P1 Locus Research Articles

Two novel regions of interstitial deletion on chromosome 8p in colorectal cancer

We have investigated interstitial deletions of chromosome 8 in 70 colorectal carcinomas and 11 colonic adenomas using 11 microsatellite markers, including eight spanning the centromeric region of chromosome 8p (p11.2-p12). Allelic loss or imbalance was observed in 38 (54%) cancers and four (36%) adenomas. Twenty-eight (40%) of the cancers had deletions of 8p11.2-p12. Two distinct and independent regions of interstitial loss were found within this region. Fluorescent in situ hybridization, using an alpha satellite repeat probe to the centromere of 8p and two probes to the P1 region, was performed in four tumours that demonstrated allelic imbalance. Localized heterozygous deletions were confirmed in all four tumours. Eleven (16%) cancers had localized deletion in the region ANK-1 to D8S255 (P1) and a further eleven (16%) cancers had a less well localized deletion in the region defined by the markers D8S87 to D8S259 (P2). Loss of both centromeric loci was identified in a further six (9%) tumours. A functional significance for these two deletion regions was sought by correlation with primary and secondary tumour characteristics. Isolated P2 deletion was associated with 'early' T1 cancers (2p=0.0002), and were also identified in 3/11 adenomas. Conversely, interstitial deletions of the P1 locus were more frequently seen in 'locally invasive' T3/4 cancers (2p=0.015), and isolated P1 deletions were also associated with the presence of liver metastases (2p=0.016). Our data provide evidence of at least two genes within the 8p11.2-p12 region, mutations in which may confer different and independent roles in the pathogenesis of colorectal cancer.

Identification of Maize Chromosome Regions Associated with Antibiosis to Corn Earworm (Lepidoptera: Noctuidae) Larvae

A better understanding of the genetic basis of antibiosis to the corn earworm, Helicoverpa zea (Boddie), in maize, Zea mays L., silks will help breeders develop hybrids with improved resistance to this pest. We identified maize chromosome regions associated with antibiosis to the com earworm, and compared the results with those previously obtained for concentration of silk maysin, a C-glycosyl flavone that inhibits larval growth. We evaluated antibiosis with a dried-silk bioassay of 76 (GT114 X GT119) F2:3 lines, derived by self-pollinating F2 plants from the high and low tails of the distribution for silk maysin concentration. Variation in B-d larval weights resulting from silks of the F2:3lines was compared with variation in restriction fragment length polymorphism genotypes at 39 flavonoid pathway loci or linked markers of corresponding F2 plants. The multiple-locus model that best explained variation of larval weights included a major effect at the p1 region of chromosome 1 and smaller effects in the umc166b region (chromosome 1) and the sh1 region (chromosome 9). The model for maysin concentration of the corresponding F2 plants was nearly identical, with the exception that the sh1 locus was replaced by the nearby umc105a locus. Our results provide evidence that in this population silk maysin concentration and corn earworm antibiosis are under similar genetic control and that the p1 locus plays the major role in determining variation in both traits. Because we evaluated the tails of the distribution and probed only at flavonoid pathway loci, all chromosome regions associated with corn earworm resistance in this population may not have been detected.

Quantitative trait loci and metabolic pathways: genetic control of the concentration of maysin, a corn earworm resistance factor, in maize silks.

Interpretation of quantitative trait locus (QTL) studies of agronomic traits is limited by lack of knowledge of biochemical pathways leading to trait expression. To more fully elucidate the biological significance of detected QTL, we chose a trait that is the product of a well-characterized pathway, namely the concentration of maysin, a C-glycosyl flavone, in silks of maize, Zea mays L. Maysin is a host-plant resistance factor against the corn earworm, Helicoverpa zea (Boddie). We determined silk maysin concentrations and restriction fragment length polymorphism genotypes at flavonoid pathway loci or linked markers for 285 F2 plants derived from the cross of lines GT114 and GT119. Single-factor analysis of variance indicated that the p1 region on chromosome 1 accounted for 58.0% of the phenotypic variance and showed additive gene action. The p1 locus is a transcription activator for portions of the flavonoid pathway. A second QTL, represented by marker umc 105a near the brown pericarp1 locus on chromosome 9, accounted for 10.8% of the variance. Gene action of this region was dominant for low maysin, but was only expressed in the presence of a functional p1 allele. The model explaining the greatest proportion of phenotypic variance (75.9%) included p1, umc105a, umc166b (chromosome 1), r1 (chromosome 10), and two epistatic interaction terms, p1 x umc105a and p1 x r1. Our results provide evidence that regulatory loci have a central role and that there is a complex interplay among different branches of the flavonoid pathway in the expression of this trait.

Effect of the parthenocarpy gene P1 and ploidy on fruit and bunch traits of plantain-banana hybrids

Plantain and banana (Musa spp. AAB and AAA groups) are perennial giant herbs of the tropics which develop parthenocarpic fruits. At least three independent but complementary dominant genes control vegetative parthenocarpy in Musa. One of these genes, P1 segregates in euploid hybrid progenies derived from crosses between triploid ‘French’ plantains and a wild nonedible diploid banana. Linear correlation and regression analyses revealed that bunch weight and fruit weight and size were positively influenced by both ploidy increases and change of recessive to dominant alleles at the P1 locus. Moreover, significant multiple regression models, including ploidy and number of copies of the P1 allele as independent variables, accounted for most of the phenotypic variation for bunch and fruit traits. The coefficients of determination of the multiple regression analyses were always smaller than estimates of broad-sense heritability for each trait. This implies that ploidy and the effect of allele substitution did not explain all the genetic variation for bunch and fruit traits. Hence, other genetic factors may explain the remaining portion of genetic variation. The potential for indirect marker-assisted selection in the seedling nursery, through the utilization of predictive multiple regression equations, was assessed by the Durbin-Watson test of residuals. The adoption of this breeding method requires the identification of DNA markers linked to the P1 gene and reliable and rapid methods to determine ploidy in seedlings

Molecular phylogeny and evolution of marsupial protamine P1 genes.

We report the DNA sequences of protamine P1 genes and flanking regions from 21 mammalian species, including representatives of all extant marsupial orders. The protamine P1 locus in marsupials displays highly conserved 5' and 3' flanking sequences, as well as a highly variable intron. Marsupial protamines examined are distinct from those of eutherian mammals in lacking cysteine residues, a feature that may be correlated with lower stability of marsupial sperm nuclei during chromatin condensation. Phylogenetic analysis of protamine sequences leads to the following conclusions: (i) the microbiothere Dromiciops is part of a clade that includes dasyurids, Notoryctes and diprotodontians but not bandicoots; (ii) dasyurids are the closest living relatives of Notoryctes; (iii) macropodids, phalangerids and pseudocheirids form a clade apart from the phascolarctids; and (iv) the closest living relatives of caenolestids are didelphids.