Intermediate progenitor cells (IPCs) are a type of

progenitor cell A progenitor cell is a biological cell that can differentiate into a specific cell type. Stem cells and progenitor cells have this ability in common. However, stem cells are less specified than progenitor cells. Progenitor cells can only differe ...

in the developing

cerebral cortex The cerebral cortex, also known as the cerebral mantle, is the outer layer of neural tissue of the cerebrum of the brain in humans and other mammals. The cerebral cortex mostly consists of the six-layered neocortex, with just 10% consisting o ...

. They are

multipolar cells A multipolar neuron is a type of neuron that possesses a single axon and many dendrites (and dendritic branches), allowing for the integration of a great deal of information from other neurons. These processes are projections from the neuron ce ...

produced by

radial glial cell Radial glial cells, or radial glial progenitor cells (RGPs), are bipolar-shaped progenitor cells that are responsible for producing all of the neurons in the cerebral cortex. RGPs also produce certain lineages of glia, including astrocytes and ol ...

s who have undergone asymmetric division. IPCs can produce neuron cells via

neurogenesis Neurogenesis is the process by which nervous system cells, the neurons, are produced by neural stem cells (NSCs). It occurs in all species of animals except the porifera (sponges) and placozoans. Types of NSCs include neuroepithelial cells (NECs ...

and are responsible for ensuring the proper quantity of cortical neurons are produced. In mammals, neural stem cells are the primary progenitors during

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 ...

whereas intermediate progenitor cells are the secondary progenitors.

Function

Neurogenesis is a vital part of

embryonic development 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 ...

. IPCs divide symmetrically, primarily in the subventricular zone (SVZ) of the

neuroepithelium Neuroepithelial cells, or neuroectodermal cells, form the wall of the closed neural tube in early embryonic development. The neuroepithelial cells span the thickness of the tube's wall, connecting with the pial surface and with the ventricular or ...

to produce either a new pair of IPC's or a pair of neurons. Fully developed neurons are most likely targeted to the upper

cortical layers The cerebral cortex, also known as the cerebral mantle, is the outer layer of neural tissue of the cerebrum of the brain in humans and other mammals. The cerebral cortex mostly consists of the six-layered neocortex, with just 10% consisting of ...

. Recent studies have shown that IPC's are activated by similar factors in both adult and embryonic development, challenging the early notion that they were only needed in embryogenesis. Neurogenesis is also a two-tiered pattern. When radial glial cells divide, they produce one replacement radial glial cell and one IPC. That IPC can then divide to form two like neurons. This method is important because it allows more neurons to be produced while still conserving glia to regenerate the cycle. The asymmetric division of radial glial cells and the subsequent symmetric division of intermediate progenitor cells may be the mechanism that resulted in the expansion of the cerebral cortex during evolution. The interactions between symmetric and asymmetric division work to enhance the productiveness during the development period and allow the cortex to grow. Some intermediate progenitor cells migrate via the

rostral migratory stream The rostral migratory stream (RMS) is a specialized migratory route found in the brain of some animals along which neuronal precursors that originated in the subventricular zone (SVZ) of the brain migrate to reach the main olfactory bulb (OB ...

to the

olfactory bulb The olfactory bulb (Latin: ''bulbus olfactorius'') is a neural structure of the vertebrate forebrain involved in olfaction, the sense of smell. It sends olfactory information to be further processed in the amygdala, the orbitofrontal cortex (O ...

and differentiate further. Overall, IPCs are crucial to both adult and embryonic neural development, but the research explaining the mechanisms for their symmetric division is still limited.

Regulation of IPCs

During development, intermediate progenitor cells are spatially associated with blood vessels. Once the vessels have passed into the brain's cortex, IPCs mimic their capillary patterns. After alignment, IPC divisions are localized to the vessel branches, suggesting that the vascular system is needed to produce the proper

stem-cell niche Stem-cell niche refers to a microenvironment, within the specific anatomic location where stem cells are found, which interacts with stem cells to regulate cell fate. The word 'niche' can be in reference to the ''in vivo'' or ''in vitro'' stem-cell ...

for differentiation. Tbr2 was also found to be organized along blood vessels. It is assumed that Tbr2 are needed to ensure the proper patterns of IPC division through its action in a

signaling cascade A biochemical cascade, also known as a signaling cascade or signaling pathway, is a series of chemical reactions that occur within a biological cell when initiated by a stimulus. This stimulus, known as a first messenger, acts on a receptor that ...

. Nfix is thought to be a necessary transcription factor facilitating proper symmetric and asymmetric division. It was identified following neurogenesis inadequacies observed when cells presented Nfix deficiencies. Tis21 was found to regulate the frequency of symmetric divisions is response to Tis21 levels, suggesting it plays some role in the mechanism for division.

References

{{reflist Cells Cerebral cortex

Function

Regulation of IPCs

See also

References