Manipulation of Developmental Function in Turtles with Notes on Alligators.

Reptiles have great taxonomic diversity that is reflected in their morphology, ecology, physiology, modes of reproduction, and development. Interest in comparative and evolutionary developmental biology makes protocols for the study of reptile embryos invaluable resources. The relatively large size, seasonal breeding, and long gestation times of turtles epitomize the challenges faced by the developmental biologist.

Late-emigrating trunk neural crest cells in turtle embryos generate an osteogenic ectomesenchyme in the plastron.

Background: The turtle plastron is composed of a keratinized epidermis overlying nine dermal bones. Its developmental origin has been controversial; recent evidence suggests that the plastral bones derive from trunk neural crest cells (NCCs).

Results: This study extends the observations that there is a turtle-specific, second wave of trunk NCC delamination and migration, after the original NCCs have reached their destination and differentiated.

The contribution of neural crest cells to the nuchal bone and plastron of the turtle shell.

The origin of the turtle plastron is not well understood, and these nine bones have been homologized to the exoskeletal components of the clavicles, the interclavicular bone, and gastralia. Earlier data from our laboratory showed that the plastral bone-forming cells stained positively for HNK-1 and PDGFRα, two markers of skeletogenic neural crest cells. We have now shown that the HNK-1(+) cells are also positive for p75 and FoxD3, affirming their neural crest identity.

Evidence that a late-emerging population of trunk neural crest cells forms the plastron bones in the turtle Trachemys scripta.

The origin of the turtle plastron is not known, but these nine bones have been homologized to the exoskeletal components of the clavicles, the interclavicular bone, and gastralia. Earlier evidence from our laboratory showed that the bone-forming cells of the plastron were positive for HNK-1 and PDGFRalpha, two markers of the skeletogenic neural crest. This study looks at the embryonic origin of these plastron-forming cells.

Epithelial Bmpr1a regulates differentiation and proliferation in postnatal hair follicles and is essential for tooth development.

Bone morphogenetic protein (BMP) signaling is thought to perform multiple functions in the regulation of skin appendage morphogenesis and the postnatal growth of hair follicles. However, definitive genetic evidence for these roles has been lacking. Here, we show that Cre-mediated mutation of the gene encoding BMP receptor 1A in the surface epithelium and its derivatives causes arrest of tooth morphogenesis and lack of external hair.

T-box gene products are required for mesenchymal induction of epithelial branching in the embryonic mouse lung.

The regulation of signaling pathways is a prerequisite for coordinating the induction between mesenchymal and epithelial tissues during morphogenesis. Mesenchymal FGF10 is known to be an important paracrine factor regulating the branching morphogenesis of the bronchial epithelium. By using antisense oligonucleotides (AS ODNs) and in vitro culture of embryonic lungs, we demonstrate that the transcription factors Tbx4 and Tbx5 are critical for the expression of mesenchymal FGF10.