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Title:Expression and function of basigin during early pregnancy and spermatogenesis
Author(s):Bi, Jiajia
Director of Research:Nowak, Romana A.
Doctoral Committee Chair(s):Nowak, Romana A.
Doctoral Committee Member(s):Bahr, Janice M.; Miller, David J.; Li, Quanxi
Department / Program:Animal Sciences
Discipline:Animal Sciences
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Basigin (BSG)
Abstract:Basigin (BSG) is a multifunctional glycoprotein that plays an important role in both female and male reproduction since female knockout (KO) mice are infertile and male KO mice are sterile. The aim of the present study was to determine 1) whether BSG is required for proliferation of the uterine luminal epithelium during early pregnancy in preparation for implantation; 2) whether BSG is required for HESCs decidualization; and 3) whether BSG is essential for the interactions between gametes and Sertoli cells during spermatogenesis. BSG protein was expressed in the uterine epithelium at estrus in βERKO mice but not in αERKO mice. However, a higher level of Bsg mRNA was observed in the uteri of αERKO mice as compared with wild type (WT) and βERKO mice. In the mouse, estrogen alone induces the proliferation of both luminal and glandular epithelial cells during early pregnancy. On day 1 of pregnancy, the expression levels of ERα and a well-known estrogen responsive gene, MUC1, appeared to be normal in the uteri of Bsg KO females. This suggested that the circulating estradiol levels in Bsg KO mice are normal. I examined proliferation in uterine epithelial cells and found that, in WT mice, uterine epithelial cells were highly proliferative as measured by expression of Ki67 in both the luminal and glandular epithelial cells. In contrast, Ki67 expression was significantly decreased in the epithelial cells of Bsg KO uteri. Immunochemistry using the BSG antibody revealed that the expression of BSG in C/EBPβ null uteri was heterogeneous and spotty in the luminal epithelium as compared with a more homogeneous expression pattern of BSG in the uterine epithelium of WT uteri. These results indicate that C/EBPβ may be one of the factors regulating the expression of BSG in mouse uterine epithelium. Decidualization of human endometrial stromal cells (HESCs) into decidual cells is carefully controlled, both spatially and temporally, by a balance of stimulatory and inhibitory signals from the uterine endometrium and is a prerequisite for successful implantation. Decidualization is associated with induction of a number of genes including wingless-type MMTV integration site family member (WNT4) and forkhead transcription factor forkhead box O1A (FOXO1). In the present study, HESCs were transfected with small interfering RNAs targeting BSG gene expression. Expression of the decidualization markers Insulin-like growth factor-binding protein 1 (IGFBP1) and Prolactin (PRL) was significantly inhibited in cells with down regulated BSG expression. Silencing of BSG in HESCs also impaired expression of several MMPs. Microarray analysis revealed that both WNT4 and FOXO1 and its downstream targets are under the regulation of BSG during decidualization in HESCs. The Bsg KO testis lacks elongated spermatids and mature spermatozoa, a phenotype similar to that of alpha-mannosidase IIx (MX) KO mice. MX regulates formation of N-acetylglucosamine (GlcNAc) terminated N-glycans that participate in germ cell-Sertoli cell adhesion. Results showed that Bsg KO spermatocytes displayed normal homologous chromosome synapsis and progression to the midpachytene stage. Both meiosis I (MI) and meiosis II (MII) spermatocytes were detected in the KO preparations. However, expression of the acrosome marker SP-10 was extremely low in germ cells of Bsg KO mice indicating that spermatogenesis in Bsg KO mice was arrested at the round spermatid stages. I observed a large increase in the number of germ cells undergoing apoptosis in Bsg KO testes. Using lectin blotting, I determined that GlcNAc terminated N-glycans are linked to BSG. GlcNAc terminated N-glycans were significantly reduced in Bsg KO testes. These observations indicate that BSG may act as a germ cell-Sertoli cell attachment molecule. Loss of BSG significantly reduced adhesion between GC-2 and SF7 cells. Moreover, WT testes showed strong expression of N-cadherin (CDH2) while expression was greatly reduced in the testes of Bsg KO mice. In addition, the integrity of the blood-testis barrier (BTB) was compromised and flow of fluid from the testis was reduced in Bsg KO testes. My findings suggest that expression of BSG protein in the uterus requires estrogen acting through ESR1, but not ESR2. Moreover, estrogen may regulate the proliferation of both luminal and glandular epithelial cells in the uterus during early pregnancy through a pathway involving BSG. Human decidualization results have provided new insights into the molecular pathways that regulate decidualization of human uterine stromal cells. Understanding the role of BSG during decidualization may help to explain the defects in decidualization-associated reproductive disorders of women. Male results indicate that although Bsg KO spermatogonia can undergo normal progression to the spermatocyte stage, BSG-mediated germ cell-Sertoli cell adhesion via GlcNAc terminated N-glycans appears to be necessary for integrity of the BTB and spermatocyte progression to mature spermatozoa.
Issue Date:2013-05-24
Rights Information:Copyright 2013 Jiajia Bi
Date Available in IDEALS:2013-05-24
Date Deposited:2013-05

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