Cytogenetic characterization of ten malignant fibrous histiocytomas

We examined 10 malignant fibrous histiocytomas (MFHs) using metaphase preparations. Six tumors showed clonal structural and/or numerical chromosomal aberrations, and four tumors had normal karyotypes. For the most part, chromosomes 1, 3, 6, 9, 12, 16, 18, and 20 were involved in structural aberrations. The breakpoint regions most frequently were in 1p32, 3p25, and the centromeric region of chromosomes 1 and 16. There was a conspicuous loss in chromosome 18. We detected ring chromosomes in two tumors. One tumor showed a high percentage of near-haploid cells. Our results show many parallels to data which have already been published. MFHs include a broad spectrum of tumors of widely different histology and clinical course. So it is not surprising to find a cytogenetic diversity of chromosomal aberrations in this study.

The p53 gene in soft tissue sarcomas: prognostic value of DNA sequencing versus immunohistochemistry

BACKGROUND

The aim of this study was to compare sequencing and immunohistochemistry (IHC) for their ability to detect p53 mutations and to assess their prognostic value in soft tissue sarcomas (STS).

MATERIAL AND METHODS

146 STS samples were investigated by single strand DNA conformation polymorphism (SSCP)-sequencing for p53 mutations. Additionally, IHC with five p53 antibodies (CM-1, Pab1801, Pab240, DO1, DO-7) was performed.

RESULTS

In 65 to 131 tumor samples (44.5% to 90.4%) elevated levels of p53 protein were recorded by IHC, depending on the antibody applied. Sixteen out of 146 STS tumor samples (11%) had p53 gene mutations. 13 cases (81.2%) of the 16 tumors with p53 mutations could be detected by DO-1. However, of the 93 DO-1 positive tumors 79 were negative by SSCP-sequencing analysis. Using multivariate regression analysis (Cox proportional hazards model) both p53 mutations (non-frameshift mutations) and IHC detection of p53 protein overexpression were prognostic predictors for poor survival.

CONCLUSIONS

This study suggests that IHC is valuable for assessing p53 mutations in STS, but sequencing provides additional important information on the molecular characteristics of the alterations.

No p16INK4A/CDKN2/MTS1 mutations independent of p53 status in soft tissue sarcomas

The p16INK4A/CDKN2/MTS1 gene encodes a specific inhibitor of cyclin-dependent kinases (CDKs) 4 and 6. This study investigates p16INK4A gene status and expression in mesenchymal tumours, in particular soft tissue sarcomas (STSs). Employing non-radioactive polymerase chain reaction-single strand conformational polymorphism (PCR-SSCP) sequencing, no p16INK4A mutation was found in 86 samples taken from 74 mesodermal tumours with known p53 gene status. This suggests that p16INK4A gene alterations, inc contrast to p53, are not involved in the progression of STS. This finding is supported by the reports of a low frequency of deletions and intragenic mutations in STS. Furthermore, by immunohistochemistry (IHC), an inverse correlation was established between p16INK4A and RB positivity for 62 per cent of the frozen tumour samples investigated. However, alterations in other components of the pRh/p16INK4A/ CDK4/cyclin D1/E2F pathway have been proven crucial for tumourigenesis in human sarcomas.

Embryonic expression and characterization of a Ptx1 homolog in Drosophila

We describe the molecular characterization of the paired-type homeobox gene D-Ptx1 of Drosophila, a close homolog of the mouse pituitary homeobox gene Ptx1 and the unc-30 gene of C. elegans, characterized by a lysine residue at position 9 of the third alpha-helix of the homeodomain. D-Ptx1 is expressed at various restricted locations throughout embryogenesis. Initial expression of D-Ptx1 in the posterior-most region of the blastoderm embryo is controlled by fork head activity in response to the activated Ras/Raf signaling pathway. During later stages of embryonic development. D-Ptx1 transcripts and protein accumulate in the posterior portion of the midgut, in the developing Malpighian tubules, in a subset of ventral somatic muscles, and in neural cells. Phenotypic analysis of gain-of-function and lack-of-function mutant embryos show that the D-Ptx1 gene is not involved in morphologically apparent differentiation processes. We conclude that D-Ptx1 is more likely to control physiological cell functions than pattern formation during Drosophila embryogenesis.

Detection of p53 autoantibodies in sera of gastric cancer patients and their prognostic relevance

BACKGROUND

Changes in the p53 gene product can be immunogenic and enable the formation of p53 serum antibodies (p53ab), detectable in patients with different cancer types. So far, there have been no reports describing the detectability of p53ab in gastric cancer patients.

METHODS

We investigated the presence of p53ab and their clinical relevance in a cohort of 74 gastric cancer patients, using an enzyme-linked immunosorbent assay system.

RESULTS

In our investigation 20.3% of all patients (15 of 74) and 46.9% of the patients with immunohistochemically (IHC) p53-positive tumors (15 of 32) showed detectable p53ab in serum. All p53ab-positive patients had IHC p53-positive tumors. We have found a significant correlation of p53ab with a higher tumor stage (P = 0.002) and also with a poor prognosis of survival (P = 0.04).

CONCLUSION

We have shown that in gastric cancer patients p53ab are also detectable and that p53ab positivity is a predictor of an unfavorable prognosis.

Prognostic value of immunohistochemistry for p53 in primary soft-tissue sarcomas: a multivariate analysis of five antibodies

Most changes of tumor suppressor p53 and its pathway involve a protein with prolonged half-life that permits immunohistochemical detection. The goal of this study was to compare the prognostic relevance of five different p53 antibodies in primary soft-tissue sarcomas (STS) with known p53 mutation status, using a multivariate Cox regression model (adjusted to tumor grading, staging, localization, tumor type, and therapy). A group of 198 primary STS of six types were investigated for p53 overexpression, using p53 antibodies DO-1, DO-7, Pab1801, Pab240, and CM-1. A positive marker frequency between 36.2% and 62.6% was detected. Out of 65 patients whose primary tumor reacted positively to all five antibodies, 52 (80%) died within the study period. Only the N-terminal-binding monoclonal antibodies DO-1, DO-7 and Pab1801 showed a multivariate correlation with survival (P = 0.0014, 0.0048 and 0.02). CM-1 and Pab240 had a univariate, but not a multivariate correlation, with a confounding effect of grading. The prognostic relevance for the five p53 antibodies was: DO-1 > Pab1801 > DO-7 > CM-1 > Pab240. This is the first study that investigates multivariately the prognostic relevance of p53 immunostaining in STS. If monoclonal antibodies with an epitope in the N-terminal region of the p53 protein (DO-1, Pab1801, DO-7) are applied, p53 immunohistochemistry provides an independent prognostic marker in STS.

Prognostic relevance of C-terminal Mdm2 detection is enhanced by p53 positivity in soft tissue sarcomas

We examined the clinical value of immunohistochemical (IHC) Mdm2 detection by an N-terminal (IF2) and a C-terminal (19E3) binding monoclonal antibody (Ab) in soft tissue sarcomas (STSs) with regard to the p53 status. Therefore, we investigated a cohort of 198 patients with STSs of six entities with known p53 IHC by using a multivariate Cox regression model to determine the prognostic value of Mdm2 staining. Only positivity with the 19E3 Ab correlated multivariately significantly with survival (RR = 2.32, p = 0.0035). We stratified the C-terminal Mdm2 staining (19E3) according to p53 IHC (DO-1) and found patients could be divided into three groups with an increasing risk: (a) patients with Mdm2 (19E3)-negative as well as p53 (DO-1)-negative tumors, (b) patients with tumors that were either Mdm2 (19E3) or p53 (DO-1) positive, and (c) patients with tumors that were Mdm2 (19E3) as well as p53 (DO-1) positive. Positive staining for both Mdm2 and p53 meant a very poor prognosis with a relative risk of 4.63 (p = 0.00001). This points to the possibility that--in addition to the p53-dependent pathway--Mdm2 could have an effect through a p53-independent pathway. Thus, our results indicate that C-terminal Mdm2 staining (19E3) constitutes an independent prognostic marker in STS.

Regulation of Drosophila spalt gene expression

The region-specific homeotic gene spalt is involved in the specification of terminal versus trunk structures during early Drosophila embryogenesis. Later in development spalt activity participates in specific processes during organogenesis and larval imaginal disc development. The multiple functions of spalt are reflected in distinct spatio-temporal expression patterns throughout development. Here we show that spalt cis-regulatory sequences for region-specific and organ-specific expression are clustered. Their organization may provide the structural basis for the diversification of expression pattern within the spalt/spalt related/spalt adjacent gene complex. We also examined the transacting factor requirement for the blastodermal spalt expression domains. They are under the genetic control of maternal and gap gene products and we show that these products are able to bind to corresponding spalt cis-acting sequences in vitro. The results suggest that the transacting factors, as defined by genetic studies, functionally interact with the spalt regulatory region. In addition, we provide evidence that a zygotic gene product of the terminal system, Tailless, cooperates with the maternal gene product Caudal and thereby activates gene expression in the terminal region of the embryo.

Mechanism and Bicoid-dependent control of hairy stripe 7 expression in the posterior region of the Drosophila embryo

Pair-rule gene hairy (h) expression in seven evenly spaced stripes, along the longitudinal axis of the Drosophila blastoderm embryo, is mediated by a modular array of separate stripe enhancer elements. The minimal enhancer element, which generates reporter gene expression in place of the most posterior h stripe 7 (h7-element), contains a dense array of binding sites for factors providing the trans-acting control of h stripe 7 expression as revealed by genetic analyses. The h7-element mediates position-dependent gene expression by sensing region-specific combinations and concentrations of both the maternal homeodomain transcriptional activators, Caudal and Bicoid, and of transcriptional repressors encoded by locally expressed zygotic gap genes. Caudal and Bicoid, which form complementing concentration gradients along the longitudinal axis of the embryo, function as redundant activators, indicating that the anterior determinant Bicoid is able to activate gene expression in the most posterior region of the embryo. The spatial limits of the h stripe-7 domain are brought about by the local activities of repressors which prevent activation. The results suggest that the gradients of Bicoid and Caudal combine their activities to activate segmentation genes along the entire axis of the embryo.

Immunohistochemical and clinical evaluation of cathepsin expression in soft tissue sarcomas

Lysosomal proteases are known to enhance the spread of epithelial tumour cells, but little is known of the possible role of proteases in the growth of soft tissue sarcomas (STS). We investigated the expression of cathepsins D, B, S, H, L and procathepsin L in frozen sections of 34 STS from 34 patients by immunohistochemistry (IHC). Cathepsins D, B and H were relatively highly expressed in STS (77-91%). The expression rate of cathepsins S and L and of procathepsin L was lower (40-66%). Cathepsin S and L expression showed a moderate (P = 0.078 and P = 0.019) and procathepsin L a strong (P = 0.00001) correlation with the survival rate of STS patients. Cathepsin S expression is also correlated with the local recurrence rate (P < 0.01). Lysosomal proteases may play a role in STS progression, and cathepsin expression may also have significance as a prognostic factor in STS.

Krüppel, a Drosophila segmentation gene, participates in the specification of neurons and glial cells

We report that the Drosophila segmentation gene Krüppel (Kr) is expressed in neural precursor cells, neurons and glial cells at different stages of neurogenesis and that Kr mutants develop aberrant peripheral (PNS) and central (CNS) nervous systems. Expression derived from a Kr minigene rescues the segmentation defects but these embryos continue to lack most of the neural Kr activity. Phenotypic analysis of the rescued embryos indicates that, in addition to overall effects on the PNS and CNS structure via its segmentation role, Kr expression in the nervous system is functionally required for establishing particular neural and glial fates.

Prognosis is correlated with p53 mutation type for soft tissue sarcoma patients

We investigated the prognostic value of p53 mutation type for 145 soft tissue sarcoma patients. In a PCR-SSCP-sequencing analysis, 15 mutations were identified: 10 non-frameshift (non-fs) and 5 frameshift (fs) mutations. Patients possessing non-fs mutations had a significantly poorer prognosis than patients without p53 mutations (P = 0.014), according to Cox's multivariate analysis. In contrast, the survival of five patients with fs mutations was not affected by their mutation type. Furthermore, occurrence of lymph node metastases and recurrences was correlated with the mutation type; i.e., 4 of 10 and 5 of 10 patients with non-fs mutations showed lymph node metastases and recurrences, respectively, whereas none of the patients with fs mutations showed lymph node metastases and only one a recurrence. Therefore, for the evaluation of prognosis, we suggest applying not the p53 mutational status in general, but the specific type of mutation.

Frequent occurrence of p53 mutations in rhabdomyosarcoma and leiomyosarcoma, but not in fibrosarcoma and malignant neural tumors

We have analyzed soft-tissue sarcomas (STS) molecularly for mutations in the tumor-suppressor gene p53 and immunohisto-chemically for expression of p53 and mdm2 proteins. In this study, tumor samples from 3 groups of soft-tissue sarcomas, i.e., fibrosarcomas, myogenic sarcomas and malignant neural tumors (MNT), were investigated. The methods applied encompass immunohistochemistry on 198 tumor samples using p53 antibodies (DO-1 and DO-7) and an mdm2 antibody (IF-2). Out of these, 100 samples were subjected to non-radioactive PCR-SSCP-sequencing analysis. Immunohistochemical detection rate for p53 (range of 57% to 67%) and for mdm2 proteins (range of 19 to 44%) was similar in all 3 groups. In higher tumor grades, an increased rate of immunopositivity was found for p53 but not for mdm2. Investigation of p53 mutational status revealed 6 mutations in myogenic sarcomas but none in malignant neural tumors or fibrosarcomas, suggesting different roles of p53 in the 3 STS groups. Interestingly, a G-->A transition in codon 245 (a CpG site) was found in 3 myogenic sarcomas. Our results and those of others suggest p53 codon 245 as a mutational hotspot in sarcomas, as recognized in carcinomas.

Germ line and embryonic expression of Fex, a member of the Drosophila F-element retrotransposon family, is mediated by an internal cis-regulatory control region

The F elements of Drosophila melanogaster belong to the superfamily of long interspersed nucleotide element retrotransposons. To date, F-element transcription has not been detected in flies. Here we describe the isolation of a member of the F-element family, termed Fex, which is transcribed in specific cells of the female and male germ lines and in various tissues during embryogenesis of D. melanogaster. Sequence analysis revealed that this element contains two complete open reading frames coding for a putative nucleic acid-binding protein and a putative reverse transcriptase. Functional analysis of the 5' region, using germ line transformation of Fex-lacZ reporter gene constructs, demonstrates that major aspects of tissue-specific Fex expression are controlled by internal cis-acting elements that lie in the putative coding region of open reading frame 1. These sequences mediate dynamic gene expression in eight expression domains during embryonic and germ line development. The capacity of the cis-regulatory region of the Fex element to mediate such complex expression patterns is unique among members of the long interspersed nucleotide element superfamily of retrotransposons and is reminiscent of regulatory regions of developmental control genes.

Molecular and immunohistochemical p53 status in liposarcoma and malignant fibrous histiocytoma: identification of seven new mutations for soft tissue sarcomas

BACKGROUND

p53 mutations are the most frequently observed tumor-related genetic changes. Mutational analysis concerns mostly carcinomas and is not comprehensive for soft tissue sarcomas. Among soft tissue sarcomas, malignant fibrous histiocytoma (MFH) and liposarcoma represent the most frequent tumor types. Most of the few identified mutations for soft tissue sarcomas are localized in the core domain of p53. A correlation between p53 positive immunoreactivity, missense mutations, and a poor prognosis is generally assumed. However, the character of p53 mutations and their functional importance for the clinical process is still unknown.

METHODS

Sixty-two soft tissue sarcoma samples were investigated for the presence of p53 mutations and for p53 immunoreactivity. Exons 4-9 of the p53 gene were amplified from genomic DNA with the polymerase chain reaction. A prescreen for mutations was performed by nonradioactive single strand conformation polymorphism analysis; striking cases were sequenced directly. For an evaluation of the immunohistochemical status, five p53 antibodies were used.

RESULTS

In 10 tumor samples 7 new p53 mutations and one polymorphism were identified. Mutations were detected for five liposarcomas (four patients) and four MFHs (three patients). Of the seven mutations, three were missense point mutations, three were deletions, and one was a complex conversion. All mutations but one were localized in the core domain of p53. Of 62 tumor samples, 56% (14 of 32 liposarcomas and 21 of 30 MFHs) were positive for p53 immunostaining.

CONCLUSIONS

The mutations identified in the core domain affect codons that are structurally or functionally involved in DNA binding. A relation between p53 positive immunoreactivity and a poor prognosis, but not with an exclusively high tumor grade, is evident. p53 mutations in soft tissue sarcomas have a similar spectrum to those in carcinomas.

Activation of posterior gap gene expression in the Drosophila blastoderm

The process of body prepatterning during Drosophila blastoderm formation relies on the localized activities of zygotic segmentation genes, which are controlled by asymmetrically distributed maternal determinants. The anterior determinant bicoid, a homeodomain transcription factor, forms an anterior-to-posterior concentration gradient. It interacts with the maternal transcription factor hunchback to activate the anterior zygotic patterning genes, including the central gap gene Krüppel (Kr). In contrast, the posterior maternal system does not provide such a decisive transcription factor, but rather prevents the repressor hunchback from acting in the posterior half so that the gap genes giant (gt) and knirps (kni) are activated by an as yet unknown transcription factor. Here we show that caudal, a conserved homeodomain protein that forms a posterior-to-anterior concentration gradient, and the anterior determinant bicoid cooperate to form a partly redundant activator system in the posterior region of the embryo.

Mesoderm-specific B104 expression in the Drosophila embryo is mediated by internal cis-acting elements of the transposon

The Drosophila melanogaster genome contains about 100 copies of the B104 transposable element, which is strongly expressed during embryogenesis. Here we show that B104 expression is restricted to the esophageal and amnioproctodeal regions of the embryo and to the developing mesoderm. Mesoderm-specific B104 expression requires the activity of the mesoderm-determining factors twist and snail. Virtually the same expression patterns were observed in Drosophila yakuba, a species that a separated from D. melanogaster by some 15 million years of evolution. We show that B104 expression is directed by internal sequences of the retrotransposon that are capable of acting as a cis-acting regulatory element in front of a heterologous Drosophila promoter. Our findings suggest that retrotransposon insertions can affect the expression patterns of endogenous genes by adding and distributing specific cis-acting control elements throughout the host genome. We therefore propose that transposable elements in addition to reducing the fitness of their hosts may also provide a rich pool of cis-acting sequences that contribute to the long-term evolutionary potential of the population in a beneficial manner.

Redundant functions of the genes knirps and knirps-related for the establishment of anterior Drosophila head structures

Developmental gene functions of Drosophila are typically characterized by a recognizable mutant phenotype. When molecular probes of such genes were used to isolate homologues, distinct spatially and temporally restricted expression patterns were observed in vertebrates as well. However, corresponding "gene knock-outs" often revealed subtle or no scorable phenotypes, a phenomenon attributed to redundant gene functions. We found that the evolutionarily related genes knirps (kni) and knirps-related (knrl) contribute to a similar phenomenon in Drosophila. The two closely situated genes show identical expression patterns in the developing embryo, including the posterior and anterior expression domains in the blastoderm. Here we show that the two biochemically equivalent gene products are both functional in the head anlage and that the lack of one gene activity can be overcome by the activity of the other. Whereas kni is also required for abdominal segmentation, knrl is nonfunctional in its posterior expression domain. Thus, the kni/knrl pair of genes provides a region-specific buffering system, rather than a case of global functional redundancy.

Sp1/egr-like zinc-finger protein required for endoderm specification and germ-layer formation in Drosophila

Much of our present knowledge of the biological processes involved in pattern formation in Drosophila is derived from segmentation analysis. Comparatively little is known about the genetic requirement and mechanisms underlying the formation and separation of germ layers by morphogenetic movements during gastrulation. Here we show that the Drosophila gene huckebein (hkb), a member of the gap-gene class of segmentation genes, is required for germ-layer formation at blastoderm. Absence of the hkb product, an Sp1/egr-like zinc-finger protein, causes the ectodermal and mesodermal primordia to expand at the expense of endoderm anlagen. Conversely, ectopic expression of hkb inhibits the formation of the major gastrulation fold which gives rise to the mesoderm and prevents normal segmentation in the ectoderm. Thus, hkb is necessary for endoderm development and its activity defines spatial limits within the blastoderm embryo in which the germ layers are established.

A two-step mode of stripe formation in the Drosophila blastoderm requires interactions among primary pair rule genes

The stripe pattern of pair rule gene expression along the anterior-posterior axis of the Drosophila blastoderm embryo represents the first sign of periodicity during the process of segmentation. Striped gene expression can be mediated by distinct cis-acting elements that give rise to individual stripe expression domains in direct response to maternal and first zygotic factors. Here we show that the expression of stripes can also be generated by a different, two-step mode which involves regulatory interactions among the primary pair rule genes hairy (h) and runt (run). Expression of h stripes 3 and 4 is directed by a common cis-acting element that results in an initial broad band of gene expression covering three stripe equivalents. Subsequently, this expression domain is split by repression in the forthcoming interstripe region, a process mediated by a separate cis-acting element that responds to run activity. This second mode of pair rule stripe formation may have evolutionary implications.

Mutations in the protein phosphatase 1 gene at 87B can differentially affect suppression of position-effect variegation and mitosis in Drosophila melanogaster

The suppressor of position effect variegation (PEV) locus Su-var(3)6 maps to 87B5-10. The breakpoints of deficiencies that define this interval have been placed on a 250-kb molecular map of the region. The locus is allelic to the ck19 complementation group previously shown to encode a type 1 serine-threonine protein phosphatase (PP1) catalytic subunit. When introduced into flies by P element-mediated transformation, a 5.8-kb genomic fragment carrying this gene overcomes the suppressor phenotype of Su-var(3)6(01) and recessive lethality of all mutations of the locus. Four of the mutant alleles at the locus show a broad correlation between high levels of suppression of PEV, a high frequency of aberrant mitosis and low PP1 activity in larval extracts. However, some alleles with low PP1 activity show weak suppression of PEV with a high frequency of abnormal mitosis, whereas others show strong suppression of PEV with normal mitosis. The basis for these discussed.

P transposon-induced dominant enhancer mutations of position-effect variegation in Drosophila melanogaster

P transposon induced modifier mutations of position-effect variegation (PEV) were isolated with the help of hybrid dysgenic crosses (pi 2 strain) and after transposition of the mutator elements pUChsneory+ and P[lArB]. Enhancer mutations were found with a ten times higher frequency than suppressors. The 19 pUChsneory(+)- and 15 P[lArB]-induced enhancer mutations can be used for cloning of genomic sequences at the insertion sites of the mutator elements via plasmid rescue. Together with a large sample of X-ray-induced (48) and spontaneous (93) enhancer mutations a basic genetic analysis of this group of modifier genes was performed. On the basis of complementation and mapping data we estimate the number of enhancer genes at about 30 in the third chromosome and between 50 and 60 for the whole autosome complement. Therefore, enhancer of PEV loci are found in the Drosophila genome as frequently as suppressor genes. Many of the enhancer mutations display paternal effects consistent with the hypothesis that some of these mutations can induce genomic imprinting. First studies on the developmentally regulated gene expression of PEV enhancer genes were performed by beta-galactosidase staining in P[lArB] induced mutations.

Formation of the Drosophila larval photoreceptor organ and its neuronal differentiation require continuous Krüppel gene activity

The Drosophila segmentation gene Krüppel (Kr) is redeployed to play a critical role for the establishment of the larval visual system. Using reporter gene expression conducted by a specific Kr cis-acting element, we were able to trace back the origin of the larval photoreceptor organ, the Bolwig organ, to a single progenitor neuron and to examine Kr function in Bolwig organ development when Kr+ activity is absent from embryos due to specific mutations or reduced by neuron-specific and temporally restricted Kr antisense RNA expression. Our results show that Kr is required for neurons to differentiate into Bolwig organs, for fasciculation of the Bolwig nerve, and for this nerve to follow a specific pathway toward the synaptic targets in the larval brain. The transcription factor encoded by Kr is likely to regulate surface molecules necessary for neuronal cell adhesion and recognition in the developing larval visual system.

Loss of gene function through rapid mitotic cycles in the Drosophila embryo

The early developmental period in Drosophila is characterized by rapid mitotic divisions, when the body pattern becomes organized by a cascade of segmentation gene activity. During this process localized expression of the gap gene knirps (kni) is required to establish abdomen segmentation. The knirps-related gene (knrl) encodes a kni-homologous nuclear hormone receptor-like protein and shares the spatial patterns of kni expression. The two genes differ with respect to the size of their transcription units; kni contains 1 kilobase and knrl 19 kilobases of intron sequences. The consequence of this difference in intron size is that knrl cannot substitute for kni segmentation function, although it gains this ability when expressed from an intronless transgene. Here we show that the length of mitotic cycles provides a physiological barrier to transcript size, and is therefore a significant factor in controlling developmental gene activity during short 'phenocritical' periods. The required coordination of cycle length and gene size provides severe constraints towards the evolution of rapid development.

Competition for overlapping sites in the regulatory region of the Drosophila gene Kruppel

A 730-base pair element regulates expression of the Drosophila gap gene Krüppel (Kr) in response to the fly anterior morphogen bicoid (bcd). Two hormone receptor-like proteins, encoded by the genes knirps (kni) and tailless (tll), bind specifically to the element. In vitro, kni protein competes with the homeodomain-containing bcd protein in binding to a 16-base pair target sequence. In vivo experiments suggest that both kni and tll act as competitive repressors of bcd-mediated activation of Kr. These results suggest a mechanism by which developmental genes can be regulated in response to an activating morphogen gradient antagonized by repressors.