NeuroD1 Protein in the Adult Rat Pineal Gland

CASTRO A.E, WELLER J., KLEIN D.C AND MUÑOZ E.M.

Buzios, Rio de Janeiro, Brasil

Congreso; I CONGRESS IBRO/LARC OF NEUROSCIENCES FOR LATIN AMERICA, CARIBBEAN AND IBERIAN PENINSULA; 2008

IBRO/LARC

NeuroD1 has been found to be a key determinant of the fate of specific endocrine and neuronal cells, including pancreatic β cells, cerebellar granule cells and retinal photoreceptors. Muñoz, Bailey, Rath, Shi, Morin, Coon, Møller and Klein (J Neurochem 102: 887-99, 2007) reported for the first time the expression pattern of NeuroD1 mRNA in the developing rat brain, including the pineal gland, and a list of genes affected in the neonatal pineal gland from BETA2/NeuroD1 KO mice. Gene expression analysis identified 127 transcripts down-regulated and 16 were up-regulated in the KO mice. The most dramatically down-regulated gene was kinesin family member 5C and the most up-regulated gene was glutamic acid decarboxylase 1. The gene that encodes the enzyme AA-NAT (arylalkylamine N-acetyltransferase) also emerged as a potential NeuroD1 target gene. NeuroD1 mRNA levels in the adult rat pineal gland were found similar during the day and night, and did not appear to be directly influenced by sympathetic neural input. These results do not invalidate the hypothesis that the NeuroD1 protein might exhibit a rhythmic nature. Immunohistochemistry studies using a rabbit polyclonal anti-NeuroD1 antibody revealed that day and night pinealocytes express NeuroD1 protein; immunostaining was mainly seen at the cytoplasmic level. A second subpopulation of NeuroD1-positive cells was only observed in the nighttime. These cells, located in clusters in the heart of the gland and next to the stalk, exhibited diverse shape and numerous NeuroD1-positive cytoplasmic processes. A few cells with nuclear immunoreactivity were identified. Further studies using antibodies that recognize neuronal and glial markers, including GAP43 and GFAP, suggest that the nocturnal niche did not co-localize with mature neurons and GFAP-positive astrocytes. Intense S-antigen-immunoreactive cells were observed in the gland periphery. Further characterization is required to establish the precise lineage and source of these nocturnal NeuroD1-positive cells. These results are promising towards elucidation of the potential role of NeuroD1 in the pineal gland phenotype and therefore, in the melatonin rhythm.