Excision of the maize transposable element Ac in periclinal chimeric leaves of 35S-Ac-rolC transgenic aspen-Populus.

The transposable element Ac from maize, in combination with the phenotypic selectable marker rolC, was employed in transformation experiments of a hybrid aspen clone. A number of transgenic clones exhibited light-green sectors on green leaves. In vitro regeneration from leaves showing a high number of light-green spots resulted in R2 plants, which also showed light-green sectored leaves. However, only one out of 385 regenerated plants obtained showed green leaves. Both PCR and northern analysis indicated Ac excision and restoration of rolC expression. In Southern blot analysis of this green plant additional bands were observed as compared to the original R1 plant. The occurrence of these bands and a suggested Ac excision in the non-green L1-epidermal layer leading to periclinal chimerism of this plant is discussed.

Mapped DNA probes from loblolly pine can be used for restriction fragment length polymorphism mapping in other conifers.

A high-density genetic map based on restriction fragment length polymorphisms (RFLPs) is being constructed for loblolly pine (Pinus taeda L.). Consequently, a large number of DNA probes from loblolly pine are potentially available for use in other species. We have used some of these DNA probes to detect RFLPs in 12 conifers and an angiosperm. Thirty complementary DNA and two genomic DNA probes from loblolly pine were hybridized to Southern blots containing DNA from five species of Pinus (P. elliottii, P. lambertiana, P. radiata, P. sylvestris, and P. taeda), one species from each of four other genera of Pinaceae (Abies concolor, Larix laricina, Picea abies, and Pseudotsuga menziesii), one species from each of three other families of Coniferales [Sequoia sempervirens (Taxodiaceae), Torreya californica (Taxaceae) and Calocedrus decurrens (Cupressaceae)], and to one angiosperm species (Populus nigra). Results showed that mapped DNA probes from lobolly pine will cross-hybridize to genomic DNA of other species of Pinus and some other genera of the Pinaceae. Only a small proportion of the probes hybridized to genomic DNA from three other families of the Coniferales and the one angiosperm examined. This study demonstrates that mapped DNA probes from loblolly pine can be used to construct RFLP maps for related species, thus enabling the opportunity for comparative genome mapping in conifers.

Linkage between a regulatory locus for melanoma cell differentiation and an esterase locus in Xiphophorus.

Linkage between an autosomal regulatory gene Diff controlling differentiation of neoplastic melanophores and an esterase locus, Est-1, has been demonstrated in Xiphophorus. The recombination values between Est-1 and Diff ranged from 21 to 29 percent depending on the melanophore pattern loci Sp, Sd, Sd, and Livar. The average recombination frequency for all genotypes investigated was 25 percent. Since Est-1 and Diff do not assort independently of each other, it is concluded that Est-1 and Diff are both located on the same chromosome. Thus, the Est-1 locus provides a marker for monitoring the presence of the Diff autosome.

Sex chromosome aberrations involving loss and translocation of tumor-inducing loci in Xiphophorus.

Karyotypic changes involving a deletion and a translocation of certain sex-linked tumor-inducing loci of the platyfish, Platypoecilus (Xiphophorus) maculatus, have been investigated. The effects of these chromosome aberrations on tumor formation and viability of the fish are discussed.

Genetic basis of susceptibility for development of neoplasms following treatment with N-methyl-N-nitrosourea (MNU) or x-rays in the platyfish/swordtail system.

Specific genotypes of the xiphophorine fish develop neoplasms following treatment with N-methyl-N-nitrosourea or X-rays. Several of these neoplasms can be related to the presence of specific chromosomes. The implication of these findings are discussed.

Genetics of susceptibility in the platyfish/swordtail tumor system to develop fibrosarcoma and rhabdomyosarcoma following treatment with N-methyl-N-nitrosourea (MNU).

About 7000 animals of 65 different genotypes of the xiphophorine fish were treated with the direct acting chemical carcinogen N-methyl-N-nitrosourea (MNU; 10(-3)M; four times for 1 hour in two week intervals), in order to find out whether the susceptibility for development of fibrosarcomas and rhabdomyosarcomas is directly related to the genotype. A genotype specific susceptibility was found, ranging from zero to about nine percent. The highest susceptibles were found in certain backcross hybrids involving P.variatus/X.helleri-hybrids and X.helleri, as the recurrent parent. These genotypes were further analysed. Both P.variatus and X.helleri, as werr as their F1 proved to be insusceptible; while from the three backcrosses, which were tested, namely the BC1, BC4 and BC15, both the BC1, and the BC4, were susceptible, but the BC15 was insusceptible. The results are interpreted on the basis of the assumption that the differential susceptibility is a function of the type of control of a tumor gene (Tu-Fi-Rh) endogenous to P.variatus and involved in development of fibrosarcomas and rhabdomyosarcomas. Accordingly, in P.variatus and in the F1 the Tu-Fi-Rh is controlled by repressing genes (R-genes) linked as well as non-linked to Tu-Fi-Rh; because simultaneous mutation of both R-genes following treatment with MNU is an extremely unlikely event, these genotypes have an extremely low susceptibility. By contrast, in the BC1 and the BC4 the non-linked R-genes become eliminated and only the linked R-gene remains for repression of Tu-Fi-Rh; this condition confers a high degree of susceptibility, because one single mutation may lead to impairment of the R-gene and to Tu-Fi-Rh-mediated formulation of fibrosarcomas and rhabdomysarcomas. In the BC15, furthermore, also the Tu-Fi-Rh has become eliminated, resulting in a loss of the susceptibility. The results suggest that in the xiphophophorine fish the susceptibility for responding to MNU-treatment with the development of fibrosarcomas and rhabdomysarcomas is related directly to the genotype.

Tissue-specific esterases in the Xiphophorine fish Platypoecilus maculatus, Xiphophorus helleri, and their hybrid.

Tissue-specific esterases of the xiphophorine fishes Platypoecilus maculatus (platyfish), Xiphophorus helleri (swordtail), and their F1 hybrid have been analyzed using disc electrophoresis. Seven esterase zones (resolved into a maximum of nine bands) exist in these fishes, and these have been classified by employing specific inhibitors. Five of the seven zones, EST-1, EST-2, EST-5, EST-6, and EST-7, appeared to be carboxylesterases; while the two remaining zones, EST-3 and EST-4, were classified as cholinesterases. In the liver of the platfish, all seven esterase zones were detected, while the liver of the swordtail exhibited only five esterase zones. EST-1 and EST-3 were lacking in the liver tissue of the swordtail. All seven esterase loci were expressed in the liver tissue of the F1 hybrid. The reciprocal crosses gave the same results. In the fin, skin, skeletal muscle, and eye tissues from all three genotypes, three major esterase zones, EST-2, EST-5, and EST-7, were detected. In addition, EST-1 was frequently detected in all these tissues of the platfish and the F1, but was lacking in the swordtail. Serum from three genotypes showed one prominent esterase zone, EST-5; however, trace activity of EST-2 and EST-7 zones could also be detected. It seems that in all tissues of the F1 hybrid there is expression of all the esterase genes from the platfish. The results of the present study are discussed in the comparison to those from other studies on teleost esterases.

Tumor formation in Nicotiana: Auxin levels and auxin inhibitors in normal and tumor-prone genotypes.

Auxin and auxin-inhibitors from acidic ether extracts of normal stem tissue of Nicotiana longiflora, N. debneyi-tabacum, their tumor producing F 1 hybrid and non-tumor and tumor-prone segregants were separated by thin-layer chromatography and measured by an Avena curvature test. A significantly higher amount of auxin, very likely IAA, was found in the F 1 hybrid and the tumor-prone segregants as compared to the non-tumor tissues. Inhibitory substances appeared at different Rf's but generally in low amounts. One inhibitor seems to be identical with the "inhibitor ß". In general, the results indicate that higher levels of auxin are associated with tumor-prone tissues in the F 1 hybrid and the segregants of a later generation carrying an alien longiflora chromosome on a debneyi-tabacum background. The role of this growth-regulating substance as related to tumor formation in Nicotiana is discussed.

Morphogenetic studies of a genetically controlled tumor-like condition in Lycopersicon hybrids.

A dominant tumor-like condition recently isolated in a tomato hybrid is described from the viewpoint of morphogenesis. Tumors, consisting of masses of enlarged parenchymatous cells, generally appear on the ventral surface of the third leaf and the subsequently formed leaves of the hybrid derivatives. These outgrowths do not differentiate into teratomas. Abortive floral buds develop under greenhouse conditions and the tumorous plants are much dwarfed compared to the normal segregants of the same population. the same tumor genotype behaves differently under the field conditions: it grows and blossoms like the normal plants, setting fruits with viable seeds, and tumors fail to develop. Thus, tumor expression and general morphology of the tumor plants are greatly modified by environmental conditions.Tissue culture studies employing a variety of media have shown that tissues excised from tumor-producing plants are not autonomous with respect to growth hormones, nor are tissues from the non-tumorous segregants. Nevertheless, tissues from tumor and non-tumor genotypes show different growth requirements. Tumor and non-tumor tomatoes can thus be distinguished on the basis of in vitro growth responses, a result consistent with their different genetic constitution. Differentiation of buds or roots was not observed in either type of tissue.