The homeotic gene fork head encodes a nuclear protein and is expressed in the terminal regions of the Drosophila embryo

A Drosophila Winged-helix nude (Whn)-like transcription factor with essential functions throughout development

A Drosophila gene, Dwhn (Drosophila whn-like), encoding a putative transcriptional regulator with a DNA binding domain similar to that of mouse Winged-helix nude (Whn) was cloned. Analyses of the phenotypes produced by a hypomorphic mutation and transgene expression suggested a role in cell fate decision during the differentiation of the compound eye, wing veins and bristles. During embryonic development, Dwhn expression started ubiquitously followed by more restricted expression in striking contrast to the expression patterns of other Drosophila forkhead (fkh) family genes whose local expression correlate well to their roles as local homeotic genes. This broad expression may correspond to the multiple defects in embryos homozygous for strong alleles, such as defects in the formation of central and peripheral nervous systems, germ band retraction, head involution, and dorsal closure. The DNA binding specificity of Dwhn differed from that of Whn despite the strong sequence conservation in the DNA binding domain. Dwhn is the first invertebrate Whn-like transcriptional regulator, and should provide insights into the basic functions and evolution of the whn family genes.

The Xenopus homologue of Bicaudal-C is a localized maternal mRNA that can induce endoderm formation

In Xenopus, zygotic transcription starts 6 hours after fertilization at the midblastula transition and therefore the first steps in embryonic development are regulated by maternally inherited proteins and mRNAs. While animal-vegetal polarity is already present in the oocyte, the dorsoventral axis is only established upon fertilization by the entry of the sperm and the subsequent rotation of the egg cortex. In a screen for maternal mRNAs whose stability is regulated by this cortical rotation, we isolated the Xenopus homologue of the Drosophila gene Bicaudal-C (xBic-C). It encodes a putative RNA-binding molecule expressed maternally and localized predominantly to the vegetal half of the egg. Upon fertilization and cortical rotation, xBic-C mRNA is displaced together with the heavy yolk towards the future dorsal side of the embryo. In UV-ventralized embryos, xBic-C is polyadenylated less than in untreated embryos that undergo cortical rotation. Overexpression of xBic-C by injection of synthetic mRNA in whole embryos or in ectodermal explants leads to ectopic endoderm formation. This endoderm-inducing activity is dependent on the presence of the RNA-binding domain of the protein. In contrast to the two other known maternally encoded endoderm inducers, Vg1 and VegT, xBic-C ectopic expression leads specifically to endoderm formation in the absence of mesoderm induction.

Expression of zebrafish fkd6 in neural crest-derived glia

The zebrafish fkd6 gene is a marker for premigratory neural crest. In this study, we analyze later expression in putative glia of the peripheral nervous system. Prior to neural crest migration, fkd6 expression is downregulated in crest cells. Subsequently, expression appears initially in loose clusters of cells in positions corresponding to cranial ganglia. Double labelling with a neuronal marker shows that fkd6-expressing cells are not differentiated neurones and generally lie peripheral to neurones in ganglia. Later, expression appears associated with the posterior lateral line and other cranial nerves. For the posterior lateral line nerve, we show that fkd6-labeling extends caudally along this nerve in tight correlation with lateral line primordium migration and axon elongation. Expression in colourless mutant embryos is consistent with these cells being satellite glia and Schwann cells.

FHX, a novel fork head factor with a dual DNA binding specificity

The HNF3/fork head family includes a large number of transcription factors that share a structurally related DNA binding domain. Fork head factors have been shown to play important roles both during development and in the adult. We now describe the cloning of a novel mammalian fork head factor that we have named FHX (fork head homologous X (FHX), which is expressed in many adult tissues. In the embryo, FHX expression showed a very early onset during the cleavage stages of preimplantation development. Polymerase chain reaction-assisted site selection experiments showed that FHX bound DNA with a dual sequence specificity. Sites recognized by FHX could be classified into two different types according to their sequences. Binding of FHX to sequences of each type appeared to occur independently. Our data suggest that either different regions of the fork head domain or different molecular forms of this domain could be involved in binding of FHX to each type of site. In transfection assays, FHX was capable of activating transcription from promoters containing FHX sites of either type.

Forkhead genes in transcriptional silencing, cell morphology and the cell cycle. Overlapping and distinct functions for FKH1 and FKH2 in Saccharomyces cerevisiae

The SIR1 gene is one of four specialized genes in Saccharomyces cerevisiae required for repressing transcription at the silent mating-type cassettes, HMLalpha and HMRa, by a mechanism known as silencing. Silencing requires the assembly of a specialized chromatin structure analogous to heterochromatin. FKH1 was isolated as a gene that, when expressed in multiple copies, could substitute for the function of SIR1 in silencing HMRa. FKH1 (Forkhead Homologue One) was named for its homology to the forkhead family of eukaryotic transcription factors classified on the basis of a conserved DNA binding domain. Deletion of FKH1 caused a defect in silencing HMRa, indicating that FKH1 has a positive role in silencing. Significantly, deletion of both FKH1 and its closest homologue in yeast, FKH2, caused a form of yeast pseudohyphal growth, indicating that the two genes have redundant functions in controlling yeast cell morphology. By several criteria, fkh1Delta fkh2Delta-induced pseudohyphal growth was distinct from the nutritionally induced form of pseudohyphal growth observed in some strains of S. cerevisiae. Although FKH2 is redundant with FKH1 in controlling pseudohyphal growth, the two genes have different functions in silencing HMRa. High-copy expression of CLB2, a G2/M-phase cyclin, prevented fkh1Delta fkh2Delta-induced pseudohyphal growth and modulated some of the fkhDelta-induced silencing phenotypes. Interestingly, deletions in either FKH1 or FKH2 alone caused subtle but opposite effects on cell-cycle progression and CLB2 mRNA expression, consistent with a role for each of these genes in modulating the cell cycle and having opposing effects on silencing. The differences between Fkh1p and Fkh2p in vivo were not attributable to differences in their DNA binding domains.

Analysis of Drosophila salivary gland, epidermis and CNS development suggests an additional function of brinker in anterior-posterior cell fate specification

Salivary glands are simple structured organs which can serve as a model system in the study of organogenesis. Following a large EMS mutagenesis we have identified a number of genes required for normal salivary gland development. Mutations in the locus small salivary glands-1 (ssg-1) lead to a drastic reduction in the size of the salivary glands. The gene ssg-1 was cloned and subsequent sequence and genetic analysis showed identity to the recently published gene brinker. The salivary gland placode in brinker mutants appears reduced along both the anterior-posterior and dorso-ventral axis. Analysis of the brinker cuticle phenotype revealed a similar loss of anterior-posterior as well as lateral cell fates. The abdominal ventral denticle belts show a reduced number of setae in the first denticle row. Furthermore, we observed a preferential loss of lateral neuroblasts in the anterior parasegment. Together, these phenotypes suggest that brinker not only plays a role in dorso-ventral but also in anterior-posterior axis patterning.

Salivary gland development in Drosophila melanogaster

The Drosophila salivary gland is proving to be an excellent experimental system for understanding how cells commit to specific developmental programs and, once committed, how cells implement such decisions. Through genetic studies, the factors that determine where salivary glands will form, the number of cells committed to a salivary gland fate, and the distinction between the two major cell types (secretory cells and duct cells) have been discovered. Within the next few years, we will learn the molecular details of the interactions among the salivary gland regulators and salivary gland target genes. We will also learn how the early-expressed salivary gland genes coordinate their activities to mediate the morphogenetic movements required to form the salivary gland and the changes in cell physiology required for high secretory activity.

Winged helix transcription factor Foxb1 is essential for access of mammillothalamic axons to the thalamus

Our aim was to study the mechanisms of brain histogenesis. As a model, we have used the role of winged helix transcription factor gene Foxb1 in the emergence of a very specific morphological trait of the diencephalon, the mammillary axonal complex. Foxb1 is expressed in a large hypothalamic neuronal group (the mammillary body), which gives origin to a major axonal bundle with branches to thalamus, tectum and tegmentum. We have generated mice carrying a targeted mutation of Foxb1 plus the tau-lacZ reporter. In these mutants, a subpopulation of dorsal thalamic ventricular cells “thalamic palisade” show abnormal persistence of Foxb1 transcriptional activity; the thalamic branch of the mammillary axonal complex is not able to grow past these cells and enter the thalamus. The other two branches of the mammillary axonal complex (to tectum and tegmentum) are unaffected by the mutation. Most of the neurons that originate the mammillothalamic axons suffer apoptosis after navigational failure. Analysis of chimeric brains with wild-type and Foxb1 mutant cells suggests that correct expression of Foxb1 in the thalamic palisade is sufficient to rescue the normal phenotype. Our results indicate that Foxb1 is essential for diencephalic histogenesis and that it exerts its effects by controlling access to the target by one particular axonal branch.

Solution structure and dynamics of the DNA-binding domain of the adipocyte-transcription factor FREAC-11

Transcription factors of the forkhead type share a highly conserved DNA-binding domain of about 100 amino acid residues. FREAC-11, expressed in adipocytes, belongs to this class. Here, we report on NMR studies that established the three-dimensional structure of the FREAC-11, DNA-binding domain. Although apparent similarities to the structures of other members within the forkhead family are observed, the structure also reveals some remarkable differences. Along with the complementary dynamics, the data provide insight into the fundamentals of sequence specificity within a highly conserved motif.

Winged helix proteins

The winged helix proteins constitute a subfamily within the large ensemble of helix-turn-helix proteins. Since the discovery of the winged helix/fork head motif in 1993, a large number of topologically related proteins with diverse biological functions have been characterized by X-ray crystallography and solution NMR spectroscopy. Recently, a winged helix transcription factor (RFX1) was shown to bind DNA using unprecedented interactions between one of its eponymous wings and the major groove. This surprising observation suggests that the winged helix proteins can be subdivided into at least two classes with radically different modes of DNA recognition.

Regulation and function of Scr, exd, and hth in the Drosophila salivary gland

Salivary gland formation in the Drosophila embryo is dependent on the homeotic gene Sex combs reduced (Scr). When Scr function is missing, salivary glands do not form, and when SCR is expressed everywhere in the embryo, salivary glands form in new places. Scr is normally expressed in all the cells that form the salivary gland. However, as the salivary gland invaginates, Scr mRNA and protein disappear. Homeotic genes, such as Scr, specify tissue identity by regulating the expression of downstream target genes. For many homeotic proteins, target gene specificity is achieved by cooperatively binding DNA with cofactors. Therefore, it is likely that SCR also requires a cofactor(s) to specifically bind to DNA and regulate salivary gland target gene expression. Here, we show that two homeodomain-containing proteins encoded by the extradenticle (exd) and homothorax (hth) genes are also required for salivary gland formation. exd and hth function at two levels: (1) exd and hth are required to maintain the expression of Scr in the salivary gland primordia prior to invagination and (2) exd and hth are required in parallel with Scr to regulate the expression of downstream salivary gland genes. We also show that Scr regulates the nuclear localization of EXD in the salivary gland primordia through repression of homothorax (hth) expression, linking the regulation of Scr activity to the disappearance of Scr expression in invaginating salivary glands.

A novel fork head gene mediates early steps during Xenopus lens formation

Xlens1 is a novel Xenopus member of the fork head gene family, named for its nearly restricted expression in the anterior ectodermal placode, presumptive lens ectoderm (PLE), and anterior epithelium of the differentiated lens. The temporal and spatial restriction of its expression suggests that: (1) Xlens1 is transcribed initially at neural plate stages in response to putative signals from the anterior neural plate that transform lens-competent ectoderm to lens-biased ectoderm; (2) further steps in the process of lens-forming bias restrict Xlens1 expression to the presumptive lens ectoderm (PLE) during later neural plate stages; (3) interactions with the optic vesicle maintain Xlens1 expression in the lens placode; and (4) Xlens1 expression is downregulated as committed lens cells undergo terminal differentiation. Induction assays demonstrate that pax6 induces Xlens1 expression, but unlike pax6, Xlens1 cannot induce the expression of the lens differentiation marker beta-crystallin. In the whole embryo, overexpression of Xlens1 in the lens ectoderm causes it to thicken and maintain gene expression characteristics of the PLE. Also, this overexpression suppresses differentiation in the lens ectoderm, suggesting that Xlens1 functions to maintain specified lens ectoderm in an undifferentiated state. Misexpression of Xlens1 in other regions causes hypertrophy of restricted tissues but only occasionally leads ectopic sites of gamma-crystallin protein expression in select anterior head regions. These results indicate that Xlens1 expression alone does not specify lens ectoderm. Lens specification and differentiation likely depends on a combination of other gene products and an appropriate level of Xlens1 activity.

Functions for Drosophila brachyenteron and forkhead in mesoderm specification and cell signalling

The visceral musculature of the larval midgut of Drosophila has a lattice-type structure and consists of an inner stratum of circular fibers and an outer stratum of longitudinal fibers. The longitudinal fibers originate from the posterior tip of the mesoderm anlage, which has been termed the caudal visceral mesoderm (CVM). In this study, we investigate the specification of the CVM and particularly the role of the Drosophila Brachyury-homologue brachyenteron. Supported by fork head, brachyenteron mediates the early specification of the CVM along with zinc-finger homeodomain protein-1. This is the first function described for brachyenteron or fork head in the mesoderm of Drosophila. The mode of cooperation resembles the interaction of the Xenopus homologues Xbra and Pintallavis. Another function of brachyenteron is to establish the surface properties of the CVM cells, which are essential for their orderly migration along the trunk-derived visceral mesoderm. During this movement, the CVM cells, under the control of brachyenteron, induce the formation of one muscle/pericardial precursor cell in each parasegment. We propose that the functions of brachyenteron in mesodermal development of Drosophila are comparable to the roles of the vertebrate Brachyury genes during gastrulation.

A double interaction screen identifies positive and negative ftz gene regulators and ftz-interacting proteins

Regulatory genes directing embryonic development are expressed in complex patterns. The Drosophila homeobox gene fushi tarazu (ftz) is expressed in a striped pattern that is controlled by several discrete and large cis- regulatory elements. One key cis-element is the ftz proximal enhancer which is required for stripe establishment and which mediates autoregulation by direct binding of Ftz protein. To identify the trans-acting factors that regulate ftz expression and autoregulation, we developed a modified yeast two hybrid screen, the Double Interaction Screen (DIS). The DIS was designed to isolate both DNA binding transcriptional regulators that interact with the proximal enhancer and proteins that interact with Ftz itself when it is bound to the enhancer. The screen identified two candidate Ftz protein cofactors as well as activators and repressors of ftz transcription that bind directly to the enhancer. One of these (Tramtrack (Ttk)) was previously shown to bind to at least five sites in the proximal enhancer; genetic studies suggested that Ttk acts as a repressor of ftz in the embryo. Here we show that, in yeast cells, Ttk protein strongly activates transcription, suggesting that yeast may be missing a necessary co-repressor which is present in Drosophila embryos. Further, we have characterized the activity of a second candidate ftz repressor isolated in the screen - the product of the pair-rule gene sloppy paired - a member of the forkhead family. We show that Slp1 is a DNA binding protein. We have identified a high affinity binding site for Slp1 in the ftz proximal enhancer. Slp1 represses transcription via this binding site in yeast cells, consistent with its role as a direct repressor of ftz stripes in interstripe regions during late stages of embryogenesis. The DIS should be a generally useful method to identify DNA binding transcriptional regulators and protein partners of previously characterized DNA binding proteins.

Developmental competence of the gut endoderm: genetic potentiation by GATA and HNF3/fork head proteins

A long-standing problem in developmental biology has been to understand how the embryonic germ layers gain the competence to differentiate into distinct cell types. Genetic studies have shown that members of the GATA and HNF3/fork head transcription factor families are essential for the formation and differentiation of gut endoderm tissues in worms, flies, and mammals. Recent in vivo footprinting studies have shown that GATA and HNF3 binding sites in chromatin are occupied on a silent gene in endoderm that has the potential to be activated solely in that germ layer. These and other data indicate that these evolutionarily conserved factors help impart the competence of a gene to be activated in development, a phenomenon called genetic potentiation. The mechanistic implications of genetic potentiation and its general significance are discussed.

Pleiotropic skeletal and ocular phenotypes of the mouse mutation congenital hydrocephalus (ch/Mf1) arise from a winged helix/forkhead transcriptionfactor gene

Congenital hydrocephalus is an etiologically diverse, poorly understood, but relatively common birth defect. Most human cases are sporadic with familial forms showing considerable phenotypic and etiologic heterogeneity. We have studied the autosomal recessive mouse mutation congenital hydrocephalus ( ch ) to identify candidate human hydrocephalus genes and their modifiers. ch mice have a congenital, lethal hydrocephalus in association with multiple developmental defects, notably skeletal defects, in tissues derived from the cephalic neural crest. We utilized positional cloning methods to map ch in the vicinity of D13Mit294 and confirm that the ch phenotype is caused by homozygosity for a nonsense mutation in a gene encoding a winged helix/forkhead transcription factor ( Mf1 ). Based on linked genetic markers, we performed detailed phenotypic characterization of mutant homozygotes and heterozygotes to demonstrate the pleiotropic effects of the mutant gene. Surprisingly, ch heterozygotes have the glaucoma-related distinct phenotype of multiple anterior segment defects resembling Axenfeld-Rieger anomaly. We also localized a second member of this gene family ( Hfh1 ), a candidate for other developmental defects, approximately 470 kb proximal to Mf1.

HyBra1, a Brachyury homologue, acts during head formation in Hydra

A homologue of the T-box gene, Brachyury, has been isolated from hydra. The gene, termed HyBra1, is expressed in the endoderm and is associated with the formation of the hypostome, the apical part of the head in four different developmental situations. In adults, which are continuously undergoing patterning, HyBra1 is continuously expressed in the hypostome. During budding, hydra's asexual form of reproduction, the gene is expressed in a small area that will eventually form the hypostome of the developing bud before any morphological sign of budding is apparent. The gene is also expressed very early during head regeneration and is confined to the region that will form the hypostome. During embryogenesis, HyBra1 is expressed shortly before hatching in the region that will form the apical end of the animal, the hypostome. The absence of expression at the apical end of decapitated animals of reg-16, a head formation-deficient mutant, provides additional evidence for a role of HyBra1 during head formation. Further, treatments that alter the head activation gradient have no effect on HyBra1 expression indicating the role of the gene is confined to head formation. Transplantation experiments indicate that the expression occurs before head determination has occurred, but expression does not irreversibly commit tissue to forming a head. A comparison of the function of the Brachyury homologues suggests an evolutionary conservation of a molecular mechanism that has been co-opted for a number of developmental processes throughout evolution.

Origin and development of the zebrafish endoderm

The segregation of cells into germ layers is one of the earliest events in the establishment of cell fate in the embryo. In the zebrafish, endoderm and mesoderm are derived from cells that involute into an internal layer, the hypoblast, whereas ectoderm is derived from cells that remain in the outer layer, the epiblast. In this study, we examine the origin of the zebrafish endoderm and its separation from the mesoderm. By labeling individual cells located at the margin of the blastula, we demonstrate that all structures that are endodermal in origin are derived predominantly from the more dorsal and lateral cells of the blastoderm margin. Frequently marginal cells give rise to both endodermal and mesodermal derivatives, demonstrating that these two lineages have not yet separated. Cells located farther than 4 cell diameters from the margin give rise exclusively to mesoderm, and not to endoderm. Following involution, we see a variety of cellular changes indicating the differentiation of the two germ layers. Endodermal cells gradually flatten and extend filopodial processes forming a noncontiguous inner layer of cells against the yolk. At this time, they also begin to express Forkhead-domain 2 protein. Mesodermal cells form a coherent layer of round cells separating the endoderm and ectoderm. In cyclops-mutant embryos that have reduced mesodermal anlage, we demonstrate that by late gastrulation not only mesodermal but also endodermal cells are fewer in number. This suggests that a common pathway initially specifies germ layers together before a progressive sequence of determinative events segregate endoderm and mesoderm into morphologically distinct germ layers.

The kidney-expressed winged helix transcription factor FREAC-4 is regulated by Ets-1. A possible role in kidney development

In this paper we show that the kidney-expressed winged helix transcription factor FREAC-4 is regulated by Ets-1, another kidney-expressed transcription factor. Through transfection experiments three Ets-1 cis-elements are identified within the first 152 nucleotides upstream of the transcription start in the freac-4 promoter. These sites are confirmed in a DNase I in vitro protection assay using recombinant Ets-1 protein. In cotransfection experiments using an Ets-1 expression vector, the induction of freac-4 reporter gene activity is attenuated approximately 6-fold when the three Ets-1 binding sites are mutated. Furthermore, we demonstrate that overexpression of Ets-1 in the human embryonic kidney cell line 293 is sufficient to increase freac-4 mRNA levels. These results are compatible with the hypothesis that Ets-1 acts as an upstream regulator of FREAC-4 expression during kidney development.

GATA transcription factors as potentiators of gut endoderm differentiation

Gene inactivation studies have shown that members of the GATA family of transcription factors are critical for endoderm differentiation in mice, flies and worms, yet how these proteins function in such a conserved developmental context has not been understood. We use in vivo footprinting of mouse embryonic endoderm cells to show that a DNA-binding site for GATA factors is occupied on a liver-specific, transcriptional enhancer of the serum albumin gene. GATA site occupancy occurs in gut endoderm cells at their pluripotent stage: the cells have the potential to initiate tissue development but they have not yet been committed to express albumin or other tissue-specific genes. The GATA-4 isoform accounts for about half of the nuclear GATA-factor-binding activity in the endoderm. GATA site occupancy persists during hepatic development and is necessary for the activity of albumin gene enhancer. Thus, GATA factors in the endoderm are among the first to bind essential regulatory sites in chromatin. Binding occurs prior to activation of gene expression, changes in cell morphology or functional commitment that would indicate differentiation. We suggest that GATA factors at target sites in chromatin may generally help potentiate gene expression and tissue specification in metazoan endoderm development.

The fork head transcription factor Hcm1p participates in the regulation of SPC110, which encodes the calmodulin-binding protein in the yeast spindle pole body

We previously identified HCM1 as a dosage-dependent suppressor of a calmodulin temperature-sensitive mutant (cmd1-1). Calmodulin performs multiple functions in yeast. Here we demonstrate that the effects of HCM1 are specific to the role of calmodulin at the spindle pole body. Overexpression of HCM1 fully suppresses the temperature sensitivity of a calmodulin mutant (cmd1-3) that only has defects in assembly of the spindle pole body but does not suppress the temperature sensitivity of a calmodulin mutant (cmd1-8) that only affects other functions of calmodulin. The DNA binding specificity of Hcm1p was determined by a selection, amplification and binding protocol. The consensus sequence for an Hcmlp binding site is WAAYAAACAAW. Mutations in the DNA binding domain of Hcm1p abolish the ability of Hcmlp to specifically recognize this binding site and abolish the ability of Hcm1p to act as a suppressor of calmodulin mutants. The promoter of SPC110 contains a match to the consensus binding site. Deletion of HCM1 does not affect the basal level of SPC110 transcription, but reduces the induction that occurs late in G1 of the cell cycle.

Mutations of the forkhead/winged-helix gene, FKHL7, in patients with Axenfeld-Rieger anomaly

Genetic linkage, genome mismatch scanning, and analysis of patients with alterations of chromosome 6 have indicated that a major locus for development of the anterior segment of the eye, IRID1, is located at 6p25. Abnormalities of this locus lead to glaucoma. FKHL7 (also called "FREAC3"), a member of the forkhead/winged-helix transcription-factor family, has also been mapped to 6p25. DNA sequencing of FKHL7 in five IRID1 families and 16 sporadic patients with anterior-segment defects revealed three mutations: a 10-bp deletion predicted to cause a frameshift and premature protein truncation prior to the FKHL7 forkhead DNA-binding domain, as well as two missense mutations of conserved amino acids within the FKHL7 forkhead domain. Mf1, the murine homologue of FKHL7, is expressed in the developing brain, skeletal system, and eye, consistent with FKHL7 having a role in ocular development. However, mutational screening and genetic-linkage analyses excluded FKHL7 from underlying the anterior-segment disorders in two IRID1 families with linkage to 6p25. Our findings demonstrate that, although mutations of FKHL7 result in anterior-segment defects and glaucoma in some patients, it is probable that at least one more locus involved in the regulation of eye development is also located at 6p25.

The Drosophila Pax gene eye gone is required for embryonic salivary duct development

What are the developmental mechanisms required for conversion of an undifferentiated, two-dimensional field of cells into a patterned, tubular organ? In this report, we describe the contribution of the Drosophila Pax gene eye gone to the development of the embryonic salivary glands and ducts. eye gone expression in salivary tissues is controlled by several known regulators of salivary fate. After the initial establishment of the salivary primordium by Sex combs reduced, fork head excludes eye gone expression from the pregland cells so that its salivary expression is restricted to the posterior preduct cells. trachealess, in contrast, activates eye gone expression in the posterior preduct cells. We have previously described the process by which fork head and the EGF receptor pathway define the border between the gland and duct primordia. Here we show that eye gone is required for the subdivision of the duct primordium itself into the posterior individual duct and the anterior common duct domains. In the absence of eye gone, individual ducts as well as the precursor of the adult salivary glands, the imaginal ring, are absent. We took advantage of this ductless phenotype to show that Drosophila larvae do not have an obligate requirement for salivary glands and ducts. In addition to its role in the salivary duct, eye gone is required in the embryo for the development of the eye-antennal imaginal disc and the chemosensory antennal organ.

Early liver differentiation: genetic potentiation and multilevel growth control

Hepatocytes undergo distinct phases of differentiation as they arise from the gut endoderm, coalesce to form the liver, and mature by birth. Gene inactivation and in vivo footprinting studies in mouse embryos have identified regulatory transcription factors and cell signaling molecules that control some but not all of these transitions. The latest studies reveal DNA-binding proteins that appear to potentiate gene activation during liver specification and the importance of signals between early hepatocytes and other cell types that promote early liver growth.

Krüppel acts as a developmental switch gene that mediates Notch signalling-dependent tip cell differentiation in the excretory organs of Drosophila

Cell proliferation in the excretory organs of Drosophila, the Malpighian tubules (MT), is under the control of a neural tip cell. This unique cell is singled out from equivalent MT primordial cells in response to Notch signalling. We show that the gene Krüppel (Kr), best known for its segmentation function in the early embryo, is under the control of the Notch-dependent signalling process. Lack-of-function and gain-of-function experiments demonstrate that Kr activity determines the neural fate of tip cells by acting as a direct downstream target of proneural basic helix-loop-helix (bHLH) proteins that are restricted in response to Notch signalling. We have identified a unique cis-acting element that mediates all spatial and temporal aspects of Kr gene expression during MT development. This element contains functional binding sites for the restricted proneural bHLH factors and Fork head protein which is expressed in all MT cells. Our results suggest a mechanism in which these transcription factors cooperate to set up a unique cell fate within an equivalence group of cells by restricting the activity of the developmental switch gene Kr in response to Notch signalling.

The human forkhead protein FREAC-2 contains two functionally redundant activation domains and interacts with TBP and TFIIB

Forkhead-related activator 2 (FREAC-2) is a human transcription factor expressed in lung and placenta that binds to cis-elements in several lung-specific genes. We have identified the parts of FREAC-2 responsible for trans-activation and found two functionally redundant activation domains on the C-terminal side of the DNA binding forkhead domain. Activation domain 1 consists of the most C-terminal 23 amino acids of FREAC-2 and contains a sequence motif conserved in an activation domain of another forkhead protein, FREAC-1. Activation domain 2 is built up by three synergistic subdomains in the central part of the FREAC-2 protein. FREAC-2 was shown to interact in vitro with TBP and TFIIB. The target site for FREAC-2 on TBP was localized to the N-terminal repeat in the core domain of TBP. TFIIB binds FREAC-2 close to the cleft between its two globular domains. The part of FREAC-2 that binds TBP was mapped to 21 amino acids in the C-terminal end of the forkhead domain. This sequence is well conserved among forkhead proteins, raising the possibility that interaction with TBP may be a general characteristic of this family of transcription factors. Overexpression of TFIIB potentiates activation by FREAC-2 in a manner dependent on the FREAC-2 activation domains. Nuclear localization of FREAC-2 was found to depend on sequences from both ends of the forkhead domain.

Molecular genetics in the diagnosis and prognosis of solid pediatric tumors

The field of molecular genetics continues to see an ever increasing number of applications to pediatric tumor analysis. Studies in pediatric tumors have identified novel genes and other genetic changes, a large number of which reflect one of the following mechanisms: (1) activation of proto-oncogenes; (2) loss of tumor suppressor genes; or (3) creation of novel fusion proteins. At least one of these mechanisms is operational in each of the following pediatric tumors: neuroblastoma, Ewing sarcoma and peripheral primitive neuroectodermal tumor (pPNET), intra-abdominal desmoplastic small-cell tumor, rhabdomyosarcoma, synovial sarcoma, and Wilms tumor. Out of this research has come not only an increased understanding of oncogenesis but also, for each of the tumors listed above, diagnostic and/or prognostic markers that can be used by the pathologist and oncologist to improve overall patient management.

Mouse HNF-3/fork head homolog-1-like gene: structure, chromosomal location, and expression in adult and embryonic kidney

Screening of a mouse kidney cDNA library with a HNF-3/fork head domain probe revealed cDNA Hfh-1L containing the highly conserved fork head DNA-binding domain. The Hfh1L cDNA shows 92.7% homology at the nucleic acid level with the fork head gene HFH-1 from rat. Southern blot analyses demonstrated that the Hfh-1L gene is highly conserved in a wide variety of species, including goldfish and frog. Sequencing the corresponding genomic clone, we found that the Hfh-1L gene is most likely intronless. By interspecific back-cross analysis, the Hfh-1L gene was localized to mouse chromosome 13. In order to analyze the expression pattern of Hfh-1L, we performed Northern blot analyses and revealed a 2.7-kb transcript in adult kidney and stomach. In situ hybridization experiments of adult mouse kidney showed Hfh-1L expression in the outer medulla of the kidney and the transitional epithelium. In light of the significance of a number of fork head genes in early embryonic development, the pattern of expression during murine embryogenesis was examined by reverse transcriptase-polymerase chain reaction (RT-PCR), and Hfh-1L transcripts were detected in mouse embryos at every stage tested from day 10.5 to 16.5 postconception (p.c.) and in the developing metanephros of 14.5- and 15.5-day p.c. embryos. This expression pattern suggests that the Hfh-1L gene is involved in the development of the kidney.

Chromatin structure and functional analysis of the mouse HNF3alpha gene

The transcription factor HNF3alpha is a member of the winged-helix family of regulatory proteins. It is expressed in the definitive endoderm, notochord, and neural tube in embryos, but in the adult is expressed primarily in endoderm-derived tissues such as liver, lung, and pancreas. We present here the cloning of the mouse HNF3alpha gene and a characterization of its chromatin structure and regulatory sequences. The HNF3alpha gene is encoded by two exons and its transcription initiates at multiple start sites at a TATA-less promoter that is highly conserved between mouse and rat. We found different patterns of DNaseI hypersensitive sites in HNF3alpha gene chromatin in different adult tissues in which HNF3alpha is expressed, suggesting distinct regulatory mechanisms occurring within different tissue derivatives of the endoderm germ layer. Cell transfection data indicate that sequences spanning certain upstream hypersensitive sites can enhance transcription from the HNF3alpha promoter, but only when stably integrated into chromatin and not when transiently transfected. The results suggest a complex regulatory interplay between distinct genetic regulatory sequences that function specifically in chromatin.

Tumor-specific PAX3-FKHR transcription factor, but not PAX3, activates the platelet-derived growth factor alpha receptor

The t(2;13) chromosomal translocation occurs at a high frequency in alveolar rhabdomyosarcoma, a common pediatric tumor of muscle. This translocation results in the production of a chimeric fusion protein derived from two developmentally regulated transcription factors, PAX3 and FKHR. The two DNA binding modules, the paired domain and the homeodomain, of PAX3 are fused in frame to the transactivation domain of FKHR. Previously, tumor-specific PAX3-FKHR has been shown to bind to DNA sequences normally recognized by wild-type PAX3 and to exhibit relatively enhanced transcriptional activity. The DNA binding sites used to demonstrate that PAX3-FKHR is a more potent transcriptional activator than PAX3 have included recognition sequences for the paired domain of PAX3. In this report, we demonstrate the ability of PAX3-FKHR to activate the product of a growth control gene, platelet-derived growth factor alpha receptor (PDGFalphaR), by recognizing a paired-type homeodomain binding site located in the PDGFalphaR promoter. PAX3 alone cannot mediate transcriptional activation of this promoter under the conditions tested. This provides the first evidence that chromosomal translocation results in altered target gene specificity of PAX3-FKHR and suggests a transcriptional target that may play a significant role in oncogenic activity and rhabdomyosarcoma development.

Targeted disruption of the gene encoding hepatocyte nuclear factor 3gamma results in reduced transcription of hepatocyte-specific genes

The winged helix transcription factor hepatocyte nuclear factor 3gamma (HNF3gamma) is expressed in embryonic endoderm and its derivatives liver, pancreas, stomach, and intestine, as well as in testis and ovary. We have generated mice carrying an Hnf3g-lacZ fusion which deletes most of the HNF3gamma coding sequence as well as 5.5 kb of 3' flanking region. Mice homozygous for the mutation are fertile, develop normally, and show no morphological defects. The mild phenotype change of the Hnf3g-/- mice can be explained in part by an upregulation of HNF3alpha and HNF3beta in the liver of the mutant animals. Analysis of steady-state mRNA levels as well as transcription rates showed that levels of expression of several HNF3 target genes (phosphoenolpyruvate carboxykinase, transferrin, tyrosine aminotransferase) were reduced by 50 to 70%, indicating that HNF3gamma is an important activator of these genes in vivo.

Role of caudal in hindgut specification and gastrulation suggests homology between Drosophila amnioproctodeal invagination and vertebrate blastopore

During early embryogenesis in Drosophila, caudal mRNA is distributed as a gradient with its highest level at the posterior of the embryo. This suggests that the Caudal homeodomain transcription factor might play a role in establishing the posterior domains of the embryo that undergo gastrulation and give rise to the posterior gut. By generating embryos lacking both the maternal and zygotic mRNA contribution, we show that caudal is essential for invagination of the hindgut primordium and for further specification and development of the hindgut. These effects are achieved by the function of caudal in activating different target genes, namely folded gastrulation, which is required for invagination of the posterior gut primordium, and fork head and wingless, which are required to promote development of the internalized hindgut primordium. caudal is not sufficient for hindgut gastrulation and development, however, as it does not play a significant role in activating expression of the genes tailless, huckebein, brachyenteron and bowel. We argue that caudal and other genes expressed at the posterior of the Drosophila embryo (fork head, brachyenteron and wingless) constitute a conserved constellation of genes that plays a required role in gastrulation and gut development.

pha-4 is Ce-fkh-1, a fork head/HNF-3alpha, beta, gamma homolog that functions in organogenesis of the C. elegans pharynx

The C. elegans Ce-fkh-1 gene has been cloned on the basis of its sequence similarity to the winged-helix DNA binding domain of the Drosophila fork head and mammalian HNF-3alpha, beta, gamma genes, and mutations in the zygotically active pha-4 gene have been shown to block formation of the pharynx (and rectum) at an early stage in embryogenesis. In the present paper, we show that Ce-fkh-1 and pha-4 are the same gene. We show that PHA-4 protein is present in nuclei of essentially all pharyngeal cells, of all five cell types. PHA-4 protein first appears close to the point at which a cell lineage will produce only pharyngeal cells, independently of cell type. We show that PHA-4 binds directly to a ‘pan-pharyngeal enhancer element’ previously identified in the promoter of the pharyngeal myosin myo-2 gene; in transgenic embryos, ectopic PHA-4 activates ectopic myo-2 expression. We also show that ectopic PHA-4 can activate ectopic expression of the ceh-22 gene, a pharyngeal-specific NK-2-type homeodomain protein previously shown to bind a muscle-specific enhancer near the PHA-4 binding site in the myo-2 promoter. We propose that it is the combination of pha-4 and regulatory molecules such as ceh-22 that produces the specific gene expression patterns during pharynx development. Overall, pha-4 can be described as an ‘organ identity factor’, completely necessary for organ formation, present in all cells of the organ from the earliest stages, capable of integrating upstream developmental pathways (in this case, the two distinct pathways that produce the anterior and posterior pharynx) and participating directly in the transcriptional regulation of organ specific genes. Finally, we note that the distribution of PHA-4 protein in C. elegans embryos is remarkably similar to the distribution of the fork head protein in Drosophila embryos: high levels in the foregut/pharynx and hindgut/rectum; low levels in the gut proper. Moreover, we show that pha-4 expression in the C. elegans gut is regulated by elt-2, a C. elegans gut-specific GATA-factor and possible homolog of the Drosophila gene serpent, which influences fork head expression in the fly gut. Overall, our results provide evidence for a highly conserved pathway regulating formation of the digestive tract in all (triploblastic) metazoa.

The forkhead/winged helix gene Mf1 is disrupted in the pleiotropic mouse mutation congenital hydrocephalus

Mf1 encodes a forkhead/winged helix transcription factor expressed in many embryonic tissues, including prechondrogenic mesenchyme, periocular mesenchyme, meninges, endothelial cells, and kidney. Homozygous null Mf1lacZ mice die at birth with hydrocephalus, eye defects, and multiple skeletal abnormalities identical to those of the classical mutant, congenital hydrocephalus. We show that congenital hydrocephalus involves a point mutation in Mf1, generating a truncated protein lacking the DNA-binding domain. Mesenchyme cells from Mf1lacZ embryos differentiate poorly into cartilage in micromass culture and do not respond to added BMP2 and TGFbeta1. The differentiation of arachnoid cells in the mutant meninges is also abnormal. The human Mf1 homolog FREAC3 is a candidate gene for ocular dysgenesis and glaucoma mapping to chromosome 6p25-pter, and deletions of this region are associated with multiple developmental disorders, including hydrocephaly and eye defects.

Partial respecification of nasotemporal polarity in double-temporal chick and chimeric chick-quail eyes

In chick embryos, naso-temporal polarity of the retina becomes established before Hamburger-Hamilton stage 10. To examine the plasticity of the early eye anlage, double-temporal eyes were made using stage 10-11 (E1.5) chick embryos and stage 8-9 quail embryos. In vivo and in vitro experiments revealed that these double-temporal compound eyes were not completely temporal but nasal in a large peripheral part of the graft. Four hours after transplantation, the nasal-specific fork head transcription factor CBF1 was not expressed in double-temporal eyes but was clearly detectable 24 h later. This suggests that in the peripheral part of the graft, temporal positional values were changed into nasal positional values by a respecification process.

Chicken winged-helix transcription factor cFKH-1 prefigures axial and appendicular skeletal structures during chicken embryogenesis

The cDNA cFKH-1 encodes a chicken winged helix/forkhead domain transcription factor that presents a dynamic expression pattern during chicken embryogenesis. Transcripts accumulate predominantly in early paraxial mesoderm, developing somites, and within mesenchymal precursors of skeletal structures. cFKH-1 RNA is first detected in the developing mesoderm of HH stage 6 embryos. During subsequent development cFKH-1 RNA accumulates in a dorsal domain of the anterior presomitic mesoderm and later in all cells of the epithelial somites before it becomes limited to the sclerotome when somites compartmentalise. cFKH-1 expression persists in the sclerotome, forming the vertebrae and in mesenchymal condensations in limb buds that will give rise later to the appendicular bones. In differentiated chondrocytes and definitive bone structures, however, cFKH-1 expression is down-regulated. Additional expression domains are found in mesenchyme of branchial arches and the head, in the dorsal aorta, and weakly in the endocardium. Based on its expression pattern and the structure of the forkhead DNA-binding domain cFKH-1 constitutes a chicken relative to the murine family of fkh-1/MF1 and MFH-1 factors. The embryonic expression of the cFKH-1 gene defines distinct mesodermal domains and suggests that it may regulate gene expression in mesenchymal cell lineages that will form cartilage in trunk and limb buds.

The Schizosaccharomyces pombe mei4+ gene encodes a meiosis-specific transcription factor containing a forkhead DNA-binding domain

The mei4+ gene of the fission yeast Schizosaccharomyces pombe was cloned by functional complementation. The mei4 disruptant failed to complete meiosis-I but could proliferate normally. mei4+ was transcribed only in meiosis-proficient diploid cells after premeiotic DNA replication. The mei4+ open reading frame encodes a 57-kDa serine-rich protein comprised of 517 amino acids with a forkhead/HNF3 DNA-binding domain in the amino-terminal region. Transcription of spo6+, a gene required for sporulation, was dependent on the mei4+ function. Two copies of the GTAAAYA consensus sequence, proposed as the binding site for human forkhead proteins, were found in the promoter region of spo6+. A gel mobility shift assay demonstrated the sequence-dependent binding of the GST-Mei4 forkhead domain fusion protein to DNA fragments with one of the consensus elements. Deletion of this consensus element from the spo6 promoter abolished the transcription of spo6+ and resulted in a sporulation deficiency. One-hybrid assay of Mei4 which was fused to the Gal4 DNA-binding domain localized the transcriptional activation domain in the C-terminal 140 amino acids of Mei4. These results indicate that Mei4 functions as a meiosis-specific transcription factor of S. pombe.

DRhoGEF2 encodes a member of the Dbl family of oncogenes and controls cell shape changes during gastrulation in Drosophila

We have identified a gene, DRhoGEF2, which encodes a putative guanine nucleotide exchange factor belonging to the Dbl family of oncogenes. DRhoGEF2 function is essential for the coordination of cell shape changes during gastrulation. In the absence of maternal DRhoGEF2 gene activity, mesodermal and endodermal primordia fail to invaginate. The phenotype seen in DRhoGEF2 mutants is more severe than the defects associated with mutations in two previously identified gastrulation genes, folded gastrulation and concertina, suggesting that DRhoGEF2 acts in a signaling pathway independent of these genes. Expression of dominant-negative DRhoA during gastrulation results in phenocopies of the DRhoGEF2 mutant, suggesting that a signaling cascade involving DRhoGEF2 and the small GTPase DRhoA is responsible for the regulation of cell shape changes during early Drosophila morphogenesis.

Cloning and characterization of three human forkhead genes that comprise an FKHR-like gene subfamily

Alveolar rhabdomyosarcomas are associated with unique chromosomal translocations t(2;13) and t(1;13), which arise from fusion of the genes for the paired box proteins PAX3 and PAX7, respectively, to the FKHR (forkhead in rhabdomyosarcoma) gene on chromosome 13q14. Here we report the identification and characterization of three novel human forkhead genes with similarity to FKHR. The three genes (HGMW-approved symbols FKHRP1, FKHRL1, and FKHRL1P1) map to chromosomal regions 5q35.2-q35.3, 6q21, and 17p11, respectively. Based on amino acid sequence comparisons of their forkhead domains, FKHRL1, FKHRL1P1, and FKHRP1 share 86, 84, and 68% identity, respectively, with FKHR. While FKHR and FKHRL1 are expressed in every human adult tissue examined, FKHRP1 mRNA expression could not be detected, and FKHRL1P1 expression was present only at low levels. FKHR and FKHRL1 share a similar genomic organization, each having a very large intron 1 (FKHR approximately 130 kb and FKHRL1 > 90 kb), which bisects their respective forkhead domains at identical positions, as well as a second intron just downstream of each stop codon. FKHRP1 and FKHRL1P1 lack introns and contain stop codons that prevent them from yielding full-length proteins. Thus, while FKHR and FKHRL1 represent functional genes, FKHRP1 and FKHRL1P1 probably are processed pseudogenes. These results suggest that these four genes represent an FKHR-like gene subfamily within the larger human forkhead gene family.

Binding of the winged-helix transcription factor HNF3 to a linker histone site on the nucleosome

The transcription factor HNF3 and linker histones H1 and H5 possess winged-helix DNA-binding domains, yet HNF3 and other fork head-related proteins activate genes during development whereas linker histones compact DNA in chromatin and repress gene expression. We compared how the two classes of factors interact with chromatin templates and found that HNF3 binds DNA at the side of nucleosome cores, similarly to what has been reported for linker histone. A nucleosome structural binding site for HNF3 is occupied at the albumin transcriptional enhancer in active and potentially active chromatin, but not in inactive chromatin in vivo. While wild-type HNF3 protein does not compact DNA extending from the nucleosome, as does linker histone, site-directed mutants of HNF3 can compact nucleosomal DNA if they contain basic amino acids at positions previously shown to be essential for nucleosomal DNA compaction by linker histones. The results illustrate how transcription factors can possess special nucleosome-binding activities that are not predicted from studies of factor interactions with free DNA.

Nucleosome positioning by the winged helix transcription factor HNF3

Nucleosome positioning at genetic regulatory sequences is not well understood. The transcriptional enhancer of the mouse serum albumin gene is active in liver, where regulatory factors occupy their target sites on three nucleosome-like particles designated N1, N2, and N3. The winged helix transcription factor HNF3 binds to two sites near the center of the N1 particle. We created dinucleosome templates using the albumin enhancer sequence and found that site-specific binding of HNF3 protein resulted in nucleosome positioning in vitro similar to that seen in liver nuclei. Thus, binding of a transcription factor can position an underlying nucleosome core.

Budhead, a fork head/HNF-3 homologue, is expressed during axis formation and head specification in hydra

Accumulating evidence indicates that a common set of genes and mechanisms regulates the developmental processes of a variety of triploblastic organisms despite large variation in their body plans. To what extent these same genes and mechanisms are also conserved among diploblasts, which arose earlier in metazoan evolution, is unclear. We have characterized a hydra homologue of the fork head/HNF-3 class of winged-helix proteins, termed budhead, whose expression patterns suggest a role(s) similar to that found in vertebrates. The vertebrate HNF-3 beta homologues are expressed early in embryogenesis in regions that have organizer properties, and later they have several roles, among them an important role in rostral head formation. In the adult hydra, where axial patterning processes are continuously active, budhead is expressed in the upper part of the head, which has organizer properties. It is also expressed during the formation of a new axis as part of the development of a bud, hydra's asexual form of reproduction. Expression during later stages of budding, during head regeneration and the formation of ectopic heads, indicates a role in head formation. It is likely that budhead plays a critical role in head as well as axis formation in hydra.

The winged-helix transcription factor Trident is expressed in actively dividing lymphocytes

We recently identified the winged-helix transcription factor Trident and described its expression pattern in synchronized fibroblasts. We have now studied Trident expression in cell lines, differentiating thymocytes and in lymphocytes derived from peripheral blood. During T cell differentiation, expression peaked in the actively dividing immature single positive cells. In peripheral blood lymphocytes, expression of Trident mRNA was absent, but could be induced upon stimulation with mitogens in vitro. These observations imply a function for Trident in dividing lymphocytes.

Autonomy of ascidian fork head/HNF-3 gene expression

We have characterized the expression pattern of a class I fork head/HNF-3 gene (HrHNF3-1) of the ascidian Halocynthia roretzi. Zygotic HrHNF3-1 expression was detectable as early as the 16-cell stage, and the transcript was evident in blastomeres of the endoderm, notochord and mesenchyme lineages of the early embryos. After the late gastrula stage, HrHNF3-1 was also expressed in the presumptive spinal cord cells and some brain cells. The spinal cord of the ascidian tadpole consists of four layers of cells; the dorsal layer, two lateral layers and the ventral layer, the latter of which simply lies on the notochord. Cross-sections of in situ hybridized specimens showed that HrHNF3-1 was expressed in cells of the ventral layer, reminiscent of the floor plate of vertebrate embryos. In addition, we found autonomy in the initiation of early HrHNF3-1 expression, because the gene was expressed in blastomeres continuously dissociated from the first cleavage until the 16-cell stage.

Fkh5-deficient mice show dysgenesis in the caudal midbrain and hypothalamic mammillary body

The murine winged helix gene Fkh5 is specifically expressed in the developing central nervous system (CNS). Early embryonic Fkh5 expression is restricted to the mammiliary body region of the caudal hypothalamus, midbrain, hindbrain and spinal cord. Postnatally, signals persist in specific nuclei of the mammillary body and in the midbrain. We generated Fkh5 deficient mice by homologous recombination to assess its in vivo function. At birth, Fkh5-deficient mice are viable and indistinguishable from wild-type and Fkh5 heterozygous littermates. However, about one third die within the first two days and another fifth before weaning. Surviving Fkh5-deficient mice become growth retarded within the first week and remain smaller throughout their whole life span. Fkh5-deficient females on 129Sv × C57BL/6 genetic background are fertile, but do not nurture their pups. More detailed analysis of Fkh5-deficient brains reveals distinct alterations in the CNS. In the midbrain, mutant mice exhibit reduced inferior colliculi and an overgrown anterior cerebellum. Furthermore, the hypothalamic mammillary body of Fkh5-deficient brains lacks the medial mammillary nucleus. These results suggest that Fkh5 plays a major role during CNS development.

Cloning and characterization of freac-9 (FKHL17), a novel kidney-expressed human forkhead gene that maps to chromosome 1p32-p34

We describe the cloning of a near full-length cDNA of 4258 nucleotides encoding freac-9 (HGMW-approved symbol FKHL17), a novel human forkhead gene. The 5' untranslated region is unusual since it is very long, 2127 nucleotides, and contains 15 upstream AUG codons. Hybridization to a panel consisting of RNA derived from 50 different tissues showed that freac-9 is transcribed exclusively in the kidney. The kidney-derived cell lines COS-7 and 293 are shown to express freac-9. A combination of fluorescence in situ hybridization and somatic cell hybrids localizes freac-9 to the chromosomal region of 1p32-p34. The conceptual translation product predicts a protein of 372 amino acids with an N-terminal domain rich in acidic amino acids and with a high likelihood of forming an amphipatic helix, a DNA binding forkhead domain, and a C-terminal region that has a high probability of forming an amphipatic beta-sheet. The amino acid sequence of the DNA binding forkhead motif of FREAC-9 is identical to that of another forkhead protein, FREAC-4, whereas 12 substitutions are present at the nucleotide level. There are no similarities in regions outside of the DNA binding domains of FREAC-9 and FREAC-4 and since freac-4 maps to a different chromosome (5q12-q13) it is likely that an evolutionary selection has acted to maintain identical DNA binding domains between these two kidney expressed transcription factors.

Essential roles of the winged helix transcription factor MFH-1 in aortic arch patterning and skeletogenesis

Mesenchyme Fork Head-1 (MFH-1) is a forkhead (also called winged helix) transcription factor defined by a common 100-amino acid DNA-binding domain. MFH-1 is expressed in non-notochordal mesoderm in the prospective trunk region and in cephalic neural-crest and cephalic mesoderm-derived mesenchymal cells in the prechordal region of early embryos. Subsequently, strong expression is localized in developing cartilaginous tissues, kidney and dorsal aortas. To investigate the developmental roles of MFH-1 during embryogenesis, mice lacking the MFH-1 locus were generated by targeted mutagenesis. MFH-1-deficient mice died embryonically and perinatally, and exhibited interrupted aortic arch and skeletal defects in the neurocranium and the vertebral column. Interruption of the aortic arch seen in the mutant mice was the same as in human congenital anomalies. These results suggest that MFH-1 has indispensable roles during the extensive remodeling of the aortic arch in neural-crest-derived cells and in skeletogenesis in cells derived from the neural crest and the mesoderm.