Neuronal clustering and fasciculation phenotype in Dscam- and Bax-deficient mouse retinas

Area of Science:

• Neuroscience
• Developmental Biology
• Retinal Cell Biology

Background:

• Retinal neurons form precise mosaics with specific spacing and dendritic coverage.
• Defects in these retinal mosaics, including cell clustering and dendritic fasciculation, are observed in Down syndrome cell adhesion molecule (Dscam) mutant mice.
• Increased cell numbers are also a feature of Dscam deficiency in certain retinal cell types.

Purpose of the Study:

• To compare the retinal mosaic defects in Dscam mutant retinas with those in Bax knockout retinas.
• To investigate the relationship between cell number, somal clustering, and dendritic fasciculation in these mutant mouse models.
• To determine if the observed retinal defects are unique to Dscam deficiency.

Main Methods:

• Immunolabeling of whole retinas from Dscam and Bax mutant mice.
• Quantitative analysis and spatial plotting of melanopsin-positive retinal ganglion cells (MRGCs) and dopaminergic amacrine cells (DACs).
• Assessment of gene dosage effects for Dscam and comparison of phenotypes across different genotypes.

Main Results:

• Dscam deficiency in mice leads to aberrant retinal neuron somal clustering and dendritic fasciculation.
• Bax knockout retinas exhibit similar clustering and fasciculation phenotypes, with intermediate cell numbers for MRGCs.
• DACs in both Dscam and Bax mutant retinas showed fasciculation not directly correlated with cell number increases, highlighting cell-type-specific responses.

Conclusions:

• Somal clustering and dendritic fasciculation in Dscam mutant retinas are not solely due to Dscam deficiency.
• These retinal mosaic disruptions can be observed in other genetic contexts, such as Bax knockout.
• The manifestation of retinal defects varies distinctly among different retinal cell types.