Pioneer neuron is a cell that is a derivative of preplate in the early stages of corticogenesis of the brain. Pioneer neurons settle in the marginal zone of the cortex and project to sub-cortical levels. In the rat, pioneer neurons are only present in prenatal brains. Unlike Cajal-Retzius cell

Cajal-Retzius cell

The term Cajal–Retzius cell is applied to reelin-producing neurons of the human embryonic marginal zone which display, as a salient feature, radial ascending processes that contact the pial surface, and a horizontal axon plexus located in the deep marginal zone...

s, these neurons are Reln

Reelin

Reelin is a large secreted extracellular matrix protein that helps regulate processes of neuronal migration and positioning in the developing brain by controlling cell–cell interactions. Besides this important role in early development, reelin continues to work in the adult brain. It modulates the...

-negative.

Pioneer neurons are born in the ventricular neuroepithelium all over the cortical primordium

Primordium

A primordium , in embryology, is defined as an organ or tissue in its earliest recognizable stage of development. Cells of the primordium are called primordial cells...

. In the rat cortex, they appear at embryonic day (E) 11.5 in the lateral aspect of the telencephalic vesicle and cover its whole surface on E12. These cells, which show intense immunoreactivity for calbindin

Calbindin

Calbindin refers to several calcium-binding proteins. They were originally described as vitamin D-dependent calcium-binding proteins in the intestine and kidney in the chick and mammals...

 and calretinin

Calretinin

Calretinin also known as 29 kDa calbindin is a vitamin D-dependent calcium-binding protein involved in calcium signaling. In humans, the calretinin protein is encoded by the CALB2 gene.- Function :...

, are characterized by their large size and axonal projection. They remain in the marginal zone after the formation of the cortical plate; they project first into the ventricular zone, and then into the subplate

Subplate

The transient fetal subplate zone, together with the marginal zone and the cortical plate, represents the developmental anlage of the mammalian cerebral cortex...

 and the internal capsule

Internal capsule

The internal capsule is an area of white matter in the brain that separates the caudate nucleus and the thalamus from the lenticular nucleus. The internal capsule contains both ascending and descending axons....

. Therefore, these cells are the origin of the earliest efferent pathway of the developing cortex.

Function

It is thought that axons of pioneer neurons serve as a pathway for additional neurons that develop later in the embryo and project their axons to the appropriate target. In many systems pioneer neurons are eliminated by programmed cell-death and are not present in the adult.

External links

• Neuronal Migration and Formation of Cellular Patterns During Brain Development - from the site of the University of Texas.

Authors of the article propose new criteria to distinguish between different cell types in the developing cortex.