Journal of Genetics and Genomics

Genomic Imprinting—The Story of the Other Half and the Conflicts of Silencing

Anjana Munshi, Shanti Duvvuri

2007, 34(2): 93-103. doi: 10.1016/S1673-8527(07)60010-1

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Abstract:
Genomic imprinting is an epigenetic mechanism that produces functional differences between the paternal and maternal genomes and plays an essential role in mammalian development and growth. There are a number of genes in our genomes that are subject to genomic imprinting where one parent's copy of the gene is expressed while the other is silent. Silencing of one allele predetermines that any function ascribed to that gene are now dependant on the single active copy. Possession of only a single active allele can lead to deleterious health consequences in humans. If imprinted genes are crucial in mammalian development, one would also expect mutations in these genes to cause diseases. Since imprinting is an epigenetic mechanism, mistakes in maintaining epigenetic mark also cause imprinting disorders. Here we in this review focus on the current understanding of this unique genetic mechanism more than two decades after the first description of theimprinting phenomenon was given by McGrath and Solter. Although the possible molecular mechanisms by which imprinting is imposed and maintained are being identified, we have a long way to go in understanding the molecular mechanisms that regulate the expression of these oddly behaving genes, the function of imprinting and the evolution. Post genomic technologies might ultimately lead to a better understanding of the ‘imprinting effects’.

Characterization of the Full-length cDNA, Chromosomal Localization, and Polymorphism of the Porcine RPLP0 Gene

Xiao Wu, Shulin Yang, Zhengmao Zhu, Shutang Feng, Kui Li

2007, 34(2): 104-108. doi: 10.1016/S1673-8527(07)60011-3

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RPLP0 gene encodes the acidic ribosomal phosphoprotein large P0 subunit, which is a component of the 60S subunit. The full-length cDNA sequence of porcine RPLP0 was obtained from skeletal muscle of fetal pig cDNA library and deposited in GenBank. The nucleotide sequence and the predicted protein sequence shared high sequence identity with other mammalian homologues. A C/A single nucleotide substitution in exon 5 was detected as Csp6?polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) shows allele frequency diversity among Tongcheng, Xiaomeishan, Yushan, Large White, Landrace, and Duroc breeds. Analyses of somatic cell hybrid panel (SCHP) and radiation hybrid (IMpRH) panel showed that the RPLP0 gene was mapped to SSC 14q22-q24 and was closely linked to locus SW1321 (25 cR, LOD = 14.54).

Characterization of Genetic Polymorphism of Novel MHC B-LB II Alleles in Chinese Indigenous Chickens

Rifu Xu, Kui Li, Guohong Chen, Hui Xu, Bayangzong Qiang, Changchun Li, Bang Liu

2007, 34(2): 109-118. doi: 10.1016/S1673-8527(07)60012-5

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Genetic polymorphism of the major histocompatibility complex (MHC)B-LB II gene was studied by amplification of exon 2 using PCR, followed by cloning and DNA sequencing in eight indigenous Chinese chicken populations. To reveal the genetic variation of the B-LB II gene, 37 types of patterns detected by PCR-SSCP were investigated first, which would be used to screen novel B-LB II sequences within the breeds. The types of PCR-SSCP patterns and final sequencing allowed for the identification of 31 novel MHC B-LB II alleles from 30 unrelated individuals of Chinese chickens that were sampled. These are the first designators for the alleles of chicken MHC B-LB II gene based on the rule of assignment for novel mammalian alleles. Sequence alignment of the 31 B-LB II alleles revealed a total of 68 variable sites in the fragment of exon 2, of which 51 parsimony informative and 17 singleton variable sites were observed. Among the polymorphic sites, the nucleotide substitutions in the first and second positions of the codons accounted for 36.76% and 35.29%, respectively. The sequence similarities between the alleles were estimated to be 90.6%–99.5%. The relative frequencies of synonymous and nonsynonymous nucleotide substitutions within the region were 2.92%±0.94% and 14.64%±2.67%, respectively. These results indicated that the genetic variation within exon 2 appeared to have largely arisen by gene recombination and balancing selection. Alignment of the deduced amino acid sequences of the β1 domain coded by exon 2 revealed 6 synonymous mutations and 27 nonsynonymous substitutions at the 33 disparate sites. In particular, the nonsynonymous substitutions at the putative peptide-binding sites are considered to be associated with immunological specificity of MHC B-LB II molecule in Chinese native chickens. These results can provide a molecular biological basis for the study of disease resistance in chicken breeding.

The Complete Mitochondrial Genome of Salt-water Crocodile (Crocodylus porosus) and Phylogeny of Crocodilians

Yan Li, Xiaobing Wu, Xuefeng Ji, Peng Yan, George Amato

2007, 34(2): 119-128. doi: 10.1016/S1673-8527(07)60013-7

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The nucleotide sequence of the complete mitochondrial DNA (mtDNA) molecule of the salt-water crocodile (Crocodylus porosus) was determined in this article. The molecule is 16,917 base pairs (bp) in length, and codes for 22 tRNAs, 13 protein-coding genes, 2 rRNAs, as well as a control region (D-loop), as is characteristic for mitochondrial genomes of other metazoans. The gene order conforms to that of other crocodilians sequenced, but the arrangement of some tRNA genes differs from other vertebrates. It shows that the gene order of crocodilians is remarkably conserved. In this study, the relationships among crocodilians were examined in the phylogenetic analysis based on the control conserved regions of 17 crocodilians. The results suggest that the gharial (Gavialis gangeticus) joins the false gharial (Tomistoma schlegelii) on a common branch, and then constitutes a sister group to traditional Crocodylidae. Thus, the result supports that G. gangeticus belongs to Crocodylidae. The analyses also suggest that the African slender-snouted crocodile (Crocodylus cataphractus) can be treated as an isolated genus, and constitutes a sister group to Crocodylus.

Analysis of the Conditional Correlations from Different Genetic Systems Between the Protein Content and the Appearance Quality Traits of Indica Rice

Guoke Ge, Xi Zheng, Jianguo Wu, Zihong Ye, Chunhai Shi

2007, 34(2): 129-137. doi: 10.1016/S1673-8527(07)60014-9

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A factorial mating design in two environments was conducted using 7 cytoplasmic male sterile lines (A) and 5 restorer lines (R) along with their F₁ (A × R) and F₂ populations. The unconditional and conditional analyses of genetic models and the corresponding statistic methods, including endospermic, cytoplasmic, and maternal plant genetic systems, were used to analyze the genetic relationships between protein content (PC) and the appearance quality traits of indica rice (Oryza sativa L.). The results from unconditional analysis indicated that PC was significantly correlated with the appearance quality traits of rice, except for the brown rice thickness (BRT). Only the genetic covariance between PC and the brown rice width (BRW) was positively correlative, whereas all the other pairwise traits were negatively correlative. The results from conditional analysis revealed that the weight of brown rice (WBR) or the amylose content (AC) could significantly affect the relationships between PC and the appearance quality traits of indica rice. The conditional analysis showed that WBR might negatively affect the relationships between PC and the brown rice length (BRL), BRW, or BRT through the genotype × environmental (GE) interaction effects, but positively affected the relationships between PC and the ratio of brown rice length to width (RLW) or the ratio of brown rice length to thickness (RLT). The amylase content could positively affect the relationships between PC and BRL, RLW, RLT through the cytoplasmic effects and maternal additive effects, but negatively affected the relationships between PC and BRW.

Chitinases in Oryza sativa ssp. japonica and Arabidopsis thaliana

Fenghua Xu, Chengming Fan, Yueqiu He

2007, 34(2): 138-150. doi: 10.1016/S1673-8527(07)60015-0

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Chitinases (EC3.2.1.14), found in a wide range of organisms, catalyze the hydrolysis of chitin and play a major role in defense mechanisms against fungal pathogens. The alignment and typical domains were analyzed using basic local alignment search tool (BLAST) and simple modular architecture research tool (SMART), respectively. On the basis of the annotations of rice (Oryza sativa L.) and Arabidopsis genomic sequences and using the bio-software SignalP3.0, TMHMM2.0, TargetP1.1, and big-Pi Predictor, 25 out of 37 and 16 out of 24 open reading frames (ORFs) with chitinase activity from rice and Arabidopsis, respectively, were predicted to have signal peptides (SPs), which have an average of 24.8 amino acids at the N-terminal region. Some of the chitinases were secreted extracellularly, whereas some were located in the vacuole. The phylogenic relationship was analyzed with 61 ORFs and 25 known chitinases and they were classified into 6 clusters using Clustal X and MEGA3.1. This classification is not completely consistent when compared with the traditional system that classifies the chitinases into 7 classes. The frequency of distribution of amino acid residues was distinct in different clusters. The contents of alanine, glycine, serine, and leucine were very high in each cluster, whereas the contents of methionine, histidine, tryptophan, and cysteine were lower than 20%. Each cluster had distinct amino acid characteristics. Alanine, valine, leucine, cysteine, serine, and lysine were rich in Clusters I to VI, respectively.

Molecular Characterization of Cotton 14-3-3L Gene Preferentially Expressed During Fiber Elongation

Haiyan Shi, Xiulan Wang, Dengdi Li, Wenkai Tang, Hong Wang, Wenliang Xu, Xuebao Li

2007, 34(2): 151-159. doi: 10.1016/S1673-8527(07)60016-2

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The 14-3-3 protein, highly conserved in all eukaryotic cells, is an important regulatory protein. It plays an important role in the growth, amplification, apoptosis, signal transduction, and other crucial life activities of cells. A cDNA encoding a putative 14-3-3 protein was isolated from cotton fiber cDNA library. The cDNA, designated as Gh14-3-3L (Gossypium hirsutum 14-3-3-like), is 1,029 bp in length (including a 762 bp long open reading frame and 5′-/3′-untranslated regions) and deduced a protein with 253 amino acids. The Gh14-3-3L shares higher homology with the known plant 14-3-3 proteins, and possesses the basic structure of 14-3-3 proteins: one dimeric domain, one phosphoralated-serine rich motif, four CC domains, and one EF Hand motif. Northern blotting analysis showed thatGh14-3-3L was predominantly expressed during early fiber development, and reached to the peak of expression in 10 days post anthers (DPA) fiber cells, suggesting that the gene may be involved in regulating fiber elongation. The gene is also expressed at higher level in both ovule and petal, but displays lower or undetectable level of activity in other tissues of cotton.

Genetic Diversity of Volatile Components in Xinjiang Wild Apple (Malus sieversii)

Xuesen Chen, Tao Feng, Yanmin Zhang, Tianming He, Jianrong Feng, Chunyu Zhang

2007, 34(2): 171-179. doi: 10.1016/S1673-8527(07)60018-6

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To evaluate genetic relationships using qualitative and/or quantitative differentiation of volatile components in Xinjiang Wild Apple (Malus sieversii (Lebed.) Roem.) and to acquire basic data for the conservation and utilization of the species, aroma components in ripe fruit of M. sieversii obtained from 30 seedlings at Mohe, Gongliu County, Xinjiang Autonomic Region, China, and in ripe fruit of 4 M. pumila cultivars (‘Ralls’, ‘Delicious’, ‘Golden Delicious’, and ‘Fuji’) were analyzed using head space-solid phase microextraction and gas chromatography-mass spectrometry. The results indicated that the values of similarity coefficient concerning volatile types between the two species were in accordance with the evolution of M. pumila cultivars (forms), and that M. sieversii seedlings showed considerable genetic variations in these aspects: the total content of volatile components, the classes and contents of each compound classes, the segregation ratio, and content of main components. The results showed significant difference among seedlings and wide genetic diversity within the populations. Comparison of the volatile components in M. sieversii with those in M. pumila cultivars showed that the common compounds whose number were larger than five with the contents over 0.04 mg/L simultaneously between M. sieversii and M. pumila cultivars belonged to esters, alcohols, aldehydes or ketones. This suggests fundamental identity in main volatile components of M. sieversii and M. pumila cultivars. The results above sustained the conclusion “M. sieversii is probably the ancestor of M. pumila”. However, there were 48 compounds present in M. pumila that were not detected in M. sieversii, including 6 character impact components (i.e., propyl acetate, (Z)-3-hexenal, 2-methyl-1-butanol acetate, pentyl acetate, 3-furanmethanol, and benzene acetaldehyde). This suggested that in the domestication of M. pumila, introgression of other apple species, except for M. sieversii, by interspecies hybridization was possible. There were 177 compounds in total belonging to 11 classes detected in 30 M. sieversii seedlings, including esters, alcohols, ketones, aldehydes, acids, benzene ramifications, terpenes, heterocycles, hydrocarbon derivates, acetals, and lactones. Among them, acetals and lactones were not detected in M. pumila cultivars, 90 compounds were unique to M. sieversii, and 7 components (1-butanol, ethyl butanoate, 1-hexanol, ethyl hexanoate, 3-octen-1-ol, ethyl octanoate, and damascenone) belonged to character impact odors. Thus, the potential of M. sieversii in “utilization conservation” is enormous as a rare germplasm on genetic improvement of M. pumila cultivars.

Phylogenetic Analysis of the Sequences of rDNA Internal Transcribed Spacer (ITS) of Phytophthora sojae

Pengfei Xu, Yingpeng Han, Junjiang Wu, Huiying Lv, Lijuan Qiu, Ruzhen Chang, Limei Jin, Jinsheng Wang, Anliang Yu, Chen Chen, Haiyang Nan, Xiuhong Xu, Ping Wang, Dayong Zhang, Shuzhen Zhang, Wenbin Li, Weiyuan Chen

2007, 34(2): 180-188. doi: 10.1016/S1673-8527(07)60019-8

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The internal transcribed spacer (ITS) region (ITS1, ITS2 and 5.8S rDNA) of the nuclear ribosomal DNA (nrDNA) was amplified via the PCR method in seventeen different isolates ofPhytophthora sojae using the common primers of the ITS of fungi. Around 800 bp-1,000 bp fragments were obtained based on the DL2000 marker and the sequences of the PCR products were tested. Taking isolate USA as outgroup, the phylogenetic tree was constructed by means of maximum parsimony analysis, and the genetic evolution among isolates was analyzed. The results showed that there is a great difference between the base constitution of ITS1 and ITS2 among various isolates. The seventeen isolates are classified into three groups, and the isolates from the same region belong to the same group, which shows the variation in geography.

Relationship Between Differential Gene Expression and Heterosis During Ear Development in Maize (Zea mays L.)

Xinjun Wang, Haihe Cao, Dengfeng Zhang, Bo Li, Yan He, Jiansheng Li, Shoucai Wang

2007, 34(2): 160-170. doi: 10.1016/S1673-8527(07)60017-4

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Maize (Zea mays L.) is one of the most important crops because of the remarkable properties of its hybrid, which is responsible for the high commercial value of hybrid maize. The genetic basis of heterosis (hybrid vigor) is not well understood. A differential display technique was performed to identify genes with differential expression across twelve maize inbred lines and thirty-three hybrids during ear development. An incomplete diallel design was used to investigate the relationship between the global framework of differential gene expression and heterosis. It was found that the genes belonging to MONO pattern (i.e., genes expressed in both parental lines and in hybrid) was the highest in percentage among the total five patterns and illustrated that the properties of differentially expressed genes are not entirely responsible for heterosis. Furthermore, a larger number of differentially expressed genes in hybrid, which serves as a major reservoir for generating novel phenotypes that exhibit heterosis of certain agronomic traits during early development and differentiation of maize ear. Moreover, there were some silent genesin hybrids that are responsible for the arrest or abortion of spikelets and for the increase in kernels weight.

2007 Vol. 34, No. 2