RESUMEN
The primary heart tube is an endocardial tube, ensheathed by myocardial cells, that develops from bilateral primary heart fields located in the lateral plate mesoderm. Earlier mapping studies of the heart fields performed in whole embryo cultures indicate that all of the myocardium of the developed heart originates from the primary heart fields. In contrast, marking experiments in ovo suggest that the atrioventricular canal, atria and conotruncus are added secondarily to the straight heart tube during looping. The results we present resolve this issue by showing that the heart tube elongates during looping, concomitant with accretion of new myocardium. The atria are added progressively from the caudal primary heart fields bilaterally, while the myocardium of the conotruncus is elongated from a midline secondary heart field of splanchnic mesoderm beneath the floor of the foregut. Cells in the secondary heart field express Nkx2.5 and Gata-4, as do the cells of the primary heart fields. Induction of myocardium appears to be unnecessary at the inflow pole, while it occurs at the outflow pole of the heart. Accretion of myocardium at the junction of the inflow myocardium with dorsal mesocardium is completed at stage 12 and later (stage 18) from the secondary heart field just caudal to the outflow tract. Induction of myocardium appears to move in a caudal direction as the outflow tract translocates caudally relative to the pharyngeal arches. As the cells in the secondary heart field begin to move into the outflow or inflow myocardium, they express HNK-1 initially and then MF-20, a marker for myosin heavy chain. FGF-8 and BMP-2 are present in the ventral pharynx and secondary heart field/outflow myocardium, respectively, and appear to effect induction of the cells in a manner that mimics induction of the primary myocardium from the primary heart fields. Neither FGF-8 nor BMP-2 is present as inflow myocardium is added from the primary heart fields. The addition of a secondary myocardium to the primary heart tube provides a new framework for understanding several null mutations in mice that cause defective heart development.
Asunto(s)
Embrión no Mamífero/metabolismo , Atrios Cardíacos/embriología , Corazón/embriología , Miocardio/metabolismo , Factor de Crecimiento Transformador beta , Proteínas de Xenopus , Animales , Proteína Morfogenética Ósea 2 , Proteínas Morfogenéticas Óseas/biosíntesis , Antígenos CD57/biosíntesis , Diferenciación Celular , Embrión de Pollo , ADN Complementario/metabolismo , Proteínas de Unión al ADN/biosíntesis , Factor 2 de Crecimiento de Fibroblastos/biosíntesis , Factor 8 de Crecimiento de Fibroblastos , Factores de Crecimiento de Fibroblastos/biosíntesis , Factor de Transcripción GATA4 , Proteína Homeótica Nkx-2.5 , Proteínas de Homeodominio/biosíntesis , Inmunohistoquímica , Hibridación in Situ , Modelos Biológicos , Mutación , Fenotipo , Codorniz , Factores de Transcripción de la Familia Snail , Factores de Tiempo , Distribución Tisular , Factores de Transcripción/biosíntesisRESUMEN
Bone morphogenetic protein 4 (BMP4) is known to regulate dorsoventral patterning, limb bud formation and axis specification in many organisms, including the chicken. In the chick developing inner ear, BMP4 expression becomes localized in two cell clusters at the anterior and posterior edges of the otic epithelium beginning at stage 16/17 and is expressed in presumptive sensory tissue at later stages. This restricted spatiotemporal pattern of expression occurs just prior to the otocyst's transition to a more complex three-dimensional structure. To further analyze the role of BMP4 in avian otic morphogenesis, cells expressing BMP4 or its antagonist, noggin, were grown on agarose beads and implanted into the periotic mesenchyme surrounding the chick otocyst. Although the BMP4-producing cells had no effect on the mature inner ear structure when implanted alone, noggin-producing cells implanted adjacent to the BMP4 cell foci prevented normal semicircular canal development. Beads implanted at the anterior BMP4 focus eliminated the anterior and/or the horizontal canals. Noggin cells implanted at the posterior focus eliminated the posterior canal. Canal loss was prevented by co-implantation of BMP4 cell beads next to noggin beads. An antibody to the chick hair cell antigen (HCA) was used to examine sensory cell distribution, which was abnormal only in the affected tissues of noggin-exposed inner ears. These data suggest a role for BMP4 in the accurate and complete morphological development of the semicircular canals.
Asunto(s)
Proteínas Morfogenéticas Óseas/fisiología , Proteínas/fisiología , Canales Semicirculares/embriología , Animales , Proteína Morfogenética Ósea 4 , Proteínas Morfogenéticas Óseas/antagonistas & inhibidores , Proteínas Morfogenéticas Óseas/genética , Células CHO , Proteínas Portadoras , Embrión de Pollo , Cricetinae , Expresión Génica , Células Ciliadas Auditivas/inmunología , Mesodermo , Fenotipo , Biosíntesis de Proteínas , Proteínas/farmacología , Canales Semicirculares/anatomía & histología , Canales Semicirculares/efectos de los fármacosRESUMEN
Early regionalized gene expression patterns within the otocyst appear to correlate with and contribute to development of mature otic structures. In the chick, the transcription factor Pax2 becomes restricted to the dorsal and entire medial side of the otocyst by stage 16/17. The dorsal region of the otocyst forms the endolymphatic duct and sac (ED/ES), and the cochlear duct is derived from the ventromedial region. In the mouse, however, Pax2 expression is reported only in the ventromedial and not the dorsal otocyst. In Pax2 null mice, the cochlea is missing or truncated, but vestibular structures differentiate normally. Here we demonstrate that in the chick, the emerging ED/ES express high levels of Pax2 even when the position of the emerging ED is altered with respect to its environment, either by 180 degrees otocyst rotations about the anterior/posterior axis or transplantation of the otocyst into the hindbrain cavity. However, the Pax2 expression pattern is plastic in the rest of the otic epithelium after 180 degrees rotation of the otocyst. Pax2 is upregulated on the medial side (formerly lateral), and downregulated on the lateral side (formerly medial and expressing Pax2) indicating that Pax2 expression is influenced by the environment. Although Pax2 is upregulated in the epithelium after 180 degrees rotations in the region that should form the cochlear duct, cochlear ducts are truncated or absent, and the ED/ES emerge in a new ventrolateral position. Ablation of the hindbrain at the placode or early otic pit stage alters the timing of regionalized Pax2 expression in the otocyst. The resulting otocysts and ears are generally smaller, vestibular structures are abnormal, ED/ES are missing but cochlear ducts are of normal length. The hindbrain and dorsal periotic mesenchyme provide unique trophic and patterning information to the dorsal otocyst. Our results demonstrate that the ED is the earliest structure patterned in the inner ear and that the hindbrain is important for its specification. We also show that, although normal Pax2 expression is required for cochlear duct development, it is downstream of ventral otocyst patterning events.
Asunto(s)
Proteínas de Unión al ADN/biosíntesis , Oído Interno/citología , Oído Interno/embriología , Factores de Transcripción/biosíntesis , Animales , Tipificación del Cuerpo/fisiología , Diferenciación Celular/fisiología , Embrión de Pollo , Proteínas de Unión al ADN/genética , Oído Interno/metabolismo , Oído Interno/trasplante , Estructuras Embrionarias/anatomía & histología , Estructuras Embrionarias/embriología , Estructuras Embrionarias/trasplante , Regulación del Desarrollo de la Expresión Génica/genética , Células Ciliadas Auditivas/citología , Inmunohistoquímica , Morfogénesis/fisiología , Especificidad de Órganos/genética , Factor de Transcripción PAX2 , Pintura , Rombencéfalo/fisiología , Rotación , Factores de Transcripción/genéticaRESUMEN
Removal of cardiac neural crest disrupts normal development of the heart and pharynx. Subtractive hybridization was used to identify differentially expressed messages after neural crest ablation in chick embryos. A 1 kb clone, homologous to PROS-28, a 28 kD alpha subunit of a Drosophila proteasome, was differentially expressed in embryos lacking neural crest. An increase of GPROS-28 expression in the head and pharyngeal arches of stages 12-21 chick embryos without cardiac neural crest accompanied generalized low-level expression throughout experimental and normal embryos. In addition, high levels of GPROS-28 expression were detected in normal embryos at particular sites and times in development in the limb buds, mesonephros, heart, liver, neural tube, dorsal root ganglia, and lung buds, when the cells in these regions were undergoing intense proliferation.