Analysis of Thyroid Response Element Activity during Retinal Development

Thyroid hormone (TH) signaling components are expressed during retinal development in dynamic spatial and temporal patterns. To probe the competence of retinal cells to mount a transcriptional response to TH, reporters that included thyroid response elements (TREs) were introduced into developing retinal tissue. The TREs were placed upstream of a minimal TATA-box and two reporter genes, green fluorescent protein (GFP) and human placental alkaline phosphatase (PLAP). Six of the seven tested TREs were first tested in vitro where they were shown to drive TH-dependent expression. However, when introduced into the developing retina, the TREs reported in different cell types in both a TH-dependent and TH-independent manner, as well as revealed specific spatial patterns in their expression. The role of the known thyroid receptors (TR), TRα and TRβ, was probed using shRNAs, which were co-electroporated into the retina with the TREs. Some TREs were positively activated by TR+TH in the developing outer nuclear layer (ONL), where photoreceptors reside, as well as in the outer neuroblastic layer (ONBL) where cycling progenitor cells are located. Other TREs were actively repressed by TR+TH in cells of the ONBL. These data demonstrate that non-TRs can activate some TREs in a spatially regulated manner, whereas other TREs respond only to the known TRs, which also read out activity in a spatially regulated manner. The transcriptional response to even simple TREs provides a starting point for understanding the regulation of genes by TH, and highlights the complexity of transcriptional regulation within developing tissue

Certain pleasures, ambiguous grounds: the etymology and evolution of the pleasure garden

Pleasure garden and pleasure ground are two terms with ambiguous meanings in the landscape historian\u27s vocabulary. While they are used to describe spatial patterns designed for human usage from the seventeenth century to the present, their specific characteristics are not constant, resulting over time in at least three different, even contradictory, definitions. Multiple uses lead to confusion in which the terms and the spaces they represent are largely irrelevant as open space models in discussions of designed landscapes. Seeking a way through which the etymology of these terms might be better understood, the author first examines references and their evolutionary uses from the seventeenth century to the present. Then the different ways that recent landscape historians have used the terms as a means through which present-day designers and landscape historians might become better acquainted with this typology\u27s evolution - are explored. © 2013 Copyright European Council of Landscape Architecture Schools