Fluoro-Jade B, like its predecessor Fluoro-Jade, is an anionic fluorescein derivative useful for the histological staining of neurons undergoing degeneration. However, Fluoro-Jade B has an even greater specific affinity for degenerating neurons. This notion is supported by the conspicuous staining of degenerating neuronal elements with minimal background staining. This improved signal-to-noise ratio means that fine neuronal processes including distal dendrites, axons and axon terminals can be more readily detected and documented. Although the staining time and dye concentration are reduced, the method is as rapid, simple and reliable as the original Fluoro-Jade technique. Like Fluoro-Jade, Fluoro-Jade B is compatible with a number of other labeling procedures including immunofluorescent and fluorescent Nissl techniques.

Hepatocyte nuclear factor 4 (HNF-4), a highly conserved member of the steroid hormone receptor superfamily critical for development and liver-specific gene expression, is very similar to another superfamily member, retinoid X receptor ␣ (RXR␣), in overall amino acid sequence and DNA binding specificity. Since RXR␣ is known to heterodimerize with many other nuclear receptors, the formation of heterodimers between HNF-4 and RXR␣ was examined. With the electrophoretic mobility shift assay, coimmunoprecipitation, and transient transfection assays, it is shown that, unlike other nuclear receptors, HNF-4 does not form heterodimers with RXR␣ either in the presence or in the absence of DNA. We also show that in vitro-translated HNF-4 does not form heterodimeric complexes on DNA with a number of other receptors, including RXR␤, RXR␥, retinoic acid receptor ␣, or thyroid hormone receptor ␣. To investigate the hypothesis that the lack of heterodimerization between HNF-4 and RXR␣ is due to a strong homodimerization activity of HNF-4, glycerol gradient sedimentation and kinetic analysis were used to show that HNF-4 is in fact a stable homodimer in solution. Finally, immunohistochemistry is used to show that the HNF-4 protein is found exclusively in the nuclei in both HepG2 cells, which express endogenous HNF-4, and transfected COS cells, which overexpress HNF-4. These findings lead us to propose that HNF-4 defines a new subclass of nuclear receptors which reside primarily in the nucleus and which bind DNA and regulate transcription as homodimers.Hepatocyte nuclear factor 4 (HNF-4) is a positive-acting transcription factor which is expressed very early in embryo development and is essential to liver development and function (reviewed in references 84 and 85). Mouse HNF-4 mRNA appears in the primary endoderm of implanting blastocysts at embryonic day 4.5 and in the liver and gut primordia at day 8.5 (20), while mice deficient in HNF-4 do not survive past day 9 postcoitus (12). HNF-4 has also been proposed to be responsible for the final commitment for cells to differentiate into hepatocytes (68). In adult rodents, HNF-4 is located primarily in the liver, kidney, and intestine, and in insects HNF-4 is found in the equivalent tissues (86, 95). HNF-4 is known to activate a wide variety of essential genes, including those involved in cholesterol, fatty acid, and glucose metabolism; blood coagulation; detoxification mechanisms; hepatitis B virus infections; and liver differentiation (reviewed in references 84 and 85).HNF-4 is a member of the superfamily of ligand-dependent transcription factors, which includes the steroid hormone receptors, thyroid hormone receptor (TR), vitamin A receptor, and vitamin D receptor (VDR), as well as a large number of receptors for which ligands have not yet been identified, the so-called orphan receptors (reviewed in references 56, 72, 73, and 88). All receptors are characterized by two conserved domains: the zinc finger region, which mediates DNA binding, and a large hydrophobic domain which mediate...

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