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Subplate cells in the mouse are generally defined as cells located in the subplate layer between the white matter and layer 6a.They are some of the earliest born and maturing cells of the cerebral cortex. All of the early birthdating studies on rodent preplate and subplate cells were of rats. (1977) and Bayer and Altman (1990) determined that rat preplate neurons are generated from E14 (plug date = E1).In this study, we have examined the birth order of rod and cone bipolar cells in the developing mouse and rat Using retroviral lineage analysis with the histochemical marker alkaline phosphatase, the percentage of cone and rod bipolar cells born on postnatal day 0 (P0), P4, and P6 were determined, based upon the well characterized morphology of these cells in the adult rat retina.In this experiment, we have demonstrated that cone bipolar genesis clearly precedes rod bipolar genesis.The postnatal subplate layer in mouse contains neurons with expression of the presynaptic protein complexin 3 (Cplx3), connective tissue growth factor (CTGF), the orphan nuclear receptor Nr4a2 (Nurr1), and the G-protein-coupled lysophosphatidic acid receptor 1 (Lpar1/Edg2). Cells born on E14 are destined for the future marginal zone, whereas cells born on E15 eventually contribute to both marginal zone and subplate zone (Rickmann et al. Some cells located in the late embryonic or postnatal rat subplate zone are also generated after E15 (Rickmann et al. Furthermore, Bayer and Altman (1990) followed the distribution of E14-born neurons in the lateral embryonic cortex and concluded that they are dispersed in the cortical plate at E16 but aggregate at the lower edge of the cortical plate by E17 and form a separate band below the cortical plate at E18, thereby highlighting that subplate cells may be born early but that the subplate layer is not formed as a cytoarchitectonically distinct structure until after the cortical plate has emerged.
These waves of bipolar genesis correspond to the order of genesis of the presynaptic photoreceptor cell types. The adult retina contains a complement of well-characterized neurons and glia in three cellular layers (outer nuclear, inner nuclear and ganglion cell layers) separated by two distinct plexiform layers (the inner and outer plexiform layers) containing cellular processes and synapses .
Morphological criteria have been established that distinguish nine types of cone bipolar cells and one type of rod bipolar cell in mouse and rat.
While anatomical and physiological aspects of bipolar types have been actively studied, little is known about the sequence of events that leads to bipolar cell type specification and the potential relationship this process may have with synapse formation in the outer plexiform layer.
Our study also demonstrates that early-born subplate neurons labeled by Cplx3, Nurr1, and Lpar1-GFP survive preferentially after the first postnatal week compared with other subplate neurons. At embryonic ages, subplate cells are involved in thalamocortical and corticofugal axon guidance, including establishment of topographical projections (Mc Connell et al. This prompted our search for molecular markers of the postnatal subplate (Hoerder-Suabedissen et al 2009), in which we reported the presynaptic protein complexin 3 (Cplx3), connective tissue growth factor (CTGF), and the orphan nuclear receptor Nr4a2 (Nurr1), among others, as molecules that are consistently expressed in the mouse subplate layer during the postnatal period.
Mouse subplate cells are generally defined as cells located in the subplate layer between the white matter (WM) and layer 6a and are among the cortical cells that are born earliest and mature first (Angevine and Sidman 1961; Price et al. Additionally, our screen identified the G-protein-coupled lysophosphatidic acid receptor 1 (Lpar1/Edg2) as another putative marker of the postnatal subplate (Hoerder 2007).