The molecular phylogeny of uterine serpins and its relationship to evolution of placentation.

This research investigates the evolution and distribution of uterine serpin (US) genes, which are associated with epitheliochorial placentation, across different species. It was discovered that these genes are present in the Laurasiatheria superorder and their evolution appears to be linked with the development of the epitheliochorial placenta.

Identification of Uterine Serpin Genes

• The main aim of the research was to identify the genes of uterine serpins (designated as SERPINA14), proteins that are expressed in the uterus in response to progesterone, in various species both within and outside the Laurasiatheria superorder which includes animals such as cows, swine, and dolphins.
• The researchers used a database of nucleotide sequences and genomic data to find known US genes in a variety of animals, such as goats, cows, pigs, and water buffalos.
• New US coding sequences were discovered in other animals, including dolphins, horses, dogs, and cats. Significantly, the sequence found in cats contained several stop codons, which signal the end of a protein.

Expression of Uterine Serpin Genes

• The researchers used a technique called reverse transcription-polymerase chain reaction to confirm that the US gene is expressed (activated to produce a protein) in the uterus of pregnant horses and dogs.
• No US sequence was found in the completed genomic sequences for primates, rodents, rabbits, opossums or duck-billed platypuses.

Evolution and Selection of Uterine Serpin Genes

• The ratio of nonsynonymous/synonymous substitutions indicates that the US gene has evolved under positive selection. This means that changes in the gene that altered the protein it produced were beneficial and favored by natural selection.
• The US gene, therefore, seems to have evolved within the Laurasiatheria superorder and has a role in supporting pregnancy in species with the epitheliochorial type of placentation, a placenta structure where fetal and maternal blood don’t mix, and a few other Laurasiatheria species with different placentation forms.
• The researchers concluded that the positive selection occurring in the US gene indicates the development of species-specific functions. This gene evolved according to the specific needs and challenges each species faced during reproduction.