A previous study showed that rHSTa ST2A2 RNA levels in male rat liver were increased by tamoxifen treatment, whereas the levels in female liver were reduced 47 tamoxifen for gyno This approach can cause problems when the gene in question is haploinsufficient, or when used in a homozygous state, since some of these null alleles will have nonwild type phenotypes alone or in conjunction with an additional ablated gene, that is, result in a synthetic phenotype