Glutathione peroxidases have been thought to function in cellular antioxidant defense. However, some recent studies on Gpx1 knockout (؊/؊) mice have failed to show a role for Gpx1 under conditions of oxidative stress such as hyperbaric oxygen and the exposure of eye lenses to high levels of H 2 O 2 . These findings have, unexpectedly, raised the issue of the role of Gpx1, especially under conditions of oxidative stress. Here we demonstrate a role for Gpx1 in protection against oxidative stress by showing that Gpx1 (؊/؊) mice are highly sensitive to the oxidant paraquat. Lethality was already detected within 24 h in mice exposed to paraquat at 10 mg⅐kg ؊1 (approximately 1 ⁄7 the LD 50 of wild-type controls). The effects of paraquat were dose-related. In the 30 mg⅐kg ؊1 -treated group, 100% of mice died within 5 h, whereas the controls showed no evidence of toxicity. We further demonstrate that paraquat transcriptionally upregulates Gpx1 in normal cells, reinforcing a role for Gpx1 in protection against paraquat toxicity. Finally, we show that cortical neurons from Gpx1 (؊/؊) mice are more susceptible to H 2 O 2 ; 30% of neurons from Gpx1 (؊/؊) mice were killed when exposed to 65 M H 2 O 2 , whereas the wild-type controls were unaffected. These data establish a function for Gpx1 in protection against some oxidative stressors and in protection of neurons against H 2 O 2 . Further, they emphasize the need to elucidate the role of Gpx1 in protection against different oxidative stressors and in different disease states and suggest that Gpx1 (؊/؊) mice may be valuable for studying the role of H 2 O 2 in neurodegenerative disorders.

Some undifferentiated F9 embryonal carcinoma cells allow adenovirus genes to be expressed independently of the Ela oncogene normally required for their activation; this has been attributed to a cellular equivalent of Ela in F9 cells. However, transcription of all early genes was low in undifferentiated OTF963 embryonic carcinoma cells during the ru-st 48 hr after infection with adenovirus type 5 (Ad5).

Studies of the development and differentiation of early mammalian embryos have been severely limited by the paucity of material. Such studies have been largely restricted to the examination of abundant genes/proteins or to developmental expression studies of known genes for which DNA sequence data are available, allowing the use of reverse transcription and polymerase chain reaction amplification (RT‐PCR). To eliminate the need for hundreds or thousands of oocytes or embryos in the construction of representative cDNA libraries, we describe a technique for generating and cloning cDNA using small caesium chloride gradient centrifugation to isolate total RNA from oocytes or embryos, followed by RT‐PCR of mRNA from this total RNA. Total RNA was isolated from 70 mouse blastocysts. A portion of the cDNA generated (equivalent to seven blastocysts) was cloned, yielding a mouse blastocyst cDNA library of 1 million clones. We show that the library is representative in that it contains β‐actin, intracisternal A‐type particles, tissue plasminogen activator, and B1 and B2 repetitive elements in frequencies comparable with published data from conventionally constructed libraries and estimates of mRNA abundance from expression studies. Furthermore, DNA sequencing of 22 clones chosen at random and compared with DNA sequence databases shows that approximately half are novel sequences. These data demonstrate that representative cDNA libraries can be constructed in situations where cell numbers are limiting and will facilitate the isolation of novel and interesting clones. © 1996 Wiley‐Liss, Inc.

Adenovirus infection was compared in F9 (OTF963) cells and cells induced to differentiate with retinoic acid, in order to study expression of early genes under the control of the reported "Ela-like factor" in F9 cells. However, not only was transcription of the viral Ela gene defective in undifferentiated cells but expression of all the other early genes was found to be reduced in OTF963 cells in comparison to differentiated cells. The defect in early gene expression was detected at the level of transcriptional initiation during the first 48 h of infection and resulted in similarly low levels of viral cytoplasmic mRNA and viral protein synthesis. Viral DNA replication was delayed and reduced. After 48 h of infection, the defect in transcription in OTF963 cells of Ela and other early genes was relieved, so that by 72 h postinfection the level of transcription was similar to that 16 h after infection of differentiated cells. At no time did adenovirus early gene expression occur independently of viral Ela. These results suggest limits to the generality and explanatory power of the hypothesis that F9 embryonal carcinoma cells contain an Ela-like factor. When embryonal carcinoma (EC) cells differentiate, radical changes in their morphology (44), proliferative rate (25, 38, 40), and tumorigenicity (45) are observed. F9 cells do not undergo spontaneous differentiation under normal culture conditions but can be induced to differentiate in vitro in the presence of retinoic acid into primitive endoderm-like cells (44), like those of the inner cell mass of the blastocyst (17). F9 cells treated with retinoic acid and dibutyryl cyclic AMP differentiate further to form either parietal or visceral endoderm (14, 46). EC cell lines have provided a useful in vitro model for the study of changes in gene regulation during differentiation (28). Genes encoding laminin B, collagen type IV, major histocompatibility complex class I antigens, P-2 microglobulin, Endo A, Endo B, and vinculin are transcriptionally activated 3 days postinduction. The cellular proto-oncogenes c-abl, c-src, and c-fos are also transcriptionally activated 1, 4, and 6 days postinduction of differentiation, respectively (28, 40). Viral genes have been used as a model system to investigate changes to gene regulation as a function of differentiation because they use cellular transcription factors and thus may reflect the regulation of cellular gene transcription. It has been found that transcription of several viral genes is repressed in undifferentiated F9 cells. However, if F9 cells are induced to differentiate, viral genes are expressed efficiently. The enhancer elements in the long terminal repeats of retroviruses, Moloney murine leukemia virus, murine sarcoma virus, and Rous sarcoma virus appear to be under negative control in undifferentiated F9 cells (10, 12, 13, 27, 49). The DNA viruses simian virus 40 (SV40), polyomavirus, and cytomegalovirus are all inactive in F9 cells due to a defect in the function of their early gene enhancers (11, 12, 32, 41, 42, 47, 4...