There has been recent evidence that G(z) may play a role in the transmission of the neurotrophic signal from nerve terminals to the cell bodies [Johanson, S.O., Crouch, M.F., Hendry, I.A., Signal transduction from membrane to nucleus: the special case for neurons, Neurochem. Res. 21 (1996) 779-785]. We examined the developmental expression of the at subunit of G(z) (G(zα)) in the peripheral and central nervous systems of the mouse. Our laboratory has developed a quantitative reverse transcription-polymerase chain reaction (RT-PCR) for G(zα), which makes use of a fragment of the PCR product shortened by 107 base pairs creating a standard which mimics the original RNA. Serial dilutions of the mouse RNA with a constant concentration of mimic RNA were made and the point where equal amounts of product are formed allows accurate measurement of G(zα) mRNA in the tissue. We have demonstrated that in the developing mouse superior cervical ganglion (SCG), dorsal root ganglion (DRG) and trigeminal ganglion the expression of G(zα) mRNA is highest perinatally. From 3 weeks of age, in all tissues with the exception of the SCG, G(zα) mRNA levels fall to lower levels in the adult animal. The developmental pattern of expression of G(zα) in both the cerebellum and the brain differs from the peripheral nervous system. In the cerebellum, G(zα) mRNA expression is highest around birth and in the brain it is highest around third postnatal week and then the levels decline as adulthood is approached. These results suggest that the highest level of G(zα) mRNA is expressed at the time when target tissue innervation is occurring. This further strengthens the hypothesis that G(zα)is important in the transfer of information from target tissues to the innervating nerve cells.
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