Nonrandom Selection and Multiple Blood Feeding of Human Hosts by Anopheles Vectors: Implications for Malaria Transmission in Papua New Guinea

Nonrandom selection and multiple blood feeding of human hosts by Anopheles mosquitoes may exacerbate malaria transmission. Both patterns of blood feeding and their relationship to malaria epidemiology were investigated in Anopheles vectors in Papua New Guinea (PNG). Blood samples from humans and mosquito blood meals were collected in villages and human genetic profiles ("fingerprints") were analyzed by genotyping 23 microsatellites and a sex-specific marker. Frequency of blood meals acquired from different humans, identified by unique genetic profiles, was fitted to Poisson and negative binomial distributions to test for nonrandom patterns of host selection. Blood meals with more than one genetic profiles were classified as mosquitoes that fed on multiple humans. The age of a person bitten by a mosquito was determined by matching the blood-meal genetic profile to the villagers' genetic profiles. Malaria infection in humans was determined by PCR test of blood samples. The results show nonrandom distribution of blood feeding among humans, with biased selection toward males and individuals aged 15-30 years. Prevalence of Plasmodium falciparum infection was higher in this age group, suggesting males in this age range could be super-spreaders of malaria parasites. The proportion of mosquitoes that fed on multiple humans ranged from 6% to 13% among villages. The patterns of host utilization observed here can amplify transmission and contribute to the persistence of malaria in PNG despite efforts to suppress it with insecticidal bed nets. Excessive feeding on males aged 15-30 years underscores the importance of targeted interventions focusing on this demographic group.

Bacterial Profiling of Soil For Forensic Investigations: Consideration of Ex Situ Changes in Questioned and Known Soil Samples

Soil, being diverse and ubiquitous, can potentially link a suspect or victim to a crime scene. Recently scientists have examined the microbial makeup of soil for determining its origin, and differentiating soil samples is well-established. However, when soil is transferred to evidence its microbial makeup may change over time, leading to false exclusions. In this research, "known" soils from diverse habitats were stored under controlled conditions, while evidence soils were aged on mock evidence. Limited quantities of soil were also assayed. Bacterial profiles were produced using next-generation sequencing of the 16S rRNA gene. Overall, known soils stored open at room temperature were more similar to evidence soils over time than were known soils stored bagged and/or frozen. Evidence soils, even as little as 1 mg, associated with the correct habitat 99% of the time, accentuating the importance of considering ex situ microbial changes in soil for its successful use as forensic evidence.

Intra- and Inter-Element Variability in Mitochondrial and Nuclear DNA from Fresh and Environmentally Exposed Skeletal Remains

Successful identification of skeletonized remains often relies upon DNA analyses, frequently focusing on the mid-diaphysis of weight-bearing long bones. This study explored intra-bone DNA variability using bovine and porcine femora, along with calcanei and tali. DNA from fresh and short-term environmentally exposed bone was extracted utilizing demineralization and standard lysis buffer protocols, and DNA quantity and quality were measured. Overall, femoral epiphyses, metaphyses, and the tarsals had more nuclear and mitochondrial DNA than did the femoral diaphyses. DNA loss was much more rapid in buried bones than in surface exposed bones, while DNA quality differed based on environment, but not bone region/element. The demineralization protocol generated more DNA in some bone regions, while the standard lysis was more effective in others, and neither significantly affected DNA quality. Taken together, these findings reinforce the importance of considering inter- and intra-bone heterogeneity when sampling skeletal material for forensic DNA-based identifications.

Time Radically Alters Ex Situ Evidentiary Soil 16S Bacterial Profiles Produced Via Next-Generation Sequencing,

Previous research has revealed the potential of soil bacterial profiling for forensic purposes; however, investigators have not thoroughly examined fluctuations in microbial profiles from soil aged on evidence. In this research, soils collected from multiple habitats were placed on evidence items and sampled over time, and then bacterial profiles were generated via next-generation sequencing of the 16S rRNA locus. Bacterial abundance charts and nonmetric multidimensional scaling plots provided visual representation of bacterial profiles temporally, while supervised classification was used to statistically associate evidence to a source. The ex situ evidence soils displayed specific, consistent taxonomic changes as they aged, resulting in their drift in multidimensional space, but never toward a different habitat. Ninety-five percent of the 364 evidentiary profiles statistically classified to the correct habitat, with misclassification generally stemming from evidence type and increased age. Ultimately, understanding bacterial changes that occur temporally in ex situ soils should enhance their use in forensic investigations.

Plasticity of host selection by malaria vectors of Papua New Guinea

Background

Host selection is an important determinant of vectorial capacity because malaria transmission increases when mosquitoes feed more on humans than non-humans. Host selection also affects the outcome of long-lasting insecticidal nets (LLIN). Despite the recent nationwide implementation of LLIN-based malaria control program in Papua New Guinea (PNG), little is known about the host selection of the local Anopheles vectors. This study investigated the host selection of Anopheles vectors in PNG.

Methods

Blood-engorged mosquitoes were sampled using the barrier screen method and blood meals analyzed for vertebrate host source with PCR-amplification of the mitochondrial cytochrome b gene. Abundance of common hosts was estimated in surveys. The test of homogeneity of proportions and the Manly resource selection ratio were used to determine if hosts were selected in proportion to their abundance.

Results

Two thousand four hundred and forty blood fed Anopheles females of seven species were sampled from five villages in Madang, PNG. Of 2,142 samples tested, 2,061 (96.2%) yielded a definitive host source; all were human, pig, or dog. Hosts were not selected in proportion to their abundance, but rather were under-selected or over-selected by the mosquitoes. Four species, Anopheles farauti (sensu stricto) (s.s.), Anopheles punctulatus (s.s.), Anopheles farauti no. 4 and Anopheles longirostris, over-selected humans in villages with low LLIN usage, but over-selected pigs in villages with high LLIN usage. Anopheles koliensis consistently over-selected humans despite high LLIN usage, and Anopheles bancroftii over-selected pigs.

Conclusions

The plasticity of host selection of an Anopheles species depends on its opportunistic, anthropophilic or zoophilic behavior, and on the extent of host availability and LLIN usage where the mosquitoes forage for hosts. The high anthropophily of An. koliensis increases the likelihood of contacting the LLIN inside houses. This allows its population size to be reduced to levels insufficient to support transmission. In contrast, by feeding on alternative hosts the likelihood of the opportunistic species to contact LLIN is lower, making them difficult to control. By maintaining high population size, the proportion that feed on humans outdoors can sustain residual transmission despite high LLIN usage in the village.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-017-2038-3) contains supplementary material, which is available to authorized users.

Mitochondrial DNA Profiling of Illegal Tortoiseshell Products Derived from Hawksbill Sea Turtles

The hawksbill sea turtle (Eretmochelys imbricata) is a highly endangered species, commonly poached for its ornate shell. "Tortoiseshell" products made from the shell are widely, although illegally, available in many countries. Hawksbills have a circumglobal distribution; thus, determining their origin is difficult, although genetic differences exist geographically. In the research presented, a procedure was developed to extract and amplify mitochondrial DNA from tortoiseshell items, in an effort to better understand where the species is being poached. Confiscated tortoiseshell items were obtained from the U.S. Fish and Wildlife Service, and DNA from 56 of them was analyzed. Multiple mitochondrial haplotypes were identified, including five not previously reported. Only one tortoiseshell item proved to be of Atlantic origin, while all others corresponded to genetic stocks in the Indo-Pacific region. The developed methodology allows for unique, and previously unattainable, genetic information on the illegal poaching of sea turtles for the decorative tortoiseshell trade.

Assessing the Utility of Soil DNA Extraction Kits for Increasing DNA Yields and Eliminating PCR Inhibitors from Buried Skeletal Remains

DNA identification of human remains is often necessary when decedents are skeletonized; however, poor DNA recovery and polymerase chain reaction (PCR) inhibition are frequently encountered, a situation exacerbated by burial. In this research, the utility of integrating soil DNA isolation kits into buried skeletal DNA analysis was evaluated and compared to a standard human DNA extraction kit and organic extraction. The soil kits successfully extracted skeletal DNA at quantities similar to standard methods, although the two kits tested, which differ mechanistically, were not equivalent. Further, the PCR inhibitors calcium and humic acid were effectively removed using the soil kits, whereas collagen was less so. Finally, concordant control region sequences were obtained from human skeletal remains using all four methods. Based on these comparisons, soil DNA isolation kits, which quickened the extraction process, proved to be a viable extraction technique for skeletal remains that resulted in positive identification of a decedent.

Osteological and molecular identification of Brucellosis in ancient Butrint, Albania

Ancient skeletal remains can harbor unique information about past civilizations at both the morphological and molecular levels. For instance, a number of diseases manifest in bone, some of which have been confirmed through DNA analysis, verifying their presence in ancient populations. In this study, anthropological analysis of skeletal remains from the ancient Albanian city of Butrint identified individuals with severe circular lytic lesions on their thoracic and lumbar vertebrae. Differential diagnosis suggested that the lesions resulted from pathologies known to affect these skeletal regions, such as tuberculosis (TB) or brucellosis. Relevant bones of two adolescent males from the 10th to 13th century AD that displayed the lesions, along with unaffected individuals, were collected in the field. Genetic screening of the skeletal samples for TB was repeatedly negative, thus additional testing for Brucella spp.-bacteria of livestock and the causative agent of brucellosis in humans-was conducted. Two Brucella DNA markers, the IS6501 insertion element and Bcsp31 gene, amplified from the affected vertebrae and/or ribs, whereas all unaffected individuals and control samples were negative. Subsequent DNA sequencing confirmed the presence of the brucellar IS6501 insertion element. On the basis of the skeletal lesions, negative tests for TB, and positive Brucella findings, we report a confirmed occurrence of brucellosis in archaeologically recovered human bone. These findings suggest that brucellosis has been endemic to the area since at least the Middle Ages.

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.

Simplified field preservation of tissues for subsequent DNA analyses

Successful DNA-based identification of mass disaster victims depends on acquiring tissues that are not highly degraded. In this study, multiple protocols for field preservation of tissues for later DNA analysis were tested. Skin and muscle samples were collected from decaying pig carcasses. Tissues were preserved using cold storage, desiccation, or room temperature storage in preservative solutions for up to 6 months. DNA quality was assessed through amplification of successively larger segments of nuclear DNA. Solution-based storage, including a DMSO/NaCl/EDTA mixture, alcohols, and RNAlater preserved DNA of the highest quality, refrigeration was intermediate, and desiccation was least effective. Tissue type and extent of decomposition significantly affected stored DNA quality. Overall, the results indicate that any tissue preservation attempt is far superior to delaying or forgoing preservation efforts, and that simple, inexpensive methods can be highly effective in preserving DNA, thus should be initiated as quickly as possible.

Gene expression during blow fly development: improving the precision of age estimates in forensic entomology

Forensic entomologists use size and developmental stage to estimate blow fly age, and from those, a postmortem interval. Since such estimates are generally accurate but often lack precision, particularly in the older developmental stages, alternative aging methods would be advantageous. Presented here is a means of incorporating developmentally regulated gene expression levels into traditional stage and size data, with a goal of more precisely estimating developmental age of immature Lucilia sericata. Generalized additive models of development showed improved statistical support compared to models that did not include gene expression data, resulting in an increase in estimate precision, especially for postfeeding third instars and pupae. The models were then used to make blind estimates of development for 86 immature L. sericata raised on rat carcasses. Overall, inclusion of gene expression data resulted in increased precision in aging blow flies.

The conviction of Dr. Crippen: new forensic findings in a century-old murder

Dr. Hawley Crippen was accused and convicted of murdering his wife in London in 1910. Key to the conviction was microscopic analysis of remains found in the Crippen's coal cellar, which were identified as Cora Crippen based on a scar she was said to have. Dr. Crippen was hanged, always proclaiming his innocence. In this study, genealogical research was used to locate maternal relatives of Cora Crippen, and their mitochondrial haplotypes were determined. Next, one of the pathology slides of the scar was obtained, DNA was isolated, and the haplotype was determined. That process was then repeated. Finally, both DNA isolates were assayed for repetitive elements on autosomes and repetitive elements specific to the Y chromosome. Based on the genealogical and mitochondrial DNA research, the tissue on the pathology slide used to convict Dr. Crippen was not that of Cora Crippen. Moreover, that tissue was male in origin.

The correlation between skeletal weathering and DNA quality and quantity

Mitochondrial DNA analysis of skeletal material is invaluable in forensic identification, although results can vary widely among remains. Previous studies have included bones of different ages, burial conditions, and even species. In the research presented, a collection of human remains that lacked major confounders such as burial age, interment style, and gross environmental conditions, while displaying a very broad range of skeletal degradation, were examined for both mitochondrial DNA (mtDNA) quality and quantity. Overall skeletal weathering, individual bone weathering, and bone variety were considered. Neither skeletal nor bone weathering influenced DNA quality or quantity, indicating that factors that degrade bone do not have the same effect on DNA. In contrast, bone variety, regardless of weathering level, was a significant element in DNA amplification success. Taken together, the results indicate that neither skeletal nor individual bone appearance are reliable indicators of subsequent mtDNA typing outcomes, while the type of bone assayed is.

Generalized additive models and Lucilia sericata growth: assessing confidence intervals and error rates in forensic entomology

Forensic entomologists use blow fly development to estimate a postmortem interval. Although accurate, fly age estimates can be imprecise for older developmental stages and no standard means of assigning confidence intervals exists. Presented here is a method for modeling growth of the forensically important blow fly Lucilia sericata, using generalized additive models (GAMs). Eighteen GAMs were created to predict the extent of juvenile fly development, encompassing developmental stage, length, weight, strain, and temperature data, collected from 2559 individuals. All measures were informative, explaining up to 92.6% of the deviance in the data, though strain and temperature exerted negligible influences. Predictions made with an independent data set allowed for a subsequent examination of error. Estimates using length and developmental stage were within 5% of true development percent during the feeding portion of the larval life cycle, while predictions for postfeeding third instars were less precise, but within expected error.

Aging blow fly eggs using gene expression: a feasibility study

Forensic entomology can aid death investigations by using predictable developmental changes to estimate the ages of flies associated with a body. In developmental stages that do not increase in size however, including the egg and pupa, it can be difficult to objectively refine an age estimate beyond the limits of the stage duration. Gene transcript levels, changing throughout development, represent a potential data source useful for objectively identify smaller units of developmental time. The expression of three genes (bcd, sll, cs) was profiled throughout the maturation of blow fly eggs to determine the feasibility of predicting age, identifying significant linear trends in expression during their development. Models estimating egg age made predictions within 2 h of true age when all expression data were available, while the presence/absence of cs transcripts identified two age classes, together indicating that gene expression can be used to more precisely predict blow fly age.

Mitochondrial DNA analysis of the domestic dog: control region variation within and among breeds

The mitochondrial DNA (mtDNA) control regions of 125 domestic dogs (Canis familiaris) encompassing 43 breeds, as well as one coyote and two wolves were sequenced and subsequently examined for sequence variation in an effort to construct a reference dog mtDNA data set for forensic analysis. Forty informative variable sites were identified that described 45 haplotypes, 29 of which were observed only once. Substantial variation was found both within and among breeds in the mtDNA derived from tissue, indicating that analysis of the mtDNA derived from dog hairs could be a valuable, discriminating piece of evidence in forensic investigations. The dog data set single nucleotide polymorphisms (SNPs) ranged from having one to six changes on a phylogenetic tree. On average, there were 1.9 character changes for each variable position on the tree. The most variable sites (with four or more changes each, listed from the most changes to the fewest) observed were 15,639 (L=6), 16,672 (L=5), 15,955 (L=4), 15,627 (L=3), 16,431 (L=3), and 16,439 (L=3). These sites were consistent with other reports on variable positions in the dog mtDNA genome. A total of 26 SNPs were chosen to best identify all major clusters in the domestic dog data set. The descriptive analyses revealed that this data set is similar to other published canine data sets and further demonstrates that this domestic dog data set is a useful resource for forensic applications. This reference data set has been compiled and validated against the published dog genetic literature with an aim to aid forensic investigations that seek to incorporate mtDNA sequences and SNPs from trace evidence such as dog hair.

The utility of whole genome amplification for typing compromised forensic samples

Biological evidence has become invaluable in the crime laboratory; however, it may exist in limited quantity and/or quality. Given this, the ability to amplify total DNA obtained from evidence, in an unbiased manner, would be highly advantageous. Methods for whole genome amplification (WGA) have the potential to fulfill this role, resulting in a virtually unlimited supply of DNA. In the research presented, two WGA methods, improved primer extension preamplification and multiple displacement amplification (MDA), were tested using commercial kits. Control DNA, artificially degraded DNA, and DNA from fresh blood, aged blood, hair shafts, and aged bones underwent WGA, followed by short tandem repeat and mitochondrial DNA analysis. The methods did amplify DNA, but performed poorly on forensically relevant samples; the maximum amplicon size was reduced, and MDA often resulted in extraneous bands following polymerase chain reaction. Taken together, WGA appears to be of limited forensic utility unless the samples are of a very high quality.

Components of developmental plasticity in a Michigan population of Lucilia sericata (Diptera: Calliphoridae)

Forensic entomologists rely on laboratory growth data to estimate the time of blow fly colonization on human remains. Several data sets exist for the development of the common blow fly Lucilia sericata (Meigen) (Diptera: Calliphoridae), and although they generally describe similar rates of preadult development, all vary. Such differences could be explained by genetic variation, environmental (rearing) variation, or both. In the study presented here, flies from a single population were reared under variable conditions of food moisture, substrate type, substrate freshness, and sampling, to determine the effect each had on developmental time. Cohorts were tested in a single incubator at a single temperature and humidity, to eliminate effects of undesired environmental variation. Fly developmental times were significantly influenced by multiple laboratory rearing treatments; food moisture, transferring postfeeding larvae to fresh substrate, and destructive sampling affected different stages of development. Developmental times ranged from 329 to 505.5 h, covering the spectrum of variation observed in published data sets. Growth was then compared with larval development on rat carcasses under the same environmental conditions, establishing a link between laboratory-controlled growth and development on carrion. Cohorts raised on rats matured to adulthood between 333 and 337 h, which was best mimicked by the fastest growth treatment observed under laboratory conditions. The large environmental influence on development observed in this study could affect forensic entomology casework and accentuates the need for a standardized means of rearing flies in a laboratory setting that is relevant to decomposition on a corpse.

Relative Degradation of Nuclear and Mitochondrial DNA: An Experimental Approach*

Single copy nuclear loci often cannot be amplified from degraded remains, necessitating the analysis of mitochondrial DNA (mtDNA). The success in analyzing mtDNA is generally thought to result from its higher copy number in the cell; however, other factors, such as cellular location or molecular features, may be equally or more important in the superior preservation of mtDNA. To explore and compare mtDNA and nuclear DNA degradation, mouse tissues (muscle, liver, and brain) were allowed to degrade at different temperatures, and the relative degradation of a mitochondrial gene, a single copy nuclear gene, and a multi-copy nuclear gene was assayed using real-time polymerase chain reaction. The tissues were also homogenized, allowing the three loci to degrade in the same cellular environment. Gene copy number and cellular location both influence DNA recovery. In some instances, multi-copy loci could be recovered when the single copy locus could not; however, the pattern of relative DNA degradation changed between whole and homogenized tissues. The overall results indicate that DNA degradation is influenced by multiple factors-including cellular location, chromatin structure, and transcriptional activity-factors that could be used to exploit loci for more robust forensic analysis from degraded biological material.

A simplified method for mitochondrial DNA extraction from head hair shafts

DNA isolation from hair shafts can involve a number of steps, each of which adds time to the procedure and increases the risk of contamination. A simple alkaline digestion procedure that directly dissolves hairs was developed and compared with a widely used glass grinding/organic extraction method, using samples collected from 30 volunteers with varying population ancestries, hair colors, and hair treatments. A 203 bp mtDNA product could be amplified from 90% of samples extracted by alkaline digestion and 73% of hairs extracted by glass grinding. DNA obtained from alkaline digested hair generated equal or greater amplification success for virtually all criteria examined, and mtDNA sequences matched buccal control sequences in all cases. The two methods were similar in DNA yield (amplification success at template dilution) and quality of DNA obtained (amplicon length). Alkaline digestion of hair shafts required 6-7 h to complete, compared to 22-24 h for glass grinding, and proved a less laborious yet equally robust method for mtDNA extraction.

The effects of skeletal preparation techniques on DNA from human and non-human bone

The forensic pathologist increasingly relies on the forensic anthropologist to be the consulting expert in human identification. Likewise, if identification is not possible from visual inspection of skeletal remains, the forensic biologist may be called upon to conduct DNA analysis. The possibility of downstream DNA testing needs to be considered when skeletal preparation techniques are employed to deflesh human remains, as they have the potential to strongly impact genetic analyses and subsequent identification. In this study, three cleaning techniques, boiling bone in water, in bleach, and in powdered detergent/sodium carbonate, were tested for their effect on nuclear and mtDNA recovery from a variety of human and non-human bones. A statistically significant reduction in DNA yields occurred in non-human bones cleaned with bleach, and DNA degradation was apparent electrophoretically. The human bones also showed much lower yields from bleach cleaning, while the detergent/carbonate method allowed the largest segments of DNA to be amplified, indicating it may have a less degradative effect on bone DNA than either of the other cleaning processes.

In search of the Boston Strangler: genetic evidence from the exhumation of Mary Sullivan

The Boston Strangler was one of the United States' most notorious serial killers, raping and strangling with decorative ligatures thirteen woman in Boston during the early 1960s. Albert DeSalvo, never a suspect in the slayings, confessed in prison (where he was later murdered) to being the Boston Strangler, and the investigation largely ended. Mary Sullivan was the last victim of the Boston Strangler, found sexually assaulted and strangled in her Boston apartment in 1964. Recently, a team of forensic scientists undertook the exhumation and subsequent scientific analysis of Mary Sullivan's remains, in hope of finding consistencies or inconsistencies between DeSalvo's confessed description of the murder and any evidence left behind. Included in these analyses was extensive DNA testing of all UV fluorescent material associated with the body. The large majority of results were negative, however, fluorescent material located on the underwear and entwined in her pubic hair generated two human mitochondrial DNA sequences. Neither of these matched the victim nor members of the forensic team who worked on the evidence. Most importantly, neither DNA sequence could have originated from Albert DeSalvo.

The fingernails of Mary Sullivan: developing reliable methods for selectively isolating endogenous and exogenous DNA from evidence

The fingernails of Mary Sullivan, the last victim of the Boston Strangler, were examined to determine if any genetic information about the murderer could be obtained. The nails were extremely friable necessitating the development of new techniques for isolating and purifying DNA. DNA yields from nails were optimized by using a NaOH-based preparation technique, which was simple, efficient, and minimized handling. Methods for selectively and thoroughly removing exogenous material on nails were also developed through use of a species-specific PCR assay, wherein mitochondrial DNA from the nail could easily be differentiated from DNA of contaminating cells.

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.