Analysis of the FMR1 gene expression in the ovary

Author(s)

Larissa Fontes

• Document type: Doctoral Thesis
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Instituto de Biociências (IBIOC/SB)
• Defense date: 2011-10-06

Examining board members

Angela Maria Vianna Morgante; Edson Borges Junior; Irina Kerkis; Mariz Vainzof

• Advisor: Angela Maria Vianna Morgante; Luciana Amaral Haddad

Abstract

This study aimed at investigating the FMR1 gene (Fragile X Mental Retardation gene 1), regarding its relationship with primary ovarian insufficiency (Fragile X-related Primary Ovarian Insufficiency, FXPOI). In Chapter I, we present a literature review on FXPOI. The FMR1 premutation is the most frequent genetic cause of predisposition to premature ovary insufficiency (POI) and, among the POI familial cases, about 10% are associated with the FMR1 gene premutation. However, little is known about the gene expression in the mammal ovary, and the mechanisms by which the premutation causes POI remain unknown. Chapter II presents the study of the FMR1 gene expression in the human and murine adult ovaries. The enormous difficulties inherent in obtaining and studying female germ cells led us to study human granulosa cells (HGC), which are easily obtained as byproducts of in vitro fertilization procedures. We also studied the FMR1 expression in granulosa cells of mice of the CD1 strain (MGC), collected from the oviducts after ovulation induction. Granulosa cells interact functionally with oocytes during folliculogenesis, transmitting signals through the ovary and supporting growth and maturation of oocytes during the later stages of follicular growth. It is, therefore, possible that cellular changes induced by the FMR1 premutation in HGCs affect follicular growth, ovulation rate and fecundity. We standardized protocols for isolation and culture of HGCs obtained from follicular fluid and confirmed the origin of the isolated cells by the expression of HGC markers, using RT-PCR, and by the lipid nature of the cytoplasmic granules, as demonstrated by the staining with the lipophilic dye DiI. We demonstrated, by RT-PCR, that HGCs isolated from follicular fluid express the FMR1 mRNA. In mice, also by RT-PCR, we detected the Fmr1 mRNA in oocytes and in the MGCs, collected from the oviduct after ovulation hyperstimulation. Using RNA in situ hybridization on cultured HCGs, we detected the FMR1 mRNA dispersed in the cytoplasm and, in the nucleus, concentrated in regions whose features indicated to be nucleoli. This same distribution was observed in cultured fibroblasts. This probable nucleolar localization of the FMR1 transcript in these cells suggests that it constitutes messenger ribonucleoproteins for further targeting to specific cytoplasmic sites where translation occurs. We verified, by Western blotting, that HGCs express high levels of the main FMRP isoforms, with molecular mass between 60 and 95 kDa. We determined the FMRP subcellular localization in HGCs and that of Fmrp in MGCs, by immunostaining. The hybridization signals were seen scattered in fine granules in the cytoplasm of both HGCs and MGCs, in a pattern of distribution similar to that observed in neurons. In the MGC filopodia, the protein labeling was concentrated at some sites, similar to the previously described pattern of Fmrp distribution in neuronal dendritic spines of rat hippocampus, where it is part of RNA granules, promoting mRNA transport and translation control. The similar distribution pattern between neurons and MGC may reflect the similarity of FMRP function in both tissues. The induction of oxidative stress in the HGC by treatment with sodium arsenite led the protein to leave its diffuse cytoplasmic distribution to become part of perinuclear stress granules, co-localized with TIA-1, a marker of these structures. Similar results were previously obtained in HeLa cells and in rat hippocampus. These results support the hypothesis that FMRP participates in the mechanism of the transient translation arrest after stress. In Chapter III, we describe our attempts to obtain an embryonic stem cell line (ESC) from knock-in mice (KI) for the FMR1 premutation. To obtain KI embryos, wild females (WT, strain C57) were crossed with males KI (strain C57/BL6), and KI females were crossed with WT males. We planned to compare the expression of the fmr1 gene in the ESCs from the KI and WT strains, including during differentiation. We did not succeed in obtaining an ESC KI line, which can be attributed to difficulties inherent to the procedure. At follow-up of the first four days of in vitro development of embryos, changes in cleavage and developmental arrest were more frequently observed in embryos obtained from KI females. Meanwhile, the average survival rates of oocytes to blastocysts, and 8-16 cell embryos to blastocysts were not statistically different between the KI and WT females. The great variability among the numbers of blastocysts obtained per female and the small size of the KI (six females) and WT (seven females) groups indicate that these results should be interpreted with caution. Immunostaining analysis of the Fmrp in blastocysts showed a probably cytoplasmic distribution, with a granular pattern of labeling, the grains being more common in blastocysts from WT females, but coarser in blastocysts from KI females. These data are suggestive that the Fmr1 premutation in murine females affects the early development of their embryos. This aspect needs further investigation (AU)

• FAPESP's process: 06/06269-8 - Functional analysis of Fmr1 gene in the ovary
• Grantee: Larissa Fontes
• Support Opportunities: Scholarships in Brazil - Doctorate