Abstract
The administration of high levels of estrogen is a well established method for producing prolactin-secreting pituitary tumors in rodents but the mechanism of tumor induction is not clear. In this paper we describe a cDNA clone (pEIC) which has been isolated from an estrogen-induced pituitary tumor cDNA library. The mRNA transcript corresponding to the pEIC clone is 0.9 kilobase in length and is not detectable in normal pituitaries but is expressed as early as 3 h after estrogen stimulation. Nucleotide sequence analysis of two 700-base pair recombinant clones shows that they encode a 124-amino acid protein which is 70% identical to the porcine galanin precursor. The sequence of 29 amino acid residues coded for by the pEIC cDNA clone is 88% identical with porcine galanin with only three amino acid substitutions near the C terminus. This extensive homology suggests that the pEIC cDNA clone codes for rat galanin or a protein belonging to the galanin gene family. These results provide the first evidence of a physiological regulator (estrogen) of the expression of the galanin gene. They also imply that galanin is secreted by prolactin-secreting tumors. Because intracerebroventricular injection of galanin can stimulate prolactin secretion and galanin inhibits hypothalamic dopamine release, it is conceivable that galanin may play a role in the induction of prolactin-secreting tumors.
Highlights
Pituitary Tumor Messenger RNA* the effects of E2 on pituitary growth are direct or indirect
In this paper we describe a cDNA clone which has been isolated from an estrogen-induced pituitary tumorcDNA library.The mRNA transcriptcorresponding to the pEIC clone is 0.9 kilobase in length andis not detectable in normalpituitariesbut is expressed as early as Materials-Radioisotopes were purchased from Du Pont-New England Nuclear
The sequence of the pEIC clone indicates that 70% of the amino acid sequence is identical to porcine galanin precursor, with all but 3 of 29 amino acid residues (88%)corresponding to the porcine galanin sequence, indicating that thepEIC cDNA cloneis either therat equivalent of galanin or less probably a sequence belonging to thegalanin gene family
Summary
From an estrogen-induced pituitary tumorcDNA library.The mRNA transcriptcorresponding to the pEIC clone is 0.9 kilobase in length andis not detectable in normalpituitariesbut is expressed as early as Materials-Radioisotopes were purchased from Du Pont-New England Nuclear. ThEe. coli DNA polymerase (Klenow fragment) and packaging kits were sequence of 29 amino acid residues coded for by the pEIC cDNAclone is 88%identicalwith porcine galanin with only three amino acid substitutions near the C from Amersham Corp. PEICcDNA clone codes for rat galanin or a protein Induction of Pituitary Tumors-Female Fisher 344 rats These results provide thfeirst evidence of a physio- tary tumors were induced in rats using the silastic tubes containing logical regulator (estrogen) oftheexpressionofthe the synthetic estrogen preparation, diethylstilbestrol, as reported galanin gene. This article must be hereby marked “advertisement” in accordance with 18U.S.C. Section treated rats, anenriched cDNA probe from the E2-induced pituitary tumor mRNA wasobtained by subtractive hybridization according to. DNA sequencing was by the dideoxy chain termination method (Sanger et al.,1977) using 36S-labeleddATPand the gradient gel modification(Biggin et al., 1983).The gels were fixedin 10%acetic acidand dried before exposure to Kodak XAR film
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