The ornithine cycle in Neurospora and its genetic control

It has been emphasized by Haldane (1) that for studies of intermediary metabolism "the new science of genetics furnishes a very powerful method." Such a method is founded upon the general premises that genes control many of the chemical reactions within an organism, and that gene mutations by blocking a reaction chain at various points may, in effect, resolve a metabolic process into some of its constituent stages. For instance, the genetics of such diseases as alcaptonuria and cystinuria have elucidated certain problems in human metabolic processes (2), and studies in the genetics of plant pigments have increased the knowledge of of the biochemistry of anthocyanins (3). But the study of metabolism by way of genetic differences in naturally occurring populations is limited not only by the low rate of mutation but also by the lethal character of most mutations of genes controlling vital functions. By increasing the mutation rate of an organism, through irradiation or otherwise, it is possible to create a number of genetic blocks at various steps in the syntheses of substances or in other processes of metabolism. The problem of preserving mutations ordinarily lethal has been met by Beadle and Tatum (4) in a general course of procedure developed around work with the ascomycetous mold Neurospora. The wild type of this organism is able to carry out all the syntheses essential to its normal growth and reproduction if biotin, inorganic salts, and a suitable source of carbon are available. Strains of Neurospora are irradiated with x-ray or ultraviolet rays on the assumption that mutations will be induced in genes controlling the syntheses of such substances as vitamins and amino acids. Mutant strains of this kind cannot grow on merely inorganic salts, sugar, and biotin, "minimal medium," but can be expected to grow if the product of the blocked synthesis is added to the minimal medium. From irradiated Neurospora there has been isolated in this laboratory a series of mutant strains which require for growth the presence of arginine in the culture medium. A study of the specific biochemical characteristics of members of this group of mutants has made it possible to demonstrate in Neurospora crassa an ornithine cycle similar to that proposed by Krebs and Henseleit (5) as occurring in mammalian liver, and to assign various steps in the cycle to the influence of particular single genes. To our knowledge the ornithine cycle has not previously been demonstrated in plants

Genetic control of sterol esterification in developing wheat endosperm

1. 1. The action of gene Pln, previously characterized by the sterol ester patterns of mature whole wheat kernels, has been found to be restricted to the endosperm and not to affect the embryo, the pericarp or the seed coat. 2. 2. The dominant allele Pln, which determines a sterol ester pattern with palmitate as the main ester, is also responsible for a low level of free sterol at maturity. A high level of free sterol is associated with the recessive allele pln, which determines an ester pattern with linoleate as the main ester. 3. 3. Divergence between the two phenotypes starts at about 21 days after anthesis, when cell proliferation has been completed, the aleurone layer has differentiated, and only cell enlargement is taking place. A marked increase in esterification, mainly by palmitate, which is controlled by the dominant allele, is concomitant with a sharp decrease in free sterol. 4. 4. The increased net esterification is non-specific with respect to 4-demethyl sterols, because it affects the four main ones, namely sitosterol, stigmasterol, campesterol and cholester

A CRISPR-Cas9 sex-ratio distortion system for genetic control.

Genetic control aims to reduce the ability of insect pest populations to cause harm via the release of modified insects. One strategy is to bias the reproductive sex ratio towards males so that a population decreases in size or is eliminated altogether due to a lack of females. We have shown previously that sex ratio distortion can be generated synthetically in the main human malaria vector Anopheles gambiae, by selectively destroying the X-chromosome during spermatogenesis, through the activity of a naturally-occurring endonuclease that targets a repetitive rDNA sequence highly-conserved in a wide range of organisms. Here we describe a CRISPR-Cas9 sex distortion system that targets ribosomal sequences restricted to the member species of the Anopheles gambiae complex. Expression of Cas9 during spermatogenesis resulted in RNA-guided shredding of the X-chromosome during male meiosis and produced extreme male bias among progeny in the absence of any significant reduction in fertility. The flexibility of CRISPR-Cas9 combined with the availability of genomic data for a range of insects renders this strategy broadly applicable for the species-specific control of any pest or vector species with an XY sex-determination system by targeting sequences exclusive to the female sex chromosome

Importance of space and competition in optimizing genetic control strategies.

Advances in the genetic modification of organisms are creating new opportunities for the control of insect pests of both agriculture and public health significance. The timing and sex specificity of lethal transgene activation can be tailored to enhance the pest population control efficiency of mass-released, genetically modified insects. We developed mathematical models to determine the optimal timing and sex specificity of lethal transgene activation for the control of different types of pest population. We show that optimal release strategies are not only sensitive to the parameters governing growth of the population but also can be drastically affected by the inclusion of insect stage structuring, competition, and space. We emphasize the necessity of including these additional levels of complexity in future theoretical assessments as they are likely important considerations for designing transgenic organisms as well as their application in genetic control

Genetic control of purothionins in wheat: problems of the aneuploid analysis when searching for regulatory genes

The study of the genetic control of purothionins in wheat endosperm illustrates some of the problems and pitfalls faced in aneuploid analysis of regulatory effects. Biochemical and genetic evidence is presented indicating that the possible regulatory effect of genes located in group 5 chromosomes on the expression of the purothionin structural genes located in group 1 chromosomes is not actually operating "in vivo"