Use of bidirectional blots in differential display analysis

Expression of odontogenic ameloblast-associated protein (ODAM) in dental and other epithelial neoplasms

We previously have communicated our discovery that the amyloid associated with calcifying epithelial odontogenic tumors is composed of N-terminal fragments of the structurally novel odontogenic ameloblast-associated protein designated ODAM. Subsequently, it was shown by other investigators that ODAM is expressed in rodent enamel organ and is likely involved in dental development. We now report that this molecule also is found in certain human tissues, principally the salivary gland and trachea, as evidenced by RNA array analysis and immunohistochemistry-utilizing antibodies prepared against synthetic ODAM-related peptides and recombinant protein. Notably, these reagents immunostained normal and malignant ameloblasts and other types of human neoplastic cells, including those of gastric, lung, and breast origin where the presence in the latter was confirmed by in situ hybridization using gene-specific molecular probes. Moreover, significant titers of anti-ODAM IgG antibodies were detected in the sera of patients with these malignancies. Our studies have provided the first evidence in humans for the cellular expression of ODAM in normal and diseased states. Based on our findings, we posit that ODAM is a developmental antigen that has an essential role in tooth maturation and in the pathogenesis of certain odontogenic and other epithelial neoplasms; further, we suggest that ODAM may serve as a novel prognostic biomarker, as well as a potential diagnostic and therapeutic target for patients with breast and other epithelial forms of cancer.

Amyloid contained in the knee joint meniscus is formed from apolipoprotein A-I

OBJECTIVE

To determine the chemical nature of amyloid deposits found in knee joint menisci.

METHODS

Amyloid was extracted from the menisci of 3 adults who underwent knee joint replacement surgery. The primary structural features of the purified proteins were determined by sequential Edman degradation and tandem mass spectrometry (MS/MS). Tissue specimens were also subjected to in situ hybridization analysis, as well as complementary DNA cloning by reverse transcriptase-polymerase chain reaction (RT-PCR). Additionally, specimens from these 3 patients, as well as other patients with amyloid in the knee joint menisci, were examined immunohistochemically.

RESULTS

Amino acid sequence and MS/MS analyses of the extracts revealed the presence of 60-77-residue components identical to the N-terminal portion of apolipoprotein A-I (Apo A-I). The Apo A-I nature of the amyloid was confirmed by the demonstration that the green birefringent congophilic deposits in the 7 meniscus samples were recognized by an anti-human Apo A-I antibody. That the meniscus itself was the source of the amyloidogenic protein was evidenced through Southern blot analysis, in which an Apo A-I product was generated by RT-PCR from synovial tissue, and further, by the demonstration that the cytoplasm of chondrocytes reacted with the specific Apo A-I probe used for in situ hybridization and was immunostained by the anti-Apo A-I antiserum.

CONCLUSION

Amyloid in the knee joint menisci is formed from Apo A-I that is produced by chondrocytes within the meniscal cartilage. This entity represents yet another localized form of amyloidosis associated with the aging process and may be of pathophysiologic import.

RNA expression microarrays (REMs), a high-throughput method to measure differences in gene expression in diverse biological samples

We have developed RNA expression microarrays (REMs), in which each spot on a glass support is composed of a population of cDNAs synthesized from a cell or tissue sample. We used simultaneous hybridization with test and reference (housekeeping) genes to calculate an expression ratio based on normalization with the endogenous reference gene. A test REM containing artificial mixtures of liver cDNA and dilutions of the bacterial LysA gene cDNA demonstrated the feasibility of detecting transcripts at a sensitivity of four copies of LysA mRNA per liver cell equivalent. Furthermore, LysA cDNA detection varied linearly across a standard curve that matched the sensitivity of quantitative real-time PCR. In REMs with real samples, we detected organ-specific expression of albumin, Hnf-4 and Igfbp-1, in a set of mouse organ cDNA populations and c-Myc expression in tumor samples in paired tumor/normal tissue cDNA samples. REMs extend the use of classic microarrays in that a single REM can contain cDNAs from hundreds to thousands of cell or tissue samples each representing a specific physiological or pathophysiological state. REMs will extend the analysis of valuable samples by providing a common broad based platform for their analysis and will promote research aimed at defining gene functions, by broadening our understanding of their expression patterns in health and disease.