MAL MESSENGER-RNA IS INDUCED DURING THE DIFFERENTIATION OF HUMAN EMBRYONAL CARCINOMA-CELLS INTO NEURONS AND IS ALSO LOCALIZED WITHIN SPECIFIC REGIONS OF THE HUMAN BRAIN

We have found that the MAL gene, which encodes a membrane proteolipid expressed during the late stages of T-lymphocyte maturation, is also a ctivated during neuronal differentiation of NTERA2 human embryonal car cinoma cells following induction with retinoic acid. An RT-PCR fragmen t with a sequence identical to MAL was found amongst 30 cloned DNA fra gments corresponding to genes putatively activated during NTERA2 diffe rentiation and isolated using a differential display PCR screen. PCR a nd Northern blot analysis with a cloned MAL cDNA as a probe confirmed that MAL is not expressed by undifferentiated NTERA2 EC cells, but is expressed, predominantly as a 1.1 kb transcript, within 7 days of reti noic acid-induced differentiation and later in the post-mitotic neuron s arising in such cultures. MAL was not expressed in the non-neuronal lineages induced by treatment of NTERA2 cells with the gratuitous indu cer hexamethylene bisacetamide. Analysis of cDNA libraries constructed from EC cells, purified neurons and a sub-population of non-neuronal cells (ME311+), confirmed that expression of the MAL gene is activated in the neural lineage of NTERA2 differentiation. Using in situ hybrid isation we found that MAL is expressed in the human CNS and especially in grey matter of the cerebral cortex, with less in the cerebellum an d the amygdala and little or none in subcortical white matter. In cont rast to reports concerning the expression pattern of a rat MAL homolog ue, MAL was expressed in the human brain predominantly in cell bodies which include neurons, correlating with in vitro data from the NTERA2 line.