MRNA levels of the differentiation-associated linker histone variant H1 zero in mitotically active and postmitotic senescent human diploid fibroblastcell populations

The mRNA levels of the linker histone variant Hlo, which is tightly associa ted with differentiation, have been studied in the present investigation in an in vitro model ageing human diploid fibroblast (HDF) cell system as a f unction of cumulative population doublings (CPDs) in mitotically active and senescent cell populations. According to our previous findings the synthes is rate of the Hlo protein does not change as a function of CPDs as long as the cells are proliferating. However, when cells reach senescence, the syn thesis rate of Hlo increases in both naturally aged as well as in cell popu lations artificially aged by treatment with sodium butyrate. In the present investigation, it is shown that the Hlo mRNA levels remain relatively cons tant in mitotic cells with a slight decrease in cell cultures of late CPDs, i.e. in populations which still retain a mitotic potential, but are toward the end of their proliferative Lifespan. However, when cells senesce and a re no longer capable of synthesizing DNA, the Hlo mRNA levels increase in n aturally aged cells while artificially aged cells still maintain mRNA level s comparable to those of mitotic cells. (C) 2001 Elsevier Science Inc. All rights reserved.