Mutants affecting position-effect heterochromatinization in Drosophila melanogaster

The dominant suppressor Su(var)b ¹⁰¹ and the dominant enhancer En(var)c ¹⁰¹ were found to affect significantly white variegation in a strongly variegating line of the w ^m4 chromosome (w ^m4h ) which has been used as standard rearrangement for a genetic dissection of position-effect variegation (Reuter and Wolff, 1981). Both mutations were also shown to affect position-effect heterochromatisation in T(1;4)w ^m258-21 and variegation in all the rearrangements tested (white, brown, scute and bobbed variegation). These results suggest that the genes identified encode functions essential for the manifestation of gene inactivation in position-effect rearrangements. It seems also reasonable to assume that in all the rearrangements tested identical heterochromatisation processes lead to inactivation of the genes whose phenotype is variegated.     

Modification of the DNA content in translocated regions of Drosophila polytene chromosomes

The DNA content of translocated polytene chromosome regions in Drosophila melanogaster is affected by heterochromatic position effect. Microdensitometric studies on w ^m258-21 translocation heterozygotes showed (Hartmann-Goldstein and Cowell, 1976; Cowell and Hartmann Goldstein, 1980) that band region 3D1-E2, adjacent to the breakpoint, contained less DNA than the homologous non-translocated region whereas the neighbouring 3C1-10 region contained more DNA than its non-translocated counterpart. In the nuclei selected for measurement the translocated X chromosome was morphologically euchromatic, but both regions undergo heterochromatisation in other nuclei within the same salivary gland. To explore the relationship between changes in DNA content and heterochromatisation, the effect on DNA content of two known modifiers of heterochromatisation has now been studied. Larvae cultured at 15° C, which exhibit more heterochromatisation than those grown at 25° C, have the same relative DNA contents as at the higher temperature. The addition of a Y chromosome markedly reduced heterochromatisation; in XXY larvae there was no difference between the DNA contents of translocated and non-translocated 3D1-E2 regions, and in region 3C1-10 the percentage excess of DNA in the translocated homologue was approximately double that found in XX larvae. The relationship between replication behaviour and compaction suggested by these results is discussed.     

Carnitine suppression of position-effect variegation in Drosophila melanogaster

Carnitine is a well-known naturally occurring compound, very similar to butyrate, with an essential role in intermediary metabolism mainly at the mitochondrial level. Since butyrate inhibits the enzyme histone deacetylase and is capable of suppressing position-effect variegation in Drosophila melanogaster, we tested a further possible function of carnitine in the nucleus, using an assay for the suppression of position-effect variegation. We tested three physiological forms of carnitine (l-carnitine, l-propionylcarnitine, l-acetylcarnitine) for the ability to suppress two different chromosomal rearrangements, inducing variegation of the white ⁺ and brown ⁺ genes. The results show that the carnitine derivatives are capable of suppressing the position-effect variegation, albeit with different efficiencies. The carnitine derivatives interact lethally with Su-var(2)1 ⁰¹, a mutation that induces hyperacetylation of histones, whilst hyperacetylated histories accumulated in both the nuclei of HeLa cells and Drosophila polytene chromosomes treated with the same compounds. These results strongly suggest that the carnitine derivatives suppress position-effect variegation by a mechanism similar to that of butyrate. It is suggested that carnitines may have a functional role in the nucleus, probably at the chromatin level.     

Position Effects and Variegation Enhancers in an Autosomal Region of DROSOPHILA MELANOGASTER

A dominant eye color mutation was found associated with a third chromosome inversion broken distally at or near the karmoisin (kar) locus in 87C and proximally within centric heterochromatin. Suppressibility of the mutant phenotype by an extra Y chromosome indicated that this was an example of dominant position-effect variegation. When heterozygous with deficiencies uncovering the kar locus, this inversion chromosome was found to be lethal unless a region in 87EF was also deleted. Extra Y chromosomes rescued inversion/deletion heterozygotes, while removal of the Y chromosome from heterozygous males deficient for the region in 87EF was lethal. Thus, a variegating lethal lies near the breakpoint in 87C, and a wild-type gene that enhances its variegation lies in 87EF. Furthermore, deletion of the region in 87EF was found to strongly suppress white-mottled-4 (w^m4) variegation, while deletion of another region in 87BC suppressed less strongly. These results indicate that essential genes on autosomes are sensitive to position effects, and loci that enhance variegation, as defined by deficiency mapping, are very common.     

Genetically directed preferential X-activation seen in mice

The nature of the O^hv mutation of the X chromosome of the mouse is defined. This locus exerts a cis position effect upon the expression of genes Tfm and Blo mapping in the same region; genes on the same chromosome as the O^hv mutation are preferentially activated and genes on the other X chromosome are usually inactive. Following the proportion of Tfm cells in the kidneys of heterozygotes confirms that the variegation seen of the locus Blo in the coat is matched in inner tissues. By introducing the sex reversal gene Sxr into these stocks, a situation can be created in which wildtype kidney cells have a selective advantage over Tfm cells in the embryonic Wolfflan duct and urogenital sinus. In spite of this difference in cell advantages, Blo coat variegation and Tfm Wolffian duct cell preponderance continue to exhibit a good correlation. This excludes the possibility that the variegation depends upon a selective advantage of cells carrying Tfm alleles after random X-inactivation and therefore reinforces the conclusion that the O^hv mutation is directly concerned in the X-activation process. A model is presented in which this locus acts as a receptor site recognized by molecules which activate one X chromosome.     

A meiotically reproducible chromosome length polymorphism in the ascomycete fungus Ophiostoma ulmi (sensu lato)

We have followed the transmission of Ophiostoma ulmis.l. chromosome length polymorphisms (CLPs) into the F₂ generation to determine the reproducibility of a genome rearrangement culminating in the conversion of a 1.0 Mb chromosome into a 800 kb chromosome. The 1.0 Mb chromosome in strain CESS16K is thus far unique among O. ulmi s.l. wild-type strains, as no other wild-type strains have been observed with chromosomes smaller than 2.3 Mb. It has been previously shown that the 1.0 Mb chromosome is mitotically stable, carries at least one normally expressed gene, and is transmitted through meiosis. In this study, a series of crosses were performed to further elucidate the pattern of inheritance of the 1.0 Mb chromosome and the process of conversion of the 1.0 Mb species to 800 kb. In crosses where the 1.0 Mb chromosome was allowed to pair with itself or with the 800 kb chromosome, all progeny inherited a copy of the 1.0 Mb or 800 kb form, further demonstrating the A-type nature of these small chromosomes. When a cross was repeated between the strains CESS16K (1.0 Mb chromosome) and FG245B^r-O (no 1.0 Mb or 800 kb chromosome), the occurrence of a 800 kb chromosome was observed in 9% of the progeny. A reciprocal cross between an 800 kb strain and a strain with no 800 kb or 1.0 Mb chromosome was conducted, and a progeny strain containing a 1.0 Mb chromosome was recovered. The reproducibility and reciprocality of the 1.0 Mb to 800 kb chromosome conversion demonstrates that meiotic processes are responsible for this CLP, and that O. ulmi s.l. strains with various divergent genome architectures can remain sexually compatible.     

A cytogenetic analysis in Psophus stridulus (L.) (Orthoptera: Acrididae): B-chromosomes and abnormal spermatid nuclei

The male chromosome complement of Psophus stridulus (L.) (Orthoptera: Acrididae) has been analyzed by using orcein staining, C-banding and silver impregnation. During spermatogenesis only one pair of autosomes (M₉) shows an active nucleolar organizer region located in a C-banded constriction. There are other chromosome pairs with constrictions but these do not show nucleolar activity. The relationship between these constrictions and the C-banding pattern exhibited by this species is analyzed.In a sample of 83 males from five populations, two different supernumerary chromosomes were observed. Four males had a metacentric B-chromosome (B^m) similar in size to the sex chromosome and mitotically stable. Its meiotic behaviour indicates that it is an isochromosome. An additional small B-chromosome (B⁸) was also found in a single follicle of one individual carrying the B^m.A high rate of abnormal spermatids (macrospermatids) was scored in the individuals carrying B's. This proportion is notably higher in the follicle containing both the B^m and the B⁸.     

X-chromosome inversion in Drosophila melanogaster accompanied by a mosaic-type position effect: an analysis using cloned DNA fragments

DNA fragments carrying the genes affected by position effect variegation in the In(1LR)pn2a chromosome were revealed. In situ hybridizations demonstrate preservation of specific DNA sequences in the polytene chromosome regions containing the inactivated genes. It was shown that both euchromatic-heterochromatic boundaries in the In(1LR)pn2a chromosome contain the mobile element B104 (roo).     

Third chromosome suppressor of position-effect variegation loci in Drosophila melanogaster

Summary As a result of a genetic analysis of 63 third chromosome suppressor mutations of position-effect variegation 12 different loci showing dominant suppression have been identified and their map positions determined. A compilcation of the genetic data available for each suppressor locus is given. The strong suppressor effects of the mutations have been quantified by measurements of white variegation inw ^m4h /w ^m4h ,w ^m4h /Y andw ^m4h /O flies. Mutant alleles of three loci were found in these studies to dominate over the strong enhancer effect of complete loss of the Y chromosome. Most of the identified loci suppressing position-effect variegation represent essential genetic funtions; only three loci represent nonessential functions. Mutations of two loci display recessive butyrate sensitivity and lethal interaction with the heterochromatic Y chromosome suggesting that these genes affect chromosomal condensation. Studies with deficiencies and triploids revealed that most of the loci represent haplo-abnormal suppressor functions. The use of the isolated mutant material for genetic, developmental and molecular studies of processes connected with gene inactivation in position-effect variegation is discussed.Dedicated to Prof. H.J. Becker on the occasion of his 6th birthday     

Extrachromosomal Element Delta in DROSOPHILA MELANOGASTER. VIII. Inseparable Association with Sensitive Second Chromosome

The presence of delta is always accompanied by a sensitive second chromosome in Drosophila melanogaster or vice versa. The separability of delta and the chromosome line was investigated in experiments designed to eliminate delta or to suppress its multiplication for a number of generations. Cy/S^b-5 males which transmit a minute amount of delta b (retained by chromosome S^b, kills S^b/S^b and S^b/S^r zygotes) to their progeny were backcrossed for 61 generations to Cy/Pm females which carried no delta. After backcrossing 465 Cy/S^b-5 males were individually examined for retention of delta, and all were found to retain delta b in its latent state. A homozygous strain for the S^r-20B chromosome which retained a minute amount of delta r (retained by chromosome S^r, kills S^r/S^r zygotes) was obtained. 1,252 Cy/S^r-20B females derived from the homozygous strains at the 21st generation were tested individually for delta retention. All females tested were found to retain delta r in its latent state. The delta retention in S^b-5 chromosome lines isolated from S^r-Cy/S^b-5 heterozygous strains which carried delta r but not delta b was examined. The descendant Cy/S^b-5 lines from the heterozygous strains had accumulated their specific delta, delta b. These findings are consistent with those obtained in an earlier study, and lead to the conclusion that delta is associated inseparably with each specific sensitive chromosome.     

Carnitine suppression of position-effect variegation in Drosophila melanogaster

Carnitine is a well-known naturally occurring compound, very similar to butyrate, with an essential role in intermediary metabolism mainly at the mitochondrial level. Since butyrate inhibits the enzyme histone deacetylase and is capable of suppressing position-effect variegation in Drosophila melanogaster, we tested a further possible function of carnitine in the nucleus, using an assay for the suppression of position-effect variegation. We tested three physiological forms of carnitine (l-carnitine, l-propionylcarnitine, l-acetylcarnitine) for the ability to suppress two different chromosomal rearrangements, inducing variegation of the white ⁺ and brown ⁺ genes. The results show that the carnitine derivatives are capable of suppressing the position-effect variegation, albeit with different efficiencies. The carnitine derivatives interact lethally with Su-var(2)1 ⁰¹, a mutation that induces hyperacetylation of histones, whilst hyperacetylated histories accumulated in both the nuclei of HeLa cells and Drosophila polytene chromosomes treated with the same compounds. These results strongly suggest that the carnitine derivatives suppress position-effect variegation by a mechanism similar to that of butyrate. It is suggested that carnitines may have a functional role in the nucleus, probably at the chromatin level.     

Photobacterium malacitanum sp. nov., and Photobacterium andalusiense sp. nov., two new bacteria isolated from diseased farmed fish in Southern Spain

Three strains, H01100409B^T, H01100413B, and H27100402H^T, were isolated from several internal organs of diseased redbanded seabream (Pagrus auriga) reared in Andalusia (Southern Spain). All strains were studied by phenotypic, including chemotaxonomy, and genomic characteristics. Phylogenetic analysis based on concatenated sequences of six housekeeping genes (gyrB, ftsZ, topA, mreB, gapA, and 16S rRNA) supported the inclusion of the strains within the clade Phosphoreum of the genus Photobacterium, and two of the strains (H27100402H^T and H01100409B^T) formed a tight group separated from the closest species P. aquimaris. Genomic analyses, including average nucleotide identity (ANIb and ANIm) and DNA–DNA hybridization (DDH), clearly separated strains H27100402H^T and H01100409B^T from the other species within the clade Phosphoreum with values below the thresholds for species delineation. The chemotaxonomic features (including FAME analysis and MALDI-TOF-MS) of H27100402H^T and H01100409B^T strains confirmed their differentiation from the related taxa. The results demonstrated that strain H01100413B was classified as P. aquimaris and the strains H27100402H^T and H01100409B^T represented a new species each in the genus Photobacterium, for which we propose the names Photobacterium malacitanum sp. nov., type strain H27100402H^T (=CECT 9190^T = LMG 29992^T), and Photobacterium andalusiense sp. nov., type strain H01100409B^T (=CECT 9192^T = LMG 29994^T).     

Design of a system of conditional lethal mutations (tab/k/com) affecting protein-protein interactions in bacteriophage T4-infected Escherichia coli

The re-direction of host-cell machinery to virus-specific functions, by the physical interaction between viral proteins and pre-existing host proteins, may be a mechanism commonly exploited in virus infection. We argue that the formation of a hybrid complex between an Escherichia coli protein and bacteriophage T4 protein controls the assembly of T4 capsid precursors into ordered structures. This early step in assembly can be blocked either by a mutation in T4 gene 31 (Laemmli et al., 1970), or by a bacterial mutation (groE, tabB) (Georgopoulos et al., 1972; Coppo et al., 1973). We show that this step can also be blocked by the interaction of bacterial mutations (tabB^k, tabB^com) and viral mutations k^B and com⁸); com^B mutations map in T4 gene 31, while k^B mutations map in either gene 31 or 23. Many k⁸ mutants are also temperature-sensitive. Phage T4 head assembly is blocked when tabB^k (or tabB^com) are infected with T4k^B (or com^B), but not when the bacterial mutant is infected with T4 wild-type, or when tab⁺ cells are infected with k^B (or com^B). We interpret this phenomenon as a case of negative complementation between altered host and viral subunits of a hybrid complex and illustrate this idea with the experiments described in the text. We describe a technique by which tabB mutants can be efficiently and specifically selected with k^B (or com^B) T4 mutants. Since many k^B mutants are temperature-sensitive, temperature-sensitive mutants in other genes also may have latent k properties, and may be used for the isolation of new tab bacterial mutants, identifying other interactions between T4 and E. coli proteins.     

A marked ring-Y-chromosome in Drosophila hydei with a new type of white variegation

A ring-Y chromosome, R(Y)w ^m, of D. hydei is described which carries a complete set of fertility genes, a NOR region and a small X-chromosomal insertion (w ^m), which may be used as a marker. The ring has been characterized by various staining techniques. It was derived from a w ^mCo Y chromosome by X-ray treatment of spermatocytes. Its mode of origin allows to fix the gene order in the distal region of the long arm of the w ^mCoY chromosome. The white ⁺ gene included in the ring shows a new type of position-effect variegation which is described and discussed in the context of an earlier hypothesis on a dual function of the white locus.     

Indole- and caffeine-resistant mutations of Schizophyllum commune are involved in the behavior of a class III B mating-type factor in trp1 cells

We have reported that a parental strain of Schizophyllun commune T11 (trp1) is fully compatible with a strain T37 (Bα1′β4, trp1), but indole- and caffeine-resistant mutants (In^R-13 and Caf^R-9 respectively) derived from the T11 are semicompatible with the same T37. The compound-resistant mutations, ind1 and cfn1, were linked to neither A nor B mating-type factors. In^R-13, Caf^R-9, and all of indole- and caffeine-resistant progenies (ind1, trp1; cfn1, trp1) were semicompatible with the T37, and compatible with a strain T40 (Bα1′β4, TRP1) although the T40 contained the same class III B mating-type factor as the T37. The In^R-13 and Caf^R-9 were also semicompatible with any tester strains (Bα1′β4, trp1) developed, and the resulting heterokaryons produced non-aggregated and semiaggregated masses of hyphae, respectively. In the mutant heterokaryons, nuclei were distributed irregularly especially in case of [trp1/trp1] background; anucleate, uninucleate, binucleate and multinucleate cells were found with modified hyphae which contained a different type of septation (pseudoclamps and simple septa other than true clamps). We concluded that the ind1 and cfn1 mutations alter the normal behavior of one of class III B mating-type factors in Trp⁻ cells.     

Regional control of nondisjunction of the B chromosome in maize

Control of nondisjunction in the maize B chromosome was studied using a set of B-10 translocations. The study focused on the possible effect of the proximal region of the B long arm. The experimental procedure utilized a combination of a 10^B chromosome from one translocation with a B¹⁰ from another translocation. The breakpoints of the two translocations were so located that combination of the two elements created a deletion in the proximal region of the B chromosome, but no deletion in chromosome 10. Two different types of deletions were established; one involved a portion of the euchromatic region and the other the entire heterochromatic portion comprising the distal half of the B long arm, except for the small euchromatic tip. Deletion of the heterochromatic portion did not exert any effect on nondisjunction. Deletions of different portions of the euchromatic region produce different responses. Some deletions resulted in typical B nondisjunctional activity; others resulted in the disappearance of this activity. It is concluded that a region within the euchromatic portion of the chromosome is critical for the nondisjunction of B chromosomes. Among 22 translocations with breakpoints in the euchromatic regions, three were proximal to the critical region, 16 were distal and the position of three others was not determined.     

The effects of inbreeding and low temperature on the pattern of chromosome synapsis in the ovarian nurse cell nuclei of Drosophila melanogaster strains

The effects of inbreeding and low temperature on the pattern of homologous chromosome synapsis in ovarian nurse cell nuclei of Drosophila melanogaster strains were studied. Exposure to decreased temperature (16°C) caused a noticeable increase in the rate of asynapses of homologous chromosomes, whereas this effect was insignificant for F₃₀ inbreeding generation. Long-term inbreeding has a substantial effect on the relative positions of chromosomes in the nurse cell nuclei. This is visually evident only in the interstrain hybrids between highly inbred strains LA (F₉₂₈) and HA (F₉₂₈) or between either strain and laboratory strain Canton S or the flies from the natural population, where abnormalities in homologous chromosome synapsis are observed in virtually all nuclei.