Abstract
Purpose :
The transcription factor FoxP2 has recently been shown to be expressed by four types of ganglion cell including direction selective cells in mouse retina (Rousso et al., Cell Reports, 2016). The same study suggested that FoxP2 is expressed by a subpopulation of midget ganglion cells in macaque retina. The aim of the present study was to identify the ganglion cell type(s) expressing FoxP2 in a non-human primate, the marmoset.
Methods :
In total five eyes from adult (one female, three males) marmosets Callithrix jacchus, were obtained after unrelated electrophysiological experiments. The vitreous was removed and the posterior eye cup was immersion fixed in 4% paraformaldehyde for 60 min. The retinas were dissected, cut into quadrants and processed with antibodies against FoxP2 and secondary antibodies coupled to Alexa 488. One quadrant was also processed with antibodies to ChAT (choline acetyl transferase). Labeled cell nuclei were injected with DiI. In addition, double labeling immunohistochemistry with antibodies against RBPMS (RNA binding protein with multiple slicing), a marker for ganglion cells, was used to determine the proportion of FoxP2 labeled ganglion cells. Preparations were imaged using a Zeiss confocal microscope and ganglion cells were classified according to dendritic field size, morphology, and stratification.
Results :
In total 110 FoxP2 positive cells were classified as wide-field ganglion cells based on the presence of an axon and a large dendritic field. The cells derived from eccentricities between 0.4 to 11.4 mm. The large majority of the injected cells (84%) were bistratified, with the majority of their dendrites in the ON sublamina. The inner dendrites stratify in stratum 4 of the inner plexiform layer, the outer dendrites are found in stratum 2. The cells from distinct dendritic tufts in their peripheral dendritic field and thus we named them “tufted cells”. The remaining cell types included broad thorny, large bistratified and smooth monostratified cells. Midget cells were never labeled. FoxP2 positive ganglion cells make up an average of 13% of the total retinal ganglion cell population at eccentricities between 2 and 4mm.
Conclusions :
In marmoset, the transcription factor FoxP2 is preferentially expressed in tufted ganglion cells. FoxP2 is not a marker for midget ganglion cells in marmoset retina.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.