Liprin-α1 mutants exhibit a specific pattern of disruption in the structure of the cartridge, the synaptic unit in the lamina. Some cartridges have either >6 or <6 R cells axons, and some adjacent cartridges fuse.
R-cells proliferate normally during the third instar larval stage in Liprin-α1 eye-specific mosaics and display normal morphological differentiation during pupal and adult stages. Liprin-α1 mutant R cell axons select appropriate ganglion-specific targets in the lamina and the medulla and induce appropriate neuronal differentiation in the lamina target field. These axons also elaborate topographically appropriate maps in each region, with glial cell differentiation in these areas also appearing largely normal.
R cell shape and rhabdomere morphology are unaffected in Liprin-α1 mutants.
The behaviour of Liprin-α1 mutant axons (generated through MARCM) is indistinguishable from wild-type along their trajectories into the lamina plexus, with each axon remaining tightly associated with the axon bundle of its wild-type neighbours from the same ommatidium. However, once within the lamina plexus, unlike wild-type R cells, Liprin-α1 mutant R cells typically display specific defects in axon extension toward their targets. Two types of defect are observed. Approximately 64% of Liprin-α1 mutant axons completely fail to extend away from the ommatidial bundle, whereas 21% make weak, morphologically abnormal extensions; the remaining axons extend normally. All R cell subtypes are equally affected.
Using the MARCM method, in 100% of cartridges in which lamina neurons are homozygous for Liprin-α1, normal spacing and structure is observed. The projections of R4 axons are invariably unaffected by the presence of mutant target cells.
Liprin-α1 has abnormal neuroanatomy | pupal stage | somatic clone phenotype, enhanceable by Scer\GAL4elav-C155/CadNUAS.cIa
Liprin-α1 has photoreceptor neuron | pupal stage | somatic clone phenotype, enhanceable by Scer\GAL4elav-C155/CadNUAS.cIa
Expression of CadNScer\UAS.cIa under the control of Scer\GAL4elav-C155 in Liprin-α1 somatic mutant clones enhances the photoreceptor targeting defects.