The Muller F element (4.2 Mb, ~80 protein-coding genes) is an unusual autosome of Drosophila melanogaster; it is mostly heterochromatic with a low recombination rate. To investigate how these properties impact the evolution of repeats and genes, we manually improved the sequence and annotated the genes on the D. erecta, D. mojavensis, and D. grimshawi F elements and euchromatic domains from the Muller D element. We find that F elements have greater transposon density (25–50%) than euchromatic reference regions (3–11%). Among the F elements, D. grimshawi has the lowest transposon density (particularly DINE-1: 2% vs. 11–27%). F element genes have larger coding spans, more coding exons, larger introns, and lower codon bias. Comparison of the Effective Number of Codons with the Codon Adaptation Index shows that, in contrast to the other species, codon bias in D. grimshawi F element genes can be attributed primarily to selection instead of mutational biases, suggesting that density and types of transposons affect the degree of local heterochromatin formation. F element genes have lower estimated DNA melting temperatures than D element genes, potentially facilitating transcription through heterochromatin. Most F element genes (~90%) have remained on that element, but the F element has smaller syntenic blocks than genome averages (3.4–3.6 vs. 8.4–8.8 genes per block), indicating greater rates of inversion despite lower rates of recombination. Overall, the F element has maintained characteristics that are distinct from other autosomes in the Drosophila lineage, illuminating the constraints imposed by a heterochromatic milieu.
An age-related decrease in elasticity of arteries has been found in clinical and experimental studies done during the past two decades. We have investigated molecular and endocrine aspects of that decrease by examining the effects of age and insulin-like growth factor-I (IGF-I) on rat aorta elastogenesis. For comparison, pulmonary elastogenesis was examined in the same experimental animals. Different aged groups of male Fischer 344 rats (barrier protected) were implanted with minipumps for a two-week infusion of either 0.1 N acetic acid (vehicle solution) or IGF-I (1.2 mg/kg/day). The DNA content (micrograms DNA/g tissue) decreased with age in aorta but remained fairly constant in lung. Administration of IGF-I increased the aortic DNA content in all but the oldest rats. Conversely, the DNA content of pulmonary tissue was significantly increased in only the youngest animals. The steady-state levels of tropoelastin mRNA decreased dramatically in both aorta and lung with increased age. The decrease was greater in lung than aorta. Administration of IGF-I elevated aortic tropoelastin mRNA steady-state levels, whereas lung tropoelastin mRNA levels were unaffected by IGF-I administration. Aortic tissue synthesized decreased amounts of insoluble elastin with increased age. These results establish a direct relationship between aortic tropoelastin mRNA levels and the synthesis of insoluble elastin in aging. Administration of IGF-I increased aortic elastin synthesis throughout the life span of the rat, although the proportionate increase diminished with age.
Using the previously cloned proteasome α-type subunit gene Pros28.1, we screened a Drosophila melanogaster genomic library using reduced stringency conditions to identify closely related genes. Two new genes, Pros28.1A (map position 92F) and Pros28.IB (map position 60D7), showing high sequence similarity to Pros28.1, were identified and characterized. Pros28.1A encodes a protein with 74% amino acid identity to PROS28.1, while the Pros28.1B gene product is 58% identical. The Pros28.1B gene has two introns, located in exactly analogous positions as the two introns in Pros28.1, while the Pros28.IA gene lacks introns. Northern blot analysis reveals that the two new genes are expressed only in males, during the pupal and adult stages. Tissue-specific patterns of expression were examined using transgenic flies carrying Zacz-fusion reporter genes. This analysis revealed that both genes are expressed in germline cells during spermatogenesis, although their expression patterns differed. Pros28.1A expression is first detected at the primary spermatocyte stage and persists into the spermatid elongation phase of spermiogenesis, while Pros28. IB expression is prominent only during spermatid elongation. These genes represent the most striking example of cell-type-specific proteasome gene expression reported to date in any system and support the notion that there is structural and functional heterogeneity among proteasomes in metazoans.
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