Expression of H1 histone genes during mouse erythroleukemia cell differentiation

Abstract

The mammalian H1 histones consist of multiple somatic H1s, a testis specific H1t, and the replacement linker histone H1{dollar}\sp0.{dollar} Increased H1{dollar}\sp0{dollar} levels are found predominantly in terminally differentiated cells and tissues with little or no proliferation, as well as in cells that are induced to differentiate in vitro. We have shown that the H1{dollar}\sp0{dollar} gene encodes a polyadenylated mRNA which is very rapidly induced at the transcriptional level during the precommitment period of mouse erythroleukemia (MEL) cell differentiation. To investigate mechanisms controlling transcriptional induction of the H1{dollar}\sp0{dollar} gene, marked mouse H1{dollar}\sp0{dollar} gene constructs containing various lengths of 5{dollar}\sp\prime{dollar} promoter sequences were transfected into MEL cells and analyzed for expression upon induction of differentiation. A major transcription regulatory element was mapped to a region lying between {dollar}-{dollar}465 and {dollar}-{dollar}430. The DNA sequences within and around this region contain five nuclear protein binding sites identified by DNase I footprinting, methylation interference and electrophoretic mobility shift assays (5{dollar}\sp\prime{dollar} III-IV-II-I-V3{dollar}\sp\prime).{dollar} Four of these sites (III, II, I, V) share a sequence motif {dollar}(\rm 5\sp{lcub}\prime A{rcub}/\sb{lcub}C{rcub}{dollar}GGGGGG{dollar}\rm\sp{lcub}A{rcub}/\sb{lcub}C{rcub}3\sp\prime){dollar} containing a G{dollar}\sb{lcub}(6){rcub}{dollar}-tract which is required for protein binding. Mutation of site IV, which is located between {dollar}-{dollar}465 and {dollar}-{dollar}430, completely abolished induction of the transfected gene. In contrast, mutation of one or even two of the four G{dollar}\sb{lcub}(6){rcub}{dollar}-tract binding sites had little effect on induction or expression of the gene. However, elimination of three of these four sites dramatically reduced both the expression level and the inducibility of the transfected gene. UV-crosslinking experiments showed that site IV binds a 85kD protein, whereas site I binds a 110kD protein. The level of both DNA binding activities does not change substantially when transcription of H1{dollar}\sp0{dollar} is induced. However, even although site II shares the G{dollar}\sb{lcub}(6){rcub}{dollar}-tract motif with sites III, I and V, it appears to bind a different nuclear protein which is induced during MEL cell differentiation.;To analyze the expression properties of additional mouse H1 histone genes, three new mouse somatic H1 histone genomic clones were isolated. One of these genes, designated H1var.2, was sequenced. The H1var.2 gene encodes a typical cell cycle-regulated polyA-histone mRNA which is not inducible during MEL cell differentiation.