The molecular clock runs at different rates among closely related members of a gene family.

The serum albumin gene family is composed of four members that have arisen by a series of duplications from a common ancestor. From sequence differences between members of the gene family, we infer that a gene duplication some 580 Myr ago gave rise to the vitamin D-binding protein (DBP) gene and a second lineage, which reduplicated about 295 Myr ago to give the albumin (ALB) gene and a common precursor to alpha-fetoprotein (AFP) and alpha-albumin (ALF). This precursor itself duplicated about 250 Myr ago, giving rise to the youngest family members, AFP and ALF. It should be possible to correlate these dates with the phylogenetic distribution of members of the gene family among different species. All four genes are found in mammals, but AFP and ALF are not found in amphibia, which diverged from reptiles about 360 Myr ago, before the divergence of the AFP-ALF progenitor from albumin. Although individual family members display an approximate clock-like evolution, there are significant deviations-the rates of divergence for AFP differ by a factor of 7, the rates for ALB differ by a factor of 2.1. Since the progenitor of this gene family itself arose by triplication of a smaller gene, the rates of evolution of individual domains were also calculated and were shown to vary within and between family members. The great variation in the rates of the molecular clock raises questions concerning whether it can be used to infer evolutionary time from contemporary sequence differences.

Avoidance of immune response prolongs expression of genes delivered to the adult rat myocardium by replication-defective adenovirus.

BACKGROUND: Gene delivery is a rapidly expanding field with potential applications to every human organ system. Recently, adenoviruses have been used as efficient vectors for in vivo gene transfer into the myocardium. These methods, however, have shown a sharp decline of gene expression after 1 week. To test the hypothesis that an immune-effector mechanism is involved in this decline, we compared the results after injection of adenovirus-5 carrying the beta-galactosidase gene (Ad beta-gal) into the left ventricular myocardium of athymic nude rats (NDRs) versus immunocompetent Sprague-Dawley rats (SDRs). METHODS AND RESULTS: Ad beta-gal (5.0 x 10(9) PFU/mL) was injected into the left ventricle of NDRs (n = 16) and SDRs (n = 22). Hearts were harvested, embedded in paraffin, and sectioned and stained for beta-gal activity, hematoxylin and eosin and picrosirius red at 4, 21, 35, 85, and 120 days. Representative samples were immunostained with antibodies directed at inflammatory markers. beta-gal activity was quantified by digital planimetry and expressed as area of staining (% +/- SEM). Peak beta-gal activity was highest at 4 days, with NDRs displaying significantly greater staining (83 +/- 3.0% versus 54 +/- 8.0%; P = .03). SDRs sustained a rapid drop in activity, such that at 35 (1 +/- 0.19%) and 85 (1 +/- 0.4%) days, only occasional cells stained positive and by 120 days (0.3 +/- 0.0%), activity had been extinguished. NDRs continued to show transgene expression at all time periods (35 and 85 days, 25 +/- 7.1% and 7.4 +/- 2.7%, respectively) and was still readily detected at 120 days. An inflammatory response was limited in NDRs compared with SDRs, in which there was intense mononuclear cell infiltration, with collagen deposition and scar formation. Immunostaining identified the majority of these inflammatory cells as not being of lymphocyte lineage, although small numbers of lymphocytes and phagocytic and activated plasma cells were identified. CONCLUSIONS: Our data suggest that immune-effector mechanisms can severely affect the expression of genes delivered by adenovirus. The present model provides efficient gene expression for at least 120 days without significant inflammatory reaction.

Complete structure of the human Gc gene: differences and similarities between members of the albumin gene family.

The sequence of the human Gc gene, including 4228 base pairs of the 5'-flanking region and 8514 base pairs of the 3' flanking region (55,136 in total), was determined from five overlapping lambda phage clones. The sequence spans 42,394 base pairs from the cap site to the polyadenylation site, and it reveals that the gene is composed of 13 exons, which are symmetrically placed within the three domains of the Gc protein. The first exon is partially untranslated, as is exon 12, which contains the termination codon TAG. Exon 13 is entirely untranslated, but contains the polyadenylation signal AATAAA. Ten central introns split the coding sequence between codon positions 2 and 3 and between codon positions 3 and 1 in an alternating pattern, exactly as has been observed in the structure of the albumin and alpha-fetoprotein genes. The Gc gene has several distinctive features which set it apart from the other members of the family. First, the gene is smaller by two exons, which results in a protein some 130 amino acids shorter than albumin or AFP. This decrease in size may result from the loss of two internal exons during the evolutionary history of the Gc gene. Second, exons 6, 8, 9, and 11 are smaller than their counterparts in albumin or AFP by a total of 8 codons (1, 4, 1, and 2, respectively). Although the mRNA and protein expressed from the Gc gene are significantly smaller, the gene itself is about 2.5 times larger than the other genes of the family.(ABSTRACT TRUNCATED AT 250 WORDS)