(57) Impact of Early Pregnancy on the Maternal Anterior Pituitary Transcriptome in Cattle

Abstract Authors: J. Kennedy ¹ , K. D. Peterson ¹ , B. M. Chitwood ¹, A. B. Lonas ¹ , M. A. Young ¹ , R. R. Payton ¹ , S. P.
Poudel ² , S. K. Behura ² , M. A. Oliver ³ , L. G. Strickland ¹ , T. M. Prado ¹ , J. L. Edwards ¹ , G.
Charpigny ⁴ , T. E. Spencer ² and D. J. Mathew ¹

1 Department of Animal Sciences, University of Tennessee, Knoxville, TN, USA
2 Division of Animal Sciences, University of Missouri, Columbia, MO, USA
3 School of Animal Sciences, Virginia Polytechnic Institute and State University, Blacksburg, VA, USA
4 INRAe, Biology of Reproduction, Environment, Epigenetics and Development, Jouy en Josas, France

Abstract Text: Successful pregnancy establishment requires synchronous communication between the
conceptus and maternal tissues. In cattle, near Day 16 of pregnancy, the conceptus abundantly
secretes interferon tau (IFNT), a type I interferon and the maternal recognition of pregnancy
(MRP) signal, inducing interferon-stimulated gene (ISG) expression within the endometrium to
support pregnancy. The effects of IFNT are not limited to the uterus. The cytokine has also been
shown to promote ISG expression in the corpus luteum, thymus, bone marrow and liver of
pregnant ruminants. However, its effects on other maternal tissues, including the anterior
pituitary (AP), a major regulator of maternal physiology and pregnancy, remain unclear. The AP
is a critical regulator of endocrine function, and its response to conceptus signals may play a role
in maternal adaptation to pregnancy. To investigate the impact of early pregnancy and IFNT on
maternal AP gene expression two independent but related experiments were conducted.
Experiment 1 (Ex1) investigates whether the presence of the conceptus alters maternal AP gene
expression, while Experiment 2 (Ex2) explores the direct effect of pregnant maternal serum and
IFNT on maternal AP gene expression. In Ex1, AP and serum (used in Ex2) were collected from
heifers on Day 16 of the estrous cycle (Control; n = 5) and from pregnant heifers on Day 16 of
gestation carrying one (n = 3) or two conceptuses (n = 3) as a result of embryo transfer.
Immunohistochemistry for growth hormone was used to confirm collection of AP tissue of
which was assayed for mRNA abundance using RNA-sequencing. Compared to Control, AP
from heifers carrying one conceptus had 21 more and 5 less abundant differentially expressed
genes (DEGs). In heifers carrying two conceptuses, 62 more and 44 less abundant DEGs were
identified, with the most significant biological process associated with the more abundant DEGs
being the immune response (FDR < 0.0001). In Ex2, non-pregnant female heifer AP explants
were cultured for 6 h in control medium (Control, n = 6), medium containing IFNT (IFNT; 1 ng,
n = 6), serum from non-pregnant heifers (Cyclic, n = 4), or serum from pregnant heifers
(Pregnant, n = 5). RT-qPCR was used to assay explant mRNA. Compared to Control or Cyclic
serum treated explants, mRNA for common ISG such as ISG15, OAS1, MX1, and CXCL10 did
not differ in explants treated with IFNT or Pregnant serum, respectively (P > 0.05). Our findings
suggest that early pregnancy may affect maternal AP gene expression but an effect of conceptus
IFNT on AP biochemistry could not be confirmed. A greater understanding of the effect of
pregnancy on the maternal AP physiology could provide insight into the broader systemic
adaptations to pregnancy and the role of endocrine regulation in maintenance of pregnancy.
Further research is required to elucidate the mechanisms by which the conceptus influences AP
activity. Funding was provided by the University of Tennessee, Department of Animal Sciences
and the USDA National Institute of Food and Agriculture (NIFA; 2020-67015-31615).