1. Senior Thesis Research Project
Genetic Fate Mapping of Hoxa5-Expressing Cells
in Mouse Embryonic Somites1
Dima Chaar
Mentor: Dr. Jennifer Mansfield
Thesis Mentor: Dr. Russell Romeo
Barnard College, Columbia University
Abstract
The Hox gene family plays a role in providing cells their positional information and identity
based on its expression along the anterior-posterior (AP) axis. This research focused on
fate-mapping Hoxa5-expressing cells and their descendants in somites to investigate
what cell types will result over a developmental time course. Hoxa5 is a gene in the Hox
family that is crucial for embryonic development because of its role in segmenting
somites. Hoxa5 patterns the cervical-thoracic transition in mice and its transcripts have
been shown to be confined to cell populations in that region. To determine the cell fates
of Hoxa5-expressing cells and their descendants, we identified the progeny of Hoxa5-
expressing cells at different stages in mouse embryos using an inducible Cre-ERT2
transgenic line. By observing reporter gene expression and mapping Hoxa5-expressing
cells and their descendants’ cell fates at the time points of E9.5, E12.5 and E13.5, we
were able to determine what tissue types the Hoxa5 descendants become, what their
spatial distributions are, and whether descendants will give rise to tissues in a temporally-
specific manner. It was observed that Hoxa5 descendants gave rise to the dermis,
perichondria and adipocytes at E9.5-13.5, in a tissue-specific manner. However, the
absence of chondrocyte descendants in the vertebral body at E9.5-10.5 suggests that
Hoxa5-expressing cells and their descendants contribute to chondrocytes in a temporal-
specific manner.
1 To be submitted for publication to “Development” journal.