Autoregulatory loop of Msx1 expression involving its antisense transcripts.

The Msx1 homeogene plays an important role in epithelial-mesenchymal interactions leading organogenesis. Msx1 gene is submitted to bidirectional transcription generating a long non-coding antisense (AS) RNA potentially involved in Msx1 expression regulation. RT-Q-PCR and RNA-FISH studies indicated that transient overexpression of the Msx1 AS transcript in 705IC5 mouse odontoblasts decreased the abundance of endogenous Msx1 S mRNA at the post-transcriptional level. Conversely, Msx1 overexpression increased the AS RNA level probably by activating AS transcription. In vivo mapping by RT-PCR evidenced both Msx1 RNAs in all adult mouse tissues tested raising the issue of Msx1 function during adulthood. The expression patterns of the two RNAs were similar, confirming the tight S/AS relationship. In particular, both Msx1 mRNAs and Msx1 protein were similarly distributed in eyes, and were found in regions with a common ectodermic origin and in cells potentially involved in regeneration. In conclusion, we report that Msx1 S RNA is negatively controlled by its AS RNA at a post-transcriptional level, and that the AS RNA is retrocontrolled positively by Msx1. The tight link between Msx1 S and AS RNAs constitutes a regulatory loop resulting in a fine-tuned expression of Msx1 which appears to be significant for adult homeostasis.

Msx1 expression regulation by its own antisense RNA: consequence on tooth development and bone regeneration.

Msx homeogenes play an important role in epithelial-mesenchymal interactions leading development. Msx1 is relevant for dental and craniofacial morphogenesis, as suggested by phenotypes of Msx1 mutations in human and Msx1 KO mice. During adulthood, Msx1 is still expressed in the skeleton where its role is largely unknown. Our group showed that the Msx1 gene is submitted to bidirectional transcription generating a long noncoding antisense (AS) RNA. During tooth development, Msx1 sense (S) and AS RNAs showed specific patterns of expression. Thus, the aim of the present study was to analyze the relation between Msx1 S and AS RNAs. In vivo mapping in adult mice showed that both Msx1 RNAs were detected in tested tissues such as bone. In vitro, Msx1 AS RNA decreased endogenous Msx1 S expression and modified Msx1 protein cell distribution. Regulations of Dlx5 and Bmp4 expression involving Msx1 S and AS RNAs showed that Msx1 AS RNA could modulate Msx1 function. The study of Msx1 S and AS RNA status is interesting in the case of tooth agenesis and bone loss to see if a disturbance of this balance could be associated with a disturbance of bone homeostasis. In that sense, our current results suggest a clear involvement of Msx1 in alveolar bone.

Nasal inverted papilloma expresses the muscle segment homeobox gene Msx2: possible prognostic implications.

Nasal inverted papilloma is a rare benign tumor of epithelial origin with aggressive evolution, bone destruction, recurrence, and malignant transformation. Msx2 is a homeobox gene implicated in organ development, bone metabolism, and tumorigenesis. Using reverse transcriptase-polymerase chain reaction and immunohistochemistry, Msx2 expression was examined in nasal inverted papilloma and in nontumorigenic tissue counterparts. For the first time, Msx2 was detected in all inverted papillomas but not in the nasal polyps or in the normal mucosa. The protein expression level was directly and significantly associated with tumor recurrence. Furthermore, Msx2 was associated with bone resorption markers receptor activator of nuclear factor-kappa B ligand and tartrate-resistant acid phosphatase, suggesting a role in osteolysis. In conclusion, Msx2 expression may represent a useful prognostic marker in inverted papilloma.

Expression and regulation of the Msx1 natural antisense transcript during development.

Bidirectional transcription, leading to the expression of an antisense (AS) RNA partially complementary to the protein coding sense (S) RNA, is an emerging subject in mammals and has been associated with various processes such as RNA interference, imprinting and transcription inhibition. Homeobox genes do not escape this bidirectional transcription, raising the possibility that such AS transcription occurs during embryonic development and may be involved in the complexity of regulation of homeobox gene expression. According to the importance of the Msx1 homeobox gene function in craniofacial development, especially in tooth development, the expression and regulation of its recently identified AS transcripts were investigated in vivo in mouse from E9.5 embryo to newborn, and compared with the S transcript and the encoded protein expression pattern and regulation. The spatial and temporal expression patterns of S, AS transcripts and protein are consistent with a role of AS RNA in the regulation of Msx1 expression in timely controlled developmental sites. Epithelial-mesenchymal interactions were shown to control the spatial organization of S and also AS RNA expression during early patterning of incisors and molars in the odontogenic mesenchyme. To conclude, this study clearly identifies the Msx1 AS RNA involvement during tooth development and evidences a new degree of complexity in craniofacial developmental biology: the implication of endogenous AS RNAs.

Altered plakoglobin expression at mRNA and protein levels correlates with clinical outcome in patients with oropharynx squamous carcinomas.

Previous studies have established that expression of plakoglobin is down-regulated during malignant transformation. The aim of this study was to evaluate for the first time the expression of plakoglobin at the mRNA and protein levels in primary oropharyngeal squamous cell carcinomas (SCCs) and determine the extent to which the patterns of expression correlated with clinical parameters. Plakoglobin expression was evaluated in 37 new tumor cases and normal oral epithelium using immunofluorescence, reverse transcriptase-polymerase chain reaction (RT-PCR), and Northern and Western blotting analysis. The results indicated that the steady-state levels of plakoglobin protein were down-regulated in all tumors compared with normal epithelium. Furthermore, in 87.1% of the tumors, plakoglobin immunoreactivity displayed an abnormal cytoplasmic localization that was inversely correlated with tumor size and directly correlated with a poor clinical outcome for the patient. Northern blotting analysis revealed that down-regulation of mRNA expression occurred in only 65.6% of the tumors, with plakoglobin mRNA levels similar to normal epithelium in the remaining cases. In the tumors expressing mRNA levels similar to those of normal tissue, a 3.7-kb transcript was detected in addition to the expected 3.4-kb transcript observed in normal epithelium. RT-PCR analysis of the 3' untranslated region of the 3.7-kb plakoglobin mRNA transcript identified a 297-base insertion from +2369 to +2666 that had been previously reported only in transformed cell lines (GenBank M23410). Interestingly, the prognosis was poor for patients with tumors expressing both RNA transcripts. These results are consistent with the concept that complex regulation of plakoglobin expression and intracellular routing may contribute to malignant transformation. The study also shows evidence that the level of expression and intracellular localization of plakoglobin may be useful in predicting the course of disease in patients with oropharyngeal SCC.

Cloning of the mRNA of overexpression in colon carcinoma-1: a sequence overexpressed in a subset of colon carcinomas.

We have identified a novel human cDNA overexpressed in a colon carcinoma cell line, TC7, established from a tumor with a normal karyotype arising in a patient with a hereditary nonpolyposis colorectal carcinoma. The OCC-1 (overexpressed in colon carcinoma-1) gene is composed of six exons and located in the q24.1 region of chromosome 12. It is transcribed as two mRNA species that differ in their 5'- and 3'-terminal ends. Abundant accumulation of both transcripts was found in placenta, skeletal muscle, kidney, and pancreas tissues. Absent or very faint expression was observed in heart, brain, lung and liver tissues. Overexpressed in colon carcinoma-1 cDNA direct in vitro translation of several polypeptides whose size is shorter than 9 kDa. Attempts to produce antibodies against these synthesized polypeptides in Escherichia coli failed. The absence of sequences at the mRNA and DNA levels hybridizing with mouse sequences together with the absence of a large open reading frame raise the possibility that OCC-1 sequences appeared recently in evolution and are transcribed as two noncoding regulatory RNA. Elevated levels of OCC-1 mRNA were observed in three of eight colon carcinomas as compared to normal mucosa of the same patient. Since these tumors shared the same characteristics of having a near diploid karyotype, OCC-1 overexpression may be a hallmark of this subset of colon carcinomas.