Expression profiling of developmental and regenerating liver in mice. Mus musculus

Normal adult liver is uniquely capable of renewal and repair after injury. Whether this response represents simple hyperplasia of various liver elements or requires recapitulation of the genetic program of the developing liver is not known. To study these possibilities, we examined transcriptional programs of adult liver after partial hepatectomy and contrasted these with developing embryonic liver. Principal component analysis demonstrated that the time series of gene expression during liver regeneration does not segregate according to developmental transcription patterns. Gene ontology analysis revealed that liver restoration after hepatectomy and liver development differ dramatically with regard to transcription factors and chromatin structure modification. In contrast, the tissues are similar with regard to proliferationassociated genes. Consistent with these findings, realtime polymerase chain reaction showed transcription factors known to be important in liver development are not induced during liver regeneration. These three lines of evidence suggest that at a transcriptional level, restoration of liver mass after injury is best described as hepatocyte hyperplasia and not true regeneration. We speculate this novel pattern of gene expression may underlie the unique capacity of the liver to repair itself after injury. Keywords: time course Overall design: In order to elucidate the molecular similarities between regenerating and developing liver, we performed high-density microarray analysis using Affymetrix MG 430 2.0 chips for targets at 0, 1, 2, 6, 12, 18, 24, 30, 48, and 72 hours after partial hepatectomy and at 10.5, 11.5, 12.5, 13.5, 14.5, and 16.5 days post conception (dpc). Each experimental time point is represented by two separate samples, each consisting of at least 3 pooled tissues from different animals. For example, 6 hepatectomies were performed for the 1 hour post-hepatectomy time point. Time 0 is used as control.