Ci protein, short for Cubitus interruptus, is a
zinc finger
A zinc finger is a small protein structural motif that is characterized by the coordination of one or more zinc ions (Zn2+) in order to stabilize the fold. It was originally coined to describe the finger-like appearance of a hypothesized struct ...
containing
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 f ...
involved in the
Hedgehog
A hedgehog is a spiny mammal of the subfamily Erinaceinae, in the eulipotyphlan family Erinaceidae. There are seventeen species of hedgehog in five genera found throughout parts of Europe, Asia, and Africa, and in New Zealand by introductio ...
signaling pathway
In biology, cell signaling (cell signalling in British English) or cell communication is the ability of a cell to receive, process, and transmit signals with its environment and with itself. Cell signaling is a fundamental property of all cellul ...
.
In the absence of a signal to the Hedgehog signaling pathway, the Ci protein is cleaved and destroyed in
proteasomes. It isn't, however, completely destroyed; part of the protein survives and acts as a
repressor in the
nucleus
Nucleus ( : nuclei) is a Latin word for the seed inside a fruit. It most often refers to:
*Atomic nucleus, the very dense central region of an atom
* Cell nucleus, a central organelle of a eukaryotic cell, containing most of the cell's DNA
Nucl ...
, keeping genes responsive to the Hedgehog signal silent.
Degradation of Ci
The degradation of Ci protein depends on a large multiprotein complex, which contains a serine/threonine
kinase of unknown function, an
anchoring protein that binds to
microtubules (to keep the Ci protein out of the nucleus) and an adaptor protein.
When the Hedgehog signaling pathway is turned on, the Ci
proteolysis is suppressed and the unprocessed CI protein enters the nucleus, where it activates the transcription of its target genes. Ci undergoes complete or partial degradation in the cells, the detailed molecular mechanism is poorly understood. It has been reported that an AAA ATPase Ter94 complex and K11/K48 ubiquitin chains are involved in the selection of Ci degradation.
Target genes
* The ''Wingless'' protein in
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 speci ...
, which is crucial to the embryogenesis of the fruit fly, and acts through the
Wnt signaling pathway
The Wnt signaling pathways are a group of signal transduction pathways which begin with proteins that pass signals into a cell through cell surface receptors. The name Wnt is a portmanteau created from the names Wingless and Int-1. Wnt signaling ...
.
* The ''Patched'' receptor protein of the
Hedgehog signaling pathway
The Hedgehog signaling pathway is a signaling pathway that transmits information to embryonic cells required for proper cell differentiation. Different parts of the embryo have different concentrations of hedgehog signaling proteins. The pathwa ...
, which production acts as a
negative feedback, since the resulting increase in Patched protein on the cell surface inhibits the Hedgehog pathway.
References
External links
*
''Drosophila'' ''cubitus interruptus'' - The Interactive Fly
{{Transcription factors
Transcription factors
Hedgehog signaling pathway