Testing the tissue-specific mechanisms of Hoxa5 function in musculoskeletal patterning - Abstract
Development of cartilage, bones, muscles, tendons and ligaments must be highly coordinated, with
tissue type differentiation and morphogenesis occuring in a concerted way that allows the resulting
tissues to function together. The axial musculoskeleton (vertebral column and ribs) develops from the
somites, in which all musculoskeletal tissue types are specified and develop coordinately. However, the
morphology of somite derivatives varies with position along the body axis. This variation is controlled by
Hox proteins, conserved transcription factors that pattern the body axis of most animal embryos. In
vertebrates, Hox proteins both confer anterior-posterior identity on nascent segments and play direct
roles in tissue morphogenesis later in development. However, we still know relatively little about their
mechanisms of action, including the cell and tissue types in which they act, the cellular behaviors they
regulate, and ultimately their transcriptional targets. Hoxa5 non-redundantly patterns musculoskeletal
elements at the cervical-thoracic transition. In order to understand how it acts, we used genetic lineage
labeling to fate map the descendants of Hoxa5 expressing cells. We found that Hoxa5 descendants
contribute to a restricted number tissue types, such as cartilage and perichondrium, but only contribute
rarely to tendon and never to muscle. This restriction of Hoxa5 descendant fate may reflect an important
aspect of its function. Here, we propose to investigate the mechanism through which Hoxa5 patterns the
cervical-thoracic transition musculoskeleton of mice, using a combination of genetic lineage labeling,
conditional and loss-of-function analysis, and high throughput sequencing. Our specific aims are
designed to: (1) Identify the tissue specificity of Hoxa5 action in patterning the axial skeleton (2)
Identify genes and gene networks regulated cell-autonomously by Hoxa5 and (3) Identify direct
transcriptional targets of Hoxa5 in the somites. Successful completion of this project will shed light on
the mechanisms through which axial patterning is regulated by Hox genes, and can also be applied to a
general understanding the mechanisms of Hoxa5 in other tissue types and cancers. More generally, the
work is relevant to human health through its application to understanding musculoskeletal tissue
patterning and differentiation during normal development and disease. Finally, this work will be
conducted with undergraduates at Barnard College, a liberal arts college for women. It will be performed
by research students in the PI’s lab, and will be introduced into a newly developed, full year laboratory
course at Barnard. Course-based research has been shown to increase participation of students,
including those from underrepresented groups, in STEM and to increase the pursuit of postgraduate
STEM training. This course will engage undergraduates in substantive original research while providing
them with training in current molecular genetics approaches.
