Transient developmental expression of CD15 in the motor and auditory cortex of the mouse.

The distribution of the glycoprotein CD15 (FAL, SSEA-1, Le(x)) in the developing cortex of the mouse has been examined by immunohistochemistry of paraffin sections. The pattern of CD15 immunoreactivity was observed to occur in 4 stages. In the first stage, the presumptive subplate region in the lateral and rostral parts of the developing isocortex was transiently labelled at E12. In the second stage, between E13 and E17, very faint label was found only in the ventricular germinal zone, possibly within radial glial fibres. The third stage began at E18, when transient labelling of several discrete cortical areas was apparent; the motor cortex (from E18 to P3), an area in the temporal lobe (presumptive primary auditory cortex; from E18 to P5.5) and the piriform and entorhinal cortices (from E18 to P3). The final stage began at P2, when a mosaic camouflage pattern of labelling started to appear throughout the developing cortex, particularly in layer I. The distribution of the transient label in the motor cortex during the perinatal period suggests that it may be associated with early events in corticospinal or other projection neuron maturation (apical dendrite growth and differentiation). The labelling in the presumptive auditory cortex (Te1) may also be involved in the differentiation of neurons in the upper cortical plate.