Cytosolic sequestration of Prep1 influences early stages of T cell development.
OBJECTIVE
Prep1 and Pbx2 are the main homeodomain DNA-binding proteins of the TALE (three amino acid loop extension) family expressed in the thymus. We previously reported reduced Pbx2 expression and defective thymocyte maturation in Prep1 hypomorphic mice. To further investigate the role of this homeodomain DNA-binding protein in T cell development, we generated transgenic mice expressing the N-terminal fragment of Pbx1 (Pbx1NT) under the control of the Lck proximal promoter.


RESULTS
Pbx1NT causes Prep1 cytosolic sequestration, abolishes Prep1-dependent DNA-binding activity and results in reduced Pbx2 expression in developing thymocytes. Transgenic thymi reveal increased numbers of CD4(-) CD8(-) CD44(-) (DN3 and DN4) thymocytes, due to a higher frequency of DN2 and DN4 Pbx1NT thymocytes in the S phase. Transgenic thymocytes however do not accumulate at later stages, as revealed by a normal representation of CD4/CD8 double positive and single positive thymocytes, due to a higher rate of apoptotic cell death of DN4 Pbx1NT thymocytes.


CONCLUSIONS
The results obtained by genetic (Prep1 hypomorphic) and functional (Pbx1NT transgenic) inactivation of Prep1 support nonredundant roles for this homeodomain protein during different stages of T cell development.
Molecular Genetics Unit, San Raffaele Scientific Institute and Università Vita Salute San Raffaele, Milan, Italy.
Dmitry
D
Penkov
Martina
M
Palazzolo
Anna
A
Mondino
Francesco
F
Blasi
D000818:Animals; D001483:Base Sequence; D003600:Cytosol / Q000378:metabolism*; D017931:DNA Primers; D024202:Electrophoretic Mobility Shift Assay; D005434:Flow Cytometry; D018398:Homeodomain Proteins / Q000378:metabolism*; D051379:Mice; D008822:Mice, Transgenic; D020133:Reverse Transcriptase Polymerase Chain Reaction; D016196:S Phase; D013601:T-Lymphocytes / Q000166:cytology*; D013950:Thymus Gland / Q000166:cytology / Q000378:metabolism
D017931:DNA Primers; D018398:Homeodomain Proteins; C491412:Pknox1 protein, mouse