Figure 6. Characterization of transglutaminase activity and TG2 protein levels in the nervous system.

A) Cold/Ca²⁺ stable tubulin was enriched in brain but was at or below levels of detection in non-neuronal tissues other than testes. The stable tubulin fraction in testes is presumably due to the stable microtubules in sperm flagella and may not be equivalent to the brain fraction. However, polyamines and TG2 are present in testes. B) Transglutaminase activity was present in various neural tissues including cerebral cortex (CC), brain stem (BS), spinal cord (SC), optic nerve (ON) and sciatic nerve (SN) from 5-week-old mice. C) Quantitative plots showed that transglutaminase activity was higher in axon-enriched compartments, like ON and SN, correlated with higher MT stability in axons. D) TG2 protein was also expressed differentially in various neural tissues. The same amount of total protein was loaded in each lane. Actin and GAPDH were loading controls. Actin was higher in axon-rich domains (ON and SN), while GAPDH was lower in axon-rich tissues as a fraction of total protein. E) Quantitative comparison shows TG2/actin ratio was lower in SN than ON but SN exhibited comparable levels of TG activity (C), thus other transglutaminase isoforms may contribute to axonal transglutaminase activity, particularly in the PNS. Statistical analysis was by Student T-test. **denotes P<0.001.