One of the earliest events in animal development is the establishment of the main, head-to-tail body axis. Embryonic cells and tissues must receive a molecular "address" along this axis, and then develop appropriately for their location. In most animals, these processes are regulated at several steps by the highly conserved Hox gene family. Hox proteins regulate the expression of other, mostly unknown, genes, and play central roles in both the development and evolution of animal body plans. Despite enormous progress toward understanding the roles of Hox proteins in development and evolution, we still know relatively little about which cellular processes they regulate in the various tissues in which they act, especially in vertebrates. This project will examine the cellular processes regulated by one Hox gene, Hoxa5, during the development of vertebrate axial tissues (bone, muscle, and connective tissues of the vertebral column and ribs). Molecular genetic methods will be employed to ask (1) which cells within developing mouse express, or have a history of expressing, Hoxa5, (2) whether there a lineage relationship between cells that express Hoxa5 at different stages of embryogenesis, (3) how cells with a history of having expressed Hoxa5 differ from cells that do not, both in terms of their development and eventual fates, and finally, (3) how changes in Hoxa5 expression influence the differentiation of vertebral segments in chick embryos. Together, these approaches are aimed at teasing apart the elusive and context-dependent roles for this Hox protein in one embryonic tissue in which it acts. In addition, the genetic reagents produced by this work will be useful for future studies examining Hoxa5's roles in other tissues. This research will be conducted at Barnard College: an undergraduate, liberal arts college for women. Undergraduates will collaborate with the PI and a research technician in all aspects of this work, from experimental design to conducting experiments to analysis of results. The broader impacts of this study are (1) to provide new insight into how Hox proteins regulate patterning and differentiation of vertebrate tissues and (2) to provide a hands-on training experience for undergraduate researchers in a lab environment where they are the driving force behind the research.

Project Report

An essential step in animal development is the designation of the body axes: cells of all types (muscle, bone, neurons, etc.) must develop in a way that is appropriate to their location within the body. The head-to-tail axis is regulated in most animals, including humans, by a conserved class of genes called the Hox genes. Various combinations of Hox genes are expressed (active) in different regions of the body, and cells and tissues use Hox expression as a ‘molecular address’. How they do this is not well understood, especially in vertebrates. Hox proteins are transcription factors; proteins that regulate the expression of other genes. Despite their well-characterized effects on development, we are just beginning to understand the ways in which Hox proteins work: for example, the cellular processes they (their transcriptional targets) regulate, or the time(s) and contexts during development when they are required. Addressing these questions has important implications for understanding animal development, including human development and disease. In addition, it is well known that variation in Hox genes’ activity and function can contribute to variation in body plans in different animal species. In this project, we investigated the cellular role of one Hox gene, Hoxa-5, with a focus on its role in vertebrae and other musculoskeletal precursors in somites. We find that Hoxa-5 has unique patterns of activity in different vertebrate species, suggesting a potentially different patterning role in each. Using functional approaches in a chick model, we find evidence that Hoxa-5 helps to regulate vertebrae at more than one developmental stage, and that its later embryonic role may be restricted to certain elements within vertebrae. We identified molecular genetic pathways involved in localizing Hoxa-5 activity to certain elements, and investigated its downstream effects on cartilage development and differentiation. Our results contribute new data to an emerging picture of Hox proteins as acting in context-specific ways, at multiple developmental times. Our work in the chick model, where Hox function is almost entirely uncharacterized, also provides comparative information for the much better studied amniote model, the mouse. Our continued work is further investigating the shared and divergent roles of Hoxa-5, both to better understand its cellular roles and its potential contribution to body patterning differences across vertebrate species. A second goal of this project was to provide hands-on research training for students. The work was conducted at Barnard College, an undergraduate liberal arts college for women. Undergraduates carried out all aspects of this work, in collaboration with the PI and a research technician. Over the course of the project, 16 undergraduates participated in various aspects of this work, the majority of whom have gone on to work or further their training in STEM fields including research, medicine, public health and education. While in the lab, students contributed to experimental design, conduct of experiments, data analysis and presentation and publication of results.

National Science Foundation (NSF)
Division of Integrative Organismal Systems (IOS)
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anthea letsou
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Barnard College
New York
United States
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