Cajal, Retzius, and Cajal-Retzius cells

Area of Science:

• Neuroscience
• Developmental Biology
• Cell Biology

Background:

• The marginal zone (MZ) of the cerebral cortex, also known as layer I, is vital for neuronal migration and cortical development.
• This layer hosts diverse cell types, including Cajal-Retzius (CR) cells, which have been studied for over a century.
• Despite extensive research, the precise phenotype and function of MZ/layer I cells, particularly CR cells, remain incompletely defined.

Purpose of the Study:

• To review the historical research on Cajal-Retzius (CR) cells by pioneers like Ramon y Cajal and Retzius.
• To connect classical morphological descriptions of CR cells with current understanding based on cellular markers.
• To propose a standardized definition of "CR cell" as reelin (Reln)-expressing neurons in the MZ/layer I.

Main Methods:

• Historical literature review of seminal works on cortical development.
• Analysis of morphological characteristics described in Golgi staining studies.
• Integration of findings from modern studies utilizing cellular markers.

Main Results:

• The term "CR cell" has been inconsistently applied since Cajal's initial descriptions.
• Current research often equates "CR cells" with reelin (Reln)-positive cells in the MZ/layer I.
• A clear link is established between historical morphological observations and contemporary marker-based identification.

Conclusions:

• Clarifying the definition of CR cells is essential for understanding their role in cortical development and function.
• The proposed definition of CR cells as Reln-expressing neurons in MZ/layer I provides a consistent framework for future research.
• Further investigation into the specific functions of these cells in prenatal, developing, and adult brains is warranted.