Extramacrochaetae
Encyclopedia
The gene extramachrochaetae (emc) is a Drosophila melanogaster
gene that codes for the Emc protein
, which has a wide variety of developmental roles. It was named, as is common for Drosophila
genes, after the phenotypic change caused by a mutation in the gene (macrochaetae are the longer bristle
s on Drosophila
).
chromosome. It is about 4100 base pair
s long, including two exon
s and one intron
. Its Fly Base designation is Dmel_emc, and its location is at 3L:749,406..753,505 [+]. 86 allele
s have been reported.
has a helix-loop-helix protein domain
without the basic region, making it unable to bind to DNA
and act as a transcription factor
. It does, however, have the ability to bind other basic-helix-loop-helix
domain-containing proteins, such as the products of the achaete-scute complex
(ac-s), to form dimer
s that inactivate the target protein, which is usually a transcription factor
. In this way, the Emc protein can have an effect on the gene expression
of many genes during Drosophila
development.
Emc in neural development
The extra sensory organs (SOs) in Drosophila
arise from cell-clusters known as sensory mother cells (SMCs). Once an imaginal disc
cell
has been selected to become an SMC, it will go on to mature into an SO. Therefore, the regulation of which imaginal disc
cell
s become SMCs is vital to neural development. This transition is caused by the Da and AS-C genes, which are transcription factors with the basic-helix-loop-helix (bHLH)
domains. The Da protein (made by the daughterless gene) is a Class I HLH protein
, meaning it has generalized distribution, whereas the AS-C proteins (made by the as-c gene complex) are Class II HLH protein
s, meaning they have restricted distribution. The Emc protein itself is a Class V HLH protein
due to its lack of the basic region and consequential inability to bind DNA
. The interaction between Da or AS-C proteins with Emc to form dimer
s renders them inactive as transcription factor
s. It is the interplay between concentrations of Da, AS-C, and Emc proteins that determines whether or not a cell will become an SMC, and later on an SO. In this way, "Emc provides positional information for SO patterning."
The levels of each of these proneural proteins is likely to be regulated by the Notch signaling
pathway, as the lack of Notch causes an excess of neural cells while "constitutive Notch signaling
...suppresses neural differentiation." Notch has been shown to mediate lateral specification
of proneural cell-clusters by restricting the expression of AS-C proteins to only the neuroblast
, while causing the surrounding dermoblast cells to cease expression of the as-c complex.
in Drosophila
is determined in part by the Sex lethal (Sxl) gene; more precisely, it is turned 'on' in female
s and 'off' in male
s. Whether or not this gene
will be expressed is determined by the ratio of sex chromosomes (X-chromosome
s) to autosomal chromosomes.
The fly embryo
assesses this ratio by the difference between concentration
s of the scute
gene
product, which is on the X-chromosome
, and the emc gene
product, which is on an autosomal chromosome. Specifically, Emc proteins inactivate the Sc protein (a transcription factor
) and stop transcription
of genes on the X-chromosome
. As females have twice the amount of Sc as males, they can overcome this obstacle and express the Sxl gene.
Similarity to vertebrate
Early support for the role of emc came from the mouse
Inhibitor of differentiation (Id) gene, which negatively regulates myogenesis
by forming a heterodimer
with the MyoD
protein and therefore inhibiting its abilities as a transcription factor
. Similar processes are also likely to exist in other mammals.
Drosophila melanogaster
Drosophila melanogaster is a species of Diptera, or the order of flies, in the family Drosophilidae. The species is known generally as the common fruit fly or vinegar fly. Starting from Charles W...
gene that codes for the Emc protein
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...
, which has a wide variety of developmental roles. It was named, as is common for Drosophila
Drosophila
Drosophila is a genus of small flies, belonging to the family Drosophilidae, whose members are often called "fruit flies" or more appropriately pomace flies, vinegar flies, or wine flies, a reference to the characteristic of many species to linger around overripe or rotting fruit...
genes, after the phenotypic change caused by a mutation in the gene (macrochaetae are the longer bristle
Bristle
A bristle is a stiff hair or feather. Also used are synthetic materials such as nylon in items such as brooms and sweepers. Bristles are often used to make brushes for cleaning uses, as they are strongly abrasive; common examples include the toothbrush and toilet brush...
s on Drosophila
Drosophila
Drosophila is a genus of small flies, belonging to the family Drosophilidae, whose members are often called "fruit flies" or more appropriately pomace flies, vinegar flies, or wine flies, a reference to the characteristic of many species to linger around overripe or rotting fruit...
).
The emc gene
The emc gene is located near the tip of the left arm of the 3rd DrosophilaDrosophila
Drosophila is a genus of small flies, belonging to the family Drosophilidae, whose members are often called "fruit flies" or more appropriately pomace flies, vinegar flies, or wine flies, a reference to the characteristic of many species to linger around overripe or rotting fruit...
chromosome. It is about 4100 base pair
Base pair
In molecular biology and genetics, the linking between two nitrogenous bases on opposite complementary DNA or certain types of RNA strands that are connected via hydrogen bonds is called a base pair...
s long, including two exon
Exon
An exon is a nucleic acid sequence that is represented in the mature form of an RNA molecule either after portions of a precursor RNA have been removed by cis-splicing or when two or more precursor RNA molecules have been ligated by trans-splicing. The mature RNA molecule can be a messenger RNA...
s and one intron
Intron
An intron is any nucleotide sequence within a gene that is removed by RNA splicing to generate the final mature RNA product of a gene. The term intron refers to both the DNA sequence within a gene, and the corresponding sequence in RNA transcripts. Sequences that are joined together in the final...
. Its Fly Base designation is Dmel_emc, and its location is at 3L:749,406..753,505 [+]. 86 allele
Allele
An allele is one of two or more forms of a gene or a genetic locus . "Allel" is an abbreviation of allelomorph. Sometimes, different alleles can result in different observable phenotypic traits, such as different pigmentation...
s have been reported.
Emc interactions with other proteins
The Emc proteinProtein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...
has a helix-loop-helix protein domain
Protein domain
A protein domain is a part of protein sequence and structure that can evolve, function, and exist independently of the rest of the protein chain. Each domain forms a compact three-dimensional structure and often can be independently stable and folded. Many proteins consist of several structural...
without the basic region, making it unable to bind to DNA
DNA
Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...
and act as a transcription factor
Transcription factor
In molecular biology and genetics, a transcription factor is a protein that binds to specific DNA sequences, thereby controlling the flow of genetic information from DNA to mRNA...
. It does, however, have the ability to bind other basic-helix-loop-helix
Basic-helix-loop-helix
A basic helix-loop-helix is a protein structural motif that characterizes a family of transcription factors.- Structure :The motif is characterized by two α-helices connected by a loop. In general, transcription factors including this domain are dimeric, each with one helix containing basic amino...
domain-containing proteins, such as the products of the achaete-scute complex
Achaete-scute complex
The achaete-scute complex is a group of four genes in the fruit fly Drosophila melanogaster. These genes encode basic helix-loop-helix transcription factors that have been best studied in their regulation of nervous system development...
(ac-s), to form dimer
Protein dimer
In biochemistry, a dimer is a macromolecular complex formed by two, usually non-covalently bound, macromolecules like proteins or nucleic acids...
s that inactivate the target protein, which is usually a transcription factor
Transcription factor
In molecular biology and genetics, a transcription factor is a protein that binds to specific DNA sequences, thereby controlling the flow of genetic information from DNA to mRNA...
. In this way, the Emc protein can have an effect on the gene expression
Gene expression
Gene expression is the process by which information from a gene is used in the synthesis of a functional gene product. These products are often proteins, but in non-protein coding genes such as ribosomal RNA , transfer RNA or small nuclear RNA genes, the product is a functional RNA...
of many genes during Drosophila
Drosophila
Drosophila is a genus of small flies, belonging to the family Drosophilidae, whose members are often called "fruit flies" or more appropriately pomace flies, vinegar flies, or wine flies, a reference to the characteristic of many species to linger around overripe or rotting fruit...
development.
Emc in neural developmentNeural developmentNeural development comprises the processes that generate, shape, and reshape the nervous system, from the earliest stages of embryogenesis to the final years of life. The study of neural development aims to describe the cellular basis of brain development and to address the underlying mechanisms...
The extra sensory organs (SOs) in DrosophilaDrosophila
Drosophila is a genus of small flies, belonging to the family Drosophilidae, whose members are often called "fruit flies" or more appropriately pomace flies, vinegar flies, or wine flies, a reference to the characteristic of many species to linger around overripe or rotting fruit...
arise from cell-clusters known as sensory mother cells (SMCs). Once an imaginal disc
Imaginal disc
An imaginal disc is one of the parts of a holometabolous insect larva that will become a portion of the outside of the adult insect during the pupal transformation. Contained within the body of the larva, there are pairs of discs that will form, for instance, the wings or legs or antennae or other...
cell
Cell (biology)
The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos....
has been selected to become an SMC, it will go on to mature into an SO. Therefore, the regulation of which imaginal disc
Imaginal disc
An imaginal disc is one of the parts of a holometabolous insect larva that will become a portion of the outside of the adult insect during the pupal transformation. Contained within the body of the larva, there are pairs of discs that will form, for instance, the wings or legs or antennae or other...
cell
Cell (biology)
The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos....
s become SMCs is vital to neural development. This transition is caused by the Da and AS-C genes, which are transcription factors with the basic-helix-loop-helix (bHLH)
Basic-helix-loop-helix
A basic helix-loop-helix is a protein structural motif that characterizes a family of transcription factors.- Structure :The motif is characterized by two α-helices connected by a loop. In general, transcription factors including this domain are dimeric, each with one helix containing basic amino...
domains. The Da protein (made by the daughterless gene) is a Class I HLH protein
Basic-helix-loop-helix
A basic helix-loop-helix is a protein structural motif that characterizes a family of transcription factors.- Structure :The motif is characterized by two α-helices connected by a loop. In general, transcription factors including this domain are dimeric, each with one helix containing basic amino...
, meaning it has generalized distribution, whereas the AS-C proteins (made by the as-c gene complex) are Class II HLH protein
Basic-helix-loop-helix
A basic helix-loop-helix is a protein structural motif that characterizes a family of transcription factors.- Structure :The motif is characterized by two α-helices connected by a loop. In general, transcription factors including this domain are dimeric, each with one helix containing basic amino...
s, meaning they have restricted distribution. The Emc protein itself is a Class V HLH protein
Basic-helix-loop-helix
A basic helix-loop-helix is a protein structural motif that characterizes a family of transcription factors.- Structure :The motif is characterized by two α-helices connected by a loop. In general, transcription factors including this domain are dimeric, each with one helix containing basic amino...
due to its lack of the basic region and consequential inability to bind DNA
DNA
Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...
. The interaction between Da or AS-C proteins with Emc to form dimer
Protein dimer
In biochemistry, a dimer is a macromolecular complex formed by two, usually non-covalently bound, macromolecules like proteins or nucleic acids...
s renders them inactive as transcription factor
Transcription factor
In molecular biology and genetics, a transcription factor is a protein that binds to specific DNA sequences, thereby controlling the flow of genetic information from DNA to mRNA...
s. It is the interplay between concentrations of Da, AS-C, and Emc proteins that determines whether or not a cell will become an SMC, and later on an SO. In this way, "Emc provides positional information for SO patterning."
The levels of each of these proneural proteins is likely to be regulated by the Notch signaling
Notch signaling
The notch signaling pathway is a highly conserved cell signaling system present in most multicellular organisms.Notch is present in all metazoans, and mammals possess four different notch receptors, referred to as NOTCH1, NOTCH2, NOTCH3, and NOTCH4. The notch receptor is a single-pass...
pathway, as the lack of Notch causes an excess of neural cells while "constitutive Notch signaling
Notch signaling
The notch signaling pathway is a highly conserved cell signaling system present in most multicellular organisms.Notch is present in all metazoans, and mammals possess four different notch receptors, referred to as NOTCH1, NOTCH2, NOTCH3, and NOTCH4. The notch receptor is a single-pass...
...suppresses neural differentiation." Notch has been shown to mediate lateral specification
Regional specification
In the field of developmental biology, regional specification is the process by which different areas are identified in the development of the early embryo. The process by which the cells become specified differs between organisms.-Cell fate determination:...
of proneural cell-clusters by restricting the expression of AS-C proteins to only the neuroblast
Neuroblast
A neuroblast is a dividing cell that will develop into neurons or glia. The characterisation of neuroblasts and their development in Drosophila melanogaster was widely achieved by Chris Doe, Corey Goodman and Mike Bate. In humans, neuroblasts produced by stem cells in the adult subventricular zone...
, while causing the surrounding dermoblast cells to cease expression of the as-c complex.
Emc in sex determination
SexSex
In biology, sex is a process of combining and mixing genetic traits, often resulting in the specialization of organisms into a male or female variety . Sexual reproduction involves combining specialized cells to form offspring that inherit traits from both parents...
in Drosophila
Drosophila
Drosophila is a genus of small flies, belonging to the family Drosophilidae, whose members are often called "fruit flies" or more appropriately pomace flies, vinegar flies, or wine flies, a reference to the characteristic of many species to linger around overripe or rotting fruit...
is determined in part by the Sex lethal (Sxl) gene; more precisely, it is turned 'on' in female
Female
Female is the sex of an organism, or a part of an organism, which produces non-mobile ova .- Defining characteristics :The ova are defined as the larger gametes in a heterogamous reproduction system, while the smaller, usually motile gamete, the spermatozoon, is produced by the male...
s and 'off' in male
Male
Male refers to the biological sex of an organism, or part of an organism, which produces small mobile gametes, called spermatozoa. Each spermatozoon can fuse with a larger female gamete or ovum, in the process of fertilization...
s. Whether or not this gene
Gene
A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...
will be expressed is determined by the ratio of sex chromosomes (X-chromosome
Chromosome
A chromosome is an organized structure of DNA and protein found in cells. It is a single piece of coiled DNA containing many genes, regulatory elements and other nucleotide sequences. Chromosomes also contain DNA-bound proteins, which serve to package the DNA and control its functions.Chromosomes...
s) to autosomal chromosomes.
The fly embryo
Embryo
An embryo is a multicellular diploid eukaryote in its earliest stage of development, from the time of first cell division until birth, hatching, or germination...
assesses this ratio by the difference between concentration
Concentration
In chemistry, concentration is defined as the abundance of a constituent divided by the total volume of a mixture. Four types can be distinguished: mass concentration, molar concentration, number concentration, and volume concentration...
s of the scute
Scute
A scute or scutum is a bony external plate or scale, as on the shell of a turtle, the skin of crocodilians, the feet of some birds or the anterior portion of the mesonotum in insects.-Properties:...
gene
Gene
A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...
product, which is on the X-chromosome
Chromosome
A chromosome is an organized structure of DNA and protein found in cells. It is a single piece of coiled DNA containing many genes, regulatory elements and other nucleotide sequences. Chromosomes also contain DNA-bound proteins, which serve to package the DNA and control its functions.Chromosomes...
, and the emc gene
Gene
A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...
product, which is on an autosomal chromosome. Specifically, Emc proteins inactivate the Sc protein (a transcription factor
Transcription factor
In molecular biology and genetics, a transcription factor is a protein that binds to specific DNA sequences, thereby controlling the flow of genetic information from DNA to mRNA...
) and stop transcription
Transcription (genetics)
Transcription is the process of creating a complementary RNA copy of a sequence of DNA. Both RNA and DNA are nucleic acids, which use base pairs of nucleotides as a complementary language that can be converted back and forth from DNA to RNA by the action of the correct enzymes...
of genes on the X-chromosome
Chromosome
A chromosome is an organized structure of DNA and protein found in cells. It is a single piece of coiled DNA containing many genes, regulatory elements and other nucleotide sequences. Chromosomes also contain DNA-bound proteins, which serve to package the DNA and control its functions.Chromosomes...
. As females have twice the amount of Sc as males, they can overcome this obstacle and express the Sxl gene.
Similarity to vertebrateVertebrateVertebrates are animals that are members of the subphylum Vertebrata . Vertebrates are the largest group of chordates, with currently about 58,000 species described. Vertebrates include the jawless fishes, bony fishes, sharks and rays, amphibians, reptiles, mammals, and birds...
genes
Early support for the role of emc came from the mouseMouse
A mouse is a small mammal belonging to the order of rodents. The best known mouse species is the common house mouse . It is also a popular pet. In some places, certain kinds of field mice are also common. This rodent is eaten by large birds such as hawks and eagles...
Inhibitor of differentiation (Id) gene, which negatively regulates myogenesis
Myogenesis
Myogenesis is the formation of muscular tissue, in particular during embryonic development.Muscle fibers form from the fusion of myoblasts into multi-nucleated fibers . In the early development of an embryo these myoblasts will proliferate if enough fibroblast growth factor is present...
by forming a heterodimer
Protein dimer
In biochemistry, a dimer is a macromolecular complex formed by two, usually non-covalently bound, macromolecules like proteins or nucleic acids...
with the MyoD
MyoD
MyoD is a protein with a key role in regulating muscle differentiation. MyoD belongs to a family of proteins known as myogenic regulatory factors . These bHLH transcription factors act sequentially in myogenic differentiation. MRF family members include MyoD, Myf5, myogenin, and MRF4 .MyoD is one...
protein and therefore inhibiting its abilities as a transcription factor
Transcription factor
In molecular biology and genetics, a transcription factor is a protein that binds to specific DNA sequences, thereby controlling the flow of genetic information from DNA to mRNA...
. Similar processes are also likely to exist in other mammals.