Insulin gene enhancer protein ISL-1 is a
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 ...
that in humans is encoded by the ''ISL1''
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 ...
.
Function
This gene encodes 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 ...
containing two
N-terminal
The N-terminus (also known as the amino-terminus, NH2-terminus, N-terminal end or amine-terminus) is the start of a protein or polypeptide, referring to the free amine group (-NH2) located at the end of a polypeptide. Within a peptide, the ami ...
LIM domain
LIM domains are protein structural domains, composed of two contiguous zinc fingers, separated by a two-amino acid residue hydrophobic linker. The domain name is an acronym of the three genes in which it was first identified (LIN-11, Isl-1 and M ...
s and one
C-terminal
The C-terminus (also known as the carboxyl-terminus, carboxy-terminus, C-terminal tail, C-terminal end, or COOH-terminus) is the end of an amino acid chain (protein or polypeptide), terminated by a free carboxyl group (-COOH). When the protein is ...
homeodomain
A homeobox is a DNA sequence, around 180 base pairs long, that regulates large-scale anatomical features in the early stages of embryonic development. For instance, mutations in a homeobox may change large-scale anatomical features of the full-g ...
. The encoded protein plays an important role in the
embryogenesis
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 sperm ...
of pancreatic
islets of Langerhans
The pancreatic islets or islets of Langerhans are the regions of the pancreas that contain its endocrine (hormone-producing) cells, discovered in 1869 by German pathological anatomist Paul Langerhans. The pancreatic islets constitute 1–2% of ...
. In mouse embryos, a deficiency of this gene results in failure to undergo neural tube motor neuron differentiation.
Interactions
ISL1 has been shown to
interact
Advocates for Informed Choice, dba interACT or interACT Advocates for Intersex Youth, is a 501(c)(3) nonprofit organization using innovative strategies to advocate for the legal and human rights of children with intersex traits. The organizati ...
with
Estrogen receptor alpha
Estrogen receptor alpha (ERα), also known as NR3A1 (nuclear receptor subfamily 3, group A, member 1), is one of two main types of estrogen receptor, a nuclear receptor (mainly found as a chromatin-binding protein)
that is activated by the sex ...
.
Role in cardiac development
ISL1 is a marker for cardiac progenitors of the
secondary heart field
Secondary may refer to: Science and nature
* Secondary emission, of particles
** Secondary electrons, electrons generated as ionization products
* The secondary winding, or the electrical or electronic circuit connected to the secondary winding i ...
(SHF) which includes the right ventricle and the outflow tract. The biological function of ISL1 is demonstrated through ISL1 mutant mice and chick embryos that have altered cell proliferation, survival, and migration of cardiogenic precursors and severe cardiac defects. More recently it has been defined as a marker for a cardiac progenitor cell lineage that is capable of differentiating into all 3 major cell types of the heart:
cardiomyocytes
Cardiac muscle (also called heart muscle, myocardium, cardiomyocytes and cardiac myocytes) is one of three types of vertebrate muscle tissues, with the other two being skeletal muscle and smooth muscle. It is an involuntary, striated muscle that ...
,
smooth muscle
Smooth muscle is an involuntary non-striated muscle, so-called because it has no sarcomeres and therefore no striations (''bands'' or ''stripes''). It is divided into two subgroups, single-unit and multiunit smooth muscle. Within single-unit mus ...
and
endothelial
The endothelium is a single layer of squamous endothelial cells that line the interior surface of blood vessels and lymphatic vessels. The endothelium forms an interface between circulating blood or lymph in the lumen and the rest of the vessel ...
cell lineages.
Research has shown that ISL1 promotes differentiation of cardiac cells and a depletion of ISL1 can respecify the cell fate of nascent cardiomyocytes, such as from ventricular to an atrial identity.
The validity of ISL1 as a marker for cardiac progenitor cells has been questioned since some groups have found no evidence that ISL1 cells serve as cardiac progenitors.
Furthermore, ISL1 is not restricted to second heart field progenitors in the developing heart, but also labels cardiac
neural crest
Neural crest cells are a temporary group of cells unique to vertebrates that arise from the embryonic ectoderm germ layer, and in turn give rise to a diverse cell lineage—including melanocytes, craniofacial cartilage and bone, smooth muscle, per ...
.
This paper supports work from the Vilquin group in 2011, which concluded that ISL1 can represent cells from both neural crest and cardiomyocyte lineages.
While it has been demonstrated by multiple groups that ISL1-positive cells can indeed differentiate into all 3 major cell types of the heart, their significance in cardiovascular development is still unclear and their clinical relevance has been seriously questioned.
References
Further reading
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External links
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{{NLM content
Transcription factors