Photoperiodic expression of two RALDH enzymes and the regulation of cell proliferation by retinoic acid in the rat hypothalamus.
Retinoic acid (RA) has been found to regulate hypothalamic function, but precisely where it acts is unknown. This study shows expression of retinaldehyde dehydrogenase (RALDH) enzymes in tanycytes that line the third ventricle in an area overlapping with the site of hypothalamic neural stem cells. The influence of RA was examined on the proliferation of progenitors lining the third ventricle using organotypic slice cultures. As has been shown in other regions of neurogenesis, RA was found to inhibit proliferation. Investigations of the dynamics of RALDH1 expression in the rat hypothalamus have shown that this enzyme is in tanycytes under photoperiodic control with highest levels during long versus short days. In parallel to this shift in RA synthesis, cell proliferation in the third ventricle was found to be lowest during long days when RA was highest, implying that RALDH1 synthesized RA may regulate neural stem cell proliferation. A second RA synthesizing enzyme, RALDH2 was also present in tanycytes lining the third ventricle. In contrast to RALDH1, RALDH2 showed little change with photoperiodicity, but surprisingly the protein was present in the apparent absence of mRNA transcript and it is hypothesized that the endocytic tanycytes may take this enzyme up from the cerebrospinal fluid (CSF).
Institute of Medical Sciences, School of Medical Sciences, University of Aberdeen, Aberdeen, Scotland, UK.
Kirsty D
KD
Shearer
Patrick N
PN
Stoney
Sonia E
SE
Nanescu
Gisela
G
Helfer
Perry
P
Barrett
Alexander W
AW
Ross
Peter J
PJ
Morgan
Peter
P
McCaffery
D000080924:Aldehyde Dehydrogenase 1 Family; D000818:Animals; D015153:Blotting, Western; D049109:Cell Proliferation / Q000187:drug effects*; D002478:Cells, Cultured; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D007031:Hypothalamus / Q000166:cytology* / Q000187:drug effects / Q000201:enzymology*; D007150:Immunohistochemistry; D017403:In Situ Hybridization; D007527:Isoenzymes / Q000096:biosynthesis; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D058953:Neural Stem Cells / Q000187:drug effects; D009924:Organ Culture Techniques; D017440:Photoperiod; D016133:Polymerase Chain Reaction; D051381:Rats; D011916:Rats, Inbred F344; D017207:Rats, Sprague-Dawley; D050697:Retinal Dehydrogenase / Q000096:biosynthesis* / Q000134:cerebrospinal fluid; D020542:Third Ventricle / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D014212:Tretinoin / Q000032:analysis / Q000494:pharmacology*
D007527:Isoenzymes; D014212:Tretinoin; D000080924:Aldehyde Dehydrogenase 1 Family; C523119:Aldh1a1 protein, rat; C521403:Aldh1a2 protein, rat; D050697:Retinal Dehydrogenase