Identification of porcine Lhx3 and SF1 as candidate genes for QTL affecting growth and reproduction traits in swine.

The distal portion of the long arm of porcine chromosome 1 has been shown to harbour several quantitative trait loci affecting growth and reproductive traits in swine. In order to identify potential candidate genes that might underlie these effects, a comparative mapping analysis was undertaken to define the extent of orthologous segments of human chromosome 9. A microsatellite associated with heat shock protein (HSP) A5 was used to define the proximal boundary of the quantitative trait loci (QTL) region, which suggests the human orthologue of the gene(s) responsible for the observed effects lies between HSPA5 and the q arm telomere of human chromosome 9. Examination of this region revealed two candidate genes with known roles in production of hormones essential to growth and reproductive function. The steroidogenic factor 1 and Lhx3 LIM homeodomain transcription factor genes were mapped to 123 and 155 cM, respectively, of the Sus scrofa chromosome 1 (SSC1) linkage group, placing both genes within the confidence interval for the observed QTL. To further evaluate Lhx3, we examined the expression profile during porcine embryonic development. Low levels were detected at early embryonic stages, when development of the nervous system is proceeding. A transient increase in expression level is observed during the time of pituitary organogenesis and again at the time of differentiation of anterior pituitary cells, with relatively high levels of expression persisting in the adult pituitary gland. This ontology is consistent with Lhx3 being a candidate gene for the QTL.