This study aims to determine species-level relationships within the genus Heteromys, as well as generic-level relationships among members of the subfamily Heteromyinae using a phylogenetic framework. Molecular sequence data were generated from two mitochondrial genes (cytochrome b and cytochrome oxidase I) and three nuclear gene segments (β-fibrinogen, engrailed protein II, and myosin heavy chain II), and analyzed under maximum parsimony, maximum likelihood, and Bayesian optimality criteria to infer relationships. Chapter 1 focuses on the phylogenetic and taxonomic implications for Heteromys from the analyses of sequence data. Phylogenies also provided a framework for delimiting species boundaries within the wide-ranging Heteromys desmarestianus complex using the Wiens and Penkrot method. Several well-supported clades within this complex were recovered, including H. goldmani, H. nubicolens, and H. oresterus, as well as five groups identified as candidate species. Heteromys oasicus was not found to be genetically diagnosable from H. anomalus, and was relegated to subspecific status. I present a revised taxonomy as follows: the monotypic subgenus Xylomys is maintained (H. nelsoni); the subgenus Heteromys is divided into three species groups – anomalus (H. anomalus [including H. oasicus], H. australis, and H. teleus), desmarestianus (H. desmarestianus, H. goldmani, H. nubicolens, H. oresterus, and the five candidate species), and gaumeri (H. gaumeri). Chapter 2 describes phylogenetic inferences made from analyses of heteromyine taxa, genera Heteromys and Liomys. Many studies have recovered Liomys as paraphyletic relative to Heteromys, and the goal of this chapter was to address this taxonomic problem. The Liomys pictus species group (L. irroratus, L. pictus, and L. spectabilis) was recovered as sister to Heteromys rather than to the L. salvini group (L. adspersus and L. salvini). I recommend a revised taxonomy for the subfamily as follows: the genus Heteromys is retained as delineated in Chapter 1; the genus Liomys is reduced in scope to include only L. irroratus, L. pictus, and L. spectabilis; the subgeneric name Schaeferia is elevated to generic rank and includes S. adspersus and S. salvini. This classification better reflects the phyletic diversity within the subfamily Heteromyinae, and requires fewer name changes; thus providing nomenclatural stability.

Yes / Engrailed-2 (EN2) is a homeodomain-containing transcription factor that has roles in boundary formation and neural guidance in early development, but which is also expressed in a range of cancers. In addition to transcriptional regulation, it is secreted by cells and taken up by others through a mechanism that is yet to be fully elucidated. In this study, the distribution of EN2 protein in cells was evaluated using immunofluorescence with a set of antibodies raised against overlapping epitopes across the protein, and through the use of an EN2-GFP construct. MX2 expression in primary prostate tumors was evaluated using immunohistochemistry. We showed that EN2 protein is present in the cell membrane and within microvesicles that can be secreted from the cell and taken up by others. When taken up by normal cells from the stroma EN2 induces the expression of MX2 (MxB), a protein that has a key role in the innate immune response to viruses. Our findings indicate that EN2 secretion by tumors may be a means of preventing viral-mediated immune invasion of tissue immediately adjacent to the tumor. / The Ringrose Family Trust supported this study through a studentship awarded to N.P.