Abstract:
In the cell, all-trans retinoic acid (ATRA), a vitamin A metabolite, binds to retinoic acid-receptor (RAR), whereas the ATRA isomere 9-cis-retinoic acid (9-cis-RA) binds to both RAR and the retinoid X receptor (RXR). Synthetic compounds such as LG100268 (LG; Ligand Laboratories) are highly specific to bind RXR, which allows to differentially study the RAR and RXR pathways. In previous work morulae treated with LG for 48 h showed to improve blastocyst development and to activate pro-apoptotic genes (in press), whereas ATRA for 24 h increased cell numbers in the inner cell mass (ICM) and the trophectoderm (TE) (Rodr�guez et al. 2006 Hum. Reprod. 21, 2149-2157). However, LG and ATRA were never both compared for 24 in medium with BSA, which is thought to be more appropriate to produce embryos for cryopreservation than serum-containing medium. In this work we analyze development, quality, and viability of morulae cultured with RAR and RXR agonists. Cumulus-oocyte complexes from slaughterhouse ovaries were matured and fertilized in vitro. Presumptive zygotes were cultured in synthetic oviduct fluid (SOF) +3 gL-1 BSA. On day 6, morulae were treated for 24 h with ATRA 0.7 µm, LG 0.1 µm, or no additives. Blastocyst development was monitored up to day 8. Differential cell counts were made on hatched blastocysts on days 7 and 8. Apoptosis and necrosis (TUNEL + nuclear histology) were made on day 8 expanded and hatched blastocysts. Data were analyzed by GLM and Duncan's test, expressed as LSM � SE, and development rates were expressed as percentages of cultured morulae (replicates [R] = 14 for development; R = 9 for cell counts; R = 4 for apoptosis; n = 1647 morulae). ATRA yielded more blastocysts on day 8 than LG and controls (72.2 � 2.2 v. 60.0 � 2.3 and 65.6 � 2.4, respectively; P < 0.02), and more expanded blastocysts than LG (48.6 � 2.3 v. 36.6 � 2.4; P < 0.02), but no more than controls (43.5 � 2.5). Day-7 and day-8 hatched blastocysts cultured with ATRA showed more total cells than day-7 controls (163.5 � 8.0 and 161.5 � 5.4 v. 137.7 � 8.9, respectively; P < 0.05). However, in the presence of ATRA, day-8 blastocysts showed a strong cell reduction in the inner cell mass (ICM), whereas their day-7 counterparts conserved ICM/total cells proportions comparable to day-7 controls (11.0 � 1.2 v. 19.7 � 1.7 and 20.6 � 1.9, respectively; P < 0.03). The LG increased apoptotic index (AI) and necrotic index (NI) in the ICM (AI: 14.5 � 2.4 v. 6.4 � 1.5 and 6.4 � 1.4; NI: 5.0 � 1.2 v. 0.9 � 0.8 and 1.6 � 0.7; for LG, ATRA, and controls, respectively; P < 0.02). Embryos produced with ATRA showed improved development and cell distribution without increasing apoptosis and necrosis. Vitrification of excellent day-7 and day-8 blastocysts is in course to evaluate cryosurvival and further embryo transfer to determine full developmental competence.<fn-group><fn>Grant Support: MEC, project AGL2005-04479. M. Mu̱oz is sponsored by FICYT.</fn></fn-group>