An IS4 transposition causes a 13-bp duplication of phage lambda DNA and results in the constitutive expression of the cI and cro gene products

We have examined the nature of the additional DNA present in lambda hyp- mutants (Eisen et al., 1982). This DNA is an IS4 element in orientation I, in the y region of bacteriophage lambda at nucleotide position 39,139 (see Moore et al., 1979). Our assignment is based on (i) the similarity in size derived from the PstI, AvaI, and HindII restriction pattern and (ii) the DNA sequence of both the left and right lambda-IS4 DNA junctions in phage lambda hyp15rev4. The IS4 integration event resulted in the duplication of 13 bp of lambda DNA in contrast to the 11- and 12-bp duplications previously observed at the sites of IS4 integrations elsewhere (Klaer et al., 1981).     

Genomic mapping of direct and correlated responses to long-term selection for rapid growth rate in mice

Understanding the genetic architecture of traits such as growth, body composition, and energy balance has become a primary focus for biomedical and agricultural research. The objective of this study was to map QTL in a large F(2) (n = 1181) population resulting from an intercross between the M16 and ICR lines of mice. The M16 line, developed by long-term selection for 3- to 6-week weight gain, is larger, heavier, fatter, hyperphagic, and diabetic relative to its randomly selected control line of ICR origin. The F(2) population was phenotyped for growth and energy intake at weekly intervals from 4 to 8 weeks of age and for body composition and plasma levels of insulin, leptin, TNFalpha, IL6, and glucose at 8 weeks and was genotyped for 80 microsatellite markers. Since the F(2) was a cross between a selection line and its unselected control, the QTL identified likely represent genes that contributed to direct and correlated responses to long-term selection for rapid growth rate. Across all traits measured, 95 QTL were identified, likely representing 19 unique regions on 13 chromosomes. Four chromosomes (2, 6, 11, and 17) harbored loci contributing disproportionately to selection response. Several QTL demonstrating differential regulation of regional adipose deposition and age-dependent regulation of growth and energy consumption were identified.     

Genome sequences of Chlamydia trachomatis MoPn and Chlamydia pneumoniae AR39

The genome sequences of Chlamydia trachomatis mouse pneumonitis (MoPn) strain Nigg (1 069 412 nt) and Chlamydia pneumoniae strain AR39 (1 229 853 nt) were determined using a random shotgun strategy. The MoPn genome exhibited a general conservation of gene order and content with the previously sequenced C.trachomatis serovar D. Differences between C.trachomatis strains were focused on an ~50 kb ‘plasticity zone’ near the termination origins. In this region MoPn contained three copies of a novel gene encoding a >3000 amino acid toxin homologous to a predicted toxin from Escherichia coli 0157:H7 but had apparently lost the tryptophan biosyntheis genes found in serovar D in this region. The C.pneumoniae AR39 chromosome was >99.9% identical to the previously sequenced C.pneumoniae CWL029 genome, however, comparative analysis identified an invertible DNA segment upstream of the uridine kinase gene which was in different orientations in the two genomes. AR39 also contained a novel 4524 nt circular single-stranded (ss)DNA bacteriophage, the first time a virus has been reported infecting C.pneumoniae. Although the chlamydial genomes were highly conserved, there were intriguing differences in key nucleotide salvage pathways: C.pneumoniae has a uridine kinase gene for dUTP production, MoPn has a uracil phosphororibosyl transferase, while C.trachomatis serovar D contains neither gene. Chromosomal comparison revealed that there had been multiple large inversion events since the species divergence of C.trachomatis and C.pneumoniae, apparently oriented around the axis of the origin of replication and the termination region. The striking synteny of the Chlamydia genomes and prevalence of tandemly duplicated genes are evidence of minimal chromosome rearrangement and foreign gene uptake, presumably owing to the ecological isolation of the obligate intracellular parasites. In the absence of genetic analysis, comparative genomics will continue to provide insight into the virulence mechanisms of these important human pathogens.     

UTERINE EFFECTS,EPIGENETICS, AND POSTNATAL SKELETAL DEVELOPMENT IN THE MOUSE

Reciprocal embryo transfer experiments show that skeletal dimensions in adult mice are significantly influenced by the genotype of the female providing the uterine environment in which they were raised. Embryo transfers among C3HeB/FeJ, SWR/J, and the C3SWF, hybrid strain (C3H females x SWR males) permit separation of uterine maternal genotype effects from effects arising from the progeny's own genotype. Many different aspects of adult skeletal form are significantly influenced by uterine genotype and, in some instances, the pattern of these effects correlates with events during skeletal embryology. Analyses involving the highly heterozygous C3SWF₁ strain demonstrate the existence of significant dominance in maternal genes affecting skeletal development in the progeny. Further, there is a large skeletal effect due to progeny heterosis. Uterine Utter size can be manipulated as a nonheritable component of variability in embryo transfer experiments, and it has a large and systemic effect on skeletal growth and morphogenesis that persists in adult mice. Heritable uterine maternal effects are epigenetic interactions during development that can be incorporated into models of evolutionary change to provide a more complete picture of the causal agents producing morphological change.