Genetics of Litter Size and Prenatal Survival in Pigs
Secreted Phosphoprotein 1 (SPP1) appears to play a role in placental and foetal development, according to the thesis by Silvia C. Hernandez Velasco for The Roslin Institute, University of Edinburgh, Scotland.Female reproductive performance is a critical component of sustainable pig production
systems. There is abundant evidence of genetic variation in these traits among pig breeds.
The aims of this study were to identify quantitative trait loci (QTL) affecting reproductive
traits and to identify and characterise positional candidate gene(s) underlying the QTL.
A Large White-Meishan F2 population was scanned for QTL with effects on reproductive
traits. This analysis revealed 13 putative QTLs on seven different chromosomes with effects
on five different traits: ovulation rate (OR), total born alive (TBA), prenatal survival (PS),
total born alive (TBA), litter size (LS). QTL for PS and LS on chromosome 8 were fine
mapped and Secreted Phosphoprotein 1 (SPP1) confirmed as a candidate gene. A genome-wide
association study was performed on a diverse population of different breeds and crosses
lines, for reproductive traits including LS, TBA, number of stillborn piglets and number of
mummified piglets. Fourteen SNPs were found significantly associated with reproductive
traits.
The functional study of SPP1 examined the hypothesis that differences in foetal growth may
be associated with the effectiveness of conceptus attachment, as measured by SPP1
expression. Patterns of SPP1 mRNA and protein expression in placental and uterine tissues
supplying the smallest and a normal-sized foetus from the same uterus were examined in
Large White-Landrace (LW-LR) and Meishan (MS) females 40 and 45 of pregnancy.
The
smallest LW-LR foetuses tended to have a higher level of SPP1 mRNA in endometrium
tissue compared to the normal-sized foetuses. However, placenta expression was higher in the
normal-sized foetuses than in the smallest ones. SPP1 protein levels in normal-sized
foetuses were significantly higher than in the smallest litter mates for all the tissues.
Significantly higher levels of SPP1 mRNA and protein were found in MS in which
significant differences between sizes were found in some tissues, with similar expression
patterns in respect to size, for both mRNA and protein in endometrial tissues.
In placenta, the
direction of the expression differed between breeds, with a higher expression of mRNA and
protein in the normal sized MS foetuses and in the smallest sized LW-LR foetuses. The
comparison of SPP1 expression between different foetal sizes and different breeds revealed
associations between breed, foetal size, and SPP1 protein, factors implicated in PS and LS.
These results, together with the genetic evidence, indicate that the potential role of SPP1 in
placental and foetal development merits further investigation, concluded Ms Hernandez Velasco.
September 2012