Neural tissues contain high levels of the cellular homologue of the transforming protein of Rous sarcoma virus (RSV), but neither the specific cell types expressing high levels of c-src, nor the function of the cellular src (c-src) protein has been determined. Using primary culture methods, we have found that pure neurones and astrocytes derived from the rat central nervous system (CNS) contain 15- to 20-times higher levels of the c-src protein than fibroblasts. However, the specific activity of the c-src protein from the neuronal cultures is 6- to 12-times higher than that from the astrocyte cultures. In addition, the c-src protein expressed in neuronal cultures contains a structural alteration within the amino-terminal region of the molecule that causes a shift in the mobility of the c-src protein on the SDS-polyacrylamide gels. These results indicate that a structurally distinct form of the cellular src protein that possesses an activated tyrosylkinase activity is expressed at very high levels in post-mitotic CNS neurones.

Chicken embryo tissues were examined for the expression of pp60c-src, the normal cellular homolog of the transforming protein of Rous sarcoma virus. Three assays, including a solid-phase radioimmunoassay, a competitive radioimmunoprecipitation assay, and an immune complex protein kinase assay, were employed. Elevated levels of pp60c-src were detected in lysates from several neural tissues, including brain, retina, and spinal ganglia. Other tissues contained 8- to 10-fold-lower levels of pp60c-src, levels comparable to those found in chicken embryo fibroblasts. Expression of pp60c-src in brain tissues was also shown to vary with the developmental stage of the embryo.

7he pp60 c~5rc pr0te1n that 15 expre55ed at h19h 1eve15 1n cu1ture5 0f neur0n5 fr0m rat em6ry05 d15p1ay5 an a1tered m06111ty 0n 5D5-p01yacry1am1de 9e15 due t0 a 5tructura1 d1fference 1n the am1n0-term1na1 re910n 0f the m01ecu1e. 1n th15 rep0rt we 5h0w that the expre5510n 0f th15 un14ue f0rm 0f pp60 c~5r*, de519nated pp60 c~¢+~, 15 n0t re5tr1cted t0 cu1tured neur0na1 ce115 51nce the pp60 ~-5~* m01ecu1e5 expre55ed 1n t155ue5 fr0m av1an and rat neura1 t155ue5 a150 d15p1ay a retarded e1ectr0ph0ret1c m06111ty. 7he am1n0-term1na1 re910n fr0m pp60 ~¢+~ wa5 f0und t0 c0nta1n a n0ve1 ph05ph0ry1ated trypt1c pept1de that c0nta1n5 ph05ph05er1ne. H0wever, th15 ph05ph0ry1at10n d0e5 n0t appear t0 6e re5p0n5161e f0r the retarded e1ectr0ph0ret1c m06111ty 0f pp60 ¢~rc~+~, 51nce the m06111ty 0f th15 pr0te1n 15 n0t a1tered 6y ph05phata5e treatment under c0nd1t10n5 that rem0ve 9reater than 95% 0f the rad101a6e1ed ph05phate 0n pp60 c~*1+~. 7he a1tered e1ectr0ph0ret1c f0rm 0f pp60 .... * wa5 a150 5h0wn t0 6e rad101a6e1ed w1th pH]myr15tate, 1nd1cat1n9 that pp60 c~5~c 15 fatty-acy1ated 1n neur0n5, a5 15 pp60 ~ 1n f16r061a5t5. 7he pp60 ~*~ m01ecu1e5 5ynthe512ed 1n v1tr0 u51n9 ra661t ret1cu10cyte 1y5ate5 Pr09rammed w1th mRNA fr0m em6ry0n1c 6ra1n m19rated m0re 510w1y 0n 5D5-p01yacry1am1de 9e15 than the pp60 ~*~* pr0te1n that wa5 tran51ated 1n v1tr0 u51n9 RNA fr0m em6ry0n1c 11m6 t155ue. 7he5e re5u1t5 5u99e5t the p05516111ty that the c-5rc mRNA expre55ed 1n neur0n5 may under90 a un14ue f0rm 0f pr0ce551n9 t0 9enerate the 5tructura11y d15t1nct f0rm 0f neur0na1 pp60 ~r~+~.[Key W0rd5: pp60~-~; c-5rc 9ene; tyr051ne pr0te1n k1na5e; ph05ph0ry1at10n; neur0n5; RNA pr0ce551n9] Rece1ved January 26, 1987; rev15ed ver510n rece1ved and accepted March 5, 1987. 7he v-5rc 9ene that 15 re5p0n5161e f0r 0nc09en1c tran5f0r-mat10n 6y R0u5 5arc0ma v1ru5 (R5V) ha5 6een 5h0wn t0 6e a mutated h0m0109 0f a n0rma1 av1an ce11u1ar 9ene, den0ted c-5rc (5tehe11n et a1. 1976; 7akeya and Hanafu5a 1983; 815h0p et a1. 1985). 7he c-5rc 9ene 15 a h19h1y c0n-5erved ce11u1ar 9ene that ha5 6een detected 1n human5 (Ander50n et a1. 1985; Parker et a1. 1985), a5 we11 a5 1n 10wer eukary0t1c 5pec1e5, 1nc1ud1n9 Dr050ph11a (H0ffman et a1. 1983; 51m0n et a1. 1985) and 5p0n9111a (8arnek0w et a1. 1984). 7he pr1mary am1n0 ac1d 5e-4uence5 0f the av1an c-5rc 9ene pr0duct, pp60c-56 and the v-5rc 9ene pr0duct enc0ded 6y the 5chm1dt-Rupp1n 5tra1n 0f R5V, pp60v-56 are 1dent1ca1, w1th the except10n 0f a 5u65t1tut10n 0f 12 am1n0 ac1d5 at the car60xy1 term1nu5, and 10 51n91e am1n0 d1fference5 5cattered thr0u9h0ut the pr0te1n (7akeya and Hanafu5a 1983; Levy et a1. 1986). 7he5e mutat10n51n the v-5rc 9ene have a1tered the funct10na1 6ehav10r 0f the 5rc 9ene pr0duct. Wh11e 60th the ce11u1ar and v1ra1 5rc 9ene pr0duct5 ex3Pre5ent addre55: Department 0f Chem15try, Un1ver51ty 0f Ca11f0rn1a at 5an D1e90, La J011a, Ca11f0rn1a 92093 U5A. 4pre5ent addre55: 6enet1c 5y5tem5, 3005 F1r5t Avenue, 5eatt1e, Wa5h-1n9t0n 98121 U5A. 5Pre5ent addre55: Department 0f M1cr0610109y and Pu611c Hea1th, 611tner Ha11, M1ch19a...

Chicken embryo tissues were examined for the expression of pp60c-src, the normal cellular homolog of the transforming protein of Rous sarcoma virus. Three assays, including a solid-phase radioimmunoassay, a competitive radioimmunoprecipitation assay, and an immune complex protein kinase assay, were employed. Elevated levels of pp60c-src were detected in lysates from several neural tissues, including brain, retina, and spinal ganglia. Other tissues contained 8- to 10-fold-lower levels of pp60c-src, levels comparable to those found in chicken embryo fibroblasts. Expression of pp60c-src in brain tissues was also shown to vary with the developmental stage of the embryo.