Population and temperature effects on Lucilia sericata (Diptera: Calliphoridae) body size and minimum development time.

Understanding how ecological conditions influence physiological responses is fundamental to forensic entomology. When determining the minimum postmortem interval with blow fly evidence in forensic investigations, using a reliable and accurate model of development is integral. Many published studies vary in results, source populations, and experimental designs. Accordingly, disentangling genetic causes of developmental variation from environmental causes is difficult. This study determined the minimum time of development and pupal sizes of three populations of Lucilia sericata Meigen (Diptera: Calliphoridae; from California, Michigan, and West Virginia) at two temperatures (20 degrees C and 33.5 degrees C). Development times differed significantly between strain and temperature. In addition, California pupae were the largest and fastest developing at 20 degrees C, but at 33.5 degrees C, though they still maintained their rank in size among the three populations, they were the slowest to develop. These results indicate a need to account for genetic differences in development, and genetic variation in environmental responses, when estimating a postmortem interval with entomological data.

A distal upstream enhancer from the myelin basic protein gene regulates expression in myelin-forming schwann cells.

In peripheral nerves, large caliber axons are ensheathed by myelin-elaborating Schwann cells. Multiple lines of evidence demonstrate that expression of the genes encoding myelin structural proteins occurs in Schwann cells in response to axonal instructions. To gain further insight into the mechanisms controlling myelin gene expression, we used reporter constructs in transgenic mice to search for the DNA elements that regulate the myelin basic protein (MBP) gene. Through this in vivo investigation, we provide evidence for the participation of multiple, widely distributed, positive and negative elements in the overall control of MBP expression. Notably, all constructs bearing a 0.6 kb far-upstream sequence, designated Schwann cell enhancer 1 (SCE1), expressed at high levels in myelin-forming Schwann cells. In addition, robust targeting activity conferred by SCE1 was shown to be independent of other MBP 5' flanking sequence. These observations suggest that SCE1 will make available a powerful tool to drive transgene expression in myelinating Schwann cells and that a focused analysis of the SCE1 sequence will lead to the identification of transcription factor binding sites that positively regulate MBP expression.

Myelin acquisition in the central nervous system of the mouse revealed by an MBP-Lac Z transgene.

Myelin has pronounced effects upon the morphology, function, and growth of axons in the mammalian CNS. Consequently, oligodendrocyte development and myelination have been investigated using a wide variety of histological, immunocytochemical, ultrastructural, and biochemical techniques. While many of the spatial and temporal features of myelin appearance have been characterized, for any one species only limited regions of the CNS have been investigated. To address this limitation, we have derived transgenic mice in which the bacterial Lac Z gene is regulated by promoter elements of the myelin basic protein gene. When differentiating oligodendrocytes begin to elaborate recognizable myelin, they initiate expression of the MBP-Lac Z transgene and accumulate readily detectable levels of beta-galactosidase. Here, we exploit the sensitivity, resolution, and ease of beta-galactosidase histochemical assays to characterize the temporal and spatial patterns of CNS myelination in the mouse. Many features of the myelination program revealed by this approach were predicted by the immunocytochemical and ultrastructural data derived from other species. Nonetheless, previously undocumented patterns were also encountered. beta-Galactosidase was expressed first by oligodendrocytes in the ventral spinal cord, 1 d prior to birth. There, myelination proceeded in a strictly rostral-caudal direction, whereas in the dorsal cord, myelination initiated in the cervical enlargement and proceeded in both rostral and caudal directions. In the cerebellum, deep regions myelinated first, and in the optic nerve, myelination initiated at the retinal end. In contrast, the lateral olfactory tracts, pons, and optic chiasm initiated myelination along their entire course.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparisons of ape and human sequences that regulate mitochondrial DNA transcription and D-loop DNA synthesis.

The mitochondrial DNA (mtDNA) control regions for common chimpanzee, pygmy chimpanzee and gorilla were sequenced and the lengths and termini of their D-loop DNA's characterized. In these and all other species for which there are data, 5' termini map to sequences that contain the trinucleotide YAY. 3' termini are 25-51 nucleotides downstream from a sequence that is moderately conserved among vertebrates. Substitutions were greater than 1.5 times more frequent in the control region than in regions encoding structural genes. Additions and deletions were also frequent, especially in gorilla. Sequences of promoters and of two of four transcription factor binding sites were highly conserved. Comparisons of sequence similarity and transition/transversion ratios suggest that human and chimpanzees may be more closely related to each other than either is to gorilla, if substitution rates are approximately equal among these species.

Evolution of two actin genes in the sea urchin Strongylocentrotus franciscanus.

The complete nucleotide sequences of two chromosomally linked actin genes from the sea urchin Strongylocentrotus franciscanus are presented. The genes are separated by 5.7 kilobases, occur in the same transcriptional orientation, and contain introns in identical positions. The structures and nucleotide sequences of the two genes are extremely similar, suggesting that they arose through a recent duplication. Comparison of the nucleotide sequences of the genes allows inferences to be made about mutational mechanisms active since the duplication event. Whereas point mutations predominate in the coding regions, the introns and flanking DNA are more heavily influenced by a variety of events that cause simultaneous changes in short regions of DNA.

Organization and evolution of the actin gene family in sea urchins.

Genomic libraries of the sea urchins Strongylocentrotus franciscanus and Lytechinus pictus were screened with an actin cDNA clone from Strongylocentrotus purpuratus. Four nonoverlapping clones were isolated and characterized from the S. franciscanus library; three were isolated and characterized from the L. pictus library. Linked genes having the same transcriptional orientation were found on all S. franciscanus clones. Three clones contained two actin genes each; the other clone contained three. In contrast, the L. pictus clones contained only one actin gene. Comparison of actin genomic clones from these three species indicated a difference in the genomic organization of sea urchin actin genes in that the genes appear to be more highly clustered in S. franciscanus than in S. purpuratus and L. pictus. Genomic dot blots and reassociation kinetics demonstrated that the copy number of actin genes in all three species is 15 to 20. Nucleotide sequence homology of actin genes within and among the species was measured by thermal elution. These experiments indicated that there is a high degree of interspecies actin gene sequence homology but that, within each species, actin gene sequences may differ by as much as 30%. Sequencing of two S. franciscanus actin genes revealed introns at the same amino acid positions, 121 and 204, reported for S. purpuratus actin genes. These data demonstrated that the genomic copy number, the transcriptional orientation of linked genes, and, to the extent studied, the intron position of actin genes have evolved similarly in these three species. In contrast, significant change has occurred in the chromosomal arrangement of sea urchin actin genes.