CDO, a member of the Ig/fibronectin type III repeat subfamily of transmembrane proteins that includes the axon guidance receptor Robo, was identified by virtue of its down-regulation by the ras oncogene. We report here that one prominent site of cdo mRNA expression during murine embryogenesis is the early myogenic compartment (newly formed somites, dermomyotome and myotome). CDO is expressed in proliferating and differentiating C2C12 myoblasts and in myoblast lines derived by treating 10T1/2 fibroblasts with 5-azacytidine, but not in parental 10T1/2 cells. Overexpression of CDO in C2C12 cells accelerates differentiation, while expression of secreted soluble extracellular regions of CDO inhibits this process. Oncogenic Ras is known to block differentiation of C2C12 cells via downregulation of MyoD. Reexpression of CDO in C2C12/Ras cells induces MyoD; conversely, MyoD induces CDO. Reexpression of either CDO or MyoD rescues differentiation of C2C12/Ras cells without altering anchorage-independent growth or morphological transformation. CDO and MyoD are therefore involved in a positive feedback loop that is central to the inverse relationship between cell differentiation and transformation. It is proposed that CDO mediates, at least in part, the effects of cell–cell interactions between muscle precursors that are critical in myogenesis.

The murine female reproductive tract differentiates during postnatal development. This process of cytodifferentiation and morphogenesis is dependent upon specific mesenchymal-epithelial interactions as well as circulating steroid hormones (Cunha, G.R., 1976. Int. Rev. Cytol. 47, 137-194; Pavlova, A. et al., 1994. Development 120, 335-346). Members of the Wnt family of signaling molecules have been recently identified in this system (Pavlova, A. et al., 1994. Development 120, 335-346; Bui, T.D. et al., 1997. Br. J. Cancer 75, 1131-1136; Miller, C., Sassoon, D.A., 1998. Development, in press). We describe the expression patterns of Wnt genes in the developing and adult female reproductive tract. Additionally, we note that changes in the levels of expression occur during the estrous cycle. Wnt gene expression patterns are regulated by the presence of epithelium in tissue graft experiments, suggesting that Wnt genes may indeed play roles in the mesenchymal-epithelial interactions critical for female reproductive tract development and function.

Diethylstilbestrol (DES) was used in the United States from 1947 to 1971 to prevent miscarriage. Approximately one-million women were exposed in utero to DES (ref. 1). Women prenatally exposed to DES commonly display epithelial and/or structural changes in the uterus, cervix, or vagina, and can develop clear cell adenocarcinoma of the vagina or cervix at an early age [2][3][4][5] . The frequency of DES-associated reproductive tract anomalies 6 and cancer 7 appears temporally related to the time of exposure, with most abnormal findings occurring in women exposed to DES in the first trimester. The specific molecular response to DES that fully accounts for the DES syndrome remains unknown. We recently reported that mice lacking Wnt7a have malformed female reproductive tracts 8 (FRTs). The observed phenotype closely resembles the reproductive tract morphologies observed in female mice prenatally exposed to DES (ref. 9), and indicates that Wnt7a may have a role in the DES response in the developing FRT.To directly compare the effects of loss of Wnt7a with the effects of DES in the FRT, we generated mice with DES-induced malformed FRTs using an established protocol 9,10 . DESexposed mice had shallow vaginal fornices, malformed oviducts that lacked coils, Wolffian duct remnants (Fig. 1a), vaginal concretions and adenotic lesions in the vagina 9,11,12 . Wnt7a −/− mice also had shallow vaginal fornices (data not shown) and malformed oviducts 8 . Similarly, Wnt7a −/− FRTs contained Wolffian duct remnants (Fig. 1b), vaginal concretions ( Fig. 1c) and epithelial inclusions in the vaginal stroma (Fig. 1d). Control FRTs (oil treated) had normal morphology and tissue cytoarchitecture (Fig. 1e). DES-exposed and Wnt7a −/− FRTs displayed stratified epithelium with reduced stroma and glands (Fig. 1f,g). DESexposed women were reported to display uterine abnormalities which were attributed to abnormal smooth muscle proliferation 13 . Both Wnt7a −/− and DES-exposed mice had a disorganized and thickened inner layer of smooth muscle (Fig. 1i-k).Wnt7a is normally expressed perinatally in the luminal epithelium of the uterus 8 . As expected, Wnt7a was found to be expressed in the epithelium of the control uterus (Fig.2 b,d). In the DES-exposed uteri, however, low levels of Wnt7a transcripts were detected at birth (Fig. 2f). Wnt7a expression in the DES-exposed uteri returned to high levels five days after birth (Fig. 2h) and was maintained at later stages (data not shown).Correspondence should be addressed to D.A.S. (dsassoo@smtplink.mssm.edu). HHS Public AccessAuthor manuscript Nat Genet. Author manuscript; available in PMC 2016 February 11. Published in final edited form as:Nat Genet. 1998 November ; 20(3): 228-230. doi:10.1038/3027. Author ManuscriptAuthor Manuscript Author Manuscript Author ManuscriptPrevious studies have shown that cytodifferentiation of the female reproductive tract in mice is determined 5-7 days after birth and is dependent on mesenchymal-epithelial interactions 14 . After this time period, the uterine epithelium ...

The murine female reproductive tract differentiates along the anteroposterior axis during postnatal development. This process is marked by the emergence of distinct cell types in the oviduct, uterus, cervix and vagina and is dependent upon specific mesenchymal-epithelial interactions as demonstrated by earlier heterografting experiments. Members of the Wnt family of signaling molecules have been recently identified in this system and an early functional role in reproductive tract development has been demonstrated. Mice were generated using ES-mediated homologous recombination for the Wnt-7a gene (Parr, B. A. and McMahon, A. P. (1995) Nature 374, 350–353). Since Wnt-7a is expressed in the female reproductive tract, we examined the developmental consequences of lack of Wnt-7a in the female reproductive tract. We observe that the oviduct lacks a clear demarcation from the anterior uterus, and acquires several cellular and molecular characteristics of the uterine horn. The uterus acquires cellular and molecular characteristics that represent an intermediate state between normal uterus and vagina. Normal vaginas have stratified epithelium and normal uteri have simple columnar epithelium, however, mutant uteri have stratified epithelium. Additionally, Wnt-7a mutant uteri do not form glands. The changes observed in the oviduct and uterus are accompanied by a postnatal loss of hoxa-10 and hoxa-11 expression, revealing that Wnt-7a is not required for early hoxa gene expression, but is required for maintenance of expression. These clustered hox genes have been shown to play a role in anteroposterior patterning in the female reproductive tract. In addition to this global posterior shift in the female reproductive tract, we note that the uterine smooth muscle is disorganized, indicating development along the radial axis is affected. Changes in the boundaries and levels of other Wnt genes are detectable at birth, prior to changes in morphologies. These results suggest that a mechanism whereby Wnt-7a signaling from the epithelium maintains the molecular and morphological boundaries of distinct cellular populations along the anteroposterior and radial axes of the female reproductive tract.

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