The Cdkn1a gene (p21Waf1/Cip1) is an inflammatory response gene in the mouse central nervous system.

We used high-density cDNA microarray analysis to examine changes in the gene expression profile of the hippocampus of C57BL/6 mice following intraperitoneal injection of lipopolysaccharide (LPS). Three hours after injection, the greatest increase in RNA expression was found for an expressed sequence tag subsequently identified as the Cdkn1a gene, coding for the cyclin-dependent kinase inhibitor p21(Waf1/Cip1). Northern blot hybridization confirmed the induction of Cdkn1a mRNA in the central nervous system (CNS), and also revealed similar increases in kidney, liver and heart. Induction of Cdkn1a expression was transient, reaching maximal levels in the CNS 3-6 h after LPS administration, and returning to untreated levels by 24 h. Combined use of laser capture microdissection and quantitative reverse transcription-polymerase chain reaction showed that there was a similar change in Cdkn1a expression for the pyramidal cell layer as for total hippocampus.