Characterisation of Foxp1 in striatal development and the adult brain

The aim of the research presented in this Thesis was twofold; firstly to further understand the role of Foxp1 in the development of striatal medium spiny neurons (MSN) and secondly its role the adult brain. Understanding the role of Foxp1 in MSN development may allow more accurate in vitro protocols to be generated for use in directing renewable cell sources for use in cell replacement therapies for diseases such as Huntington’s disease (HD). Additionally, its functional role in MSN development may not be exclusive, and thus have a more generalised role transferable to other neuronal processes. Thus what is learnt about its function can possibly be applied to cell transplantation protocols in general, as well as be useful in the drug discovery field. In mice, the transcription factors (TF) Foxp1 and Mef2c were shown to be significantly up-regulated during peak MNS development (embryonic day (E) E12-16) in a genetic screen carried out in the host lab in 2004. Consequently the majority of work in this thesis was focused on the characterisation of the most significantly up-regulated gene, Foxp1. Experiments initially focused on a Foxp1 knock out (KO) line, both in vitro and following transplantation into the quinolinic acid (QA) lesioned adult mouse brain. Additionally, owing to embryonic lethality at E14, a conditional Foxp1 KO (CKO) line was also developed to study the effects of the loss of Foxp1 in the adult brain with a focus on the loss of Foxp1 from the cortex. Owing to lethality at E9 a Mef2c CKO line was also developed and initial in vitro findings from this line are presented in Appendix 8 of this Thesis. Chapter 3 characterised the wild type (WT) expression pattern of FOXP1 from E10 to P7 through the co-localisation of FOXP1 with the established MSN markers CTIP2 and DARPP-32. In vitro characterisation of cultures generated from striate of Foxp1-/- mice showed a decrease in the number of CTIP2 and DARPP-32 positive cells compared to littermate controls but that there were no differences in the proliferation of these cells between groups. Finally, results from immunohistochemistry on selected striatal KO brain sections suggested that Foxp1 may function downstream of Ascl1 and Gsh2 in striatal development. In Chapter 4 E14 or E12 striatal tissue from all three genotypes was grafted into an adult QA-lesion mouse model. Such experiments allowed striatal neurons from Foxp1-/- mice to survive for much longer periods than was possible in vitro and provided them with the opportunity to make some of their normal connections. Results showed that there were fewer DARPP-32 positive cells in grafts from Foxp1-/-compared to controls, as with in Chapter 3. Moreover, FOXP1 was identified as a novel maker of P-zones in grafts derived from whole ganglionic eminence. Chapter 5 addressed the generation of a Foxp1 CKO mouse model under the control of an hGFAP-Cre line (Foxp1 CKO). Histology showed that FOXP1 was lost from all layers of the cortex, but expression was maintained in the striatum. Mice appeared hyperactive in the home cage compared to littermate controls, and as mutations in FOXP1 have been associated with autism spectrum disorders, of which ADHD falls under, led to directed behavioural analysis targeting the symptoms of ADHD. Analysis revealed Foxp1 CKO mice were significantly hyperactive (activity boxe and open-field data) and inattentive (5 choice serial reaction time task) but had no anxiety problems (elevated plus maze and marble burying task). These symptoms were shown to be reduced following the administration of atomoxetine, a drug prescirbed to patients with ADHD. Results collectively suggested that the Foxp1 CKO line is a new mouse model of ADHD.