ACUTE EXPRESSION OF THE PRL RECEPTOR GENE AFTER OVARIECTOMY IN MIDPREGNANT MOUSE MAMMARY-GLAND

In order to examine the time-dependent expression of the PRL receptor (PRL-R) gene at lactogenesis, the level of PRL-R mRNA was determined f ollowing ovariectomy in pregnant mouse mammary gland. Following revers e transcription, the quantity of mRNA was measured by the competitive polymerase chain reaction. The casein (a 22000 molecular weight compon ent) mRNA level was measured as a marker for milk synthesis. Following ovariectomy, the onset of abortion occurred mostly at 22-23 h and the level of casein mRNA began to increase at 12 h. The long and short fo rms of PRL-R mRNAs were detected in a molar ratio of 1:0.2 on day 12 o f pregnancy. Eight h after ovariectomy, the long form of PRL-R mRNA be gan to increase, showing a bell-shaped profile with the highest peak a t 16 h. The short form of PRL-R mRNA was at low levels and remained co nstant. The levels of the long form of PRL-R mRNA decreased similarly in the presence and absence of foster pups from 24 to 48 h. Conversely , casein mRNA were maintained at high levels by supplying foster pups. The level of the long form of PRL-R mRNA reached a maximum prior to a bortion. The present experiments demonstrated that the acute expressio n of the PRL-R gene occurred in the mammary gland at lactogenesis.