ABSTRACT
La vía de señalización NOTCH es un mecanismo de señalización célula-célula conservado evolutivamente entre las especies, el cual es indispensable para un correcto desarrollo embrionario, mediando una variedad de procesos celulares como proliferación, diferenciación, apoptosis, transformación epitelio- mesénquimal, migración, angiogénesis, mantenimiento de células madre y definición de destino celular. Varios genes componentes de esta vía han sido implicados en el desarrollo de estructuras craneofaciales. El 80% de los pacientes con síndrome de Alagille, presentan mutaciones en el gen que codifica para el receptor Jagged1 (Jag1), acompañado de hipoplasia del tercio medio facial y de craneosinostosis esporádica. Ratones con mutaciones homocigotas en el gen Jagged2 (Jag2) presentan paladar hendido, como resultado de fusiones ectópicas entre la lengua y los procesos palatinos. Por otro lado, mutaciones inducidas en el gen Hes1 generan defectos en el desarrollo de estructuras craneofaciales, derivadas de las células de la cresta neural craneal (CCNC) que incluyen: paladar hendido, agenesia del hueso frontal, malformación de base craneal y disminución en el tamaño del maxilar superior e inferior. Recientes estudios han evidenciado alteraciones durante la morfogénesis dental de ratones mutantes Jagged2-/-, acompañada de defectos en la citodiferenciación de ameloblastos y deficiente deposición de matriz de esmalte. Estos estudios muestran cómo la vía de señalización NOTCH está implicada en el desarrollo de una variedad de estructuras craneofaciales como paladar, dientes, maxilares y cráneo. Por esta razón, el propósito del presente artículo es presentar una revisión de las diferentes funciones de la vía NOTCH durante el desarrollo de estas estructuras craneofaciales, y de las alteraciones resultantes cuando existen mutaciones en algunos genes componentes de la vía NOTCH, como Jagged2, Jagged1, Hes1, Notch1 y Notch2.
Subject(s)
Receptors, NotchABSTRACT
Background: Orofacial clefts are common worldwide and result from insufficient growth and/or fusion during the genesis of the derivatives of the first pharyngeal arch and the frontonasal prominence. Recent studies in mice carrying conditional and tissue-specific deletions of the human ortholog Dicer1, an RNAse III family member, have highlighted its importance in cell survival, differentiation, proliferation, and morphogenesis. Nevertheless, information regarding Dicer1 and its dependent microRNAs (miRNAs) in mammalian palatogenesis and orofacial development is limited. Aims: To describe the craniofacial phenotype, gain insight into potential mechanisms underlying the orofacial defects in the Pax2-Cre/Dicer1 CKO mouse, and shed light on the role of Dicer1 in mammalian palatogenesis. Materials And Methods: Histological and molecular assays of wild type (WT) and Pax2-Cre/Dicer1 loxP/loxP (Dicer1 CKO) mice dissected tissues have been performed to characterize and analyze the orofacial dysmorphism in Pax2-Cre/Dicer1 loxP/loxP mouse. Results: Dicer1 CKO mice exhibit late embryonic lethality and severe craniofacial dysmorphism, including a secondary palatal cleft. Further analysis suggest that Dicer1 deletion neither impacts primary palatal development nor the initial stages of secondary palatal formation. Instead, Dicer1 is implicated in growth, differentiation, mineralization, and survival of cells in the lateral palatal shelves. Histological and molecular analysis demonstrates that secondary palatal development becomes morphologically arrested prior to mineralization around E13.5 with a significant increase in the expression levels of apoptotic markers (P < 0.01). Conclusions: Pax2-Cre-mediated Dicer1 deletion disrupts lateral palatal outgrowth and bone mineralization during palatal shelf development, therefore providing a mammalian model for investigating the role of miRNA-mediated signaling pathways during palatogenesis.
ABSTRACT
In order to understand the effect of retinoic acid (RA) on the craniofacial pattern formation during embryogenesis, we injected RA intraperitoneally into the pregnant female rat on day 11 post coitum (p.c.) and then embryos of day 13 to day 17 p.c. were isolated consequently. The overall morphology and the differential gene expression patterns were analyzed by the microscopic and (DD) RT-PCR methods, respectively. For the morphological study, the retardation of craniofacial region, the shortage of crown rump length and limbs were analyzed in the RA-treated embryos. In the RA-treated embryos of day 17, it was observed that the palatogenesis was completely finished just like in the normal embryos. However, the cleft plate was observed in 36 out of 52 total samples with the distance of cleft palate being 0.80+/-0.36 mm in average. The temporal expression pattern of Hox genes through RT-PCR revealed that the expression of Hoxa7 reached its peak on day 13 then slowly declined in the normal embryos. Whereas in the RA-treated embryos, the expression peak was observed on day 15, then declined subsequently. With the Hoxc8 gene, its expression was low in all stages until the day 16 of normal embryogenesis. On the other hand, Hoxc8 gene expression was detected slightly early on day 15 in the RA-treated embryos. In the study of Bcl-2 family genes, uniformly strong expression of anti-apoptotic and pro-apoptotic genes was observed from day 13 to day 17 of normal embryos, whereas anti-apoptotic gene expressions were decreased after day 16 in the RAtreated embryos. Additionally, a dramatic decline of pro-apoptotic gene expression was observed from day 13 to day 15 of the RA-treated embryos. Therefore, we believe that RA is a potential factor that is actively involved in the cleft palate formation. Moreover, it is profoundly linked with the regulation of Hox and Bcl-2 family gene expression pattern that leads to the embryonic malformation.
Subject(s)
Animals , Female , Humans , Pregnancy , Rats , Cleft Palate , Crown-Rump Length , Embryonic Development , Embryonic Structures , Extremities , Gene Expression , Genes, Homeobox , Hand , Palate , TretinoinABSTRACT
Retinoic acid (RA) is widely used to treat the dermatologic disorders, such as acne and psoriasis, but its usage is limited because of teratogenic effects. Moreover, it is known that RA induces cleft palate by influencing epithelial differentiation and mesenchymal cells in palatine processes. We studied the ultrastructures of the epithelial and mesenchymal cells in rat palatine shelves treated with RA, in comparison with those of the normal developing rat. In this experiment, pregnant Sprague -Dawley rats were treated with 100 mg/kg of all -trans retinoic acid at day 10 of gestation. Pregnant rats were killed at 14 th and 16 th day of gestation. Fetuses were removed and palatine processes were dissected. The specimen were observed with a transmissiom electron microscope. The results were as follows. 1. Palatine epithelium of control rats was made up of two cell layers at day 14 of gestation, and that of RA treated rats consisted of multicellular layers. At the 16th day of gestation, many apoptotic bodies were observed in triangular area of the palatine epithelium of the control rat. In contrast, apoptotic cells were hardly observed in RA treated rats. 2. Mesenchymal cells of control rats contained cytoplasmic process, oval -shaped nucleus, well -developed rough endoplasmic reticulum, Golgi complex, and mitochondria. RA treated mesenchymal cells showed atrophied cisternae of Golgi complex, rough endoplasmic reticulum with sacculated, fragmented and ribosome detached cisternae, mitochondria with dissolved mitochondrial cristae, and multivesicular body. After RA exposure during palatogenesis, the frequency of apoptotic bodies was low in palatine epithelium, and mesenchymal cells were severely damaged. In conclusion, it is suggested the RA may induce direct cytotoxic effects on mesenchymal cells and influence normal apoptosis process in developing epithelium.