N. B. Fedorova

The Main Effect of Chromosomal Rearrangement Is Changing the Action of Regulatory Genes

Effect of chromosomal rearrangements on the expression of mutations was studied in Drosophila melanogaster regulatory genes. These were facultative dominant lethals and recessive lethals on the X chromosome obtained by the classical Muller-5 method. Chromosomal rearrangements drastically changed the expression of regulatory gene mutations. Rearrangements either caused the lethal effect of mutations or suppressed the already present lethality. The action of rearrangements exhibited the maternal or paternal effect. Irrespective of the presence in the genome of mutations of regulatory genes, a rearrangement acted as a factor decreasing fertility of the organism. The rearrangement effect is identical to the expression of regulatory genes per se. It is concluded that the chromosomal rearrangement affects the examined regulatory genes indirectly through a change in the operation of regulatory genes located within the rearrangement. Thus, rearrangements gain great importance for the definition of the pattern of genome functional activity. Widespread distribution of rearrangements in individual genotypes and their effectivity in the process of speciation are thus explained.

Genes Controlling Development: Morphoses, Phenocopies, Dimorphs, and Other Visible Expressions of Mutant Genes

We studied facultative dominant lethal mutations obtained earlier inDrosophila melanogaster. In some genotypes, these mutations were expressed as lethals, but in other genotypes they lacked this expression. The mutations were maintained in the following cultures: (1) females Muller-5 heterozygous for the mutation; (2) males crossed to attached-Xfemales; and (3) females and males homozygous for the mutation. During culturing, many mutations were found to give rise to phenotypically abnormal progeny. Generally, these abnormalities were morphoses involving various body parts; they were mostly asymmetric and nonheritable. Maternal and paternal effects in the formation of morphoses were observed. In four cases, dimorphic mutations were recorded: a female homozygous for the mutation had mutant phenotype whereas its male counterpart was phenotypically normal. The mutations were recessive with regard to the norm. New phenotypes behaving as mutations with incomplete penetrance arose during culturing. In cultures of mutant homozygotes phenocopies would appear en masse; they would persist for one or two generations and disappear. One wave of phenocopies succeeded another. Visible phenotypes appeared, which further behaved as ordinary recessive mutations. We concluded that these visible manifestations are characteristic for regulatory mutations controlling ontogeny. Their appearance is explained by the activation of new regulatory scenarios caused by blocking standard regulatory pathways.

From Genetics of Intraspecific Differences to Genetics of Intraspecific Similarity

Based on the Mendelian approach to heredity, modern genetics describes inheritance of characters belonging to the category of intraspecific difference. the other large category of characters,intraspecific similarity, stays out of investigation. In this review, the genome part responsible for intraspecific similarity is considered as invariant and regulatory. An approach to studying the invariant part of the Drosophila melanogaster genome is formulated and the results of examining this genome part are presented. The expression of mutations at genes in the invariant genome part is different from that of Mendelian genes. We conclude that these genes are present in the genome in multiple copies and they are functionally haploid in the diploid genome. Severe abnormalities of development appearing in the progeny of mutant parents suggest that the mutant genes are genes regulating ontogeny. A hypothesis on an elementary ontogenetic event is advanced and the general scheme of ontogeny is presented. A concept on two types of gene allelism (cis- and trans-allelism) is formulated. This approach opens a possibility for studying genetic material responsible for the formation of intraspecific similarity characters at different taxonomic levels on the basis of crossing individuals of the same species.

The elementary event of development.

In biological terms, individual development consistsof “three closely related but, to a certain degree, inde-pendent processes: the increase in the number of cells,cell specialization, and tissue morphogenesis” [1]. Ingenetic terms, it consists in the activation of structuralgenes controlled by regulatory genes [2]. The geneticdescription of ontogeny should also include the multi-plication of the genetic system itself in the course ofcell division. Both descriptions seem comprehensive;however, neither of them explains either the drivingforce or the algorithm of individual development.Mutations of regulatory genes were identified in Drosophila melanogaster with the use of a new proce-dure [3]. This paper describes an unusual characteristicof these mutations, namely, malformations (morpho-ses) caused by them. The authors conclude that themutant genes controlled ontogeny. The parental (mater-nal and paternal) effects on the formation of morphoseswere discovered. Taking them into account, it was sup-posed that the products of the genes controlling ontog-eny function in subsequent cell generations, rather thanin the sites of their synthesis. This is the fundamentaldifference of the genes controlling ontogeny from usualMendelian genes.The fact that genes may generate regulatory prod-ucts “for exportation” became a principle of the theoryof ontogeny. An ontogenetic gene encodes an inactiveregulatory product and initiates cell division. Cell divi-sion activates the product that the daughter cells receivealong with parental genome, thus repressing the pre-ceding gene and activating the next one. The transfer ofactivity from the gene controlling ontogeny to anothergene via the cell-division event has been termed the ele-mentary event of development. In this way, the chainreaction of three related ontogenetic processes—theactivation of genetic information, the increase in cellmass, and the distribution of the activated informationin it—is initiated and maintained.MATERIALS AND METHODSMutations were induced in D. melanogaster. Thecriterion for the selection of mutations for the study wasa lethal effect in a certain genotype and its absence inanother genotype. The mutations were induced by threemethods. Protocol 1. Male Drosophila were γ -irradiated andcrossed with females with attached-X chromosomes.The resultant male offspring contained an irradiatedX chromosome and a haploid set of irradiated auto-somes. Each of the male offspring was individuallycrossed with females from strain yellow . The malewhose offspring did not contain females was consid-ered to carry the X-chromosome mutation [3]. Protocol 2. Male Drosophila were γ -irradiated andcrossed with females carrying inversion Curly in auto-some 2. The resultant male offspring carrying an irradi-ated autosome 2 and autosome Curly were individuallycrossed with females from strain yellow . The malewhose offspring did not contain females or males witha normal phenotype (without Curly ) was considered tocarry the mutation in autosome 2 [4]. Protocol 3. The classical Muller-5 method was usedto obtain recessive lethal mutations in the X chromo-some of Drosophila. To maintain the lethal mutations,we performed crosses between In(1)Muller -5/ lethal females and In(1)Muller -5 males. These crosses did notyield normal males. Crossing females with wild-typemales, we detected cultures in which normal malesappeared. These cultures contained the required muta-tion.The obtained mutations in the X chromosome wereintroduced into culture via crossing a mutant male withfemales that had either linked or inverted X chromo-somes. The mutations in autosome 2 existed in culturesthat contained the mutation in one autosome 2 and thecomplex inversion In(2LR)CyO in the other one. Whenexamining the cultures visually, we found that some ofthe offspring had malformations (morphoses). Morpho-ses were also observed in the offspring of some crossesperformed when studying mutations. Pictures of themorphoses made by means of a digital video camerawere transferred into a computer and stored as separatefiles.

Conditional mutations in Drosophila melanogaster: On the occasion of the 150th anniversary of G. Mendel's report in Brünn

The basis for modern genetics was laid by Gregor Mendel. He proposed that traits belonging to the intraspecific variability class be studied. However, individuals of one species possess traits of another class. They are related to intraspecific similarity. Individuals never differ from each other in these traits. By analogy with traits varying within a species and determined by genes, it is conjectured that intraspecific similarity is determined by genes, too. If so, mutations in these genes can be obtained. This paper provides a review of works published in 2000-2014 that: (1) propose breeding methods for detection of mutations in Drosophila melanogaster genes that lead intraspecific similarity; these mutations were called conditional; (2) describe collections of conditional mutations in chromosomes X, 2, and 3 of Drosophila; (3) show unusual features of epigenetic nature in the mutants; and (4) analyze these features of the mutants. Based on the peculiarities of manifestation it is supposed that the recognized conditional mutations occur in genes responsible for intraspecific similarity. The genes presumably belong to the so-called regulatory network of the Drosophila genome. This approach expands the scope of breeding analysis introduced by G. Mendel for heredity studies 150 years ago.

Genetic mutation affects the energy status of Drosophila

Conditional dominant lethals (CDL) represent a special class of genetic mutations observed in Drosophila. Mutation manifests as a dominant lethal in one genotype, but lethality is not expressed in another genotype. CDL mutants exhibit a set of traits discriminating them from classic mutations. We observed unusually high mobility of flies and high sexual activity of males carrying these mutations. We used special tests for evaluation of energy metabolism of CDL mutants. Indirect calorimetry (CO2 excretion measurement) has been used for estimation of energy exchange in four mutant and two control fly lines. A special device has been used for evaluation of locomotor activity of these fly lines. Energy exchange and locomotor activity in CDL mutants were significantly higher than in control lines. We conclude that some genetic mutations are capable of increasing energy dissipation in their carriers.

Parental effects of conditional mutations and their explanations

A study of the properties of conditional dominant and recessive lethals in Drosophila melanogaster has demonstrated parental effects in the inheritance and manifestation of these mutations. Maternal and paternal effects are present when conditional mutations interact with (1) one another, (2) the Y chromosome, or (3) chromosomal rearrangements, as well as (4) when the visual expression of a conditional mutation is inherited or (5) during the formation of morphoses (monstrosities) in mutant offspring. The maternal and paternal effects do not exclude one another: the same mutation can display both patterns. The characters manifesting themselves at late developmental stages (morphoses) are inherited according to a parental effect pattern. A general concept of the parental effect is proposed and its types are classified.

Delayed Activation of the Maternal Genome During Early Development of Drosophila

The synkaryon, which comprises both the maternal and paternal chromosome material, is surrounded by the maternal cytoplasm in the zygote. Early embryonic development in Drosophila , as in many other animals, depends only on the presence of RNA templates and some cytoplasmic proteins [1]. Gene activation in Drosophila does not occur until the late blastula or gastrula stage, and it is still unknown what is the sequence of gene activation events and how synchronously paternal and maternal alleles start to operate. Conceivably, master genes, which play a key role in the structural features of the organism [2], are the first to become activated. Recessive lethal mutations with unusual properties were recovered in Drosophila melanogaster. When brought to a zygote by a sperm, these recessive mutations become dominant. Maternal chromosome rearrangements reduce their penetrance. It was suggested the expression of the recessive lethals becomes dominant when the maternal genome is inactive on the background of the active paternal genome. Delayed activation of the maternal genome is thought to be a mechanism for eliminating mutations in a special group of genes, namely, the genes that are the first to become activated.

Conditional Mutations in Drosophila: Concept of Genes That Control Individual Development

The conditional mutations in D. melanogaster are produced by gamma-irradiation, maintained in laboratory cultures, and inherited as gene mutations. However, their manifestation differs from the conventional mutations by several specific features. The most noticeable specific feature is their conditional nature, i.e., a conditional mutation manifests itself in the individuals of a certain genotype being silent in the individuals with another genotype. A particular procedure for mutation recovery determines what these genotypes will be. An overwhelming number of mutations are conditional dominant lethals. The viable mutation carriers display a drastically decreased fertility. Early zygotic lethality is inherited according to parental type (maternal or paternal). The carriers of conditional mutations give the offspring with a high rate of monstrosities. The possibility for the offspring to form monstrosities is inherited according to a parental (maternal or paternal) type. The level of fertility of conditional mutants is altered by chromosomal rearrangements. The chromosomal rearrangements themselves cause a decrease in fertility. Lethality of the progenies produced by the parents carrying rearrangements is inherited according to a parental (maternal or paternal) type. The results allow for a set of logical arguments in favor of that 1) the genome has a specialized system of genes (ontogenes) that control the course of individual development; 2) unlike a classical gene, acting according to the scheme DNA a RNA a protein, the ontogene implements the regulation according to the scheme DNA a RNA; and 3) the course of individual development is programmed by double-strand RNAs produced by ontogenes in germline cells.