The process whose specific outcome is the progression of the liver over time, from its formation to the mature structure. The liver is an exocrine gland which secretes bile and functions in metabolism of protein and carbohydrate and fat, synthesizes substances involved in the clotting of the blood, synthesizes vitamin A, detoxifies poisonous substances, stores glycogen, and breaks down worn-out erythrocytes.

The synthesis of RNA from a DNA template by RNA polymerase II (RNAP II), originating at an RNA polymerase II promoter. Includes transcription of messenger RNA (mRNA) and certain small nuclear RNAs (snRNAs).

The emergence of an immature organism from a protective structure.

The process whose specific outcome is the progression of the hatching gland over time, from its formation to the mature structure. The cells of the hatching gland contain enzymes responsible for solubilization of the egg chorion, facilitating the hatching process.

Blood vessel formation when new vessels emerge from the proliferation of pre-existing blood vessels.

The process whose specific outcome is the progression of the liver over time, from its formation to the mature structure. The liver is an exocrine gland which secretes bile and functions in metabolism of protein and carbohydrate and fat, synthesizes substances involved in the clotting of the blood, synthesizes vitamin A, detoxifies poisonous substances, stores glycogen, and breaks down worn-out erythrocytes.

The multiplication or reproduction of endothelial cells, resulting in the expansion of a cell population. Endothelial cells are thin flattened cells which line the inside surfaces of body cavities, blood vessels, and lymph vessels, making up the endothelium.

Any process that activates or increases the frequency, rate, or extent of immunoglobulin production.

The chemical reactions and pathways resulting in the breakdown of a protein or peptide by hydrolysis of its peptide bonds, initiated by the covalent attachment of a ubiquitin group, or multiple ubiquitin groups, to the protein.

The activation of genes whose promoters contain a specific sequence elements such as the unfolded protein response element (UPRE; consensus CAGCGTG) or the ER stress-response element (ERSE; CCAAN(N)9CCACG), as a result of signaling via the unfolded protein response.

Any process that decreases the stability of a protein, making it more vulnerable to degradative processes or aggregation.

Any process involved in the maintenance of an internal steady state of triglyceride within a cell or between a cell and its external environment.

Any process that results in a change in state or activity of a cell (in terms of movement, secretion, enzyme production, gene expression, etc.) as a result of deprivation of glucose.

Any process involved in the maintenance of an internal steady state of cholesterol within an organism or cell.

Any process that stops, prevents, or reduces the frequency, rate or extent of cell death by apoptotic process.

Any process that activates or increases the frequency, rate or extent of the chemical reactions and pathways resulting in the formation of MHC class II.

Any process that activates or increases the frequency, rate or extent of B cell differentiation.

Any process that activates or increases the frequency, rate or extent of T cell differentiation.

Any process that activates or increases the frequency, rate or extent of adipocyte differentiation.

Any process that activates or increases the frequency, rate or extent of transcription from an RNA polymerase II promoter.

Any process that activates or increases the frequency, rate or extent of transcription from an RNA polymerase II promoter.

Any process that activates or increases the frequency, rate or extent of transcription from an RNA polymerase II promoter.

Any process involved in the maintenance of an internal steady state of fatty acid within an organism or cell.

Any process involved in the maintenance of an internal steady state of sterol within an organism or cell.

The process whose specific outcome is the progression of adipose tissue over time, from its formation to the mature structure. Adipose tissue is specialized tissue that is used to store fat.

Any process that results in a change in state or activity of a cell (in terms of movement, secretion, enzyme production, gene expression, etc.) as a result of a lipopolysaccharide stimulus; lipopolysaccharide is a major component of the cell wall of gram-negative bacteria.

Any process that results in a change in state or activity of a cell (in terms of movement, secretion, enzyme production, gene expression, etc.) as a result of an amino acid stimulus. An amino acid is a carboxylic acids containing one or more amino groups.

Any process that results in a change in state or activity of a cell (in terms of movement, secretion, enzyme production, gene expression, etc.) as a result of an interleukin-4 stimulus.

Any process that results in a change in state or activity of a cell (in terms of movement, secretion, enzyme production, gene expression, etc.) as a result of a peptide hormone stimulus. A peptide hormone is any of a class of peptides that are secreted into the blood stream and have endocrine functions in living animals.

Any process that results in a change in state or activity of a cell (in terms of movement, secretion, enzyme production, gene expression, etc.) as a result of a fluid shear stress stimulus. Fluid shear stress is the force acting on an object in a system where the fluid is moving across a solid surface.

Any process that results in a change in state or activity of a cell (in terms of movement, secretion, enzyme production, gene expression, etc.) as a result of a laminar fluid shear stress stimulus. Laminar fluid flow is the force acting on an object in a system where the fluid is moving across a solid surface in parallel layers.

Any process that activates or increases the frequency, rate or extent of plasma cell differentiation.

Any process that activates or increases the frequency, rate or extent of lactation.

Any process that results in a change in state or activity of a cell or an organism (in terms of movement, secretion, enzyme production, gene expression, etc.) as a result of an insulin-like growth factor stimulus.

Any process that activates or increases the frequency, rate or extent of hepatocyte proliferation.

Any process that stops, prevents, or reduces the frequency, rate or extent of transcription mediated by RNA polymerase II.

Any process that stops, prevents, or reduces the frequency, rate or extent of transcription mediated by RNA polymerase II.

Blood vessel formation when new vessels emerge from the proliferation of pre-existing blood vessels.

Any process that modulates the frequency, rate, extent or direction of cell growth.

Any process that modulates the frequency, rate, extent or direction of cell growth.

Any process that activates or increases the frequency, rate or extent of addition of phosphate groups to amino acids within a protein.

Any process that activates or increases the frequency, rate or extent of addition of phosphate groups to amino acids within a protein.

The multiplication or reproduction of endothelial cells, resulting in the expansion of a cell population. Endothelial cells are thin flattened cells which line the inside surfaces of body cavities, blood vessels, and lymph vessels, making up the endothelium.

The multiplication or reproduction of endothelial cells, resulting in the expansion of a cell population. Endothelial cells are thin flattened cells which line the inside surfaces of body cavities, blood vessels, and lymph vessels, making up the endothelium.

The developmental process, independent of morphogenetic (shape) change, that is required for an epithelial cell to attain its fully functional state. An epithelial cell is a cell usually found in a two-dimensional sheet with a free surface.

Any process that activates or increases the frequency, rate, or extent of immunoglobulin production.

Any process that activates or increases the frequency, rate, or extent of immunoglobulin production.

The synthesis of RNA from a DNA template by RNA polymerase II (RNAP II), originating at an RNA polymerase II promoter. Includes transcription of messenger RNA (mRNA) and certain small nuclear RNAs (snRNAs).

The synthesis of RNA from a DNA template by RNA polymerase II (RNAP II), originating at an RNA polymerase II promoter. Includes transcription of messenger RNA (mRNA) and certain small nuclear RNAs (snRNAs).

The chemical reactions and pathways resulting in the breakdown of a protein or peptide by hydrolysis of its peptide bonds, initiated by the covalent attachment of a ubiquitin group, or multiple ubiquitin groups, to the protein.

The chemical reactions and pathways resulting in the formation of a fatty acid, any of the aliphatic monocarboxylic acids that can be liberated by hydrolysis from naturally occurring fats and oils. Fatty acids are predominantly straight-chain acids of 4 to 24 carbon atoms, which may be saturated or unsaturated; branched fatty acids and hydroxy fatty acids also occur, and very long chain acids of over 30 carbons are found in waxes.

Any immune system process that functions in the calibrated response of an organism to a potential internal or invasive threat.

The activation of genes whose promoters contain a specific sequence elements such as the unfolded protein response element (UPRE; consensus CAGCGTG) or the ER stress-response element (ERSE; CCAAN(N)9CCACG), as a result of signaling via the unfolded protein response.

The activation of genes whose promoters contain a specific sequence elements such as the unfolded protein response element (UPRE; consensus CAGCGTG) or the ER stress-response element (ERSE; CCAAN(N)9CCACG), as a result of signaling via the unfolded protein response.

Any process that activates or increases the rate or extent of cell proliferation.

Any process that activates or increases the rate or extent of cell proliferation.

Any process that activates or increases the rate or extent of cell proliferation.

Any process that modulates the frequency, rate or extent of autophagy. Autophagy is the process in which cells digest parts of their own cytoplasm.

Any process that modulates the frequency, rate or extent of autophagy. Autophagy is the process in which cells digest parts of their own cytoplasm.

Any process that activates, maintains or increases the rate of autophagy. Autophagy is the process in which cells digest parts of their own cytoplasm.

Any process that activates, maintains or increases the rate of autophagy. Autophagy is the process in which cells digest parts of their own cytoplasm.

Any process that decreases the frequency, rate or extent of myotube differentiation. Myotube differentiation is the process in which a relatively unspecialized cell acquires specialized features of a myotube cell. Myotubes are multinucleated cells that are formed when proliferating myoblasts exit the cell cycle, differentiate and fuse.

A series of reactions within the signal-receiving cell, mediated by the intracellular phosphatidylinositol 3-kinase (PI3K). Many cell surface receptor linked signaling pathways signal through PI3K to regulate numerous cellular functions.

A series of reactions within the signal-receiving cell, mediated by the intracellular phosphatidylinositol 3-kinase (PI3K). Many cell surface receptor linked signaling pathways signal through PI3K to regulate numerous cellular functions.

Any process that activates or increases the frequency, rate or extent of cell migration.

Any process that activates or increases the frequency, rate or extent of cell migration.

Any process that stops, prevents, or reduces the frequency, rate or extent of any TGF-beta receptor signaling pathway.

The series of molecular signals generated as a consequence of the presence of unfolded proteins in the endoplasmic reticulum (ER) or other ER-related stress; results in changes in the regulation of transcription and translation.

The series of molecular signals generated as a consequence of the presence of unfolded proteins in the endoplasmic reticulum (ER) or other ER-related stress; results in changes in the regulation of transcription and translation.

The process whose specific outcome is the progression of the exocrine pancreas over time, from its formation to the mature structure. The exocrine pancreas produces and store zymogens of digestive enzymes, such as chymotrypsinogen and trypsinogen in the acinar cells.

Any process that activates or increases the frequency, rate or extent of the covalent addition of methyl groups to histones.

Any process that activates or increases the frequency, rate or extent of the covalent addition of methyl groups to histones.

Any process that affects the structure and integrity of a protein, altering the likelihood of its degradation or aggregation.

Any process that affects the structure and integrity of a protein, altering the likelihood of its degradation or aggregation.

Any process that decreases the stability of a protein, making it more vulnerable to degradative processes or aggregation.

Any process that decreases the stability of a protein, making it more vulnerable to degradative processes or aggregation.

Any process that results in a change in state or activity of a cell (in terms of movement, secretion, enzyme production, gene expression, etc.) as a result of a nutrient stimulus.

Any process that activates or increases the frequency, rate or extent of TOR signaling.

Any process that activates or increases the frequency, rate or extent of TOR signaling.

Any process that results in a change in state or activity of a cell (in terms of movement, secretion, enzyme production, gene expression, etc.) as a result of an insulin stimulus. Insulin is a polypeptide hormone produced by the islets of Langerhans of the pancreas in mammals, and by the homologous organs of other organisms.

Any process that results in a change in state or activity of a cell (in terms of movement, secretion, enzyme production, gene expression, etc.) as a result of oxidative stress, a state often resulting from exposure to high levels of reactive oxygen species, e.g. superoxide anions, hydrogen peroxide (H2O2), and hydroxyl radicals.

Any process that results in a change in state or activity of a cell (in terms of movement, secretion, enzyme production, gene expression, etc.) as a result of oxidative stress, a state often resulting from exposure to high levels of reactive oxygen species, e.g. superoxide anions, hydrogen peroxide (H2O2), and hydroxyl radicals.

Any process that results in a change in state or activity of a cell (in terms of movement, secretion, enzyme production, gene expression, etc.) as a result of a stress acting at the endoplasmic reticulum. ER stress usually results from the accumulation of unfolded or misfolded proteins in the ER lumen.

Any process involved in the maintenance of an internal steady state of triglyceride within a cell or between a cell and its external environment.

Any process that increases the rate, frequency, or extent of blood vessel formation when new vessels emerge from the proliferation of pre-existing blood vessels and contribute to the series of events that restore integrity to damaged vasculature.

Any process that increases the rate, frequency, or extent of blood vessel formation when new vessels emerge from the proliferation of pre-existing blood vessels and contribute to the series of events that restore integrity to damaged vasculature.

Any process that results in a change in state or activity of a cell (in terms of movement, secretion, enzyme production, gene expression, etc.) as a result of a vascular endothelial growth factor stimulus.

Any process that results in a change in state or activity of a cell (in terms of movement, secretion, enzyme production, gene expression, etc.) as a result of a vascular endothelial growth factor stimulus.

A series of molecular signals mediated by the endoplasmic reticulum stress sensor IRE1 (Inositol-requiring transmembrane kinase/endonuclease). Begins with activation of IRE1 in response to endoplasmic reticulum (ER) stress, and ends with regulation of a downstream cellular process, e.g. transcription. One target of activated IRE1 is the transcription factor HAC1 in yeast, or XBP1 in mammals; IRE1 cleaves an intron of a mRNA coding for HAC1/XBP1 to generate an activated HAC1/XBP1 transcription factor, which controls the up regulation of UPR-related genes. At least in mammals, IRE1 can also signal through additional intracellular pathways including JNK and NF-kappaB.

A series of molecular signals mediated by the endoplasmic reticulum membrane stress sensor ATF6 (activating transcription factor 6). Begins with activation of ATF6 in response to endoplasmic reticulum (ER) stress, and ends with regulation of a downstream cellular process, e.g. transcription. Under conditions of endoplasmic reticulum stress, ATF6 translocates to the Golgi where it is processed by proteases to release a cytoplasmic domain (ATF6f), which operates as a transcriptional activator of many genes required to restore folding capacity.

Any process that results in a change in state or activity of a cell (in terms of movement, secretion, enzyme production, gene expression, etc.) as a result of deprivation of glucose.

Any process that activates or increases the frequency, rate or extent of movement of proteins from the cytoplasm into the nucleus.

Any process that activates or increases the frequency, rate or extent of movement of proteins from the cytoplasm into the nucleus.

Any process that results in a change in state or activity of a cell or an organism (in terms of movement, secretion, enzyme production, gene expression, etc.) as a result of a drug stimulus. A drug is a substance used in the diagnosis, treatment or prevention of a disease.

Any process involved in the maintenance of an internal steady state of cholesterol within an organism or cell.

Any process that stops, prevents, or reduces the frequency, rate or extent of cell death by apoptotic process.

Any process that activates or increases the frequency, rate or extent of the chemical reactions and pathways resulting in the formation of MHC class II.

Any process that activates or increases the frequency, rate or extent of the chemical reactions and pathways resulting in the formation of MHC class II.

Any process that activates or increases the frequency, rate or extent of B cell differentiation.

Any process that activates or increases the frequency, rate or extent of B cell differentiation.

Any process that activates or increases the frequency, rate or extent of T cell differentiation.

Any process that activates or increases the frequency, rate or extent of T cell differentiation.

Any process that activates or increases the frequency, rate or extent of adipocyte differentiation.

Any process that activates or increases angiogenesis.

Any process that activates or increases angiogenesis.

Any process that activates or increases the frequency, rate or extent of transcription from an RNA polymerase II promoter.

Any series of molecular signals initiated by the binding of an extracellular ligand to a vascular endothelial growth factor receptor (VEGFR) located on the surface of the receiving cell, and ending with regulation of a downstream cellular process, e.g. transcription.

Any series of molecular signals initiated by the binding of an extracellular ligand to a vascular endothelial growth factor receptor (VEGFR) located on the surface of the receiving cell, and ending with regulation of a downstream cellular process, e.g. transcription.

The process whose specific outcome is the progression of a neuron over time, from initial commitment of the cell to a specific fate, to the fully functional differentiated cell.

Any process that activates or increases the frequency, rate or extent of the regulated release of immunoglobulins from a cell.

Any process that results in a change in state or activity of a cell or an organism (in terms of movement, secretion, enzyme production, gene expression, etc.) as a result of an electrical stimulus.

Any process involved in the maintenance of an internal steady state of fatty acid within an organism or cell.

Any process involved in the maintenance of an internal steady state of sterol within an organism or cell.

The regulated release of serotonin by a cell, in which released serotonin acts as a neurotransmitter.

Any process that decreases the rate, frequency or extent of pathway-restricted SMAD protein phosphorylation. Pathway-restricted SMAD proteins and common-partner SMAD proteins are involved in the transforming growth factor beta receptor signaling pathways.

The process whose specific outcome is the progression of adipose tissue over time, from its formation to the mature structure. Adipose tissue is specialized tissue that is used to store fat.

The developmental process, independent of morphogenetic (shape) change, that is required for an epithelial cell of the salivary gland to attain its fully functional state.

A series of molecular signals in which an intracellular signal is conveyed to trigger the apoptotic death of a cell. The pathway is induced in response to a stimulus indicating endoplasmic reticulum (ER) stress, and ends when the execution phase of apoptosis is triggered. ER stress usually results from the accumulation of unfolded or misfolded proteins in the ER lumen.

Any process that stops, prevents, or reduces the frequency, rate or extent of signal transduction mediated by the ERK1 and ERK2 cascade.

Any process that results in a change in state or activity of a cell (in terms of movement, secretion, enzyme production, gene expression, etc.) as a result of a lipopolysaccharide stimulus; lipopolysaccharide is a major component of the cell wall of gram-negative bacteria.

Any process that results in a change in state or activity of a cell (in terms of movement, secretion, enzyme production, gene expression, etc.) as a result of a lipopolysaccharide stimulus; lipopolysaccharide is a major component of the cell wall of gram-negative bacteria.

Any process that results in a change in state or activity of a cell (in terms of movement, secretion, enzyme production, gene expression, etc.) as a result of an amino acid stimulus. An amino acid is a carboxylic acids containing one or more amino groups.

Any process that results in a change in state or activity of a cell (in terms of movement, secretion, enzyme production, gene expression, etc.) as a result of a fructose stimulus.

Any process that results in a change in state or activity of a cell (in terms of movement, secretion, enzyme production, gene expression, etc.) as a result of a glucose stimulus.

Any process that results in a change in state or activity of a cell (in terms of movement, secretion, enzyme production, gene expression, etc.) as a result of an interleukin-4 stimulus.

Any process that results in a change in state or activity of a cell (in terms of movement, secretion, enzyme production, gene expression, etc.) as a result of a peptide hormone stimulus. A peptide hormone is any of a class of peptides that are secreted into the blood stream and have endocrine functions in living animals.

Any process that results in a change in state or activity of a cell (in terms of movement, secretion, enzyme production, gene expression, etc.) as a result of a fluid shear stress stimulus. Fluid shear stress is the force acting on an object in a system where the fluid is moving across a solid surface.

Any process that results in a change in state or activity of a cell (in terms of movement, secretion, enzyme production, gene expression, etc.) as a result of a laminar fluid shear stress stimulus. Laminar fluid flow is the force acting on an object in a system where the fluid is moving across a solid surface in parallel layers.

Any process that activates or increases the frequency, rate or extent of plasma cell differentiation.

Any process that activates or increases the frequency, rate or extent of plasma cell differentiation.

Any process that stops, prevents or reduces the frequency, rate or extent of endoplasmic reticulum unfolded protein response.

Any process that stops, prevents or reduces the frequency, rate or extent of endoplasmic reticulum unfolded protein response.

Any process that activates or increases the frequency, rate or extent of endoplasmic reticulum unfolded protein response.

Any process that activates or increases the frequency, rate or extent of endoplasmic reticulum unfolded protein response.

Any process that activates or increases the frequency, rate or extent of protein acetylation.

Any process that activates or increases the frequency, rate or extent of protein acetylation.

Any process that stops, prevents or reduces the frequency, rate or extent of an endoplasmic reticulum stress-induced intrinsic apoptotic signaling pathway.

Any process that stops, prevents or reduces the frequency, rate or extent of an endoplasmic reticulum stress-induced intrinsic apoptotic signaling pathway.

Any process that activates or increases the frequency, rate or extent of lactation.

Any process that results in a change in state or activity of a cell or an organism (in terms of movement, secretion, enzyme production, gene expression, etc.) as a result of an insulin-like growth factor stimulus.

Any process that results in a change in state or activity of a cell (in terms of movement, secretion, enzyme production, gene expression, etc.) as a result of a leukemia inhibitory factor stimulus.

Any process that activates or increases the frequency, rate or extent of hepatocyte proliferation.

Any process that activates or increases the frequency, rate or extent of endothelial cell apoptotic process.

Any process that activates or increases the frequency, rate or extent of endothelial cell apoptotic process.

Any process that activates or increases the frequency, rate or extent of interleukin-6 secretion.

Any process that modulates the frequency, rate or extent of cellular DNA-templated transcription.

The series of molecular signals generated as a consequence of the presence of unfolded proteins in the endoplasmic reticulum (ER) or other ER-related stress; results in changes in the regulation of transcription and translation.

Any process that results in a change in state or activity of a cell (in terms of movement, secretion, enzyme production, gene expression, etc.) as a result of a stress acting at the endoplasmic reticulum. ER stress usually results from the accumulation of unfolded or misfolded proteins in the ER lumen.

Any process that results in a change in state or activity of a cell or an organism (in terms of movement, secretion, enzyme production, gene expression, etc.) as a result of a drug stimulus. A drug is a substance used in the diagnosis, treatment or prevention of a disease.

Any process that results in a change in state or activity of a cell or an organism (in terms of movement, secretion, enzyme production, gene expression, etc.) as a result of an electrical stimulus.

The regulated release of serotonin by a cell, in which released serotonin acts as a neurotransmitter.

Any process that results in a change in state or activity of a cell (in terms of movement, secretion, enzyme production, gene expression, etc.) as a result of an antibiotic stimulus. An antibiotic is a chemical substance produced by a microorganism which has the capacity to inhibit the growth of or to kill other microorganisms.

Any process that stops, prevents or reduces the frequency, rate or extent of an endoplasmic reticulum stress-induced intrinsic apoptotic signaling pathway.

All of the contents of a cell excluding the plasma membrane and nucleus, but including other subcellular structures.

The irregular network of unit membranes, visible only by electron microscopy, that occurs in the cytoplasm of many eukaryotic cells. The membranes form a complex meshwork of tubular channels, which are often expanded into slitlike cavities called cisternae. The ER takes two forms, rough (or granular), with ribosomes adhering to the outer surface, and smooth (with no ribosomes attached).

A membrane-bounded organelle of eukaryotic cells in which chromosomes are housed and replicated. In most cells, the nucleus contains all of the cell's chromosomes except the organellar chromosomes, and is the site of RNA synthesis and processing. In some species, or in specialized cell types, RNA metabolism or DNA replication may be absent.

A membrane-bounded organelle of eukaryotic cells in which chromosomes are housed and replicated. In most cells, the nucleus contains all of the cell's chromosomes except the organellar chromosomes, and is the site of RNA synthesis and processing. In some species, or in specialized cell types, RNA metabolism or DNA replication may be absent.

That part of the nuclear content other than the chromosomes or the nucleolus.

All of the contents of a cell excluding the plasma membrane and nucleus, but including other subcellular structures.

The irregular network of unit membranes, visible only by electron microscopy, that occurs in the cytoplasm of many eukaryotic cells. The membranes form a complex meshwork of tubular channels, which are often expanded into slitlike cavities called cisternae. The ER takes two forms, rough (or granular), with ribosomes adhering to the outer surface, and smooth (with no ribosomes attached).

The irregular network of unit membranes, visible only by electron microscopy, that occurs in the cytoplasm of many eukaryotic cells. The membranes form a complex meshwork of tubular channels, which are often expanded into slitlike cavities called cisternae. The ER takes two forms, rough (or granular), with ribosomes adhering to the outer surface, and smooth (with no ribosomes attached).

The part of the cytoplasm that does not contain organelles but which does contain other particulate matter, such as protein complexes.

The part of the cytoplasm that does not contain organelles but which does contain other particulate matter, such as protein complexes.

The component of the endoplasmic reticulum membrane consisting of the gene products and protein complexes having at least some part of their peptide sequence embedded in the hydrophobic region of the membrane.

The component of the endoplasmic reticulum membrane consisting of the gene products and protein complexes having at least some part of their peptide sequence embedded in the hydrophobic region of the membrane.

A membrane-bounded organelle of eukaryotic cells in which chromosomes are housed and replicated. In most cells, the nucleus contains all of the cell's chromosomes except the organellar chromosomes, and is the site of RNA synthesis and processing. In some species, or in specialized cell types, RNA metabolism or DNA replication may be absent.

A membrane-bounded organelle of eukaryotic cells in which chromosomes are housed and replicated. In most cells, the nucleus contains all of the cell's chromosomes except the organellar chromosomes, and is the site of RNA synthesis and processing. In some species, or in specialized cell types, RNA metabolism or DNA replication may be absent.