Identification of a new aspartic proteinase expressed by the outer chorionic cell layer of the equine placenta.

The researchers discovered a new kind of proteinase in the perrisodactyl order (e.g. horses and zebras), which they’ve labeled ePAG. This proteinase, derived from a predecessor similar to pepsinogen, is found in the placenta and plays a role in the breakdown of hemoglobin protein as well as autolysis.

Introduction

• The paper discusses the identification of a new protein called ‘equine PAG’ or ‘ePAG’, which is a placental antigen (PAG).
• PAGs were initially known as pregnancy indicators within the maternal circulation of certain species, primarily in the Artiodactyla order which includes animals like cattle, camels, and pigs.
• No members of this family have previously been characterized in species outside the Artiodactyla order. This study does so by describing the cloning and initial characterization of ePAG in the placenta of horses and zebras, members of the Perrisodactyla order.

Methodology and Results

• The ePAG is a proteinase or enzyme that can degrade 14C-hemoglobin and can catalyze the removal of its own pro-peptide. This indicates the protein’s activity in protein breakdown processes during pregnancy.
• The ePAG mRNA, the molecule that carries the code to make the ePAG protein, is found only in the chorion, both prior to implantation and in the term placenta.
• The ePAG protein is expelled from cultured placental tissue in both processed and unprocessed forms.

Characteristics and Hypotheses

• The ePAG shows a similar identification pattern with both PAGs and pepsinogens, suggesting that it probably evolved from a predecessor similar to pepsinogen which developed the capability for expression in the placenta.
• The promoter of the ePAG gene – a region of DNA that initiates transcription of a particular gene – shares sequence similarities with the promoter from a bovine PAG gene but not with promoters of other aspartic proteinases.
• Based on their findings, the researchers hypothesize that ePAG is a leftover from the pepsinogen-like progenitor gene that expanded in the Artiodactyla order to create the large and diverse family of PAGs.