The complete gene for the full-length 52-kD protein (alpha form, 52 alpha) spans 10 kb of DNA and is composed of seven exons. Exon 1 contains only the 5' untranslated sequence, while the translation initiation codon is located 3 kb downstream in exon 2, which also encodes the three zinc finger motifs. Exon 4 encodes amino acids 168-245, including the coiled coil/leucine zipper domain. Exon 7 is the longest and encodes the rfp-like domain and the 3' untranslated region. The cDNA p52-2 can now be accounted for as a product of alternative messenger RNA (mRNA) derived from the splicing of exon 3 to exon 5, skipping exon 4, which results in a smaller protein (52 beta) with a predicted molecular weight of 45,000. An initial approach to identifying this alternatively spliced form in the human heart used a ribonuclease protection assay. Using an RNA probe corresponding to bases 674-964 of the full-length cDNA, two protected mRNA fragments were identified, a 290-bp fragment corresponding to expression of 52 alpha and a smaller fragment of 144 bp, the predicted size of 52 beta. Using reverse transcription followed by polymerase chain reaction, cDNAs from a 16-wk fetal heart, 24-wk heart, and adult heart were amplified with primers flanking exon 4. Two polymerase chain reaction products were observed in each tissue, one 1.0 kb likely representing 52 alpha and a second 0.78 kb, consistent with 52 beta. The 0.78-kb fragment identified in the 16-wk heart was cloned, and DNA sequencing confirmed the 52 beta type. Immunoprecipitation of in vitro-translated 35S-labeled 52 beta form was performed to evaluate the antigenicity of this novel form of 52-kD SS-A/Ro. 26 (87%) of 30 sera tested from mothers whose children were known to have neonatal lupus immunoprecipitated the 52 beta form.(ABSTRACT TRUNCATED AT 400 WORDS)

SUBMITTER: Chan EK

PROVIDER: S-EPMC2192297 | biostudies-other | 1995 Oct

REPOSITORIES: biostudies-other

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Project description:BACKGROUND: The CHD7 (Chromodomain Helicase DNA binding protein 7) gene encodes a member of the chromodomain family of ATP-dependent chromatin remodeling enzymes. Mutations in the CHD7 gene are found in individuals with CHARGE, a syndrome characterized by multiple birth malformations in several tissues. CHD7 was identified as a binding partner of PBAF complex (Polybromo and BRG Associated Factor containing complex) playing a central role in the transcriptional reprogramming process associated to the formation of multipotent migratory neural crest, a transient cell population associated with the genesis of various tissues. CHD7 is a large gene containing 38 annotated exons and spanning 200 kb of genomic sequence. Although genes containing such number of exons are expected to have several alternative transcripts, there are very few evidences of alternative transcripts associated to CHD7 to date indicating that alternative splicing associated to this gene is poorly characterized. FINDINGS: Here, we report the cloning and characterization by experimental and computational studies of a novel alternative transcript of the human CHD7 (named CHD7 CRA_e), which lacks most of its coding exons. We confirmed by overexpression of CHD7 CRA_e alternative transcript that it is translated into a protein isoform lacking most of the domains displayed by the canonical isoform. Expression of the CHD7 CRA_e transcript was detected in normal liver, in addition to the DU145 human prostate carcinoma cell line from which it was originally isolated. CONCLUSIONS: Our findings indicate that the splicing event associated to the CHD7 CRA_e alternative transcript is functional. The characterization of the CHD7 CRA_e novel isoform presented here not only sets the basis for more detailed functional studies of this isoform, but, also, contributes to the alternative splicing annotation of the CHD7 gene and the design of future functional studies aimed at the elucidation of the molecular functions of its gene products.

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52-kD SS-A/Ro: genomic structure and identification of an alternatively spliced transcript encoding a novel leucine zipper-minus autoantigen expressed in fetal and adult heart.

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