Hmga1 is required for normal sperm development

The Hmgi protein family of chromosomal architectural factors is extensively studied for its roles in embryogenesis and its association with benign mesenchymal tumors. Although the biochemical function of Hmga1 has been studied in vitro, to provide in vivo insight into its biological function, a targeted disruption of Hmga1 was initiated. Chimeric founder mice were derived from embryonic stem (ES) cells harboring a targeted mutation in a single Hmga1 allele. These 14 different chimeric founders produced 494 black progeny. Since none of these 494 progeny were agouti, none of them were derived from ES cells. Control injections of the wild-type ES cell lines resulted in ES cell derived agouti mice, indicating that the ES cells were totipotent. Therefore, our results indicate that one intact Hmga1 allele was not sufficient for germ-line transmission of the ES cells. Seven chimeric founder mice that were examined histologically demonstrated aberrant regions in their reproductive organs. Aberrant regions of seminiferous tubules were reduced in diameter, demonstrated vacuolated Sertoli cells, and had an absolute deficiency of sperm. While the Hmga1(+/-) ES cells were shown to contribute to the formation of the epididymides, they did not significantly contribute to the testes of chimeric founder mice. No sperm isolated from any of the Hmga1(+/-) chimeric mice were shown to arise from the ES cells, as none of them contained the targeted disruption of the Hmga1 gene. Our results suggest that both alleles of Hmga1 are required for normal sperm production in the mouse.     

BRCA1-hapoinsufficiency: Unraveling the molecular and cellular basis for tissue-specific cancer

Over the past 20 years tremendous progress has been made in understanding the function of BRCA1 gene products. Yet one question still remains: why is mutation of BRCA1 typically associated with preferential development of breast and ovarian cancers and not tumors in other tissues? Here we discuss recent evidence documenting the effect of BRCA1-haploinsufficiency in different cells and tissues and synthesize a model for how mutations in a single BRCA1 allele in human cells might preferentially confer increased cancer risk in breast epithelial cells.     

Causes and effects of haploinsufficiency

Haploinsufficiency is a form of genetic dominance and is the underlying mechanism of numerous human inherited conditions in which the causal genes are sensitive to altered dosage. This review examines the poorly understood relationships between haploinsufficiency, dosage sensitivity and genetic dominance, whose common theme is the existence of nonlinear relationships between genotype and phenotype. We present an up‐to‐date account of the bases of haploinsufficiency from the perspective of theoretical and experimental models. We also discuss human conditions caused by haploinsufficiency, including developmental syndromes and cancer. Connections between the understanding of these conditions' genetic mechanisms and advances in treatments are also described.     

A genome–wide screen to identify genes controlling the rate of entry into mitosis in fission yeast

We have carried out a haploinsufficiency (HI) screen in fission yeast using heterozygous deletion diploid mutants of a genome-wide set of cell cycle genes to identify genes encoding products whose level determines the rate of progression through the cell cycle. Cell size at division was used as a measure of advancement or delay of the G2-M transition of rod-shaped fission yeast cells. We found that 13 mutants were significantly longer or shorter (greater than 10%) than control cells at cell division. These included mutants of the cdc2, cdc25, wee1 and pom1 genes, which have previously been shown to play a role in the timing of entry into mitosis, and which validate this approach. Seven of these genes are involved in regulation of the G2-M transition, 5 for nuclear transport and one for nucleotide metabolism. In addition we identified 4 more genes that were 8–10% longer or shorter than the control that also had roles in regulation of the G2-M transition or in nuclear transport. The genes identified here are all conserved in human cells, suggesting that this dataset will be useful as a basis for further studies to identify rate-limiting steps for progression through the cell cycle in other eukaryotes.     

Prevalent mutations in prostate cancer

Quantitative and structural genetic alterations cause the development and progression of prostate cancer. A number of genes have been implicated in prostate cancer by genetic alterations and functional consequences of the genetic alterations. These include the ELAC2 (HPC2), MSR1, and RNASEL (HPC1) genes that have germline mutations in familial prostate cancer; AR, ATBF1, EPHB2 (ERK), KLF6, mitochondria DNA, p53, PTEN, and RAS that have somatic mutations in sporadic prostate cancer; AR, BRCA1, BRCA2, CHEK2 (RAD53), CYP17, CYP1B1, CYP3A4, GSTM1, GSTP1, GSTT1, PON1, SRD5A2, and VDR that have germline genetic variants associated with either hereditary and/or sporadic prostate cancer; and ANXA7 (ANX7), KLF5, NKX3-1 (NKX3.1), CDKN1B (p27), and MYC that have genomic copy number changes affecting gene function. More genes relevant to prostate cancer remain to be identified in each of these gene groups. For the genes that have been identified, most need additional genetic, functional, and/or biochemical examination. Identification and characterization of these genes will be a key step for improving the detection and treatment of prostate cancer.     

Toward a complete Drosophila deficiency kit

Targeted chromosome engineering has facilitated the development of new deletions that now cover virtually the entire genome of Drosophila, providing greater precision and resolution.     

Upregulation of SYNGAP1 expression in mice and human neurons by redirecting alternative splicing

1. Download : Download high-res image (185KB)
2. Download : Download full-size image

     

Progranulin haploinsufficiency causes biphasic social dominance abnormalities in the tube test

Loss‐of‐function mutations in progranulin (GRN) are a major autosomal dominant cause of frontotemporal dementia (FTD), a neurodegenerative disorder in which social behavior is disrupted. Progranulin‐insufficient mice, both Grn^+/? and Grn ^?/? , are used as models of FTD due to GRN mutations, with Grn^+/? mice mimicking the progranulin haploinsufficiency of FTD patients with GRN mutations. Grn^+/? mice have increased social dominance in the tube test at 6 months of age, although this phenotype has not been reported in Grn ^?/? mice. In this study, we investigated how the tube test phenotype of progranulin‐insufficient mice changes with age, determined its robustness under several testing conditions, and explored the associated cellular mechanisms. We observed biphasic social dominance abnormalities in Grn^+/? mice: at 6–8 months, Grn^+/? mice were more dominant than wild‐type littermates, while after 9 months of age, Grn^+/? mice were less dominant. In contrast, Grn ^?/? mice did not exhibit abnormal social dominance, suggesting that progranulin haploinsufficiency has distinct effects from complete progranulin deficiency. The biphasic tube test phenotype of Grn^+/? mice was associated with abnormal cellular signaling and neuronal morphology in the amygdala and prefrontal cortex. At 6–9 months, Grn^+/? mice exhibited increased mTORC2/Akt signaling in the amygdala and enhanced dendritic arbors in the basomedial amygdala, and at 9–16 months Grn^+/? mice exhibited diminished basal dendritic arbors in the prelimbic cortex. These data show a progressive change in tube test dominance in Grn^+/? mice and highlight potential underlying mechanisms by which progranulin insufficiency may disrupt social behavior.     

Chd8 haploinsufficiency impacts rearing experience in C57BL/6 mice

Mutations in CHD8 are one of the highest genetic risk factors for autism spectrum disorder. Studies in mice that investigate underlying mechanisms have shown Chd8 haploinsufficient mice display some trait disruptions that mimic clinical phenotypes, although inconsistencies have been reported in some traits across different models on the same strain background. One source of variation across studies may be the impact of Chd8 haploinsufficiency on maternal-offspring interactions. While differences in maternal care as a function of Chd8 genotype have not been studied directly, a previous study showed that pup survival was reduced when reared by Chd8 heterozygous dams compared with wild-type (WT) dams, suggesting altered maternal care as a function of Chd8 genotype. Through systematic observation of the C57BL/6 strain, we first determined the impact of Chd8 haploinsufficiency in the offspring on WT maternal care frequencies across preweaning development. We next determined the impact of maternal Chd8 haploinsufficiency on pup care. Compared with litters with all WT offspring, WT dams exhibited less frequent maternal behaviors toward litters consisting of offspring with mixed Chd8 genotypes, particularly during postnatal week 1. Dam Chd8 haploinsufficiency decreased litter survival and increased active maternal care also during postnatal week 1. Determining the impact of Chd8 haploinsufficiency on early life experiences provides an important foundation for interpreting offspring outcomes and determining mechanisms that underlie heterogeneous phenotypes.     

A cross-disorder dosage sensitivity map of the human genome

1. Download : Download high-res image (341KB)
2. Download : Download full-size image

     

Strong dominance of functional alleles over gene deletions in both intensely growing and deeply starved yeast cells

Previous studies with diploid yeast have shown that the deletion of one allele at a single locus typically has little impact on fitness under conditions promoting fast growth. Here, we confirm and quantify this finding. The strong dominance of functional over nonfunctional alleles is predicted by the metabolic control theory which assumes that the cell is a system of metabolic fluxes and that the total metabolic rate is equivalent to fitness. To test whether these requirements are critical, we tested dominance under conditions of long‐term starvation when metabolism is low and thus the metabolic activities of proteins are likely inadequate or imbalanced. More fundamentally, the central assumption of the model, that high metabolic rate translates into high fitness, appears implausible. Contrary to these conjectures, we found that the mean rate of survival of starving heterozygotes was affected only slightly more than was the mean rate of growth under good conditions. Under none of the two treatments the central prediction of the model, that fitness of heterozygous strains is higher for the enzymatic proteins than for nonenzymatic ones, was confirmed. Our data add to growing uncertainty whether the metabolic control theory is sufficient to explain the remarkable ubiquity of strong genetic dominance.     

A p53-dependent translational program directs tissue-selective phenotypes in a model of ribosomopathies

1. Download : Download high-res image (151KB)
2. Download : Download full-size image

     

Sex‐specific behavioral traits in the Brd2 mouse model of juvenile myoclonic epilepsy

Idiopathic generalized epilepsy represents about 30–35% of all epilepsies in humans. The bromodomain BRD2 gene has been repeatedly associated with the subsyndrome of juvenile myoclonic epilepsy (JME). Our previous work determined that mice haploinsufficient in Brd2 (Brd2+/?) have increased susceptibility to provoked seizures, develop spontaneous seizures and have significantly decreased gamma‐aminobutyric acid (GABA) markers in the direct basal ganglia pathway as well as in the neocortex and superior colliculus. Here, we tested male and female Brd2+/? and wild‐type littermate mice in a battery of behavioral tests (open field, tube dominance test, elevated plus maze, Morris water maze and Barnes maze) to identify whether Brd2 haploinsufficiency is associated with the human behavioral patterns, the so‐called JME personality. Brd2+/? females but not males consistently displayed decreased anxiety. Furthermore, we found a highly significant dominance trait (aggression) in the Brd2+/? mice compared with the wild type, more pronounced in females. Brd2+/? mice of either sex did not differ from wild‐type mice in spatial learning and memory tests. Compared with wild‐type littermates, we found decreased numbers of GABA neurons in the basolateral amygdala, which is consistent with the increase in aggressive behavior. Our results indicate that Brd2+/? haploinsufficient mice show no cognitive impairment but have behavioral traits similar to those found in patients with JME (recklessness, aggression). This suggests that either the BRD2 gene is directly responsible for influencing many traits of JME or it controls upstream regulators of individual phenotypes.     

Chemical genetic profiling of the microtubule-targeting agent peloruside A in budding yeast Saccharomyces cerevisiae

Peloruside A, a microtubule-stabilising agent from a New Zealand marine sponge, inhibits mammalian cell division by a similar mechanism to that of the anticancer drug paclitaxel. Wild type budding yeast Saccharomyces cerevisiae (haploid strain BY4741) showed growth sensitivity to peloruside A with an IC(50) of 35μM. Sensitivity was increased in a mad2Δ (Mitotic Arrest Deficient 2) deletion mutant (IC(50)=19μM). Mad2 is a component of the spindle-assembly checkpoint complex that delays the onset of anaphase in cells with defects in mitotic spindle assembly. Haploid mad2Δ cells were much less sensitive to paclitaxel than to peloruside A, possibly because the peloruside binding site on yeast tubulin is more similar to mammalian tubulin than the taxoid site where paclitaxel binds. In order to obtain information on the primary and secondary targets of peloruside A in yeast, a microarray analysis of yeast heterozygous and homozygous deletion mutant sets was carried out. Haploinsufficiency profiling (HIP) failed to provide hits that could be validated, but homozygous profiling (HOP) generated twelve validated genes that interact with peloruside A in cells. Five of these were particularly significant: RTS1, SAC1, MAD1, MAD2, and LSM1. In addition to its known target tubulin, based on these microarray 'hits', peloruside A was seen to interact genetically with other cell proteins involved in the cell cycle, mitosis, RNA splicing, and membrane trafficking.     

Modeling the Pathological Long-Range Regulatory Effects of Human Structural Variation with Patient-Specific hiPSCs

1. Download : Download high-res image (236KB)
2. Download : Download full-size image