Abstract:
Methylmercury (MeHg) is a developmental neurotoxicant in rodents, primates and humans. The primary effects of developmental exposure include changes in cell cycling, cell migration and gene expression. We have previously demonstrated significant alterations in the expression of P21 and Gadd153 in primary rat embryonic midbrain CNS cells in vitro following a 24-hr MeHg exposure. To identify changes in the expression of other, unidentified gened in response to NeHg exposure, we have utilized Differential Display to isolate 24 cDNA fragments (designated cDNAs A through X) which are induced/repressed in rat embryonic CNS cells following a 24-hr MeHg exposure.. Of these cDNAs, 20 have been cloned into PGEM-T vectors and sequenced. A preliminary search in GenBank has revealed that 4 of the 20 sequenced cDNAs (A, E, J, and V) have high hmology to known genes. cDNA A appears to encode for the rat nuclear RNA U1A. cDNA E appears to encode for the S27 ribosomal protein. cDNAs J and V have high homology to a sequence 3' to the mitochondrial cytochrome c oxidase subunits I, II and III, and the subunit 6 of the ATPase gene. Northern blot analysis confirmed the Differential Display results for the cDNA J and showed an average 2.3-fold induction of cDNA J. Cytochrome c Oxidase subunit I was shown to be induced on average 2.5 fold in rat embryonic CNS cells exposed to MeHg. The mitochondrial Cytochrome c Oxidase subunits II, III and ATPase subunit 6 were shown to not be changed by exposre to MeHg in rat embryonic CNC cells, although the band sizes on Northern blots matched in expected transcript length of mitochondrial Cytochrome c Oxidase subunits. A model was proposed to explain the relationship between MeHg-induced apoptosis and cell death and the transcriptional induction of Cytochrome c Oxidase subunits. Characterization of th altered expression of these genes following MeHg exposure should help in assessing the mechanisms and cellular impacts of MeHg developmental toxicity.