Abstract
The Finnish Landrace (Finnsheep) is a well known high-prolificacy sheep breed and has been used in many countries as a source of genetic material to increase fecundity of local breeds. Analyses to date have indicated that mutations with a large effect on ovulation rate are not responsible for the exceptional prolificacy of Finnsheep. The objectives of this study were to ascertain if: 1) any of 12 known mutations with large effects on ovulation rate in sheep, or 2) any other DNA sequence variants within the candidate genes GDF9 and BMP15 are implicated in the high prolificacy of the Finnish Landrace breed; using material from lines developed by divergent selection on ovulation rate. Genotyping results showed that none of 12 known mutations (FecBB, FecXB, FecXG, FecXGR, FecXH, FecXI, FecXL, FecXO, FecXR, FecGE, FecGH, or FecGT) were present in a sample of 108 Finnsheep and, thus, do not contribute to the exceptional prolificacy of the breed. However, DNA sequence analysis of GDF9 identified a previously known mutation, V371M, whose frequency differed significantly (P<0.001) between High and Low ovulation rate lines. While analysis of ovulation rate data for Finnsheep failed to establish a significant association between this trait and V371M, analysis of data on Belclare sheep revealed a significant association between V371M and ovulation rate (P<0.01). Ewes that were heterozygous for V371M exhibited increased ovulation rate (+0.17, s.e. 0.080; P<0.05) compared to wild type and the effect was non-additive (ovulation rate of heterozygotes was significantly lower (P<0.01) than the mean of the homozygotes). This finding brings to 13 the number of mutations that have large effects on ovulation rate in sheep and to 5, including FecBB, FecGE, FecXO and FecXGR, the number of mutations within the TGFβ superfamily with a positive effect on prolificacy in the homozygous state.
Highlights
It is well established that both BMP15 and GDF9 play central roles in normal ovarian development and function in mammals, and that mutations in these genes or in their receptors can cause large increases in ovulation rate of sheep [1,2,3]
The objectives of this study were to: 1) ascertain if any of 12 known mutations with large effects on ovulation rate in sheep contribute to the exceptionally high prolificacy of the Finnish Landrace breed using material from lines developed by divergent selection on ovulation rate, and 2) re-sequence the coding regions of candidate genes BMP15 and GDF9 to identify if any other variants may be involved in Finnsheep prolificacy
None of 12 mutations, across BMP15, GDF9 and BMPR1B, known to be associated with large effects on ovulation rate in sheep were present in the Finnsheep tested, in agreement with the findings of Davis et al [18] where the Booroola mutation and FecXI were shown to be absent from a smaller sample of High and Control line Finnsheep
Summary
It is well established that both BMP15 and GDF9 play central roles in normal ovarian development and function in mammals, and that mutations in these genes or in their receptors can cause large increases in ovulation rate of sheep [1,2,3]. Since the demonstration that the exceptional prolificacy of the Booroola Merino was attributable to the effect of a single gene [4], mutations with a major effect on litter size and ovulation rate (OR) have been invoked to explain the exceptional prolificacy observed in many sheep populations In some of these populations the causative mutations have been identified, including the Booroola Merino [FecBB] [5], Romney [FecXI and FecXH] [6], Cambridge [FecXG and FecGH] and Belclare [FecXG, FecXB and FecGH] [7], Lacaune [FecXL] [8], Icelandic sheep [FecGT] [9], Santa Ine‘s (FecGE) [10], Rasa Aragonesa (FecXR) [11], and Olkuska (FecXO) and Grivette (FecXGR) [12]. Subsequent selection on ovulation rate was used to develop High and Low lines, leading to a divergence of between 2 and 2.5 ova, depending on age; a Control line was maintained [13,15]
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