Multiple tyrosine hydroxylase transcripts and immunoreactive forms in the rat: Differential expression in the anterior pituitary and adrenal gland

Abstract

Several regulatory neurofactors, classically associated with the hypothalamus, may be synthesized in the anterior pituitary (AP). Dopamine (DA) is the main prolactin-inhibiting factor. Its de novo synthesis in the normal AP has not been proved, although the TH transcript has been previously demonstrated by RT/PCR in the AP. We investigated tyrosine hydroxylase (TH) gene expression at both the protein and mRNA levels in the AP of normal random cycling female rats and in a catecholaminergic tissue, the adrenal gland (AG). The Western blot analysis of AP homogenates revealed two immunoreactive forms of TH in the AP, both differing from the TH present in the AG. RT/PCR products from AP and AG mRNA were subcloned and sequenced. In addition to the full-length form, we identified two TH transcripts generated by alternative splicing either involving the use of a new alternate splice-donor site within exon 2 or skipping exon 11. The form lacking exon 11 was not isolated from the AG. In the AP, all three forms were present. Although the AP contained the full-length TH mRNA, the expected size protein was not detected. Thus, there is alternative splicing of the TH primary transcript, and putative additional post-translational regulation may yield TH proteins with no enzymatic activity, at least in non-catecholaminergic tissues.

Analysis of Hypertrophic Thyrotrophs in Pituitaries of Athyroid Pax8−/− Mice

“…Because dopamine is well known to act as a potent inhibitor of lactotrophic activity [e.g. dopamine agonists such as bromocriptine are clinically used for the treatment of prolactinomas (44)], synthesis of dopamine by the anterior pituitary has been discussed previously (42,45,46) but not convincingly demonstrated as yet. Our data suggest that under athyroid conditions dopamine produced by the thyrotrophic cells may act as a paracrine factor to inhibit the lactotrophic cells in Pax8 Ϫ/Ϫ mice.…”

Catecholamine‐independent transient expression of tyrosine hydroxylase in primary auditory neurons is coincident with the onset of hearing in the rat cochlea

“…The function of this TH expression in the absence of the other CA‐synthesizing enzymes essentially remains a matter of hypothesis (Schussler et al ., 1995; Ugrumov et al ., 2002). It appears to be related to stimuli‐induced cellular activation (Asmus & Newman, 1994; Marsais & Calas, 1999; Bezin et al ., 2000; Abramova et al ., 2002; Marsais et al ., 2002) and is most often found transiently expressed during the last stages of maturation of the central nervous system.…”

Snap-Frozen Brain Tissue Sections Stored With Desiccant at Ambient Laboratory Conditions Without Chemical Fixation are Resistant to Degradation for a Minimum of 6 Months

“…3). Two bands were identified as possible rat-specific isoforms of TH 12. Furthermore, equal loading between all samples was verified by GAPDH detection.…”

“…The chosen epitope target was TH, a critical enzyme with various levels of activity present in all catecholaminergic cells, especially in tissues that react to the sympathetic response, such as brain, heart, and kidneys 13. Additionally, it is worth noting that the different molecular weight bands observed for TH can be explained by the recent evidence that 2 isoforms of TH exist in the rat whereas only 1 isoform is known to be produced in subprimate species 12–14. To normalize sample loading, the membranes were blotted for GAPDH, a ubiquitous housekeeping protein found in almost all tissues.…”