Functional and structural analyses of mouse genomic regions screened by the morphological specific-locus test

Antimicrobial, antioxidant, anti-inflammatory and cytotoxic study of extracts of Guibourtia tessmanii (harms) J. Léonard from Gabon

Background

Gabonese flora abounds in a significant reserve of plants in medical matter. Thus, medicinal plants occupy a significant place in African pharmacopeia. Aim of this work was to evaluate the antimicrobial, antioxidant, anti-inflammatory and cytotoxic properties of extracts of Guibourtia tessmanii (Harms) J. Léonard.

Methods

The test for sensitivity to microorganisms was performed by the diffusion method, while the MICs and MBCs were evaluated by the microdilution technique. Antioxidant tests were performed by scavenging the DPPH and ABTS radicals. Anti-inflammatory activity was determined by protein denaturing and membrane stabilization methods. The cytotoxicity was evaluated on the tadpoles of the green frog.

Results

The antibacterial activity shows that the Gt F2 fraction and the water-acetone extract produced the greatest inhibitions. The water, water-ethanol and water-acetone extracts exhibited bactericidal effects on the majority of bacteria. In the case of trapping of the DPPH radical, the IC50 values varied from 6.92 ± 0.48 to 16.64 ± 0.20 μg/mL. For the decolouration of ABTS, oxidation was mainly inhibited by the water-acetetone, water-ethanol extracts and some fractions. The water and water-acetone extracts showed good inhibition of denaturation. The hemolysis test confirmed the good activities of the extracts. The lethal test showed that the LC50 drops from 171.37 ± 9.25 to 58.25 ± 7.21 μg/mL after 24 and 96 h of exposure. In tadpoles exposed to 7.81 μg / mL of extracts, the first mortalities (12.5%) were observed on the second day of exposure. From the ninth day, the mortality rate increased (25%) until the 16th day.

Conclusion

Our results show that Guibourtia tessmanii may be a promising product for the isolations of molecules responsible for biological activities.

Mutation of l7Rn3 shows that Odz4 is required for mouse gastrulation

A mouse homolog of the Drosophila pair-rule gene Odd Oz (Odz4) maps to the critical region of the l7Rn3 locus on mouse chromosome 7. Here we show that Odz4 is an excellent candidate for this allelic series because (1) it spans the entire critical region, (2) the phenotypes correlate with embryonic expression, (3) the complex genetic inheritance of the alleles is consistent with complex transcriptional regulation, and (4) one allele has a mutation in a conserved amino acid. Odz4 uses five alternate promoters that encode both secreted and membrane-bound proteins. Intragenic complementation of the l7Rn3 alleles is consistent with these multiple-protein isoforms. Further, the allelic series shows that Odz4 is required to establish the anterior-posterior axis of the gastrulating mouse embryo and is necessary later for mesoderm-derived tissues such as somites, heart, and skeleton. Sequencing of RT-PCR products from five of the six alleles reveals a nonconservative amino acid change in the l7Rn3(m4) allele. This amino acid is important evolutionarily, as it is conserved to Drosophila. Together, our data indicate that Odz4 is mutated in the l7Rn3 allele series and performs roles in the mouse brain, heart, and embryonic patterning similar to those of its Drosophila counterpart.

Overlapping deletions define novel embryonic lethal loci in the mouse t complex

SUMMARY

The t complex region of mouse chromosome 17 contains genetic information critical for embryonic development. To identify and map loci required for normal embryogenesis, a set of overlapping deletions (D17Aus9(df10J), D17Aus9(df12J), and D17Aus9(df13J)) surrounding the D17Aus9 locus and one encompassing the T locus, Del(17)T(7J), were bred in various combinations and the consequences of nullizygosity in overlapping regions were examined. The results indicated that there are at least two functional units within 1 cM of D17Aus9. l17J1 is a peri-implantation lethal mutation within the region deleted in D17Aus9(df13J), whereas l17J2 is a later-acting lethal defined by the region of overlap between Del(17)T(7J) and D17Aus9(df12J). Del(17)T(7J)/D17Aus9(df12J) embryos die around 10.5 dpc. The development of the mutant embryos is characterized by lack of axial rotation, an abnormal notochord structure, and a ballooning pericardium. These studies demonstrate the value of overlapping deletion complexes, as opposed to individual deletion complexes, for the identification, mapping, and analysis of genes required for embryonic development.

The mouse Cer1 (Cerberus related or homologue) gene is not required for anterior pattern formation

Cer1 is the mouse homologue of the Xenopus Cerberus gene whose product is able to induce development of head structures during embryonic development. The Cer1 protein is a member of the cysteine knot superfamily and is expressed in anterior regions of the mouse gastrula. A segmental pattern of expression with nascent and newly formed somites is also seen. This suggests an additional role in development of the axial skeleton, musculature, or peripheral nervous system. Xenopus animal cap assays and mouse germ-layer explant recombination experiments indicate that the mouse protein can act as a patterning molecule for anterior development in Xenopus, including induction of Otx2 expression, and suggest it may have a similar role in mouse development. However, we present here genetic data that demonstrate that Cer1 is not necessary for anterior patterning, Otx2 expression, somite formation, or even normal mouse morphogenesis.

Mutagenicity of anticancer drugs in mammalian germ cells

The evidence for mammalian germ cell mutagenicity induced by anticancer drugs is summarized. Primary attention is paid to the three major mouse germ cell mutagenicity tests- the dominant lethal, heritable translocation, and morphological specific locus tests- from which most germ cell mutagenicity data historically have been obtained. Of the 21 anticancer drugs reviewed, 16 have been tested in one or more of these three tests; with all 16 tested in the most common germ cell test, the male dominant lethal test, and 9 of the 16 also tested in the female dominant lethal test. The patterns of germ cell stage specificity for most of the anticancer drugs are similar, and generally resemble the patterns seen with other types of chemicals; however, some of the patterns are unique. For example, 2 of the 8 chemicals shown to induce dominant lethal mutations in female oocytes, do not induce dominant lethal mutations in male germ cells (adriamycin and platinol). Ten of the 16 chemicals tested in the dominant lethal test were positive in post-meiotic stages (spermatids through mature sperm), and seven also induced reciprocal translocations and/or specific locus mutations in post-meiotic stages. This propensity to induce mutations in post-meiotic stages has been observed with most mutagens. However, 5 of the anticancer drugs also induced dominant lethal mutations in spermatocytes (meiotic prophase cells) and one of them, 6-mercaptopurine, uniquely induced dominant lethal mutations exclusively in preleptotene spermatocytes. Finally, three of the anticancer drugs (melphalan, mitomycin C, procarbazine) are members of a very select group of chemicals shown to induce specific locus mutations in spermatogonial stem cells of mice. The implications for human risk are discussed.

Structural differences between specific-locus mutations induced by different exposure regimes in mouse spermatogonial stem cells

It was first shown by W.L. Russell (1962), and confirmed by him and others, that a 24-h interval between dose fractions (but not shorter or longer ones) elevates the rate of radiation-induced spermatogonial specific-locus mutations to levels considerably above the linear extrapolation made from lower-dose results. We have now analyzed the nature of mutations induced either in previously undisturbed or in "sensitized" spermatogonial stem cells, i.e., those that received a challenging dose of X-rays 24 h following a priming dose. Results are based on molecular studies of a large set of viable albino mutations [using probes derived from the tyrosinase (c) gene and from the regions surrounding c], and on retrospective classifications of mutations at c and two additional loci into LL (large lesions), IG (intragenic mutations), and OL (other lesions), utilizing criteria developed earlier. A significant difference (P = 0.016) was found between previously undisturbed and sensitized stem-cell spermatogonia; the latter have a higher LL/IG ratio, similar to the ratio observed for mutations induced in poststem-cell stages. This finding of a qualitative difference indicates that the additional mutations produced by a 24-h fractionated treatment are the result of the second (challenging) dose. The qualitative difference, further, indicates that the mutation-rate-augmenting effects of 24-h fractionation are not due, merely, to an increase (caused by the priming dose) of a normally responsive component of the spermatogonial population. The finding that the additional mutations that are produced by the challenging dose are primarily large DNA lesions suggests that the nuclear state of sensitized stem-cell spermatogonia may be different from the state of previously undisturbed spermatogonia. This state, which appears to be similar to that of postspermatonial stages, may be conducive to the formation of LLs, even by agents that are not LL inducers in other systems. The results further indicate that the relative paucity of LLs characteristic of treated (previously undisturbed) spermatogonial stem cells is probably not the result of selection against such mutations during subsequent germ-cell development.

Molecular analysis of viable spontaneous and radiation-induced albino (c)-locus mutations in the mouse

Thirty-one homozygous-viable, radiation-induced or spontaneous mutations at the albino (c) locus in mouse chromosome 7 were analyzed by Southern blot analysis with a tyrosine cDNA clone and with probes derived from the closely linked proviral integration sites Pmv-31 and Emv-23, which flank the tyrosinase gene on the proximal and distal sides, respectively. Thirteen of 27 radiation-induced and one of four spontaneous mutations manifested deletions or rearrangements for the tyrosinase gene. The sizes of four deletions found to break within the tyrosinase gene itself were estimated to be < or = 36 kb, < or = 40 kb, approximately 260 kb, and approximately 480 kb. Two homozygous-viable deletions were found to include flanking proviral loci, suggesting that they could be from 1500-2000 kb in length, if not longer. The existence of these very large, homozygous-viable deletions suggests that the one-to-two megabases including and surrounding the c locus harbor no genes essential for normal viability or fertility, although genes controlling more subtle (or "nonessential") phenotypes are likely to be present. These data thus provide some insight into the molecular structure of a number of viable c-locus mutations, whose nature could not be predicted solely on the basis of genetic analysis, as could be done for either lethal or reduced-pigment c mutations.

Cloning of the mouse agouti gene predicts a secreted protein ubiquitously expressed in mice carrying the lethal yellow mutation

The mouse agouti gene controls the deposition of yellow and black pigment in developing hairs. Several dominant alleles, including lethal yellow (Ay), result in the exclusive production of yellow pigment and have pleiotropic effects that include obesity and increased tumor susceptibility. In an interspecific backcross, we established genetic limits for the agouti gene and found that the Ay and the lethal non-agouti (ax) allele were not separated from a previously identified probe at the breakpoint of the Is1GsO chromosomal rearrangement. Using the Is1GsO probe, we isolated the agouti gene, and find that it has the potential to code for a secreted protein expressed in hair follicles and the epidermis, and that the level of expression correlates with the synthesis of yellow pigment. In the Ay mutation, there is a chromosomal rearrangement that results in the production of a chimeric RNA expressed in nearly every tissue of the body. The 5' portion of this chimeric RNA contains highly expressed novel 5' sequences, but the 3' portion retains the protein-coding potential of the nonmutant allele. We speculate that dominant pleiotropic effects of Ay are caused by ectopic activation of a signaling pathway similar to that used during normal hair growth.

Genetic, cytogenetic, and molecular analyses of mutations induced by melphalan demonstrate high frequencies of heritable deletions and other rearrangements from exposure of postspermatogonial stages of the mouse

Specific-locus experiments have previously shown melphalan to be mutagenic in all male germ-cell stages tested and particularly so in early spermatids. All but 2 of 24 specific-locus mutations recovered were tested genetically, cytogenetically, and/or molecularly. At least 12 of 15 tested mutations recovered from postspermatogonial stages but only 1 of 7 mutations recovered from stem-cell or differentiating spermatogonia gave evidence of being deletions or other rearrangements. Melphalan-induced mutations, thus, confirm the pattern of dependence of mutation structure on germ-cell stage that had been shown earlier for other chemicals. Results of the present investigation illustrate the capabilities of combined genetic, cytogenetic, and molecular analyses for characterizing the nature of specific-locus mutations. Fine-structure molecular mapping of long regions surrounding specific loci has been greatly facilitated by the availability of genetic reagents (particularly, deletion complexes) generated in specific-locus experiments over the course of decades. Reciprocally, this mapping permits increasingly detailed characterization of the nature of lesions induced by mutagenic exposures of germ cells, adding great powers for qualitative analysis of mutations to the specific-locus test. Cytogenetic and genetic investigations also provide evidence on lesion type, especially for loci at which mutations cannot yet be analyzed molecularly. Melphalan, like chlorambucil, can generate many mutations, a high proportion of which are deletions and other rearrangements, making this chemical valuable for generating mutations (at any locus) amenable to molecular access.

Construction, analysis, and application of a radiation hybrid mapping panel surrounding the mouse agouti locus

The region surrounding the agouti coat color locus on mouse Chromosome 2 contains several genes required for peri-implantation development, limb morphogenesis, and segmentation of the nervous system. We have applied radiation hybrid mapping, a somatic cell genetic technique for constructing long-range maps of mammalian chromosomes, to eight molecular markers in this region. Using a mathematical model to estimate the frequency of radiation-induced breakage, we have constructed a map that spans approximately 20 recombination units and 475 centirays8000. The predicted order of markers, Prn-p-Pygb-Emv-13-Psp-Xmv-10-Emv-15-Src-Ada, is consistent with a previously derived multipoint meiotic map for six of the eight markers and suggests that Xmv-10 may lie relatively close to one or more of the agouti recessive lethal mutations. The resolution of our map is approximately 40-fold higher than the meiotic map, but the median retention frequency of mouse DNA in hybrid cells, 0.12, is 4-fold lower than similar experiments with human chromosomes. From one of the radiation hybrid lines that contained a minimum amount of mouse DNA, 25 independent cosmids were isolated with a mouse-specific hybridization probe. Single-copy fragments from two of these cosmids were shown to originate from mouse Chromosome 2, and the meiotic map position of one was found to be within 10 recombination units of the region of interest. Our results indicate more precise map positions for Pygb and Xmv-10, demonstrate that radiation hybrid mapping can provide high-resolution map information for the mouse genome, and establish a new method for isolating large fragments of DNA from a specific subchromosomal region.

Molecular characterization of a region of DNA associated with mutations at the agouti locus in the mouse

Molecular characterization of a radiation-induced agouti (a)-locus mutation has resulted in the isolation of a segment of DNA that maps at or near the a locus on chromosome 2 in the mouse. This region of DNA is deleted in several radiation- or chemical-induced homozygous-lethal a-locus mutations and is associated with specific DNA structural alterations in two viable a-locus mutations. We propose that DNA probes from this region of chromosome 2 will be useful for ultimately characterizing the individual gene or genes associated with a-locus function.

Ionizing radiation and genetic risks. II. Nature of radiation-induced mutations in experimental mammalian in vivo systems

This paper reviews data on the nature of spontaneous and radiation-induced mutations in the mouse. The data are from studies using a variety of endpoints scorable at the morphological or the biochemical level and include pre-selected as well as unselected loci at which mutations can lead to recessive or dominant phenotypes. The loci used in the morphological recessive specific-locus tests permit the recovery of a wide spectrum of induced changes. Important variables that affect the nature of radiation-induced mutations (assessed primarily using tests for viability of homozygotes) include: germ cell stage, type of irradiation and the locus. Most of the results pertain to irradiated stem cell spermatogonia. The data on morphological specific-locus mutations show that overall, more than two-thirds of the X- or gamma-ray-induced mutations are lethal when homozygous. This proportion may be lower for those that occur spontaneously, but the numbers of tested mutants are small. For spontaneous mutations, there is evidence for the occurrence of mosaics and for proviral insertions. Most or all tested induced enzyme activity variants, dominant visibles (recovered in specific-locus experiments) and dominant skeletal mutations are lethal when homozygous and this is true of 50% of dominant cataract mutations, but again, the numbers of tested mutants are small. Electrophoretic mobility variants, which are known to be due to base-pair changes, are seldom induced by irradiation. At the histocompatibility loci, no radiation-induced mutations have been recovered, presumably because deletions are incompatible with survival even in heterozygotes. All these findings are consistent with the view that in mouse germ cells, most radiation-induced mutations are DNA deletions. Some mutations (in the morphological specific-locus tests) which had previously been inferred to be deletions on the basis of genetic analyses have now been shown to be DNA deletions by molecular methods. However, the possibility cannot be excluded that at least a small proportion of induced mutations may be intragenic changes. The data on the rates of induction of recessive lethals and of dominant skeletal and dominant cataract mutations (and proportions of the latter two which are homozygous lethal) can be used to estimate the proportions of recessive lethals which are expressed as skeletal abnormalities or cataracts. These calculations show that about 10% of recessive lethals manifest themselves as skeletal and less than 0.2% as cataract mutations.(ABSTRACT TRUNCATED AT 400 WORDS)

Development of a possible nonmammalian test system for radiation-induced germ-cell mutagenesis using a fish, the Japanese medaka (Oryzias latipes)

To develop a specific-locus test (SLT) system for environmental mutagenesis using vertebrate species other than the mouse, we first established a tester stock of the fish medaka (Oryzias latipes) that is homozygous recessive at three loci. The phenotypic expression of these loci can be easily recognized early in embryonic development by observation through the transparent egg membrane. We irradiated wild-type males with 137Cs gamma-rays to determine the dose-response relationships for dominant lethal and specific-locus mutations induced in sperm, spermatids, and spermatogonia. Through observation of 322,666 loci in control offspring and 374,026 loci in offspring obtained from 0.64-, 4.75-, or 9.50-Gy-irradiated gametes, specific-locus mutations were phenotypically detected during early development. These putative mutations, designated "total mutation," can be recognized only in embryos of oviparous animals. The developmental fate of these mutant embryos was precisely followed. During subsequent embryonic development, a large fraction died and thus was unavailable for test-crossing, which was used to identify "viable mutations." Our medaka SLT system demonstrates that the vast majority of total mutations is associated with dominant lethal mutations. Thus far only one spontaneous viable mutation has been observed, so that all doubling calculations involving this endpoint carry a large error. With these reservations, however, we conclude that the quantitative data so far obtained from the medaka SLT are quite comparable to those from the mouse SLT and, hence, indicate the validity of the medaka SLT as a possible nonmammalian test system.

Induction of specific-locus mutations in male germ cells of the mouse by acrylamide monomer

Acrylamide monomer (AA), injected into male mice at the maximum tolerated dose of 5 x 50 mg/kg (24-h intervals), significantly increased the specific-locus mutation rate in certain poststem-cell stages of spermatogenesis, but not in spermatogonial stem cells. Germ-cell stages in which the treatment induced dominant lethals--namely, exposed spermatozoa and late spermatids (number of surviving offspring only 3% and 27%, respectively, of those in concurrent controls)--jointly yielded the highest frequency of specific-locus mutations. AA thus conforms to Pattern 1 in our earlier classification of chemicals according to the spermatogenic stage at which they elicit maximum response (Russell et al., 1990). No specific-locus mutations were observed among 17,112 offspring derived from exposed spermatogonial stem cells, a result which rules out (at the 5% significance level) an induced mutation rate greater than 2.3 times the historical control rate. A sustained high productivity in matings made for several months following week 3 indicates that there is no significant spermatogonial killing and that cell selection is presumably not the explanation for the negative result. On the basis of genetic and/or cytogenetic evidence, the mutations induced postmeiotically by AA were 'large lesions' (multi-locus), while one of 2 recovered from exposure of differentiating spermatogonia is probably a small lesion. An earlier survey of mammalian mutagenesis results led us to conclude that, regardless of the classification of a chemical according to the stage at which it elicits its maximum response, the nature of mutations is determined by the germ-cell stage in which they are induced (Russell et al., 1990). The AA results on lesion size and on distribution of mutations among the loci fit the general pattern.

Mast cell growth factor maps near the steel locus on mouse chromosome 10 and is deleted in a number of steel alleles

Many spontaneous, chemical-induced, and radiation-induced dominant white spotting (W) and steel (Sl) mutations have been identified in the mouse. W and Sl mutations have similar phenotypic effects including deficiencies in pigment cells, germ cells, and blood cells, Numerous studies have suggested that W acts within the affected cell while Sl instead exerts its effects in the extracellular environment. Recent findings demonstrating that W encodes the c-kit proto-oncogene, a tyrosine kinase membrane receptor, have suggested that Sl encodes a ligand for c-kit. In the accompanying article we report the identification and purification of mast cell growth factor (MGF), a c-kit ligand. Here we describe the cloning of sequences encoding MGF. Furthermore, we show that Mgf maps near Sl in the distal region of mouse chromosome 10 and is deleted in a number of Sl alleles. These findings strongly support the notion that Sl encodes the mast cell growth factor.

Molecular and genetic characterization of a radiation-induced structural rearrangement in mouse chromosome 2 causing mutations at the limb deformity and agouti loci

Molecular characterization of mutations in the mouse, particularly those involving agent-induced major structural alterations, is proving to be useful for correlating the structure and expression of individual genes with their function in the whole organism. Here we present the characterization of a radiation-induced mutation that simultaneously generated distinct alleles of both the limb deformity (ld) and agouti (a) loci, two developmentally important regions of chromosome 2 normally separated by 20 centimorgans. Cytogenetic analysis revealed that an interstitial segment of chromosome 17 (17B- 17C; or, possibly, 17A2-17B) had been translocated into the distal end of chromosome 2, resulting in a smaller-than-normal chromosome 17 (designated 17del) and a larger form of chromosome 2 (designated 2(17). Additionally, a large interstitial segment of the 2(17) chromosome, immediately adjacent and proximal to the insertion site, did not match bands 2E4-2H1 at corresponding positions on a normal chromosome 2. Molecular analysis detected a DNA rearrangement in which a portion of the ld locus was joined to sequences normally tightly linked to the a locus. This result, along with the genetic and cytogenetic data, suggests that the alleles of ld and a in this radiation-induced mutation, designated ldIn2 and ajIn2, were associated with DNA breaks caused by an inversion of an interstitial segment in the 2(17) chromosome.

Genetic and molecular analysis of chlorambucil-induced germ-line mutations in the mouse

Eighteen variants recovered from specific locus mutation rate experiments involving the mutagen chlorambucil were subjected to several genetic and molecular analyses. Most mutations were found to be homozygous lethal. Because lethality is often presumptive evidence for multilocus-deletion events, 10 mutations were analyzed by Southern blot analysis with probes at, or closely linked to, several of the specific locus test markers, namely, albino (c), brown (b), and dilute (d). All eight mutations (two c; three b; two d; and one dilute-short ear [Df(d se)]) that arose in post-spermatogonial germ cells were deleted for DNA sequences. No evidence for deletion of two d-se region probes was obtained for the remaining two d mutations that arose in stem-cell spermatogonia. Six of the primary mutants also produced low litter sizes ("semisterility"). Karyotypic analysis has, to date, confirmed the presence of reciprocal translocations in four of the six. The high frequency of deletions and translocations among the mutations induced in post-spermatogonial stages by chlorambucil, combined with its overall high efficiency in inducing mutations in these stages, should make chlorambucil mutagenesis useful for generating experimentally valuable germ-line deletions throughout the mouse genome.