# Transcriptomic Profiling of Peripheral Blood Identifies Candidate Genes for Early Pregnancy Diagnosis in Sika Deer

## TL;DR

Researchers identified genes in sika deer blood that could help detect early pregnancy, offering a non-invasive method for better reproductive management.

## Contribution

The study identifies candidate genes for early pregnancy detection in sika deer using transcriptomic profiling of peripheral blood.

## Key findings

- Interferon-stimulated genes and immune-regulatory genes are upregulated by day 7 post-insemination, indicating maternal recognition of pregnancy.
- Genes related to embryo implantation and placental formation are enriched by days 15–20, suggesting roles in early pregnancy development.
- Cysteine metabolism genes are upregulated early, supporting corpus luteum development through redox homeostasis.

## Abstract

Early pregnancy diagnosis is widely used in livestock farming for timely determining pregnancy status after insemination, which is crucial for efficient herd management and improved reproductive efficiency. Compared to traditional early pregnancy diagnostic methods such as rectal palpation and transrectal ultrasonography, non-invasive diagnostic techniques based on detecting suitable biomarkers in blood, milk, or urine enable earlier pregnancy detection with the minimal impact on reproduction. Sika deer are being increasingly farmed due to the medicinal value of their antlers, but research on early pregnancy biomarkers remains relatively limited compared to other ruminants such as cattle and sheep. In this study, we conducted transcriptome analysis of peripheral blood from four successfully pregnant sika deer on days 0, 7, 15, and 20 after artificial insemination. On day 7, we identified classic interferon-stimulated genes related to maternal recognition of pregnancy, as well as other genes involved in regulating maternal immune tolerance. On days 15 and 20, we screened genes involved in embryo implantation and early placental formation. These findings provide new references for developing early pregnancy diagnostic systems in sika deer.

With estrus confined to three winter months, early pregnancy detection is essential for reproductive management in farmed sika deer. However, the development of reliable non-invasive early pregnancy detection techniques has been hindered by limited understanding of their reproductive physiology. To identify pregnancy-specific biomarkers in sika deer, we performed RNA-sequencing (RNA-Seq) on maternal peripheral blood collected on days 0, 7, 15, and 20 after artificial insemination. Using time-series clustering analysis and weighted gene co-expression network analysis (WGCNA), we identified key genes and pathways at each stage. Notably, maternal-fetal recognition-related interferon-stimulated genes (ISGs; IFNAR1/2, STAT1/2, MX1/2, and RSAD2), anti-apoptotic and immune-regulatory genes (BCL2, XIAP, and IL10), and cysteine metabolism genes (CTH, CBS, GCLC, and GCLM) were upregulated by day 7, suggesting their role in supporting corpus luteum development through immune regulation and redox homeostasis. By days 15–20, upregulated genes were enriched in pathways related to mitochondrial function, cell adhesion, and cell cycle regulation, indicating their involvement in embryo adhesion and syndesmochorial placentation. In conclusion, this study demonstrates that ISGs, immune-regulatory genes and cysteine metabolism genes are detectable as early as day 7 post-insemination, highlighting their promise as early pregnancy biomarkers and providing a molecular basis for non-invasive diagnostic development in sika deer.