204 RELATIVE MESSENGER RNA ABUNDANCE OF HYALURONAN RECEPTORS AND SYNTHASES ON IN VITRO- AND IN VIVO-DERIVED DAY 7 AND DAY 13 BOVINE EMBRYOS

Abstract

Hyaluronan (HA), which progressively increases during embryogenesis, is a glycosaminoglycan that plays a major role in oocyte/embryo development (Fenderson et al. 1993 Differentiation 54, 85–95). One of the main functions of HA is to participate in the cell proliferation and migration that are controlled by HA receptors, RHAMM and C44, and by the presence of different HA synthases, Has1, Has2, and Has3. All have very distinctive features and functions at different stages of embryo development. The objective of this study was to determine the relative mRNA abundance of HA receptors and synthases in Day 7 and 13 bovine embryos derived in vitro or in vivo. In vitro embryos were produced by standard oocyte maturation and fertilization procedures. Presumptive zygotes were cultured in groups of 25 in 25-μL droplets of synthetic oviduct fluid supplemented with 5% FCS at 39°C, 5% CO₂, and 5%O₂ with maximum humidity. In vivo blastocysts were collected from superovulated heifers on Day 7 (estrus = Day 0) by uterine flushing and on Day 13 immediately after slaughter by flushing the dissected reproductive tracts. All embryos were frozen in LN₂ and stored at –80°C for mRNA extraction. Quantification of transcripts for RHAMM and CD44 receptors and Has2 and Has3 synthases was performed on groups of ten Day 7 blastocysts (3 groups for in vivo or in vitro) and individual Day 13 embryos (7 embryos in vivo or in vitro) by real-time quantitative RT-PCR. Data on differences in transcript abundance were analyzed by ANOVA. The relative abundance of the Has2 and Has3 synthases was similar between in vivo and in vitro embryos, irrespective of their developmental stage. The quantity of CD44 was significantly higher in in vitro compared with in vivo embryos only on Day 7. However, the quantity of RHAMM receptor was higher on Day 13 in in vitro compared with in vivo embryos. When the comparison was done between developmental stages (Day 7 v. Day 13) for in vivo and in vitro embryos, we found that in vivo-produced Day 7 blastocysts expressed significantly more RHAMM receptor than embryos on Day 13. The reverse pattern of expression was shown for CD44 receptor. For in vitro embryos, the only difference observed was for Has3, which was up-regulated on Day 13 compared with Day 7 embryos. In conclusion, the present study demonstrates, for the first time, developmental changes in the abundance of RHAMM and CD44 receptor mRNA and Has2 and Has3 synthase mRNA in in vivo and in vitro bovine-derived embryos on Day 7 and 13. We believe that our results will provide new insight into the potential role of this intriguing multifunctional molecule in bovine early embryo development.