The gene ''extramachrochaetae (emc)'' is a ''

Drosophila melanogaster ''Drosophila melanogaster'' is a species of fly (the taxonomic order Diptera) in the family Drosophilidae. The species is often referred to as the fruit fly or lesser fruit fly, or less commonly the "vinegar fly" or "pomace fly". Starting with Ch ...

'' gene that codes for the Emc

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...

, which has a wide variety of developmental roles. It was named, as is common for ''

Drosophila ''Drosophila'' () is a genus of flies, belonging to the family Drosophilidae, whose members are often called "small fruit flies" or (less frequently) pomace flies, vinegar flies, or wine flies, a reference to the characteristic of many species ...

'' genes, after the phenotypic change caused by a mutation in the gene ( macrochaetae are the longer

bristle A bristle is a stiff hair or feather (natural or artificial), either on an animal, such as a pig, a plant, or on a tool such as a brush or broom. Synthetic types Synthetic materials such as nylon are also used to make bristles in items such as br ...

s on ''

'').

The ''emc'' gene

The ''emc'' gene is located near the tip of the left arm of the 3rd ''

'' chromosome. It is about 4100

base pair A base pair (bp) is a fundamental unit of double-stranded nucleic acids consisting of two nucleobases bound to each other by hydrogen bonds. They form the building blocks of the DNA double helix and contribute to the folded structure of both DNA ...

s long, including two

exon An exon is any part of a gene that will form a part of the final mature RNA produced by that gene after introns have been removed by RNA splicing. The term ''exon'' refers to both the DNA sequence within a gene and to the corresponding sequen ...

s and one

intron An intron is any nucleotide sequence within a gene that is not expressed or operative in the final RNA product. The word ''intron'' is derived from the term ''intragenic region'', i.e. a region inside a gene."The notion of the cistron .e., gene. ...

. Its FlyBase designation is Dmel_emc, and its location is at 3L:749,406..753,505 86

allele An allele (, ; ; modern formation from Greek ἄλλος ''állos'', "other") is a variation of the same sequence of nucleotides at the same place on a long DNA molecule, as described in leading textbooks on genetics and evolution. ::"The chro ...

s have been reported.

Emc interactions with other proteins

The Emc

has a helix-loop-helix protein domain without the basic region, making it unable to bind to DNA and act as a

transcription factor In molecular biology, a transcription factor (TF) (or sequence-specific DNA-binding factor) is a protein that controls the rate of transcription of genetic information from DNA to messenger RNA, by binding to a specific DNA sequence. The fu ...

. 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 Dimer may refer to: * Dimer (chemistry), a chemical structure formed from two similar sub-units ** Protein dimer, a protein quaternary structure ** d-dimer * Dimer model, an item in statistical mechanics, based on ''domino tiling'' * Julius Dimer ( ...

s that inactivate the target protein, which is usually a

. In this way, the Emc protein can have an effect on the

gene expression Gene expression is the process by which information from a gene is used in the synthesis of a functional gene product that enables it to produce end products, protein or non-coding RNA, and ultimately affect a phenotype, as the final effect. The ...

of many genes during ''

'' development.

Emc in neural development

The extra sensory organs (SOs) in ''

'' arise from cell-clusters known as

sensory mother cell Sensory may refer to: Biology * Sensory ecology, how organisms obtain information about their environment * Sensory neuron, nerve cell responsible for transmitting information about external stimuli * Sensory perception, the process of acquiri ...

s (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 cells 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 proteins, 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

s renders them inactive as

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 In vertebrates, a neuroblast or primitive nerve cell is a postmitotic cell that does not divide further, and which will develop into a neuron after a migration phase. In invertebrates such as ''Drosophila,'' neuroblasts are neural progenitor cells ...

, while causing the surrounding dermoblast cells to cease expression of the ''as-c'' complex.

Emc in sex determination

Sex Sex is the trait that determines whether a sexually reproducing animal or plant produces male or female gametes. Male plants and animals produce smaller mobile gametes (spermatozoa, sperm, pollen), while females produce larger ones (ova, oft ...

in ''

'' is determined in part by the '' Sex lethal'' (''Sxl'') gene; more precisely, it is turned 'on' in

female Female (Venus symbol, symbol: ♀) is the sex of an organism that produces the large non-motile ovum, ova (egg cells), the type of gamete (sex cell) that fuses with the Sperm, male gamete during sexual reproduction. A female has larger gamet ...

s and 'off' in

male Male (symbol: ♂) is the sex of an organism that produces the gamete (sex cell) known as sperm, which fuses with the larger female gamete, or ovum, in the process of fertilization. A male organism cannot reproduce sexually without access to ...

s. Whether or not this

gene In biology, the word gene (from , ; "...Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a ba ...

will be expressed is determined by the ratio of

sex chromosome A sex chromosome (also referred to as an allosome, heterotypical chromosome, gonosome, heterochromosome, or idiochromosome) is a chromosome that differs from an ordinary autosome in form, size, and behavior. The human sex chromosomes, a typical ...

s (X-

chromosome A chromosome is a long DNA molecule with part or all of the genetic material of an organism. In most chromosomes the very long thin DNA fibers are coated with packaging proteins; in eukaryotic cells the most important of these proteins are ...

s) to

autosomal chromosome An autosome is any chromosome that is not a sex chromosome. The members of an autosome pair in a diploid cell have the same morphology, unlike those in allosome, allosomal (sex chromosome) pairs, which may have different structures. The DNA in au ...

s. The fly

embryo An embryo is an initial stage of development of a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male spe ...

assesses this ratio by the difference between

concentration In chemistry, concentration is the abundance of a constituent divided by the total volume of a mixture. Several types of mathematical description can be distinguished: '' mass concentration'', ''molar concentration'', ''number concentration'', an ...

s of the '' scute''

product, which is on the X-

, and the ''emc''

product, which is on an

. Specifically, Emc proteins inactivate the Sc protein (a

) and stop

transcription Transcription refers to the process of converting sounds (voice, music etc.) into letters or musical notes, or producing a copy of something in another medium, including: Genetics * Transcription (biology), the copying of DNA into RNA, the fir ...

of genes on the X-

. As females have twice the amount of Sc as males, they can overcome this obstacle and express the ''Sxl'' gene.

Similarity to vertebrate genes

Early support for the role of ''emc'' came from the

mouse A mouse ( : mice) is a small rodent. Characteristically, mice are known to have a pointed snout, small rounded ears, a body-length scaly tail, and a high breeding rate. The best known mouse species is the common house mouse (''Mus musculus' ...

'' Inhibitor of differentiation'' (''Id'') gene, which negatively regulates myogenesis by forming a

heterodimer In biochemistry, a protein dimer is a macromolecular complex formed by two protein monomers, or single proteins, which are usually non-covalently bound. Many macromolecules, such as proteins or nucleic acids, form dimers. The word ''dimer'' has ...

with the MyoD protein and therefore inhibiting its abilities as a

. Similar processes are also likely to exist in other mammals.

References

{{reflist Drosophila melanogaster genes Animal developmental biology