Extramacrochaetae

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 bristles on "Drosophila").

The "emc" gene

The "emc" gene is located near the tip of the left arm of the 3rd "Drosophila" chromosome. It is about 4100 base pairs long, including two exons and one intron. Its [http://flybase.bio.indiana.edu/ Fly Base] designation is Dmel_emc, and its location is at 3L:749,406..753,505 [+] . 86 alleles have been reported.

Emc interactions with other proteins

The Emc protein 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 dimers 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.cite journal
quotes =
last = Campuzano
first = S.
authorlink =
coauthors =
date = 20 December 2001
year = 2001
month = December
title = Emc, a negative HLH regulator with multiple functions in "Drosophila" development
journal = Oncogene
volume = 20
issue = 58
pages = 8299–8307
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url = http://www.nature.com/onc/journal/v20/n58/abs/1205162a.html
language = English
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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 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 dimers renders them inactive as transcription factors. 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."cite journal
quotes =
last = Lai
first = Eric C.
authorlink =
coauthors =
date = February 18, 2004
year = 2004
month = February
title = Notch signaling: control of cell communication and cell fate
journal = Development
volume = 131
issue =
pages = 965–973
issn =
pmid =
doi = 10.1242/10.1242/dev.01074
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url = http://dev.biologists.org/cgi/content/full/131/5/965
language = English
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quote = ] 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.cite journal
quotes =
last = Artavanis-Tsakonas
first = Spyros
authorlink =
coauthors = Kenji Matsuo, Mark E. Fortini
date = April 14, 1995
year = 1995
month = April
title = Notch Signaling
journal = Science
volume = 268
issue = 5208
pages = 225–232
issn =
pmid = 7716513
doi =
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url =
language = English
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quote = ]

Emc in sex determination

Sex in "Drosophila" is determined in part by the "Sex lethal" ("Sxl") gene; more precisely, it is turned 'on' in females and 'off' in males. Whether or not this gene will be expressed is determined by the ratio of sex chromosomes (X-chromosomes) to autosomal chromosomes.The fly embryo assesses this ratio by the difference between concentrations 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 genes

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.cite journal
quotes =
last = Cabrera
first = Carlos V.
authorlink =
coauthors = Maria C. Alonso and Hella Huikeshoven
date = 19 August 1994
year = 1994
month = August
title = Regulation of scute function by extramacrochaetae "in vitro" and "in vivo"
journal = Development
volume = 120
issue = 12
pages = 3595–3603
issn =
pmid = 7821225
doi =
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url =
language = English
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quote = ] Similar processes are also likely to exist in other mammals.

References