Development and application of a PBPK modeling strategy to support antimalarial drug development

As part of a collaboration between Medicines for Malaria Venture (MMV), Certara UK and Monash University, physiologically-based pharmacokinetic (PBPK) models were developed for 20 antimalarials, using data obtained from standardized in vitro assays and clinical studies within the literature. The models have been applied within antimalarial drug development at MMV for more than 5 years. During this time, a strategy for their impactful use has evolved. All models are described in the supplementary material and are available to researchers. Case studies are also presented, demonstrating real-world development and clinical applications, including the assessment of the drug-drug interaction liability between combination partners or with co-administered drugs. This work emphasizes the benefit of PBPK modeling for antimalarial drug development and decision making, and presents a strategy to integrate it into the research and development process. It also provides a repository of shared information to benefit the global health research community.

Development of a physiologically based pharmacokinetic model of actinomycin D in children with cancer

Aims

Use of the anti‐tumour antibiotic actinomycin D is associated with development of hepatotoxicity, particularly in young children. A paucity of actinomycin D pharmacokinetic data make it challenging to develop a sound rationale for defining dosing regimens in younger patients. The study aim was to develop a physiologically based pharmacokinetic (PBPK) model using a combination of data from the literature and generated from experimental analyses.

Methods

Assays to determine actinomycin D Log P, blood:plasma partition ratio and ABCB1 kinetics were conducted. These data were combined with physiochemical properties sourced from the literature to generate a compound file for use within the modelling‐simulation software Simcyp (version 14 release 1). For simulation, information was taken from two datasets, one from 117 patients under the age of 21 and one from 20 patients aged 16–48.

Results

The final model incorporated clinical renal and biliary clearance data and an additional systemic clearance value. The mean AUC_0‐26h of simulated subjects was within 1.25‐fold of the observed AUC_0‐26h (84 ng h ml⁻¹ simulated vs. 93 ng h ml⁻¹ observed). For the younger age ranges, AUC predictions were within two‐fold of observed values, with simulated data from six of the eight age/dose ranges falling within 15% of observed data. Simulated values for actinomycin D AUC_0‐26h and clearance in infants aged 0–12 months ranged from 104 to 115 ng h ml⁻¹ and 3.5–3.8 l h⁻¹, respectively.

Conclusions

The model has potential utility for prediction of actinomycin D exposure in younger patients and may help guide future dosing. However, additional independent data from neonates and infants is needed for further validation. Physiological differences between paediatric cancer patients and healthy children also need to be further characterized and incorporated into PBPK models.

Does age affect gastric emptying time? A model-based meta-analysis of data from premature neonates through to adults

Purpose. Gastric emptying (GE) is often reported to be slower and more irregular in premature neonates than in older children and adults. The aim of this study was to investigate the impact of age and other covariates on the rate of GE. Methods. The effect of age on the mean gastric residence times (MGRT) of liquid and solid food was assessed by analysing 49 published studies of 1457 individuals, aged from 28 weeks gestation to adults. The data were modelled using the nonlinear mixed‐effects approach within NONMEM version 7.2 (ICON, Dublin, Ireland), with evaluation of postnatal age, gestational age and meal type as covariates. A double Weibull function was selected as a suitable model since it could account for the typical biphasic nature of GE. Results. Age was not a significant covariate for GE but meal type was. Aqueous solutions were associated with the fastest emptying time (mean simulated gastric residence time of 45 min) and solid food was associated with the slowest (98 min). Conclusions. These findings challenge the assertion that GE is different in neonates, as compared with older children and adults due to age, and they reinforce the significance of food type in modulating GE. © 2015 The Authors. Biopharmaceutics & Drug Disposition Published by John Wiley & Sons Ltd.

Structural analysis of yeast HSF by site-specific crosslinking

We have introduced cysteine substitutions into the yeast HSF1 gene at a variety of locations. Most have no phenotypic effect, and therefore provide site-specific probes for thiol-specific reagents. Crosslinking of single mutants identifies locations where equivalent regions of individual monomers can approach each other in the HSF trimer. Crosslinking of double mutants indicates regions that can approach closely within a single subunit. Results for the DNA binding domain and trimerization domain are consistent with known structural information, and provide essential controls on the validity of the technique. In contrast to these two domains, the N-terminal and C-terminal domains, wherein lie the transcriptional activators, are highly flexible, and do not appear to be in stable contact with any other portions of the protein. None of these patterns are affected by the conformational change that is induced by superoxide or heat shock. We suggest a new model for the mechanism of HSF regulation that accomodates the structural information provided by these studies.

Complex regulation of the yeast heat shock transcription factor

The yeast heat shock transcription factor (HSF) is regulated by posttranslational modification. Heat and superoxide can induce the conformational change associated with the heat shock response. Interaction between HSF and the chaperone hsp70 is also thought to play a role in HSF regulation. Here, we show that the Ssb1/2p member of the hsp70 family can form a stable, ATP-sensitive complex with HSF-a surprising finding because Ssb1/2p is not induced by heat shock. Phosphorylation and the assembly of HSF into larger, ATP-sensitive complexes both occur when HSF activity decreases, whether during adaptation to a raised temperature or during growth at low glucose concentrations. These larger HSF complexes also form during recovery from heat shock. However, if HSF is assembled into ATP-sensitive complexes (during growth at a low glucose concentration), heat shock does not stimulate the dissociation of the complexes. Nor does induction of the conformational change induce their dissociation. Modulation of the in vivo concentrations of the SSA and SSB proteins by deletion or overexpression affects HSF activity in a manner that is consistent with these findings and suggests the model that the SSA and SSB proteins perform distinct roles in the regulation of HSF activity.

The yeast heat shock transcription factor changes conformation in response to superoxide and temperature

In vitro DNA-binding assays demonstrate that the heat shock transcription factor (HSF) from the yeast Saccharomyces cerevisiae can adopt an altered conformation when stressed. This conformation, reflected in a change in electrophoretic mobility, requires that two HSF trimers be bound to DNA. Single trimers do not show this change, which appears to represent an alteration in the cooperative interactions between trimers. HSF isolated from stressed cells displays a higher propensity to adopt this altered conformation. Purified HSF can be stimulated in vitro to undergo the conformational change by elevating the temperature or by exposing HSF to superoxide anion. Mutational analysis maps a region critical for this conformational change to the flexible loop between the minimal DNA-binding domain and the flexible linker that joins the DNA-binding domain to the trimerization domain. The significance of these findings is discussed in the context of the induction of the heat shock response by ischemic stroke, hypoxia, and recovery from anoxia, all known to stimulate the production of superoxide.

Activity of a C. elegans GATA transcription factor, ELT-1, expressed in yeast

The GATA motif (WGATAR) is found in the promoter regions of numerous Caenorhabditis elegans genes, including two intestine-specific genes, vit-2 and ges-1, in which it has been shown to be required for promoter function. The protein ELT-1, encoded by a single-copy gene homologous to the GATA family of vertebrate transcription factors, is potentially capable of interacting with this element. In order to determine whether ELT-1 is a transcriptional activator that recognizes this sequence, we have expressed it under the control of the GAL1 promoter in yeast. lacZ driven by the CYC1 promoter lacking an upstream activation sequence (UAS) but containing GATA sequences was used as a reporter. beta-Galactosidase was expressed upon induction only when GATA sequences were present, and expression was increased dramatically by additional binding sites. Deletion analysis demonstrated that the C terminus, containing only one of the two zinc fingers, is sufficient for activation. In addition, the DNA-binding domain and two transactivation regions were identified by fusing these isolated domains to previously defined domains of heterologous transcription factors. While most single base alterations in the GATA core sequence eliminated activity, an A to C change in position four, creating a GATC core, was found to increase activity significantly. The deleted ELT-1 protein containing only the C-terminal Zn finger was sufficient for activation in response to GATA, but both fingers were required for activation at GATC. A variety of sites with non-optimal sequences surrounding the GATA core also were found to be excluded better by the protein containing both Zn fingers. Furthermore, a fusion protein containing the entire ELT-1 DNA binding domain fused to the VP16 activation domain was found to have an even greater preference for the GATC core, as well as the optimal flanking bases. We conclude that, although ELT-1 having only its C-terminal finger is capable of activation in response to the WGATAR site, the presence of the upstream finger supplies additional base specificity.

Genetic identification of the site of DNA contact in the yeast heat shock transcription factor

The heat shock transcription factor (HSF), a trimeric transcription factor, activates the expression of heat shock genes in eukaryotes. We have isolated mutations in the HSF1 gene from Saccharomyces cerevisiae that severely compromise the ability of HSF to bind to its normal binding site, repeats of the module nGAAn. One of these mutations, Q229R, shows a "new specificity" phenotype, in which the protein prefers the mutant sequence nGACn. These results identify the region of HSF that contacts DNA, in complete agreement with the crystal structure of HSF of Kluyveromyces lactis and the nuclear magnetic resonance data from HSF of Drosophila melanogaster. To determine the orientation of the DNA-binding domain on the nGAAn motif, we performed site-specific cross-linking between cysteine residues of single-cysteine substitutions. Cysteines placed at the N terminus of the DNA contact helix formed cross-links readily, while cysteines placed at the C terminus of the helix did not.

Interactions between DNA-bound trimers of the yeast heat shock factor

The heat shock transcription factor (HSF) is a trimer that binds to DNA containing inverted repeats of the sequence nGAAn. HSF can bind DNA with the sequence nGAAnnTTCn or with the sequence nTTCnnGAAn, with little preference for either sequence over the other. However, (nGAAnnTTCn)2 is considerably less active as a heat shock response element (HSE) than is (nTTCnnGAAn)2. The electrophoretic mobilities of DNA-protein complexes and chemical cross-linking between protein monomers indicate that the sequence (nGAAnnTTCn)2 is capable of binding a single HSF trimer. In contrast, the sequence with higher biological activity, (nTTCnnGAAn)2, is capable of binding two trimers. Thus, the ability of four-nGAAn-element HSEs to bind one or two trimers depends on the permutation with which the elements are presented. A survey of naturally occurring HSEs shows the sequence (nTTCnnGAAn)2 to be the more prevalent. We suggest that the greater ability of one permutation over the other to bind two HSF trimers accounts for the initial identification of the naturally occurring heat shock consensus sequence as a region of dyad symmetry.

Translational readthrough at nonsense mutations in the HSF1 gene of Saccharomyces cerevisiae

The HSF1 gene of Saccharomyces cerevisiae directs the synthesis of the heat shock transcription factor, HSF. The gene is essential; disruption mutations are lethal. Using a plasmid shuffle screen, we isolated mutations in the HSF1 gene after in vitro mutagenesis of plasmid DNA with hydroxylamine. From a collection of both conditional (temperature-sensitive) and unconditional lethal mutations, we recovered mutations that map exclusively to the 5' half of the gene. All are nonsense mutations, including conditional mutations that map 5' to the portion of the HSF1 gene that encodes the DNA-binding domain of the transcription factor. For one such mutation, we demonstrated that the nonsense mutation is subject to translational readthrough, even though there are no known nonsense suppressors in the genetic background of our strain. Our results suggest that the HSF protein is highly tolerant of amino acid changes, a conclusion that is consistent with the very low degree of evolutionary conservation among HSF proteins. Our results also suggest that translational readthrough occurs with moderate efficiency in yeast, particularly when the terminator codon is followed immediately by an A or C residue. This result illustrates that the inference of gene function from mutant phenotype depends critically upon the analysis of a true null allele, and not merely an amber or ochre allele.

Temperature-dependent regulation of a heterologous transcriptional activation domain fused to yeast heat shock transcription factor

The heat shock transcription factor (HSF) of the yeast Saccharomyces cerevisiae is posttranslationally modified. At low growth temperatures, it activates transcription of heat shock genes only poorly; after shift to high temperatures, it activates transcription readily. In an effort to elucidate the mechanism of this regulation, we constructed a series of HSF-VP16 fusions that join the HSF DNA-binding domain to the strong transcriptional activation domain from the VP16 gene of herpes simplex virus. Replacement of the endogenous C-terminal transcriptional activation domain with that of VP16 generates an HSF derivative that exhibits behavior reminiscent of HSF itself: low transcriptional activation activity at normal growth temperature and high activity after heat shock. HSF can thus restrain the activity of the heterologous VP16 transcriptional activation domain. To determine what is required for repression of activity at low temperature, we deleted portions of HSF from this HSF-VP16 fusion to map the regulatory domain. We also isolated point mutations that convert the HSF-VP16 fusion into a constitutive transcriptional activator. We conclude that the central, evolutionarily conserved domain of HSF, encompassing the DNA-binding and multimerization domains, contains a major determinant of temperature-dependent regulation.

Genetic analysis of chromosome region 63 of Drosophila melanogaster

The salivary chromosome region including cytological division 63 of Drosophila melanogaster was genetically analyzed in order to (1) characterize this previously unstudied region and (2) attempt to isolate mutations in the hsp82 gene. Seven deletions which span this region were isolated, including four which remove the hsp82 gene. A Minute mutation was mapped to this region and this Minute was used to isolate duplications in the 63 region. These duplications map the Minute to 63B8-C1. F2 screens were initiated using deletions which remove the hsp82 gene. Over 15,000 chromosomes were screened, yielding 40 lethal mutations which comprise 14 complementation groups. Several of these mutations map outside the 63 region and appear to give second site interaction with the Minute locus. Four loci, including the Minute gene, are candidates for hsp82 mutations by cytogenetic mapping. These loci were tested for complementation with a P element carrying the hsp82 gene. However, none of the mutations was rescued.

Vectors for the expression and analysis of DNA-binding proteins in yeast

A series of 13 vectors is described. All are yeast centromere plasmids with the LEU2 gene for selection in yeast, and pUC19 sequences for growth in Escherichia coli. All contain the GAL1 promoter directing transcription into a multiple cloning site (MCS). For twelve of the plasmids, synthetic oligodeoxyribonucleotides create an ATG start codon, in a productive context for yeast, prior to the MCS. Spacing between the ATG and the MCS is variable, to facilitate the cloning of gene fragments in the appropriate reading frame. Nine of the plasmids also contain the strong transcriptional activator from the herpes simplex virus VP16 gene, joined downstream from the MCS. In these nine vectors, all possible combinations of reading frames are available. The suitability of these plasmids for the expression and analysis of DNA-binding domains is tested by cloning into them fragments of the yeast HSF1 gene, encoding the heat shock transcription factor (HSF). The regulation of reporter gene expression by the chimeric HSF-VP16 fusions is described, as is the utility of these vectors for other applications.

Electron microscopical analysis of Drosophila polytene chromosomes. V. Characteristics of structures formed by transposed DNA segments of mobile elements

An electron microscopical (EM) analysis was performed on regions of polytene chromosomes which contained DNA segments of different genetic composition, inserted by P element-mediated transformation into the Drosophila melanogaster genome. In seven of ten regions examined, containing insertions of the hsp28-ry, hsp70-Adh, ryhsp 70-beta-gal genes and of the ry gene tetramer, new bands appeared. Lack of new bands in three other strains is apparently connected with the fusion of the inserted material to preexisting bands. The new bands do not differ morphologically from the usual bands of polytene chromosomes, and their formation is likely due to predominant insertion of DNA segments into interbands. Among the constructs examined, the minimal length of a DNA segment which appears as a new band is about 5 kb; the DNA packing ratio in the new bands varies from 30 to 50. Activation of the inserted genes by heat shock has enabled us to observe the puffing characteristics of new bands. A sequence of some one kb forms a large interband, or micropuff; the puff size is correlated with the length of the genes being activated. If a DNA segment contains a single gene, then its activation causes the decompaction of the whole band; however, when a DNA segment consists of two genes and the promoter element of the activated gene is positioned in the middle of the sequence, the band splits and only part is decompacted and puffed. The DNA packing ratio in the puffs is 1.4-3.5. The subsequent deletion of the hsp70 promoter but retention of 23, 59, and 73 by from the transcription start points leads to failure of puff formation. In all the transformed sites an increase in the total length of the interbands adjacent to the insert as compared with the initial interband was observed. This increase appears to be due to decompaction of the P element DAN flanking the inserted segments. It is shown that a DNA segment, consisting of four tandemly repeated ry gene copies and interspersed by material which includes P DNA, forms a complex of loose chromatin in which, however, four bands can be resolved. We also observed a lengthening of interband regions containing only the P element sequence itself. Insertion of the complete 2.9 kb P element into the large single 10A1-2 bound of the X chromosome (an insertion in the region approximately 10 kb to the right of the v gene) causes splitting of the band into two parts and formation of a new interband.(ABSTRACT TRUNCATED AT 400 WORDS)

Use of promoter fusions in Drosophila genetics: characterization of a YP1-ADH fusion gene

In Drosophila melanogaster the yolk protein (YP) genes are normally expressed only in the fat body and follicular epithelium of adult females--never in males or in larvae. We describe here a first step toward a genetic examination of the developmental controls that restrict the activity of the YP genes to adult female tissues. A YP1 promoter that contains the tissue-, temporal-, and sex-specific controlling elements for expression was fused to the reporter gene, alcohol dehydrogenase (Adh). The gene fusion was transformed into an Adh-deficient genotype. As assayed by a number of criteria, that the fusion gene is expressed in the same physiological manner as the endogenous yolk protein genes. The fusion gene's activity is modulated in trans by a temperature-sensitive allele of the sex determination gene, tra-2. The Adh enzyme serves as a selectable marker and therefore these flies are suitable for use in genetic screens for trans-acting mutations that affect the expression of the yolk protein genes.

Genetic analysis of chromosomal region 67A-D of Drosophila melanogaster

In an effort to (1) characterize the 67 interval of chromosome 3 of Drosophila melanogaster genetically and (2) isolate mutations of the 67B1 small heat shock protein (hsp) gene cluster specifically, we undertook a mutational analysis of the 67A-D subinterval. Using a deficiency of the 67A2 to 67D11-13 region, Df(3L)AC1, we screened 8700 diepoxybutane-treated chromosomes and 7800 ethyl methanesulfonate-treated chromosomes for visible and lethal mutations throughout this interval and recovered 74 independent recessive lethal mutations, but no visible mutations. One of the lethal mutations, d29A6, was identified as an overlapping deficiency extending from 66F3 to 67B1. An additional 6000 diepoxybutane-treated chromosomes were screened for lethality over d29A6, yielding another four lethal mutations within the 67A2-B1 subinterval. These 78 lethal mutations, along with two others isolated in other laboratories, define 23 essential loci--6 within the 67A2-B1 subinterval and 17 within the 67A2 to D11-13 subinterval. Many of these loci appear to be required for imaginal development only, exhibiting late larval to pharate adult lethal phases. Examination of the 67A2-B1 lethal complementation groups for (1) earlier onset of lethality following a heat shock, (2) missing or altered small hsps on two-dimensional protein gels, and (3) restoration of viability by transformed wild-type copies of the small hsp genes indicates that none of these mutations affect the small hsps. On the basis of this analysis and the known homology of the genes, we conclude that the small hsps are functionally equivalent.

Mutations that induce the heat shock response of Drosophila

We have isolated a number of mutations in D. melanogaster that result in the constitutive expression of the heat shock response in a tissue-specific manner. These mutations induce alcohol dehydrogenase (ADH) when the ADH structural gene is fused to the promoter for the 70 kd heat shock protein (hsp70) gene. Flies carrying these mutations, the hsp70-Adh fusion, and a deletion in their endogenous Adh genes are ethanol tolerant and exhibit elevated ADH levels. Several of the tissue-specific mutations have also been shown to induce an hsp26-Adh fusion gene in trans. The mutation Act88FKM75, a G----A transition in the indirect flight muscle-specific actin gene, also exhibits this phenotype. Comparisons with the Act88FKM75 mutation suggest that the tissue-specific mutations induce the heat shock response by disrupting the physiology of the cells in which the variant gene product is expressed.

Deletion polymorphism in a Drosophila melanogaster heat shock gene

We have continued the transcriptional analysis of the region of cytological locus 67B that contains the four small heat shock genes and other genes. Transcription from one of the heat shock genes in the region, hsp 26, takes place during high temperature treatment and at certain developmental stages, without heat shock, in several tissues, such as imaginal discs and adult ovaries. Observations of unexpected products after nuclease protection experiments provided the first indication of what genomic blot experiments showed to be small deletions. The alleles containing the deletion are expressed at the same level as the wild type allele. The deletion shortens the protein product, implying that it is in the coding region. Furthermore, flies homozygous for one of the deletion alleles are viable.

Small heat shock proteins of Drosophila associate with the cytoskeleton

Fractionation of heat-shocked Drosophila melanogaster Kc cells reveals that both the small heat shock proteins (hsp28, -26, -23, and -22) and vimentin-like intermediate filament proteins (IFPs) are abundantly represented in the nuclear fraction. Cofractionation of the IFPs with nuclei is due to the collapse of the IFP network against the nucleus upon heat shock, raising the possibility that cofractionation of the small hsps is by a similar mechanism. Indirect immunofluorescence supports this possibility. In salivary glands, both the hsps and the IFPs are cytoplasmic after mild-to-moderate heat shocks and only enter the nucleus upon severe--indeed, lethal--shocks. Double-label experiments with Schneider line 2 cells show that the IFPs and small hsps colocalize to the same perinuclear aggregates in 70% of the cells examined. Thus, the small hsps are associated with the cytoskeleton rather than with nuclear structures.

Clonal analysis of two mutations in the large subunit of RNA polymerase II of Drosophila

Two mutations in the gene, RpII215, were analyzed to determine their effects on cell differentiation and proliferation. The mutations differ in that one, RpII215ts (ts), only displays a conditional recessive lethality, while the other, RpII215Ubl (Ubl), is a recessive lethal mutation that also displays a dominant mutant phenotype similar to that caused by the mutation Ultrabithorax (Ubx). Ubl causes a partial transformation of the haltere into a wing; however, this transformation is more complete in flies carrying both Ubl and Ubx. The present study shows that patches of Ubl/-tissue in gynandromorphs are morphologically normal. cuticle that has lost the wild-type copy of the RpII215 locus fails to show a haltere to wing transformation, nor does it show the synergistic enhancement of Ubx by Ubl. We conclude that an interaction between the two RpII215 alleles, Ubl and RpII215+, is responsible for the mutant phenotype. Gynandromorphs carrying the ts allele, when raised at permissive temperature, display larger patches of ts/-cuticle than expected, possibly indicating that the proliferation of ts/+ cells is reduced. This might result from an antagonistic interaction between different RpII215 alleles. Classical negative complementation does not appear to be the cause of the antagonistic interactions described above, as only one RpII215 subunit is thought to be present in an active multimeric polymerase enzyme. We have therefore coined the term 'negative heterosis' to describe the aforementioned interactions. We also observed that the effects of mutationally altered RNA polymerase II on somatic cells are different from its effects on germ cells.(ABSTRACT TRUNCATED AT 250 WORDS)

The use of promoter fusions in Drosophila genetics: isolation of mutations affecting the heat shock response

We have constructed a gene fusion using the promoter of Drosophila hsp70 and the structural gene for Drosophila alcohol dehydrogenase (Adh) and used this construct to transform Adh-deficient flies. In these transformants, Adh is expressed only after heat shock. Like hsp70 itself, this heat-shock-inducible Adh (Adhhs) is induced in a wide variety of tissues. It fails to be induced in primary spermatocytes. Although the tissue distribution of Adh activity is very different from wild type, this does not appear to be deleterious. Indeed, the induction of Adhhs allows flies to survive exposure to ethanol. We have used this latter characteristic to select dominant, trans-acting mutations that alter the response of flies to heat shock.

Glucocorticoid-induced cleft palate genes in chromosome 17: genetic linkage and mapping analyses

Genes that influence susceptibility to dexamethasone-induced cleft palate and tentatively designated Dep are linked to the major histocompatibility complex H-2 in chromosome 17 of the mouse. Experiments presented refine the map of genes. The results show two or three Dep loci. The two-locus model maps Dep genes to the class II gene E beta and to the chromosomal region between the S and D genes. The three-locus model maps the Dep genes to the chromosomal regions from the centromere to E beta, from E beta to S, and from D to Pgk-2. Experiments were done by comparing the dexamethasone-induced cleft palate dose response of congenic strains with H-2 haplotypes that are recombinants of H-2a and H-2b. The analysis of genetic linkage between H-2 and Dep was expanded to include reciprocal backcrosses. A maternal factor was found to influence the frequency of dexamethasone-induced cleft palate in the backcross fetuses. The factor's origin is associated with the H-2 haplotype of the outcross mother, so the effect is actually a "grandmother effect" that probably is transmitted horizontally. Finally, the sexes were distributed unevenly between the fetuses with cleft palate in two of the congenic strains. This suggests interaction between the H-2-linked Dep genes and a Dep sex-associated gene that modulates susceptibility to dexamethasone-induced cleft palate.

Map of major histocompatibility complex subregions influencing vaginal septa frequency

The frequency of dorso-ventral vaginal septa (DVS) in mice in influenced by genes associated with the major histocompatibility complex, H-2. Data shows that two subregions within the H-2 complex, K-E beta and D, have a very strong influence on the frequency, while the E beta-S subregion appears to have a weak effect.

Glucocorticoid-induced cleft palate in the mouse: two major histocompatibility complex, H-2, loci with different mechanisms

Isolated cleft palate is induced in the progeny of pregnant mice that are given glucocorticoids. The incidence varies among inbred strains and with dose and stage of gestation when the drug is given. One chromosomal region responsible for strain-associated differences in sensitivity is the major histocompatibility complex, H-2. H-2a is associated with susceptibility, H-2b with resistance. There appear to be both maternal and embryonic genetic factors affecting the sensitivity to glucocorticoids. In experiments reported here congenic strains of mice with H-2a, H-2d and H-2k haplotypes on a C57BL/10 genomic background were used. This allowed the determination of the effect on sensitivity by two H-2 subregions; the subregions are H-2K to I-E and I-C to H-2D. Methods included dose-response analysis and reciprocal cross analysis using dexamethasone given on day 12 of pregnancy. Results show that each subregion affects the strain's sensitivity to dexamethasone-induced cleft palate. The regression coefficients for B10.A-H-2a (45.4 +/- 4.13) were different from those for B10.BR-H-2k (67.2 +/- 10.8) and B10.D2-H-2d (70.5 +/- 9.74). The estimated mean arcsine % cleft palate at 160 mg/kg was different for each strain: B10.A-H-2a, 53.1 +/- 2.19; B10.BR-H-2k, 33.1 +/- 2.27; B10.D2-H-2d, 25.0 +/- 2.75. Different patterns of change in sensitivity were observed among the reciprocal crosses. In summary, the H-2K to I-E subregion seemed to influence both maternal and embryonic factors, whereas only embryonic factors were influenced by the I-C to H-2D subregion. These data suggest that the mechanisms affecting glucocorticoid sensitivity which are genetically encoded within each H-2 subregion are different, and there is an interaction between the alleles. The mode of interaction can be either complementation or epistasis.

Backcross test demonstrates the linkage of glucocorticoid-induced cleft palate susceptibility to H-2

Data in this report demonstrate a linkage between glucocorticoid-induced cleft palate susceptibility and H-2. B10.A X C57BL/10F1 females were backcrossed to C57BL/10 males. Cleft palate was induced in the BC1 fetuses by giving pregnant females 80 mg/kg of dexamethasone intraperitoneally (IP) on day 12 of gestation. The H-2a/b haplotype was detected on day 18 BC1 fetal spleen cells with an indirect immunofluorescent labeling technique. Fetuses without antigen H-2Kk were H-2b/b . H-2a/b fetuses had a cleft palate frequency of 29%; 11% of the H-2b/b fetuses had cleft palate (P less than .01), demonstrating that the higher susceptibility to cleft palate segregates with the H-2a halotype.

Cleft palate susceptibility maps in two H-2 subregions, H-2K to I-B and G to H-2D

Data presented here defines the map of H-2 associated genes which affect the glucocorticoid-induced cleft palate frequency to the regions H-2K to I-B and G to H-2D. This was done by observing in four congenic strains the frequency of cleft palate induced by 160 mg/kg of dexamethasone administered to pregnant females on day 12 of gestation. The strains used were B10.A/Sg.Sn, C57BL/10Sn, B10.A (5R)/SgSn and B10.A(18R)/Sg. Additionally the cleft palate frequency was observed in a large number of litters from saline-treated pregnant females. The cleft palate frequency in this control was very low and the rank of strains was the same as for the glucocorticoid-induced cleft-palate frequency. This observation suggests that the induced cleft palate frequency reflects the spontaneous occurrence of isolated cleft palate in these strains.

RNA polymerase II transcribes all of the heat shock induced genes of Drosophila melanogaster

Heat shock of Drosophila melanogaster induces the transcription of a small number of RNAs. Some of these encode protein products, but not all. We have investigated whether the several induced RNAs are transcribed by RNA polymerase II or by some other RNA polymerase. Immunochemical staining of polytene chromosomes indicates that, on heat shock, RNA polymerase II is relocalized; it "migrates" from previously-active transcription sites to the heat shock induced loci. All heat shock induced puffs show immunochemical staining. Such staining correlates with RNA polymerase II activity as judged by the sensitivity of RNA synthesis at these sites to low concentrations of alpha-amanitin. Thus the protein-coding and non-protein-coding heat shock-induced RNAs are transcribed by this polymerase specifically. We have also identified several non-puffed chromosomal sites at which RNA synthesis is induced by heat shock.

HLA phenotype frequencies in individuals with cleft lip and/or cleft palate

The HLA types of 133 patients with cleft lip and/or cleft palate were determined. Caucasian patients with isolated cleft palate showed a possible association with HLA. Ten of 11 male patients had HLA--A2 as compared to one out of eight female patients (P less than 0.005). Caucasian males with cleft lip and cleft palate had a slight increased frequency of HLA--Aw24 (P = 0.07) and Mexican-American males with cleft lip and/or cleft palate showed an increase of antigen HLA-A28 (P = 0.07), though neither were statistically significant. Females with cleft lip and/or cleft palate from either racial group had no differences from the controls. The serum from 90 mothers of patients with cleft lip and/or cleft palate were reacted against their child's lymphocytes. Of these crossmatch tests, 12% were found to be positive. These preliminary results suggest that male patients with isolated cleft palate are worthy of further studies with respect of HLA associations.

Ecdysone-stimulated RNA synthesis in salivary glands of drosophila melanogaster: assay by in situ hybridization

3H-RNA was isolated from nuclei and cytoplasm of Drosophila melanogaster larval salivary glands after labeling in organ culture in the presence or absence of ecdysone. Hybridization to the sites of the ecdysone-induced puffs 74EF and 75B could be detected only if the RNA was labeled in the presence of ecdysone, while hybridization to the ecdysone-repressed puff 68C was found primarily in the cytoplasmic RNA sample labeled in the absence of ecdysone. Hybridization at the site of an ecdysone-insensitive puff, 50CD, was readily detectable in all RNA samples. RNA hybridizing to the unpuffed region 60D seemed to be restricted to the nucleus of salivary gland cells and was present at only a low level in cytoplasmic RNA samples. The data indicate that in situ hybridization can be used to detect specific hormone-induced changes in transcription.

Polytene chromosome puffing and in situ hybridization measure different aspects of RNA metabolism

Direct autoradiography of Drosophila melanogaster polytene chromosomes which have incorporated 3H-uridine suggests that the chromosomal puffs are the most active sites of incorporation; that the puffs are not the only sites of incorporation; and that there are sites which do not incorporate at all. In situ hybridization of 3H-RNA from salivary gland nuclei labels all three types of chromosomal sites. Labeling by in situ hybridization is not proportional to labeling by direct autoradiography. The differences may be explained by several models. Nuclear RNA of salivary glands probably contains transcripts from multiply repeated genes; these transcripts may hybridize to many chromosomal sites. The data furthermore suggest that the phenomenon of puffing may not be a simple reflection of transcription rate, since several puffs hybridize RNAs with quite different metabolic characteristics.

Ecdysone-stimulated RNA synthesis in imaginal discs of Drosophila melanogaster. Assay by in situ hybridization

Cytoplasmic RNA from imaginal discs of Drosophila melanogaster, labeled by uridine incorporation in organ culture, has been assayed by hybridization to cytological preparations of polytene chromosomes. RNA labeled during the early stages (first four hours) of ecdysone stimulation was compared to RNA labeled in the absence of the hormone. For the poly(A)-containing fraction (oligo-dT bound), several loci hybridize only RNA labeled in the presence of ecdysone; one locus hybridizes only control RNA. The majority of hybridizing loci are unaffected by the hormone. Of the loci hybridizing RNA not bound to oligo-dT, several appear specific for the ecdysone-treated sample, though most are labeled more heavily with this RNA than with the control. None of the ecdysone-sensitive loci visualized by in situ hybridization are the sites of salivary gland puffs induced by ecdysone on the same time scale.

The effect of heat shock on RNA synthesis in Drosophila tissues

Total RNA from Drosophila imaginal discs, labeled under conditions of heat shock, is analyzed by hybridization in situ to salivary gland polytene chromosomes. Grain densities over the hybridizing bands are compared, showing that the response to heat shock is similar for several disc types and fly stocks. Alteration of the culture medium used for labeling during heat shock results in the specific induction (in discs, salvary glands, or fat body) of one of the heat-shock loci to a level far beyond that normally seen. We discuss the implications of this specific induction regarding the mechanism of response. We also discuss the observed difference between transcription labeling of salivary gland chromosomes and labeling by in situ hybridization.

Method of evaluating intrauterine versus genetic influences on craniofacial anomalies

A method has been proposed that enables discrimination between genetic and intrauterine influences within the etiology of teratogen-induced craniofacial anomalies. The experimental approach is the transplantation of embryos at the blastocyst stage from mouse strains that are either highly resistant or highly susceptible to cortisone-induced cleft lip and cleft palate formation into pseudopregnant foster mothers that are reciprocally either resistant or susceptible to the congenital birth defect.

Induction and regulation of chloroplast replication in mature tobacco leaf tissue

Chloroplast replication was induced in mature tobacco leaf tissue (Nicotiana tabacum L.) by culturing leaf discs on a sterile medium composed of salts and sucrose. Chloroplast replicaton is greatly enhanced by the addition of kinetin to this medium. Kinetin also enhances cell enlargement, but cell division does not occur. Chloroplast replication is nonsynchronous and proceeds most rapidly when the cell enlargement rate decreases. Chloroplast replication is light-dependent, but cell enlargement occurs in both light and dark. Chloroplast replication resumes when discs cultured in the dark are returned to the light. It appears that chloroplast replication is related to cell expansion. The possibility of inducing synchronous replication of chloroplasts in tobacco cells is discussed.