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IntroductionThe globin genes and their products have been intensively investigated for the past 50 years. Those studies led to the description of structural and regulatory elements that are useful for the recognition and comparison of hundreds of globin gene family members. The divergence of ancestral ␣-and ␤-globin genes is estimated to have occurred 500 million years ago. Those genes subsequently evolved and were modified by a variety of genetic processes, including duplication events. 1 In humans, the ␣-globin gene family resides on chromosome 16p13.3 and is composed of a cluster of 3 genes (2-␣2-␣1) with protein products that bind heme and assemble into hemoglobin. Transcription of the 2 gene is silenced during fetal life, and the 2 ␣ genes (␣2 and ␣1) are expressed in a balanced fashion for the remainder of ontogeny. In addition to those 3 genes, concerted efforts in the 1980s led to the discovery of other ␣-like sequences. The downstream region of the ␣ locus contains an unusual gene named -globin that generates no detected globin protein in humans. 2,3 -globin gene transcription is regulated, and the transcripts contain no obvious defects to explain the lack of detectable protein in erythroid tissues. 2-5 Three pseudo-globin genes (pseudo-1, 6 pseudo-␣2, 7 and pseudo-␣1 8 ) were also identified in the ␣-globin locus.During the past 2 years, investigators have begun a transition toward postgenomic approaches to basic and clinical research. Hypotheses are now generated with the knowledge of whole genomic DNA sequences, 9 full-length cDNA collections, 10 and millions of expressed sequence tags (ESTs) 11 from humans and other species. Comparisons of DNA and RNA sequences with advanced bioinformatics analyses 12 have become essential. Hematology is ideally suited for this type of genome-based research due to the ease with which purified populations of hematopoietic cells are isolated. We hypothesized that human reticulocytes contain sufficient mRNA from the terminal stages of differentiation for the study of globin gene expression patterns in high throughput. Levels of globin mRNA detection and differences in globin gene transcription between cord and adult blood were studied to determine the potential of this approach for clinical assessments of hemoglobinopathies and hemoglobin switching. Using oligonucleotide arrays, significantly different globin transcription patterns were found in cord and adult blood samples. Evidence for transcription of the major globin genes was clearly demonstrated. Surprisingly, we also identified transcription from the genomic region previously thought to encode the pseudo-␣2 gene. The source of that transcription is characterized in this report as a previously unrecognized globin gene. Materials and methods Preparation of reticulocyte RNABlood was collected from healthy adult donors and from placental umbilical cords. All cells were collected according to approved guidelines regarding human subjects. Blood samples were centrifuged, and plasma and buffy coat layers were removed. P...