Promoter sequences from two different Brassica napus tapetal oleosin-like genes direct tapetal expression of beta-glucuronidase in transgenic Brassica plants

To investigate the sequences responsible for the regulated expression of tapetal-specific oleosin-like genes, ca. 2 kb of the 5'-upstream regions from two divergent genes, OlnB;4 and OlnB;13, were isolated, sequenced and fused to the reporter gene beta-glucuronidase for study in transgenic Brassica napus plants. Although the proteins encoded by these two genes are highly divergent, except for the conserved oleosin-like domain, the first 250 bp of their 5'-upstream regions was 86% identical, including a region of 150 bp upstream from the TATA box. Analysis of 42 independent transformants by histochemical and fluorometric methods showed that both promoters directed tapetal-specific expression that peaked at the 4 mm flower bud stage.

The promoter of aBrassica napus polygalacturonase gene directs pollen expression ofβ-glucuronidase in transgenicBrassica plants

A 647-bp 5'-flanking fragment obtained from genomic clone Sta 44G(2) belonging to a family of polygalacturonase genes expressed inBrassica napus pollen was fused to theβ-glucuronidase (GUS) marker gene. This fusion construct was introduced intoB. napus plants viaAgrobacterium tumefaciens transformation. Analysis of the transgenicB. napus plants revealed that this promoter fragment is sufficient to direct GUS expression specifically in the anther and that GUS activity increases in pollen during maturation.

Molecular analysis of two Brassica napus genes expressed in the stigma

A partial cDNA clone, Pis 63, corresponding to a mRNA highly expressed in Brassica napus pistils, was isolated by differential screening. PCR was used to complete the Pis 63 sequence (Pis 63-1) and to obtain the sequence of another related cDNA (Pis 63-2). Northern blot and in situ analyses demonstrated that these transcripts are expressed in the stigma throughout flower development. Pis 63-1 and Pis 63-2 display similarity to a cotton fibre cDNA clone.

Isolation and characterization of a polygalacturonase gene highly expressed in Brassica napus pollen

A cDNA clone, Sta 44-4, corresponding to a mRNA highly expressed in Brassica napus cv. Westar stamens, was isolated by differential screening and characterized. Northern blot and in situ analyses demonstrated that Sta 44-4 is synthesized in pollen beginning at the late uninucleate stage and reaches a maximum in trinucleate microspores. Sta 44-4 displayed significant sequence similarity to known pollen polygalacturonase genes. The B. napus pollen polygalacturonase gene was shown to be part of a small gene family and to display some polymorphism among different cultivars.

RB-mediated tumor suppression of a lung cancer cell line is abrogated by an extract enriched in extracellular matrix

To examine whether the expression of retinoblastoma (RB) protein could mediate tumor suppression in a lung carcinoma cell line carrying multiple genetic defects, we transfected the Rb gene into a non-small cell lung cancer cell line with absent RB protein. We observed that the stable expression of a functional RB product was associated with a decreased efficiency of soft agar cloning and partial suppression of tumorigenicity in nude mice. The suppression of tumorigenicity was marked when 10(6) cells were injected into the flanks of nude mice but was less prominent when 10(7) cells were injected. RB-mediated tumor suppression, however, was consistently blocked by preincubation of the transfected cells with an extract enriched with an extracellular matrix (Matrigel). Analysis of tumors harvested from nude mice showed that they continued to express detectable levels of human RB protein which retained functional E1A binding activity and nuclear localization. RB-mediated inhibition of soft agar cloning was also blocked in a dose-dependent manner by the addition of Matrigel. These observations demonstrate that the expression of wild-type RB may suppress certain parameters of tumorigenicity in lung carcinoma cells that contain multiple genetic alterations. In addition, the reversal of tumor suppression by an extract enriched in basement membrane components may offer clues for further investigations into the mechanism of RB-mediated tumor suppression.

Recessive oncogenes in lung cancer

The observation that carcinogen exposure is strongly associated with the probability of developing pulmonary neoplasms has suggested for many years that acquired somatic mutations play a key role in the genesis of these environmentally induced cancers. With the advent of new techniques in cytogenetics and in the molecular analysis of DNA extracted from lung tumors, it has now become possible to test this hypothesis and to search for candidate genes that may be targeted by the chronic exposure of these environmental insults. Early work in this field, studying lung tumors of different histologic types, appears to implicate several distinct chromosomal loci (at chromosomes 3p, 13q, 17p, and others), suggesting that sequential genetic events occur during the initiation and progression pathways to pulmonary tumorigenesis. Identifying the candidate gene products and understanding the chronology and stringency of mutational events at these loci will be an essential goal to understanding the cellular basis of lung tumors and for developing strategies for the next generation of diagnostic and therapeutic studies.

A single amino acid substitution results in a retinoblastoma protein defective in phosphorylation and oncoprotein binding

We have previously identified a small-cell lung cancer cell line (NCI-H209) that expresses an aberrant, underphosphorylated form of the retinoblastoma protein RB1. Molecular analysis of RB1 mRNA from this cell line revealed a single point mutation within exon 21 that resulted in a nonconservative amino acid substitution (cysteine to phenylalanine) at codon 706. Stable expression of this mutant RB1 cDNA in a human cell line lacking endogenous RB1 demonstrated that this amino acid change was sufficient to inhibit phosphorylation. In addition, this cysteine-to-phenylalanine substitution also resulted in loss of RB1 binding to the simian virus 40 large tumor and adenovirus E1A transforming proteins. These results confirm the importance of exon 21 coding sequences and suggest that the cysteine residue at codon 706 may play a role in achieving a specific protein conformation essential for protein-protein interactions.