LOCALIZATION AND ALTERNATIVE SPLICING OF AGRIN MESSENGER-RNA IN ADULT-RAT BRAIN - TRANSCRIPTS ENCODING ISOFORMS THAT AGGREGATE ACETYLCHOLINE-RECEPTORS ARE NOT RESTRICTED TO CHOLINERGIC REGIONS

Agrin is a protein implicated in the formation and maintenance of the neuromuscular junction. In addition to motor neurons, agrin mRNA has b een detected in the brains of embryonic rat and chick and adult marine ray, suggesting that this molecule may also be involved in the format ion of synapses between neurons. As a step toward understanding agrin' s role in the CNS, we utilized Northern blot and in site hybridization techniques to analyze the regional distribution and cellular localiza tion of agrin mRNA in the spinal cord and brain of adult rats. The res ults of these studies indicate that the agrin mRNA is expressed predom inantly by neurons broadly distributed throughout the adult CNS. Moreo ver, expression of agrin mRNA is not restricted to cholinergic structu res or regions of the brain receiving cholinergic input. Recently, RNA isolated from rat embryonic spinal cord was shown to contain four alt ernatively spliced agrin mRNAs, referred to as agrin(0), agrin(8), agr in(11), and agrin(19), each of which encodes agrin proteins that are a ctive in acetylcholine receptor aggregating assays (Ferns et al., 1992 ). Using the polymerase chain reaction we demonstrate that all four of these agrin transcripts are expressed within the adult CNS. Agrin(0), agrin(6), and agrin(19) were present in all regions analyzed. In cont rast, agrin(11) was detected only in forebrain. Results of these studi es indicate that both the level of expression and pattern of alternati ve splicing of agrin mRNA are differentially regulated in the brain. T he broad and predominantly neuronal distribution of agrin mRNA in the adult brain suggests that, in addition to its role at the neuromuscula r junction, agrin may play a role in formation and maintenance of syna pses between neurons in the CNS.