IGF-1 on embryo development and survival, as well as, the potential mechanisms involved is

depicted in Figure 5-1.

 Treatment of embryos with IGF-1 altered the relative abundance of several mRNA

transcripts in Chapter 2. This action of IGF-1 could be important for embryo survival at day 14

as well as at day 21-28 of gestation. Embryos produced in vitro have altered gene expression

patterns compared to embryos produced in vivo (Wrenzycki et al., 1996; Wrenzycki et al., 1998;

Lazzari et al., 2002; Rizos et al., 2002 Sagirkaya et al., 2006). In general, embryos produced in

vitro have an increased abundance of Hsp70 (Lazzari et al., 2002; Sagirkaya et al., 2006) and a

reduced abundance of the tight junction protein connexin-43 (Wrenzycki et al., 1996; Wrenzycki

et al., 1998; Rizos et al., 2002). The results of Chapter 2 indicate that embryos cultured with

IGF-1 have an increased abundance of Na/K and Dc II and a reduced abundance of Hsp70

(Figure 5-1A). Desmocollin II is involved in the formation of desmosomes and these play a

critical role in stabilizing the TE during blastocyst formation and expansion (Fleming et al.,

1991; Collins et al., 1995). In addition, Na/K regulates the accumulation of fluid in the

blastoceole (Watson and Barcroft, 2001) as well as the formation of tight junctions during

blastocyst expansion (Violette et al., 2006). The reduced abundance of Hsp70 transcripts in

Chapter 2 is consistent with the idea that IGF-1 can reduce cellular stress (Jousan and Hansen,

2004, 2006; Kurzawa et al., 2002). Taken together, such effects could contribute to higher

survival (Figure 5-1B). In contrast to the effects of IGF-1 on mRNA abundance, IGF-1

treatment did not affect blastocyst cell number, cell allocation or apoptosis. These results

suggest that such characteristics may not be important for the enhanced survival of IGF-1 treated

embryos (Figure 5-1C).