Reporter transgene based on s human HOX regulatory element is expressed dynamically during mouse development

In the previous experiment, we have transiently analyzed a 307 bp cis-acting regulatory element of HOXA-7 in transgenic mice (TG). Since it was sufficient to direct a reporter gene to be expressed at the specific region of day 12.5 post coitum (p.c.) embryo with a sharp anterior boundary, we generated transgenic mice line using the NM307 (307 bp/tk promoter/LacZ/SV40 poly A) construct in order to see the temporal expression pattern following embryonic development. Through polymerase chain reaction (PCR) with LacZ specific primers and genomic DNAs isolated from ear tissue, 4 transgenic mice (founder mice, F0) were obtained and 3 exhibited characteristic expression pattern. The expression detected as early as day 8.5 p.c. in the neuroectoderm and epiblast at the posterior region; from the closed neural tube around the region S10-12 to the adjacent posterior neural fold, neural groove and to the posterior epiblast along the anteroposterior axis. At day 7.5 p.c., however, LacZ expression was not detected. As embryo develops, the expression was restricted in the neural tube from S10 area to the end of tail of day 9.5 p.c. embryo, among which rather low level of expression was detected particularly in the region of S10-13, and the overall expression pattern continued through the following day. From day 11.5 to 12.5 p.c. weak spreading of the expression was detected to the anterior of S10 and a repression at the tail region. These results altogether indicate that the 307 bp is a temporal as well as a spatial regulatory element of HOXA-7 initiating the function at around day 7.5.~8.5 p.c. and continuing through mid gestation.ope