Hoxd1 is Expressed by Oligodendroglial Cells and Binds to a Region of the Human Myelin Oligodendrocyte Glycoprotein Promoter in vitro

(1) Little information exists on the role of clustered Hox genes in oligodendrocyte (OG) development. This study examines the expression profile of Hoxd1 and identifies a potential downstream target in the OG lineage. (2) Immunocytochemical analysis of primary mixed glial cultures demonstrated Hoxd1 was expressed throughout OG development. (3) A human myelin protein gene, myelin oligodendrocyte glycoprotein (MOG), was identified as a putative downstream target of Hoxd1 through Genbank searches utilizing the Hoxd1 homeodomain consensus binding sequence. (4) The dissociation coefficient constant (K _D) and dissociation rate constant (k _d) of the Hoxd1–MOG complex, determined using electrophoretic mobility shift assays (EMSAs), were estimated to be 1.9 × 10⁻⁷ M and 1.3 × 10⁻³ s⁻¹, respectively. The DNA–Hoxd1 homeodomain complex had a half-life (t _1/2) of 15 min. (5) Mutational analysis of Hoxd1–MOG complexes revealed the binding affinity of M1 (with mutation from ⁻¹⁰⁵⁴5′-TAAT-3′⁻¹⁰⁵¹ to TACT within the consensus binding site) and M2 (with mutation from ^-10545′-TAATTG-3′^-1049 to TAATCC within the consensus binding site) probes to the MOG promoter was severely affected. Thus the TAATTG core of the binding sequence appears important for Hoxd1 specificity. (6) Analysis of the involvement of TAAT sites adjacent to the consensus sequence in Hoxd1 binding showed the binding affinity of the M3 probe was affected, but not as severely as the M1 and M2 probes. These in vitro results suggest the TTTAATTGTA sequence is involved in Hoxd1 binding to the MOG promoter but neighboring TAAT sites may also be needed. Thus, MOG may be a target of Hoxd1.