Cellular interactions and genetic restriction

These studies emphasize the limitations of in vitro colony assays utilizing heterogeneous cell populations for the identification of cell-cell interactions that may involve genetic restriction. Obviously, different strategies are required to determine if Class II molecules have any role, alone or in combination with other determinants, in mediating hematopoietic cell-cell interactions. In this report, we present preliminary data derived from two approaches designed to address this issue. First, clonal cell lines developed to mimic Class II expression of normal precursors have been used to study structure-function relationships of HLA-D region gene products. Second, the lymphocyte adhesion assay has been adopted to study binding of precursors to marrow stroma. We hypothesize that the strategies should make it possible to identify hematopoietic cell-cell interactions and determine to what extent Class II molecules participate in these interactions.     

The genetic basis of cardiac function: dissection by zebrafish (Danio rerio) screens

The vertebrate heart differs from chordate ancestors both structurally and functionally. Genetic units of form, termed 'modules', are identifiable by mutation, both in zebrafish and mouse, and correspond to features recently acquired in evolution, such as the ventricular chamber or endothelial lining of the vessels and heart. Zebrafish (Danio rerio) genetic screens have provided a reasonably inclusive set of such genes. Normal cardiac function may also be disrupted by single-gene mutations in zebrafish. Individual mutations may perturb contractility or rhythm generation. The zebrafish mutations which principally disturb cardiac contractility fall into two broad phenotypic categories, 'dilated' and 'hypertrophic'. Interestingly, these correspond to the two primary types of heart failure in humans. These disorders of early cardiac function provide candidate genes to be examined in complex human heart diseases, including arrhythmias and heart failure.     

Cellular bases of behavioral plasticity: establishing and modifying synaptic circuits in the Drosophila genetic system

Genetic malleability and amenability to behavioral assays make Drosophila an attractive model for dissecting the molecular mechanisms of complex behaviors, such as learning and memory. At a cellular level, Drosophila has contributed a wealth of information on the mechanisms regulating membrane excitability and synapse formation, function, and plasticity. Until recently, however, these studies have relied almost exclusively on analyses of the peripheral neuromuscular junction, with a smaller body of work on neurons grown in primary culture. These experimental systems are, by themselves, clearly inadequate for assessing neuronal function at the many levels necessary for an understanding of behavioral regulation. The pressing need is for access to physiologically relevant neuronal circuits as they develop and are modified throughout life. In the past few years, progress has been made in developing experimental approaches to examine functional properties of identified populations of Drosophila central neurons, both in cell culture and in vivo. This review focuses on these exciting developments, which promise to rapidly expand the frontiers of functional cellular neurobiology studies in Drosophila. We discuss here the technical advances that have begun to reveal the excitability and synaptic transmission properties of central neurons in flies, and discuss how these studies promise to substantially increase our understanding of neuronal mechanisms underlying behavioral plasticity.     

The emerging genetic landscape underlying cardiac conduction system function

Proper function of an organized Cardiac Conduction System (CCS) is vital to the survival of metazoans ranging from fly to man. The routine use of non-invasive electrocardiogram measures in the diagnosis and monitoring of cardiovascular health has established a trove of reliable CCS functional data in both normal and diseased cardiac states. Recent combination of echocardiogram (ECG) data with genome-wide association studies has identified genomic regions implicated in ECG variability which impact CCS function. In this study, we review the substantial recent progress in this area, highlighting the identification of novel loci, confirming the importance of previously implicated loci in CCS function, and exploring potential links between genes with important roles in developmental processes and variation in function of the CCS.     

The genetic dissection of essential hypertension

QTL mapping in humans and rats has identified hundreds of blood-pressure-related phenotypes and genomic regions; the next daunting task is gene identification and validation. The development of novel rat model systems that mimic many elements of the human disease, coupled with advances in the genomic and informatic infrastructure for rats, promise to revolutionize the hunt for genes that determine susceptibility to hypertension. Furthermore, methods are evolving that should enable the identification of candidate genes in human populations. Together with the computational reconstruction of regulatory networks, these methods provide opportunities to significantly advance our understanding of the underlying aetiology of hypertension.     

The central complex and the genetic dissection of locomotor behaviour

The central complex is one of the most prominent, yet functionally enigmatic structures of the insect brain. Recently, behavioural, neuroanatomical and molecular approaches in Drosophila have joined forces to disclose specific components of higher locomotion control in larvae and adult flies, such as those that guarantee the optimal length and across-body symmetry of strides and an appropriate activity.     

A genetic dissection of the LlaJI restriction cassette reveals insights on a novel bacteriophage resistance system

Background  

Restriction/modification systems provide the dual function of protecting host DNA against restriction by methylation of appropriate bases within their recognition sequences, and restriction of foreign invading un-methylated DNA, such as promiscuous plasmids or infecting bacteriphage. The plasmid-encoded LlaJI restriction/modification system from Lactococcus lactis recognizes an asymmetric, complementary DNA sequence, consisting of 5'GACGC'3 in one strand and 5'GCGTC'3 in the other and provides a prodigious barrier to bacteriophage infection. LlaJI is comprised of four similarly oriented genes, encoding two 5mC-MTases (M1.LlaJI and M2.LlaJI) and two subunits responsible for restriction activity (R1.LlaJI and R2.LlaJI). Here we employ a detailed genetic analysis of the LlaJI restriction determinants in an attempt to characterize mechanistic features of this unusual hetero-oligomeric endonuclease.     

Complexities in the genetic dissection of quantitative trait loci

The analysis of complex traits, including those involved in many common diseases, has encountered significant difficulties, and, despite major efforts during the past decade, has had little success. Current advances in genomics, however, promise to change this. Recently, Steinmetz et al. used a new technique to produce the first complete quantitative trait locus (QTL) analysis of a complex trait from phenotype to gene to be published entirely in a single report. This marks a significant advance over previous QTL analyses, which took several years. The work exemplifies some of the complexities of QTL mapping and demonstrates a novel method to resolve the underlying genetic architecture of QTLs in yeast. Here we discuss this work in the general context of genetic dissection of complex traits and QTLs.     

Cellular spinning in pulsed rotating electric fields

Living cells, dead cells, and other particles suspended in aqueous media of low conductivity can be easily caused to spin if a rotating electrical field is applied. The background and theory are presented for the use of three-electrode systems provided with seriate square electrical pulses to spin cells.     

Cellular spin resonance in rotating electric fields

Cells and certain other electrically polarizable objects can be seen to spin when in a rotating electric field. When a rotating field (from four Pt electrodes) is applied over a frequency range of 500 to 75,000 Hz, living cells exhibit two or three response peaks, whereas dead cells exhibit only one response peak. Yeast (Saccharomyces cerevisiae) exhibit two peaks. The nature of these cellular spin resonances is under active study.     

Position-effect variegation and the genetic dissection of chromatin regulation in Drosophila

In position-effect variegation (PEV) genes become silenced by heterochromatisation. Genetic dissection of this process has been performed by means of dominant suppressor [Su(var)] and enhancer [E(var)] mutations. Selective genetic screens allowed mass isolation of more than 380 PEV modifier mutations identifying about 150 genes. Genetic fine structure studies revealed unique dosage dependent effects. Most of the haplo-dependent Su(var) and E(var) genes do not display triplo-dependent effects. Several Su(var) loci with triplo-dependent opposite enhancer effects have been identified and shown to encode heterochromatin-associated proteins. From these the evolutionary conserved histone H3 lysine 9 methyltransferase SU(VAR)3-9 plays a central role in heterochromatic gene silencing. Molecular function of most PEV modifier genes is still unknown also including genes identified with mutations displaying lethal interaction to heterochromatin. Their analysis should contribute to further understanding of processes connected with regulation of higher order chromatin structure and epigenetic programming.     

The genetic dissection of floral pollination syndromes

A major factor in the evolution of the angiosperms is the adaptation of plants to animal pollinators. The specific morphology of a flower, its color, nectar composition and scent production can all contribute to reproductive success by attracting pollinators and by limiting out-crossing with other species. It has now become feasible to dissect the genetic basis of plant adaptation to different pollinators.