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.