The liver is the largest internal organ and performs a wide variety of functions to maintain organismal homeostasis. While some liver functions are carried out by all hepatocytes, other functions are restricted to certain populations of hepatocytes within the liver. This phenomenon, called zonal gene regulation or liver zonation, controls may metabolic processes within the liver including ammonia detoxification; glucose homeostasis; bile acid and glutamine synthesis; and metabolism of xenobiotics, lipids, and amino acids. The liver also expresses many genes in a developmental or sex-biased manner. Some genes are expressed at higher levels early or late in development, or alternatively, in male or female liver. Several years ago, our lab identified a transcription factor called Zinc finger and homeoboxes 2 (Zhx2) based on its ability to control the silencing of genes that are normally expressed in the fetal liver. Zhx2 belongs to a small gene family that also includes Zhx1 and Zhx3. These four exon genes have a rather unique structure in that their entire protein coding region is located on an unusually large third exon. Preliminary studies indicate that these proteins are found only in vertebrates. I have performed a comprehensive analysis of Zhx proteins across a number of chordate species to determine their relationship throughout chordate evolution. Using multiple sequence alignment and phylogenetic tree-building, my studies have found that the primordial Zhx gene is most related to Zhx3 and that this gene exists in lower chordates including lancelet, sea squirt, and sea lamprey. Additional studies from our lab showed that Zhx2 regulates numerous hepatic genes in the adult liver, including cytochrome p450 (Cyp) genes as well as other genes that exhibit sex-biased expression. Previous studies have demonstrated that female-biased expression of Cyp2a4, is controlled, in part, by Zhx2. I have extended these studies to perform a comprehensive analysis of Cyp2a4 and the highly related Cyp2a5 gene. Despite the high similarity of these two Cyp genes, my data indicate that these genes exhibit different zonal expression patterns and are differentially regulated in the regenerating liver. In the course of these studies, I discovered and characterized antisense transcripts for both Cyp2a4 and Cyp2a5. Both Cyp2a4as and Cyp2a5as have positively correlated expression patterns compared to their sense counterparts. In contrast to Cyp2a4 and Cyp2a5, Cyp2a4as and Cyp2a5as show sex-biased expression patterns earlier in development, suggesting that they might contribute to later sex-biased patterns established for Cyp2a4 and Cyp2a5.