Expression of the full-length and alternatively spliced equine luteinizing hormone/chorionic gonadotropin receptor mRNAs in the primary corpus luteum and fetal gonads during pregnancy.

The study is focused on analyzing the presence and forms of the equine luteinizing hormone/chorionic gonadotropin (LH/CG) receptor in the primary corpus luteum and fetal gonads during pregnancy in horses, indicating its potential role in the regulation of pregnancy-related hormonal transitions.

Isolation and Characterization of eLH/CG-R Isoforms

• The researchers were successful in isolating the full-length LH/CG receptor, named eLH/CG-RA, as well as two truncated isoforms of it, referred to as eLH/CG-RB and eLH/CG-RC, from luteal tissue, which is a temporary structure involved in menstrual and pregnancy cycles.
• The complete sequence of eLH/CG-RA consisted of 680 amino acids, and was found to have 87 to 92% homology with LH/CG-receptor types in other mammals, indicating a significant correlation in its structure and function.
• eLH/CG-RB and eLH/CG-RC were altered variants of the original eLH/CG-RA, as they lacked certain portions of the original receptor’s genetic information. They contained an out-of-frame splicing and an in-frame stop codon, respectively. Consequently, the proteins they encoded lacked transmembrane and intracellular domains found in the full-length receptor.

Expression of eLH/CG-R mRNAs in Fetal Tissues

• The researchers studied the expression of all three versions of LH/CG-R in the primary corpus luteum and fetal gonads during pregnancy, looking specifically at early and mid-pregnancy stages.
• From day 14 to 83 of pregnancy, all three isoforms (eLH/CG-RA,B,C) were found to be expressed in the primary corpus luteum. Similarly, from day 44 to 222, all three receptors were expressed in fetal gonads.
• The primary corpus luteum on days 89 and 151 only expressed the truncated isoforms, eLH/CG-RB and eLH/CG-RC.
• The researchers also noted a decrease in the major 7, 5.7, 3.9 and 1.8 kb eLH/CG-R mRNA transcripts in the primary CL, while a specific 1.8 kb eLH/CG-R mRNA was consistently expressed in the fetal gonads throughout pregnancy.

Implications of the Study

• The findings of this study suggest that the expression of eLH/CG-R mRNAs occurs in the fetal gonads before ceasing in the primary corpus luteum, hinting that eCG (equine chorionic gonadotropin) might be significant in the switch from luteal to fetal-placental steroid production during horse pregnancies.
• The presence of the truncated receptor isoforms at certain pregnancy stages suggests they might have distinct roles related to hormonal regulation during equine pregnancy.