Maiti et al. (1996) , who referred to Pem as an orphan homeo box gene, reported a surprisingly high rate of evolutionary
change. As a rule, homeo box genes show a high degree of sequence conservation in distantly-related species. The
N-terminal portion of the Pem homeodomain, which includes the first 2 alpha-helices, exhibits only 44% sequence identity
between rat and mouse. In contrast, the third helix, which is known to confer most of the base-specific contacts of
homeodomains with DNA, is almost identical in rat and mouse. Both the rat and mouse genes reside on the X chromosome,
possess identical exon/intron splice junctions, and encode a distinctive motif upstream of the homeodomain that is unique to
Pem. In the rat a Pem pseudogene was identified whose sequence and chromosomal localization indicated that it was
derived by reverse transcription and reinsertion into the genome. The functional rat Pem gene is expressed selectively in
placenta, testis, epidermis, and ovary.
General function
DNA binding, Transcription factor
Comment
Cellular localization
Nuclear
Comment
Ovarian function
Comment
Rao MK, et al the PEM homeobox gene promoter is regulated by Ets and Sp1 family
members in normal granulosa cells and diverse tumor cell types.
. This
promoter normally drives the expression of the Pem homeobox gene in specific cell types in ovary
and placenta but is aberrantly expressed in lymphomas, neuroblastomas, retinoblastomas,
carcinomas, and sarcomas. By deletion analysis it was identified that a region between nt -80 and -104 was absolutely critical for the expression from this distal Pem promoter (Pem Pd). Site-specific
mutagenesis and transfection studies revealed that this region contains two consensus Ets sites and a
single Sp1 site that were necessary for Pem Pd expression. Gel-shift analysis showed that Ets and
Sp1 family members bound to these sites. Transfection studies demonstrated that the Ets family
members Elf1 and Gabp and the Sp1 family members Sp1 and Sp3 transactivated the Pem Pd.
Activation by either Elf-1 or Gabp required an intact Sp1 family member-binding site, suggesting that
Ets and Sp1 family members cooperate to activate Pem Pd transcription.
Expression regulated by
Comment
Ovarian localization
Granulosa
Comment
Regulation of the Rhox5 Homeobox Gene in Primary Granulosa Cells: Preovulatory Expression and Dependence on SP1/SP3 and GABP Maclean Ii JA, et al .
Homeobox genes encode transcription factors that regulate embryonic development and postnatal events. Rhox5 (previously called Pem), the founding member of a homeobox gene cluster that we recently identified on the X chromosome, is selectively expressed in granulosa cells in the ovary and other somatic-cell types in other reproductive organs. In this report, we investigate its regulation in granulosa cells in the rat ovary. We found that Rhox5 expression in the ovary is governed by the Rhox5 distal promoter and is expressed at least as early as day 5 post partum. Rhox5 mRNA levels are regulated during the ovarian cycle, peaking prior to ovulation. Deletion analysis revealed a 25-nt element essential for distal promoter transcription in primary granulosa cells. This distal promoter element contains two ETS and one SP1 transcription-factor family binding sites that mutagenesis analysis indicated were essential for high-level transcription. This element was both necessary and sufficient for transcription, as it activated transcription when placed upstream of a heterologous minimal promoter. Cold competition and EMSA studies demonstrated that SP1, SP3, and the ETS family transcription factor GABP bound this element. Dominant-negative forms of GABP and SP3 repressed distal promoter expression in primary rat granulosa, showing that these factors are crucial for Rhox5 expression. Co-transfection of dominant-negative mutants indicated that Rhox5 expression in granulosa cells is regulated by the JNK (MAPK8) and RAS pathways, which are known to be upstream of ETS family transcription factors. The discovery that Rhox5 expression in granulosa cells is regulated by MAPK pathways and ETS and SP1 family members provides an opportunity to understand how these regulatory pathways and factors collaborate to regulate gene expression during the ovarian cycle.