Differential Colocalization of Islet-1 and Estrogen Receptor α in the Murine Preoptic Area and Hypothalamus during Development

Abstract

Estrogen receptor (ER) expression and regulation is vital to the correct functioning of the neuroendocrine brain. Islet-1 (Isl-1) is a LIM homeodomain-containing transcription factor that has been implicated in neuronal differentiation, is located in the hypothalamus, and can alter ER function in vitro. We have determined that Isl-1 is localized in several regions of the hypothalamus, including the ER rich areas of the ventromedial nucleus (VMH), the preoptic area, and the anterior hypothalamus. Using double-label immunocytochemistry, we examined the overlap between immunoreactive ERα and Isl-1 in these different hypothalamic brain regions. In the developing brain, almost 100% of VMH cells that contain immunoreactive ERα also contain Isl-1. However, in older animals, the percentage of double-label cells decreased below 70%. This change is due to a decrease in the number of cells containing Isl-1, because there was no difference in the number of ERα-containing cells. By contrast, in more anterior regions of the hypothalamus, cells containing both Isl-1 and ERα were less common, with the two populations adjacent to each other, rather than overlapping. These data suggest that, although Isl-1 and ERα can interact, they are not always found in the same cells and that regulation of ERα function is not under the same control in the VMH, preoptic area, and the anterior hypothalamus.