Reticulon 1 and 3 are essential for axonal growth and synaptic maintenance associated with the intellectual development.

Reticulon (RTN) proteins are a family of proteins biochemically identified for shaping tubular endoplasmic reticulum (ER), a subcellular structure important for vesicular transport and cell to cell communication. In our recent study of mice with knockout of both reticulon 1 (Rtn1) and Rtn3, we discovered that Rtn1-/-;Rtn3-/- (brief as R1R3dKO) mice exhibited neonatal lethality, despite mice deficient in either RTN1 or RTN3 exhibit no discernible phenotypes. This has been the first case to find early lethality in animals with deletion of partial members of RTN proteins. The entire penetrant for neonatal lethality can be attributed to multiple defects including impaired neuromuscular junction found in the diaphragm. We also observed significantly impaired axonal growth in a regional specific manner, detected by immunohistochemical staining with antibodies to neurofilament light chain (NFL) and neurofilament medium chain (NFM). Ultrastructural examination by electron microscopy revealed a significant reduction in synaptic active zone length in the hippocampus. Mechanistic exploration by unbiased proteomic assays revealed reduction of proteins such as FMR1, Staufen2, Cyfip1, Cullin-4B and PDE2a, which are known components in the fragile X mental retardation pathway. Together, our results reveal that RTN1 and RTN3 are required to orchestrate neurofilament organization and intact synaptic structure of the central nervous system.