Expression and cellular localization of the transcription factor NeuroD1 in the developing and adult rat pineal gland

Abstract

Circadian rhythms govern many aspects of mammalian physiology.The daily pattern of melatonin synthesis and secretion is one of the classicexamples of circadian oscillations. It is mediated by a class of neuroendocrinecells known as pinealocytes which are not yet fully defined. An establishedmethod to evaluate functional and cytological characters is through theexpression of lineage-specific transcriptional regulators. NeuroD1 is a basichelix-loop-helix transcription factor involved in the specification andmaintenance of both endocrine and neuronal phenotypes. We have previouslydescribed developmental and adult regulation of NeuroD1 mRNA in therodent pineal gland. However, the transcript levels were not influenced by theelimination of sympathetic input, suggesting that any rhythmicity of NeuroD1might be found downstream of transcription. Here, we describe NeuroD1protein expression and cellular localization in the rat pineal gland duringdevelopment and the daily cycle. In embryonic and perinatal stages, proteinexpression follows the mRNA pattern and is predominantly nuclear.Thereafter, NeuroD1 is mostly found in pinealocyte nuclei in the early part ofthe night and in cytoplasm during the day, a rhythm maintained intoadulthood. Additionally, nocturnal nuclear NeuroD1 levels are reduced aftersympathetic disruption, an effect mimicked by the in vivo administration ofa- and b-adrenoceptor blockers. NeuroD1 phosphorylation at two sites, Ser274and Ser336, associates with nuclear localization in pinealocytes. These datasuggest that NeuroD1 influences pineal phenotype both during developmentand adulthood, in an autonomic and phosphorylation-dependent manner.