Transgenic Mice with Cre Recombinase Expressed in Lactotropes and with tissue-selective deletion of the dopamine D2R

MARÍA INÉS PÉREZ MILLÁN; ANA ORNSTEIN; DANIELA NOAIN; MARCELO RUBINSTEIN; DAMASIA BECÚ-VILLALOBOS

Washington DC

Congreso; The Endocrine Society´s annual meeting; 2009

Prolactin secreting adenomas are the most frequent type among pituitary tumors. Macroprolactinomas are benign, although they can be locally highly aggressive, and invade adjacent structures, resulting in neurological dysfunction. Pharmacological therapy with dopamine agonists remains the mainstay of treatment. But a high percentage of patients with prolactin-secreting pituitary tumors, shows dopamine agonist resistance. To study these tumors, we have generated a transgenic mouse that expresses Cre recombinase within the anterior pituitary gland under the transcriptional control of the prolactin promoter (Prl-Cre). We obtained five lines of these transgenic mice, and by real time PCR we showed that Cre mRNA was specifically expressed in the pituitary, and absent in different tissues (hypothalamus, kidney, liver). To determine if Cre mRNA was capable of being translated into an active protein that could excise loxP flanked genomic DNA, Cre +/- mice were crossed with ROSA26-EGFP reporter mice, in order to activate EGFP expression in lactotropes. Different tissue, brain and pituitaries, were taken from Cre+/- EGFP +/- and EGFP +/- mice (as negative controls) and processed for inmunohistochemistry with antibodies for Cre, EGFP and Prl. Double immunocytochemistry of pituitaries revealed the majority of lactotropes expressed EGFP if Cre was also present, and no EGFP in these mice was observed in the brain. Finally, to develop a new model of prolactinomas, we crossed two of the lines of Prl-Cre transgenic mice, (N 6 and 8), with low and high expression of Cre, respectively, with mice whose exon 2 of the D2R is flanked by LoxP sequences. In order to verify the deletion of the gene of the D2R in lactotropes, we evaluated serum prolactin levels, basally and after a stimulus with haloperidol (3mg/kg) in both lines. Line 6, and not line 8, showed higher basal prolactin level than paired wildtypes, and failed to evoke an increase in prolactin levels after the stimulus with haloperidol, in contrast to the positive response observed in wildtype mice. This indicated that the D2R in the pituitary in this line is not functional. This new transgenic mouse will provide a valuable tool for the study of resistant prolactinomas.