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Updated: Mar 22, 2026
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Dissection and Flat-mounting of the Threespine Stickleback Branchial Skeleton
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Development of the turtle plastron, the order-defining skeletal structure
Ritva Rice1, Aki Kallonen2, Judith Cebra-Thomas3
1Developmental Biology, Institute of Biotechnology, University of Helsinki, Helsinki 00014, Finland; ritva.rice@helsinki.fi sgilber1@swarthmore.edu.
Summary
Turtle plastron (ventral shell) development involves osteogenesis and suppressed chondrogenesis, distinct from typical skeletal development. This unique process allows for the evolution of the turtle
Area of Science:
- Developmental Biology
- Paleontology
- Evolutionary Biology
Background:
- The turtle shell comprises a dorsal carapace and a ventral plastron, which are developmentally distinct.
- The plastron is an exoskeletal structure unique to the order Testudines, but its evolutionary origins and developmental mechanisms remain incompletely understood.
- Previous studies suggest a progression of bony elements ancestral to the plastron in transitional forms.
Purpose of the Study:
- To investigate the molecular mechanisms underlying the development and patterning of plastron bones in the cryptodire turtle, *Trachemys scripta*.
- To elucidate the cellular processes involved in plastron formation and its relationship to other skeletal elements.
Main Methods:
- Analysis of molecular development and cellular patterning during plastron bone formation.
- Identification of key developmental stages and cellular signaling pathways involved in osteogenesis and chondrogenesis.
- Comparative analysis with sternal development in avian and mammalian models.
Main Results:
- Plastron development initiates at developmental stage 15 with the formation of osteochondrogenic mesenchyme condensates at the ventral edge.
- These condensates commit to an osteogenic fate, actively suppressing chondrogenesis.
- Plastron bone development is coordinated with carapacial ridge formation, indicating synchronized dorsal and ventral shell development.
Conclusions:
- Turtle plastron formation is characterized by a unique developmental strategy involving osteogenesis induction and chondrogenesis suppression in the ventral mesenchyme.
- This distinct developmental pathway is crucial for establishing the order-specific ventral morphology of turtles.
- The coordinated development of the carapace and plastron suggests an integrated genetic and cellular program underlying shell formation.
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