The function of Gli proteins in the specification of ossification pathways in pectoral girdle development and evolution

One of the long-standing, and extensively debated, questions in evolutionary biology is how vertebrates transitioned from water to land. The transition required dramatic changes to the composition and architecture of the skeleton to enable terrestrial feeding, respiration, and locomotion. Despite the critical importance of the skeletal changes for vertebrate evolution, the sparse fossil record has rendered its evolutionary trajectory and the underlying mechanisms largely unknown.

This project investigates the genetic mechanisms of the skeletal transition of shoulder girdle bones from fish to tetrapods. The integrative nature of our research is well-suited for a training of bridging multiple disciplines (comparative anatomy, genetics, and genomics) to create a dynamic environment where students learn through hands-on research activities and group discussion.

Towards the goal of embedding multidisciplinary science into undergraduate curriculum, the PI established a new educational program that explores fish-to-tetrapod transition with the American Museum of Natural History (AMNH) in 2018. Students that take this course will participate in group discussions at Rutgers U and AMNH, learn how to bridge different disciplines, and address questions related to the fish-to-tetrapod transition.

Collectively, this integrated research and educational program will reciprocally facilitate the deep understanding of fish evolution, foster undergraduates and graduate students, and inform lay people with the answers to the mysteries of the “missing link” which attracts large amount of interest in our society.

The main goal of this project is to identify the specification mechanisms of the two distinct types of bones found in vertebrates, intramembranous and endochondral, focusing on the pectoral (shoulder) girdle. Focus on the pectoral girdle is based on the established appreciation that during the evolution into tetrapods changes in the ratios of two bone types in fish disconnected the pectoral girdle from the skull, thus paving the way to the terrestrial locomotion and way of life.

Intriguingly, previous studies showed that one of the gli family gene gli3 regulates a balance of intramembranous and endochondral ossification in pectoral girdle development. Prior work also determined that Gli3 regulates genes involved in osteoblast and chondrocyte differentiation. Objective 1 will identify the roles of the Gli level in the specification of intramembranous and endochondral ossification, and characterize the embryonic and adult phenotypes of gli family gene knockout fish.

Objective 2 will test the hypothesis that the amount of Gli regulates the battery of genes involved in osteoblast and chondrocyte differentiation. Objective 3 will test the function of Gli target genes in the specification of ossification pathways using transgenic fish. These objectives will reveal how two distinct types of bones are specified in the vertebrate pectoral girdle and suggest that changes in this signaling pathway could underly the pectoral girdle evolution from fish to tetrapods.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.