RESUMO
Retinoic acid (RA) plays pivotal roles in organogenesis, and both excessive and reduced amounts of RA cause developmental abnormalities. Reproductive organs are susceptible to teratogen toxigenicity, and the genital tubercle (GT) is one such representative organ. The physiological function of endogenous RA signaling and the mechanisms of RA-induced teratogenicity are poorly understood during the GT development. The objective of this study is to understand the developmental and teratogenic roles of RA during GT development by analyzing genetically modified mouse models. We found dynamic patterns of gene expression for the RA-synthesizing enzyme, Raldh2, and for the RA-catabolizing enzyme, Cyp26b1, during GT development. Rarb, an indicator gene for RA signaling, starts its expression in the prospective corpus cavernosum penis and in the urethral plate epithelium (UE), which plays central roles during GT development. Excessive RA signaling in Cyp26b1(-/-) mutants leads to abnormal extents of cell proliferation and differentiation during GT development, and also upregulates expression of growth factor signalings. They include Sonic hedgehog (Shh) signaling and Bone morphogenetic protein (Bmp) signaling, which are expressed in the UE and its bilateral mesenchyme. RA signaling positively regulatesShh and Bmp4 expression during GT development as testified also by the experiment of RA administration and analyses of loss-of-function of RA signaling mutants. Thus, RA signaling is involved in the developmental cascade necessary for UE formation and GT development.
Assuntos
Proteínas Morfogenéticas Ósseas/metabolismo , Genitália/embriologia , Genitália/metabolismo , Proteínas Hedgehog/metabolismo , Transdução de Sinais/efeitos dos fármacos , Tretinoína/toxicidade , Animais , Proteínas Morfogenéticas Ósseas/genética , Diferenciação Celular/efeitos dos fármacos , Diferenciação Celular/genética , Proliferação de Células/efeitos dos fármacos , Sistema Enzimático do Citocromo P-450/deficiência , Feminino , Regulação da Expressão Gênica no Desenvolvimento/efeitos dos fármacos , Genitália/efeitos dos fármacos , Genitália/patologia , Proteínas Hedgehog/genética , Proteínas de Homeodomínio/genética , Proteínas de Homeodomínio/metabolismo , Peptídeos e Proteínas de Sinalização Intercelular/genética , Peptídeos e Proteínas de Sinalização Intercelular/metabolismo , Camundongos , Mutação/genética , Ácido Retinoico 4 Hidroxilase , Transdução de Sinais/genética , Tretinoína/administração & dosagemAssuntos
Fatores de Crescimento de Fibroblastos/genética , Fatores de Crescimento de Fibroblastos/fisiologia , Camundongos Knockout , Animais , Sistema Nervoso Central/embriologia , Condrogênese/genética , Epiderme/embriologia , Camundongos , Músculo Esquelético/fisiologia , Organogênese/genética , Osteogênese/genética , Regeneração/genética , Transdução de Sinais/genética , Transdução de Sinais/fisiologiaRESUMO
beta-catenin signaling is one of the key factors regulating the fate of hair follicles (HFs). To elucidate the regulatory mechanism of embryonic HF fate determination during epidermal development/differentiation, we analyzed conditional mutant mice with keratinocytes expressing constitutively active beta-catenin (K5-Cre Catnb(ex3)fl/+). The mutant mice developed scaly skin with a thickened epidermis and showed impaired epidermal stratification. The hair shaft keratins were broadly expressed in the epidermis but there was no expression of the terminal differentiation markers K1 and loricrin. Hair placode markers (Bmp2 and Shh) and follicular dermal condensate markers (noggin, patched 1 and Pdgfra) were expressed throughout the epidermis and the upper dermis, respectively. These results indicate that the embryonic epidermal keratinocytes have switched extensively to the HF fate. A series of genetic studies demonstrated that the epidermal switching to HF fate was suppressed by introducing the conditional mutation K5-Cre Catnb(ex3)fl/+Shhfl/- (with additional mutation of Shh signaling) or K5-Cre Catnb(ex3)fl/+BmprIAfl/fl (with additional mutation of Bmp signaling). These results demonstrate that Wnt/beta-catenin signaling relayed through Shh and Bmp signals is the principal regulatory mechanism underlying the HF cell fate change. Assessment of Bmp2 promoter activities suggested a putative regulation by beta-catenin signaling relayed by Shh signaling towards Bmp2. We also found that Shh protein expression was increased and expanded in the epidermis of K5-Cre Catnb(ex3)fl/+BmprIAfl/fl mice. These results indicate the presence of growth factor signal cross-talk involving beta-catenin signaling, which regulates the HF fate.