Expression of retinaldehyde dehydrogenase 1 in the anterior pituitary glands of adult rats

Abstract

Retinoic acid (RA) plays a critical role in cell growth and tissue development and is also a regulatory factor of pituitary function. However, whether RA is generated in the pituitary gland and plays a role as a paracrine and/or autocrine factor is generally unknown. RA is synthesized from retinoids through oxidation processes. Dehydrogenases that catalyze the oxidation of retinal to RA are members of the retinaldehyde dehydrogenase (RALDH) family. Recently, we demonstrated that RALDH2 and RALDH3, but not RALDH1, were expressed in the developing anterior pituitary gland of rats, but the expression of RALDHs in the adult pituitary gland was not determined. Therefore, we have now examined the expression of RALDH1, RALDH2, and RALDH3 mRNAs in the pituitary gland of adult rats. Analysis by quantitative real-time polymerase chain reaction of adult pituitary glands has revealed a high level of RALDH1 mRNA but not of RALDH2 mRNA or RALDH3 mRNA. We have also detected mRNA expression for RALDH1 in the anterior pituitary gland by in situ hybridization with digoxigenin-labeled cRNA probes. Double-staining for RALDH1 mRNA and pituitary hormones or S-100 protein, a marker of folliculo-stellate cells (FS-cells), has revealed RALDH1 mRNA expression in a portion of prolactin-producing cells, marginal layer cells, and FS-cells. Our results suggest that RA is generated in the adult anterior pituitary gland, and that it may act locally on pituitary cells.

Estrogen Suppresses Retinaldehyde Dehydrogenase 1 Expression in the Anterior Pituitary Glands of Female Rats

“…We previously reported that RALDH1 mRNA is expressed in the anterior pituitary gland of adult male rats [4]. RALDH1 mRNA was expressed in a portion of the prolactin-producing cells (lactotrophs), marginal layer cells that line the hypophysial cleft and folliculostellate cells, in male rats.…”

“…We recently also reported that RALDH1 mRNA, but not RALDH2 or RALDH3 mRNA, is expressed in the anterior pituitary gland of adult rats [4]. We speculated that RA may play a role as an autocrine and/or paracrine signaling molecule in the anterior pituitary gland.…”

“…In situ hybridization was performed according to our previous report [4]. Rat RALDH1 DNA fragments (GenBank accession # BC061526; 935-1485) were amplified from rat anterior pituitary gland cDNA by polymerase chain reaction (PCR) with forward (5'-CTA CCA TCA AGG CCA ATG CT-3') and reverse (5'-CAC CCA GTT CTC GTC CAT TT-3') primers.…”

“…Quantitative real-time PCR was performed according to our previous report [4]. Total RNA was extracted from the pituitary gland by using Trizol reagent (Invitrogen) according to the manufacturer's instructions and was incubated with RNase-free DNase I (1 U per tube, Promega) to remove genomic DNA contamination.…”

“…However, the mechanism that regulates the gene expression of these enzymes in the pituitary gland is not known. We previously identified RALDH1 mRNA expression in the lactotrophs (prolactin-producing cells in the adult pituitary gland) of male rats [4]. The functions of lactotrophs, including cell proliferation and hormone synthesis and release, are controlled by estrogen in the female animals [5][6][7].…”