Characterization of the Equine Glycoprotein Hormone Alpha-Subunit Gene Reveals Divergence in the Mechanism of Pituitary and Placental Expression1

Abstract

The equine glycoprotein hormone alpha-subunit gene is expressed in both pituitary and placenta, unlike that of all other nonprimate mammals studied, in which expression is limited to pituitary. Previous studies of the 5'-flanking region of the equine alpha-subunit promoter have revealed unique characteristics as well as similarities with the human alpha-subunit promoter, which demonstrates a similar pattern of tissue-specific expression. We have cloned and sequenced the equine alpha-subunit gene and have used tissue culture systems and transgenic mice to characterize its expression. Unlike the human promoter, the cloned equine alpha-subunit promoter failed to direct trophoblast-specific expression in either tissue culture or transgenic mouse models, suggesting an entirely different mechanism for expression. In contrast, the equine alpha-subunit promoter was able to direct gonadotroph expression in both tissue culture and transgenic mouse models. In alphaT3-1 cells, 550 base pair (bp) was sufficient for expression. This expression involves promoter elements identified in other species as playing a role in gonadotroph expression, but mutation of these elements reveals differences in their relative contributions to promoter activity. In mice, 2800 bp of 5'-flanking sequence allowed specific expression in gonadotrophs but not in thyrotrophs or placenta. The pattern of estrogen regulation observed in transgenic mice matched neither the repression that has been observed with human and bovine alpha-subunit promoters in transgenic mice nor the stimulation in mRNA levels reported in mares, suggesting a unique mechanism that is not recapitulated in the transgenic model. Thus the equine alpha-subunit promoter uses a combination of conserved and unique features of gene regulation to direct its pattern of tissue-specific expression.

Immortalization of equine trophoblast cell lines of chorionic girdle cell lineage by simian virus-40 large T antigen

“…Steger and co-workers reported that an -activating element located within proximal 5 flanking region of eCG subunit promoter was responsible for PKA induction when evaluated in the JEG-3 human choriocarcinoma cell line (Steger et al 1991). In contrast, Farmerie and co-workers reported that activation of the PKA pathway did not stimulate activity of the eCG subunit promoter in the BeWo human choriocarcinoma cell line (Farmerie et al 1997). Nonetheless, our data strongly suggest that the PKA pathway regulates expression of the endogenous eCG subunit gene in our clonal cell lines.…”

“…Our data indicate that GCMa is not expressed in the equine clonal cell lines or endometrial cups and, therefore, presumably does not play a role in initiating expression of the eCG subunit gene. The 5 flanking region of eCG subunit promoter harbors a consensus nuclear receptor half-site (AGGTCA) (Farmerie et al 1997), and so far, two orphan nuclear receptors (ERR and ) have been shown to be expressed in the placenta and are essential for placental development (Luo et al 1997, Heard et al 2000. ERR expression is restricted to the chorion during embryogenesis and to a limited number of adult tissues (Pettersson et al 1996).…”

“…The PKA and PKC signal transduction pathways have been shown to regulate the expression of both human CG subunits (Jameson et al 1987, Milsted et al 1987, Andersen et al 1988, Nilson et al 1989, Albanese et al 1991. Two previous studies have examined PKA regulation of the eCG subunit promoter in human placental cell lines (Steger et al 1991, Farmerie et al 1997. Steger and co-workers reported that an -activating element located within proximal 5 flanking region of eCG subunit promoter was responsible for PKA induction when evaluated in the JEG-3 human choriocarcinoma cell line (Steger et al 1991).…”

The Human Preprotachykinin-A Gene Promoter Has Been Highly Conserved and Can Drive Human-like Marker Gene Expression in the Adult Mouse CNS

“…For example several nonmouse gene promoters that have been introduced into transgenic mice which have not been able to direct appropriate expression of marker genes to the areas expected. These promoter elements include those of the human glucagon gene (Nian et al, 1999), the equine glycoprotein hormone ␣-subunit gene (Farmerie et al, 1997), the human and chick type X-collagen gene (Beier et al, 1996), and a lamprey homeobox gene (Carr et al, 1998). We have used a 380-kb human YAC construct containing the PPT gene, tagged with the LacZ gene, to determine whether the promoter of the human PPTA gene could drive relevant expression of a marker gene within the mouse.…”

Gonadotropes and Gonadotropin-Releasing Hormone Signaling

“…The β subunits of LH and FSH appear to be rate limiting in the formation of these heterodimeric hormones and confer individual hormone specificity. [426][427][428][429][430][431][432] This includes a rather complex analysis of the contributions of combinations of cis regulatory elements in a so-called combinatorial code that control cell-specific regulation. A great deal of research has focused on the cell type-specific regulation of the gonadotropin subunit gene promoters due to their central importance to the regulation of gonadal function and fertility.…”