The Effect of Species-Specific FSH Administration During In vitro Maturation of Bovine Oocytes on Embryonic Developmental Capability

Abstract

Follicle-stimulating hormone (FSH) is a heterodimeric glycoprotein synthesized and secreted by the anterior pituitary gland under hypothalamic control. This hormone is involved in the regulation of essential mammalian reproductive processes such as gametogenesis, follicular growth, and ovulation. An important aspect of the structure of FSH is its double species-specificity, at both the amino acid and sugar level. In fact, both the amino acid sequence and the oligosaccharide structure significantly differ among species (Green and Baenziger, 1988; Wallis, 2001). For example, bovine (bFSH) and human FSH (hFSH) differ by 45 amino acids (sequence identity: α-subunit 75%; β-subunit 90%), and in addition they show strikingly different profiles with respect to their oligosaccharide side-chains (the relative distribution of sialylated, sulfated and neutral Asn-linked oligosaccharides in human FSH is 88%, 7% and 5%, while in the bovine it is 56%, 13% and 31%). Both protein and sugar structures affect the biological activity of FSH (e.g. hormonereceptor interactions)(Ulloa-Aguirre et al., 2003), however, the molecular basis of FSH functions in domestic animals are usually studied by heterologous experimental models. Examples are the in vitro bioassays based on rat and mouse primary cultures of Sertoli and granulosa cells, and the bioassays based on recombinant cell lines expressing the cloned FSH rat and human receptors (Christin-Maitre and Bouchard, 1996). Another non speciesspecific application involves the use of supraphysiological doses of recombinant hFSH or pituitary pig FSH during in vitro bovine embryo production (IVP) protocols (Ali and Sirard, 2002). The objective of the present study was to develop a species-specific in vitro bioassay to study the molecular mechanisms underlying the biological activity of bovine FSH (bFSH). We used cumulus-oocyte complexes (COCs) isolated from bovine ovaries in order to evaluate the ability of pituitary bFSH to stimulate cumulus expansion, and blastocyst development