2002), and both DPYL proteins and their companion semaphorins
have been reported to be up-regulated in response to nervous system injury (Murphey et al.
Third, two classes of molecular inhibitors to growth are present in the lesioned CNS to actively block axonal growth: inhibitory extracellular matrix proteins, including chondroitin sulfate proteoglycans, and inhibitory proteins present on adult myelin, including Nogo, myelin-associated glycoprotein, oligodendrocyte-myelin glycoprotein, netrin, semaphorins
, Wnt proteins, and others [64-66].
Semaphorins are a large family of proteins that act as guidance molecules in the developing nervous system.
This may mean that while semaphorin 3F is attracting immature myelin- making cells to sites needing repair, increased signals from semaphoring 3A are preventing repair from occurring.
Semaphorins are embryologically active molecules that regulate nerve growth and direction.
They have also identified a possible method of regulating the growth of new nerves and axons through a protein called semaphorin 4F.
Axons--the long extensions formed by growing brain cells--display neuropilin-1, which reacts to proteins called semaphorins
or collapsins, which serve as axonal stop signs.
Tessier-Lavigne explains that repellent molecules, such as a group known as collapsins or semaphorins
, send a chemical message to axons, saying, "Don't come this way.