Epigenetics in insects

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Epigenetics in insects is the role that epigenetics (hertiable characteristics that do not involve changes in DNA sequence) plays in insects.

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Epigenetic mechanisms are regulatory mechanisms, which change expression levels of genes. Several mechanisms are considered epigenetic, including DNA methylation, histone modifications and non-coding RNAs. Epigenetic mechanisms play a role in processes like development, learning and memory formation, aging, diseases, cell differentiation and genome defence.

DNA methylation

DNA methylation is an epigenetic mechanism. It is a chemical modification of the DNA where a methyl group is attached to cytosine. This modification is set by DNA methyltransferases (Dnmts). There are three known types of DNA methyltransferases in mammals. Those DNA methyltransferases are present in insects as well, although it varies between different species which specific Dnmt types are present. It still is a matter of discussion what the specific role of DNA methylation in insects is, as some insects such as Drosophila melanogaster just have traces of DNA methylation in their genome and in general insect genomes are much less methylated compared to mammalian genomes (0.034% vs. 7.6% in Mus musculus). [1] In a comparison of different insect species and their respective methylation levels, there was a clear relationship between cell turn over and DNA methylation, but not between genome size or the number of repetitive sequences and DNA methylation.

In honeybees

Honeybees (Apis mellifera) marked after hatching with colour Honeybees (Apis mellifera) marked after hatching with colour.jpg
Honeybees (Apis mellifera) marked after hatching with colour

Honeybees ( Apis mellifera ) possess homologs for all three DNA methyltransferases known in mammals. [2] [3] But unlike mammals they possess two DNA methyltransferases 1 and just one DNA methyltransferase 3. DNA methylation predominantly occurs in coding regions in honeybees. [4] The function of the DNA methylation in honey bees is to regulate gene alternative splicing [5]

Development

DNA methylation plays a major role in honeybee caste and subcaste development. In honeybees there are two different castes which are workers and queens. They are genetically the same, but show morphological, physiological and behavioral differences. Among the worker caste there are two subcastes, which are nurses and foragers. Which subcaste a worker bee belongs to depends on its age. The DNA methylation pattern in queens and workers, [4] [6] [7] and between nurses and foragers is different. [8] [9] DNA methylation also increases in worker larvae with age, especially in coding regions and CpG islands. If DNA methyltransferase 3 is silenced in honeybee larvae they develop into queens, whereas they otherwise would develop into workers. [10]

Associative learning

Using the DNA methyltransferase inhibitor zebularine, the role of DNA methyltransferases during learning and memory formation has been studied. If DNA methyltransferases are inhibited during an associative learning paradigm, in which the bee is trained to associate an odour with a food reward, the odour specific associative long-term memory of bees is impaired, [11] as well as their extinction memory. [12] Short-term memory formation and acquisition are not affected by DNA methyltransferase inhibition.

In fruitflies

The fruitfly D. melanogaster possess just one DNA methyltransferase, which is Dnmt 2-like. Dnmt 2 is not known to methylate DNA in mammals. In Drosophila however a knock down of Dnmt 2-like protein is sufficient to deplete DNA methylation completely and an overexpression of Dnmt 2 causes hypermethylation of the DNA. [13] However, lines deficient for Dnmt 2 retain genomic methylation, implying the presence of a novel methyltransferase. [14]

Related Research Articles

<span class="mw-page-title-main">Epigenetics</span> Study of DNA modifications that do not change its sequence

In biology, epigenetics are stable heritable traits that cannot be explained by changes in DNA sequence, and the study of a type of stable change in cell function that does not involve a change to the DNA sequence. The Greek prefix epi- in epigenetics implies features that are "on top of" or "in addition to" the traditional genetic mechanism of inheritance. Epigenetics usually involves a change that is not erased by cell division, and affects the regulation of gene expression. Such effects on cellular and physiological phenotypic traits may result from environmental factors, or be part of normal development. They can lead to cancer.

Methylation, in the chemical sciences, is the addition of a methyl group on a substrate, or the substitution of an atom by a methyl group. Methylation is a form of alkylation, with a methyl group replacing a hydrogen atom. These terms are commonly used in chemistry, biochemistry, soil science, and biology.

<span class="mw-page-title-main">5-Methylcytosine</span> Chemical compound which is a modified DNA base

5-Methylcytosine is a methylated form of the DNA base cytosine (C) that regulates gene transcription and takes several other biological roles. When cytosine is methylated, the DNA maintains the same sequence, but the expression of methylated genes can be altered. 5-Methylcytosine is incorporated in the nucleoside 5-methylcytidine.

<span class="mw-page-title-main">Alternative splicing</span> Process by which a gene can code for multiple proteins

Alternative splicing, or alternative RNA splicing, or differential splicing, is an alternative splicing process during gene expression that allows a single gene to code for multiple proteins. In this process, particular exons of a gene may be included within or excluded from the final, processed messenger RNA (mRNA) produced from that gene. This means the exons are joined in different combinations, leading to different (alternative) mRNA strands. Consequently, the proteins translated from alternatively spliced mRNAs usually contain differences in their amino acid sequence and, often, in their biological functions.

<span class="mw-page-title-main">DNA methyltransferase</span> Class of enzymes

In biochemistry, the DNA methyltransferase family of enzymes catalyze the transfer of a methyl group to DNA. DNA methylation serves a wide variety of biological functions. All the known DNA methyltransferases use S-adenosyl methionine (SAM) as the methyl donor.

<span class="mw-page-title-main">Royal jelly</span> Secretion from the glands of nurse bees

Royal jelly is a honey bee secretion that is used in the nutrition of larvae and adult queens. It is secreted from the glands in the hypopharynx of nurse bees, and fed to all larvae in the colony, regardless of sex or caste.

<span class="mw-page-title-main">DNA methylation</span> Biological process

DNA methylation is a biological process by which methyl groups are added to the DNA molecule. Methylation can change the activity of a DNA segment without changing the sequence. When located in a gene promoter, DNA methylation typically acts to repress gene transcription. In mammals, DNA methylation is essential for normal development and is associated with a number of key processes including genomic imprinting, X-chromosome inactivation, repression of transposable elements, aging, and carcinogenesis.

<span class="mw-page-title-main">DNA (cytosine-5)-methyltransferase 3A</span> Protein-coding gene in the species Homo sapiens

DNA (cytosine-5)-methyltransferase 3A (DNMT3A) is an enzyme that catalyzes the transfer of methyl groups to specific CpG structures in DNA, a process called DNA methylation. The enzyme is encoded in humans by the DNMT3A gene.

<span class="mw-page-title-main">Western honey bee</span> European honey bee

The western honey bee or European honey bee is the most common of the 7–12 species of honey bees worldwide. The genus name Apis is Latin for "bee", and mellifera is the Latin for "honey-bearing" or "honey carrying", referring to the species' production of honey.

The genetics of social behavior is an area of research that attempts to address the question of the role that genes play in modulating the neural circuits in the brain which influence social behavior. Model genetic species, such as D.melanogaster and Apis mellifera, have been rigorously studied and proven to be instrumental in developing the science of genetics. Many examples of genetic factors of social behavior have been derived from a bottom-up method of altering a gene and observing the change it produces in an organism. Sociogenomics is an integrated field that accounts for the complete cellular genetic complement of an organism from a top-down approach, accounting for all biotic influences that effect behavior on a cellular level.

While the cellular and molecular mechanisms of learning and memory have long been a central focus of neuroscience, it is only in recent years that attention has turned to the epigenetic mechanisms behind the dynamic changes in gene transcription responsible for memory formation and maintenance. Epigenetic gene regulation often involves the physical marking of DNA or associated proteins to cause or allow long-lasting changes in gene activity. Epigenetic mechanisms such as DNA methylation and histone modifications have been shown to play an important role in learning and memory.

Behavioral epigenetics is the field of study examining the role of epigenetics in shaping animal and human behavior. It seeks to explain how nurture shapes nature, where nature refers to biological heredity and nurture refers to virtually everything that occurs during the life-span. Behavioral epigenetics attempts to provide a framework for understanding how the expression of genes is influenced by experiences and the environment to produce individual differences in behaviour, cognition, personality, and mental health.

<span class="mw-page-title-main">Major royal jelly protein</span> Family of proteins secreted by honey bees

Major royal jelly proteins (MRJPs) are a family of proteins secreted by honey bees. The family consists of nine proteins, of which MRJP1, MRJP2, MRJP3, MRJP4, and MRJP5 are present in the royal jelly secreted by worker bees. MRJP1 is the most abundant, and largest in volume. The five proteins constitute 82–90% of the total proteins in royal jelly. Royal jelly is a nutrient-rich mixture of vitamins, sugars, fats, proteins, and enzymes. It is used for feeding larvae. Royal jelly has been used in traditional medicine since ancient times, and the MRJPs are shown to be the main medicinal components. They are synthesised by a family of nine genes, which are in turn members of the yellow family of genes, such as in the fruitfly (Drosophila) and bacteria. They are involved in the differential development of queen larva and worker larvae, thus establishing division of labour in the bee colony.

H3K4me1 is an epigenetic modification to the DNA packaging protein Histone H3. It is a mark that indicates the mono-methylation at the 4th lysine residue of the histone H3 protein and often associated with gene enhancers.

H3K14ac is an epigenetic modification to the DNA packaging protein Histone H3. It is a mark that indicates the acetylation at the 14th lysine residue of the histone H3 protein.

H3K36me is an epigenetic modification to the DNA packaging protein Histone H3, specifically, the mono-methylation at the 36th lysine residue of the histone H3 protein.

Commensalibacter is a genus of Gram-negative, aerobic and rod-shaped bacteria from the family of Acetobacteraceae which was originally isolated from Drosophila melanogaster. The complete genome of the type strain C. intestini A911T has been sequenced.

H3R17me2 is an epigenetic modification to the DNA packaging protein histone H3. It is a mark that indicates the di-methylation at the 17th arginine residue of the histone H3 protein. In epigenetics, arginine methylation of histones H3 and H4 is associated with a more accessible chromatin structure and thus higher levels of transcription. The existence of arginine demethylases that could reverse arginine methylation is controversial.

Juvenile hormone acid O-methyltransferase (JHAMT) is a ~33 kDa enzyme that catalyzes the conversion of inactive precursors of Juvenile hormones (JHs) to active JHs in the final stages of JH biosynthesis in the corpora allata of insects. More specifically, the enzyme catalyzes the transfer of a methyl group from S-adenosyl-L-methionine (SAM) to the carboxylate group of JH precursors.

H3R8me2 is an epigenetic modification to the DNA packaging protein histone H3. It is a mark that indicates the di-methylation at the 8th arginine residue of the histone H3 protein. In epigenetics, arginine methylation of histones H3 and H4 is associated with a more accessible chromatin structure and thus higher levels of transcription. The existence of arginine demethylases that could reverse arginine methylation is controversial.

References

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