Phyllis A. Dennery

Icterus neonatorum, or neonatal jaundice, has long been recognized.1 The term “kernicterus” was introduced in the early 1900s to refer to the yellow staining of the basal ganglia observed in infants who died with severe jaundice.2 From the 1950s through the 1970s, because of a high incidence of Rh hemolytic disease and kernicterus, pediatricians were aggressive in treating jaundice.3 However, several factors have changed the management of jaundice. Studies in the 1980s and 1990s suggested that kernicterus from jaundice was rare and that too many infants were being treated unnecessarily.47 Also, newborn infants were being discharged from the hospital . . .

Control of gene expression often involves an interwoven set of regulatory processes. As information regarding regulatory pathways may be lost in ex vivo analyses, we used bioluminescence to monitor gene expression in living mammals. Viral promoters fused to firefly luciferase as transgenes in mice allowed external monitoring of gene expression both superficially and in deep tissues. In vivo bioluminescence was detectable using either intensified or cooled charge-coupled device cameras, and could be detected following both topical and systemic delivery of substrate. In vivo control of the promoter from the human immunodeficiency virus was demonstrated. As a model for DNA-based therapies and vaccines, in vivo transfection of a luciferase expression vector (SV-40 promoter and enhancer controlling expression) was detected. We conclude that gene regulation, DNA delivery and expression can now be noninvasively monitored in living mammals using a luciferase reporter. Thus, real-time, noninvasive study of gene expression in living animal models for human development and disease is possible.

Oxygen radicals, or reactive oxygen species (ROS) act as primary or secondary messengers to promote cell growth or death. Many instances demonstrate an important direct role of ROS in development because redox status regulates key transcription factors that influence cell signaling pathways involved in proliferation, differentiation, and apoptosis. Therefore, oxidative stress can alter many important reactions that affect embryonic development both positively and negatively. During particular periods in development, the embryo is more or less susceptible to oxidative stress, and teratogens, which can modify redox status, such as thalidomide, phenytoin, and ethanol, will disrupt fetal development. Various events in pregnancy such as diabetes also alter the redox state. Fortunately, antioxidants can obviate these effects through modification of gene expression, transcription factor signaling, and cell cycle alterations. A better understanding of ROS-mediated reactions and their impact on embryonic development is important to ensure optimal outcomes.

Heme oxygenase-1 (HO-1), the rate-limiting enzyme in heme degradation, is an integral membrane protein of the smooth endoplasmic reticulum. However, we detected an HO-1 immunoreactive signal in the nucleus of cultured cells after exposure to hypoxia and heme or heme/hemopexin. Under these conditions, a faster migrating HO-1 immunoreactive band was enriched in nuclear extracts, suggesting that HO-1 was cleaved to allow nuclear entry. This was confirmed by the absence of immunoreactive signal with an antibody against the C terminus and the lack of a C-terminal sequence by gas chromatographymass spectrometry. Incubation with leptomycin B prior to hypoxia abolished nuclear HO-1 and the faster migrating band on Western analysis, suggesting that this process was facilitated by CRM1. Furthermore, preincubation with a cysteine protease inhibitor prevented nuclear entry of green fluorescent protein-labeled HO-1, demonstrating that protease-mediated C-terminal cleavage was also necessary for nuclear transport of HO-1. Nuclear localization was also associated with reduction of HO activity. HO-1 protein, whether it was enzymatically active or not, mediated activation of oxidant-responsive transcription factors, including activator protein-1. Nevertheless, nuclear HO-1 protected cells against hydrogen peroxide-mediated injury equally as well as cytoplasmic HO-1. We speculate that nuclear localization of HO-1 protein may serve to up-regulate genes that promote cytoprotection against oxidative stress.