Retrograde signaling
In this regard, the chloroplast or mitochondria act as a sensor for internal external stimuli which activate a signaling pathway.
[7] Originally believed to be photosynthetic bacteria, the mitochondria and chloroplast transferred some of their DNA to the membrane protected nucleus.
This transfer of DNA further required a network of communication to properly respond to external and internal signals and produce requisite proteins.
In Saccharomyces cerevisiae, if the mitochondria fails to develop properly, they will stop growing until the issue is addressed or cell death is induced.
[15] Reactive oxygen species are created as a by-product of aerobic respiration and act on genes involved in the stress response.
[15] Depending on the stress, reactive oxygen species can act on neighboring cells to initiate a local signal.
Detection of these stresses in the cell will induce the formation of compounds that can then act on the nucleus to produce pathogen resistance genes or drought tolerance.
[23][24] Retrograde signaling may also play a role in long-term potentiation (LTP), a proposed mechanism of learning and memory, although this is controversial.
[31] Additionally, literature suggests that NO can act as intracellular messengers in the brain and can also have an effect on the presynaptic glutamatergic and GABAergic synapses.
[33] The activation of endocannabinoids results in the release of particular neurotransmitters at the excitatory and inhibitory synapses of a neuron, ultimately impacting various forms of plasticity.
A flurry of work in the early 1990s to demonstrate the existence of a retrograde messenger and to determine its identity generated a list of candidates including carbon monoxide,[40] platelet-activating factor,[41][42] arachidonic acid,[43] and nitric oxide.
Nitric oxide has received a great deal of attention in the past, but has recently been superseded by adhesion proteins that span the synaptic cleft to join the presynaptic and postsynaptic cells.
[39] The endocannabinoids anandamide and/or 2-AG, acting through G-protein coupled cannabinoid receptors, may play an important role in retrograde signaling in LTP.
