Administration of All-Trans Retinoic Acid to Pregnant Sows Improves the Developmental Defects of Hoxa1-/- Fetal Pigs

Abstract

Hoxa1 mutation adversely affect fetal pig development, but whether all-trans retinoic acid (ATRA) administration to Hoxa1^+/- pregnant sows can improve Hoxa1^-/- fetal pig development defects has not been reported. A total of 24 healthy Hoxa1^+/- sows were mated with a healthy Hoxa1^+/- boar and randomly assigned to one control group and nine experiment groups. ATRA was orally administered to pregnant sows at the doses of 0, 4, 5, or 6 mg/kg maternal body weight on 12, 13, and 14 days post coitum (dpc), respectively, and a total of 146 live piglets were delivered including 37 Hoxa1^-/- piglets and 109 non-Hoxa1^-/- piglets. Results indicated that Hoxa1^-/- piglets delivered by sows in control group had bilateral microtia, canal atresia and ear's internal defects, and had lower birth liveweight and external ear score than non-Hoxa1^-/- neonatal piglets (P < 0.05). Maternal administration with ATRA can effectively correct the development defects of Hoxa1^-/- fetal pigs, Hoxa1^-/- neonatal piglets delivered by sows administered ATRA at a dose of 4 mg/kg body weight on 14 dpc had higher birth liveweight (P > 0.05) and higher scores of external ear (P < 0.05) compared to Hoxa1^-/- neonatal piglets from the control group, but had no significantly difference in terms of birth liveweight and external ear integrity than non-Hoxa1^-/- piglets from the control group (P > 0.05). The time of ATRA administration significantly affected Hoxa1^-/- fetal development (P < 0.05). Administration of ATRA to Hoxa1^+/- pregnant sows at 4 mg/kg body weight on 14 dpc can effectively improve the birth liveweight and ear defects of Hoxa1^-/- piglets.

Keywords: Hoxa1 mutation; all-trans retinoic acid; ear defects; fetal pig; intrauterine growth retardation.

Figure 1

Score criteria for left and right external ear of neonatal piglets. Grade I: normal pinna with ear hole of external auditory canal, score 5. Grade II: small pinna with ear hole of external auditory canal, score 4. Grade III: strip pinna with atresia of external acoustic meatus, score 3. Grade IV: 2-3 “peanut” auricle with atresia of external acoustic meatus, score 2. Grade V: anotia, score 1.

Figure 2

Hoxa1-c.451 G>TC genotyping by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) assay. M: marker. Lane 1, 2, and 3: mutant (Hoxa1^−/−), abnormal external ear. Lane 4, 7, and 8: wild type (Hoxa1^+/+), normal external ear. Lane 5, 6, and 9: heterozygote (Hoxa1^+/−), normal external ear.

Figure 3

Phenotypic comparison of the differences between normal and defected external ears and the differences of repairing defected external ears with ATRA. (A) One non-Hoxa1^−/− neonatal piglet from control groups with normal bilateral external ears. (B) The representatives of Hoxa1^−/− neonatal piglets from control groups with different defected external ears (C) four Hoxa1^−/− neonatal piglets from G7: the left one with the completely repaired bilateral external ears; the middle one and the right two with the partially repaired external ears.

Figure 4

High-resolution CT imaging of internal structures of ears. (A) The non-Hoxa1^−/− piglet of Figure 3A had the normal internal structures of ears on each side of the head. (B) The Hoxa1^−/− piglet of Figure 3B had the complete absence of EAM, TC and MP. (C) The Hoxa1^−/− piglet from the middle of Figure 3C had the partially repaired internal structures of ears. (D) The Hoxa1^−/− piglet from the left of Figure 3C had the same normal internal structures of ears as the non-Hoxa1^−/− piglet of Figure 3A had. EAM, external auditory meatus. MP, mastoid process. TC, tympanic cavity. AO, auditory ossicle. SCC, semicircular canals. V, vestibule. C, cochlea.