Institute of Medical Sciences, School of Medical Sciences, University of Aberdeen, Aberdeen, Scotland, UK.
J Neurochem. 2012 Aug;122(4):789-99. doi: 10.1111/j.1471-4159.2012.07824.x. Epub 2012 Jul 9.
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).
视黄酸（RA）已被发现可调节下丘脑功能，但它的确切作用部位尚不清楚。本研究显示醛脱氢酶（RALDH）酶在第三脑室排列的室管膜细胞中的表达，该区域与下丘脑神经干细胞的位置重叠。使用器官型切片培养物研究了 RA 对第三脑室衬里祖细胞增殖的影响。正如在神经发生的其他区域中所显示的那样，发现 RA 抑制了增殖。对大鼠下丘脑中 RALDH1 表达的动态研究表明，这种酶在光周期控制下存在于室管膜细胞中，在长日与短日相比时表达水平最高。与 RA 合成的这种转变平行的是，第三脑室中的细胞增殖在 RA 水平最高的长日时最低，这意味着 RALDH1 合成的 RA 可能调节神经干细胞增殖。第二种 RA 合成酶 RALDH2 也存在于排列在第三脑室的室管膜细胞中。与 RALDH1 相反，RALDH2 的光周期性变化很小，但令人惊讶的是，该蛋白的存在似乎没有 mRNA 转录，并且假设内吞室管膜细胞可能从脑脊液（CSF）中摄取该酶。
