Murine Cdx-4 bears striking similarities to the Drosophila caudal gene in its homeodomain sequence and early expression pattern

A third member of the murine caudal-like gene family, Cdx-4, has been isolated. In situ hybridization and immunohistochemistry have been used to study the localization of mRNA and protein during murine embryogenesis. Cdx-4 is expressed transiently from 7.0 d.p.c. (days post coitum) until 10 d.p.c., starting at the beginning of gastrulation (7.0-7.5 d.p.c.) in the allantois and posterior tip of the primitive streak. At the mid-streak stage, Cdx-4 expression moves rostrally, and protein and mRNA are detected in all cells over the posterior half of the primitive streak. As development proceeds, Cdx-4 gene products continue to be restricted to the posterior of the embryo, including the remnants of the primitive streak. Cdx-4 is expressed in neurectoderm, presomitic and lateral plate mesoderm, and hindgut endoderm, but the anterior boundary in the paraxial mesoderm is staggered with respect to the other germ layers. At all stages analyzed, Cdx-4 exhibits a graded expression pattern with a posterior maximum, a distribution highly reminiscent of the Drosophila caudal gene. These data add to the recently described distributions of other vertebrate caudal-like genes, and further support the idea that members of this homeobox gene subfamily have regulatory roles in the specification of anteroposterior axial polarity in early embryos.

Biosynthesis and in vivo localization of the decapentaplegic-Vg-related protein, DVR-6 (bone morphogenetic protein-6)

DVR-6 (BMP-6 or Vgr-1) is a member of the TGF-beta superfamily of polypeptide signaling molecules. In situ hybridization studies have previously shown that DVR-6 RNA is expressed in a variety of cell types in the mouse embryo, but no information has been available on protein localization and biosynthesis. We have produced a polyclonal antibody to the proregion of DVR-6 and used it to localize the protein in whole mount and sectioned embryonic, newborn, and adult mouse tissues. DVR-6 protein is expressed in the mouse nervous system beginning at 9.5 days postcoitum (d.p.c.) and continues through adulthood. A variety of epithelial tissues also produce DVR-6 protein, including the suprabasal layer of the skin, bronchiolar epithelium, and the cornea. Additionally, a stably transfected cell line, BMGE+H/D6c4, is used to study the biosynthesis of DVR-6 protein and evidence is presented for translational regulation of DVR-6 expression.

A Hox 3.3-lacZ transgene expressed in developing limbs

We describe transgenic mouse lines that express lacZ under the control of the Hox 3.3 Promoter II. The correct anterior boundary can be fixed by 3.6 kb of promoter DNA (plus 1.6 kb of 5' transcribed sequences), both in tissues of ectodermal and mesodermal origin. The posterior border, however, is not respected, and lacZ expression continues into the tail region. One line has particularly strong graded expression in the anterior proximal limb bud. Other lines, containing a shorter promoter fragment (0.6 kb), have ectopic expression in the head region, including one line that has expression in the anterior half of the retina. Such mouse lines make it possible to molecularly distinguish cells in regions of the embryo that look otherwise identical and may be useful in studying the establishment of molecular differences in the mouse embryo.

Mox-1 and Mox-2 define a novel homeobox gene subfamily and are differentially expressed during early mesodermal patterning in mouse embryos

We have isolated two mouse genes, Mox-1 and Mox-2 that, by sequence, genomic structure and expression pattern, define a novel homeobox gene family probably involved in mesodermal regionalization and somitic differentiation. Mox-1 is genetically linked to the keratin and Hox-2 genes of chromosome 11, while Mox-2 maps to chromosome 12. At primitive streak stages (approximately 7.0 days post coitum), Mox-1 is expressed in mesoderm lying posterior of the future primordial head and heart. It is not expressed in neural tissue, ectoderm, or endoderm. Mox-1 expression may therefore define an extensive ‘posterior’ domain of embryonic mesoderm before, or at the earliest stages of, patterning of the mesoderm and neuroectoderm by the Hox cluster genes. Between 7.5 and 9.5 days post coitum, Mox-1 is expressed in presomitic mesoderm, epithelial and differentiating somites (dermatome, myotome and sclerotome) and in lateral plate mesoderm. In the body of midgestation embryos, Mox-1 signal is restricted to loose undifferentiated mesenchyme. Mox-1 signal is also prominent over the mesenchyme of the heart cushions and truncus arteriosus, which arises from epithelial-mesenchymal transformation and over a limited number of craniofacial foci of neural crest-derived mesenchyme that are associated with muscle attachment sites. The expression profile of Mox-2 is similar to, but different from, that of Mox-1. For example, Mox-2 is apparently not expressed before somites form, is then expressed over the entire epithelial somite, but during somitic differentiation, Mox-2 signal rapidly becomes restricted to sclerotomal derivatives. The expression patterns of these genes suggest regulatory roles for Mox-1 and Mox-2 in the initial anterior-posterior regionalization of vertebrate embryonic mesoderm and, in addition, in somite specification and differentiation.

DVR-4 (bone morphogenetic protein-4) as a posterior-ventralizing factor in Xenopus mesoderm induction

Establishment of mesodermal tissues in the amphibian body involves a series of inductive interactions probably elicited by a variety of peptide growth factors. Results reported here suggest that mesodermal patterning involves an array of signalling molecules including DVR-4, a TGF-beta-like molecule. We show that ectopic expression of DVR-4 causes embryos to develop with an overall posterior and/or ventral character, and that DVR-4 induces ventral types of mesoderm in animal cap explants. Moreover, DVR-4 overrides the dorsalizing effects of activin. DVR-4 is therefore the first molecule reported both to induce posteroventral mesoderm and to counteract dorsalizing signals such as activin. Possible interactions between these molecules resulting in establishment of the embryonic body plan are discussed.

Expression and modification of Hox 2.1 protein in mouse embryos

A polyclonal antibody, alpha Hox 2.1a, has been generated and used to immunolocalize Hox 2.1 protein in mouse embryos. Protein is present in nuclei of all tissues previously shown to express Hox 2.1 RNA. In addition, protein is seen in somites and proximal regions of the limb buds, tissues in which Hox 2.1 RNA expression was not clearly detected previously by in situ hybridization. At the 7 somite stage, protein is detectable in the neural tube up to the level of somite 1, but later retracts to a more posterior position. Immunoblot, in vitro translation, and immunoprecipitation experiments were carried out to characterize the Hox 2.1 protein. The results show that the Hox 2.1 gene produces at least two related phosphorylated proteins present in different proportions in different tissues.

Vertebrate homeobox genes

Recent highlights in vertebrate homeobox gene research include the discovery of new genes with novel expression patterns, observations that peptide growth factors and retinoic acid influence homeobox gene expression, and the generation of mutant phenotypes of embryos homozygous for null mutations. These combined studies reinforce the idea that homeobox genes function near the top of the gene hierarchies controlling vertebrate embryogenesis.

Organizer-specific homeobox genes in Xenopus laevis embryos

The dorsal blastopore lip of the early Xenopus laevis gastrula can organize a complete secondary body axis when transplanted to another embryo. A search for potential gene regulatory components specifically expressed in the organizer was undertaken that resulted in the identification of four types of complementary DNAs from homeobox-containing genes that fulfill this criterion. The most abundant of these encodes a DNA-binding specificity similar to that of the Drosophila melanogaster anterior morphogen bicoid. The other three are also homologous to developmentally significant Drosophila genes. These four genes may participate in the regulation of the developmental potential of the organizer.

Overexpression of a homeodomain protein confers axis-forming activity to uncommitted Xenopus embryonic cells

The anteroposterior character of mesoderm induced by a peptide growth factor (XTC-MIF) was tested by transplantation into host Xenopus gastrulae. Both retinoic acid and a homeodomain protein were able to override the anteriorizing effect of the growth factor. Microinjection of a posteriorly expressed homeobox mRNA can respecify anteroposterior identity, transforming head mesoderm into tail-inducing mesoderm. Unexpectedly, overexpression of XIHbox 6 protein in the transplanted cells, without addition of growth factors, caused the formation of tail-like structures. The cells overexpressing XIHbox 6 were able to recruit cells from the host into the secondary axis. The results suggest that vertebrate homeodomain proteins are part of the biochemical pathway leading to the generation of the body axis.

Selective photochemical treatment of oestrogen receptor in a Xenopus liver extract destroys hormone binding and transcriptional activation but not DNA binding

Photochemical excitation of a simple derivative of oestradiol using light in the UV-A range totally, permanently and selectively inactivates the oestrogen receptor protein present in a Xenopus liver extract without affecting its overall size. Inactivation of the binding site proceeds to completion with simple, first-order kinetics. Inactivation is prevented by excess oestradiol but not by non-oestrogenic steroids. Using an in vitro transcription system, we show that the treatment eliminates transcription of vitellogenin genes, which are normally oestrogen-responsive, but has no effect on the transcription of albumin genes, which are not. Native receptor binds to the two imperfectly palindromic sequences in the vitellogenin B2 gene which together constitute an oestrogen-response unit. Its affinity for one sequence is greater than its affinity for the other, suggesting that a compulsory binding order operates when receptor interacts with the B2 gene. Photoinactivated receptor still binds to both sequences, but with reduced affinity. We also discuss our findings in the context of the current concern over the effects of UV-A on human tissues.

Expression of a homeobox gene product in normal and mutant zebrafish embryos: evolution of the tetrapod body plan

An antibody was used to detect antigens in zebrafish that appear to be homologous to the frog homeodomain-containing protein XlHbox 1. These antigens show a restricted expression in the anteroposterior axis and an anteroposterior gradient in the pectoral fin bud, consistent with the distribution of XlHbox 1 protein in frog and mouse embryos. In the somitic mesoderm, a sharp anterior limit of expression coincides exactly with the boundary between somites 4 and 5, and the protein level fades out posteriorly. A similar, graded expression of the antigen is seen within the series of Rohon-Beard sensory neurons of the CNS. We also immunostained the mutant spt-1 ('spadetail'), in which the trunk mesoderm is greatly depleted and disorganized in the region of XlHbox 1 expression. The defects stem from misdirected cell movements during gastrulation, but nervertheless, newly recruited cells that partially refill the trunk mesoderm express the antigen within the normal span of the anteroposterior axis. This finding suggests that the mutation does not delete positional information required for activation of the XlHbox 1 gene.

Interference with function of a homeobox gene in Xenopus embryos produces malformations of the anterior spinal cord

XIHbox 1 is expressed in a narrow band across the cervical region of Xenopus embryos. The gene produces two related proteins: "long" and "short" XIHbox 1 homeodomain proteins. Injection of antibodies to the long XIHbox 1 protein into 1-cell embryos caused a phenotype in which the anterior spinal cord was morphologically transformed into a hindbrain-like structure. This alteration was restricted to the region normally expressing long XIHbox 1 protein. Injection of long protein mRNA disrupted segmentation and tissue organization without inhibiting cell proliferation. Injection of short protein mRNA into 1-cell embryos produced spinal cord malformations similar, but not identical, to those caused by the antibodies, suggesting antagonistic roles for long and short XIHbox 1 proteins. We immunostained tadpoles carrying extended hindbrains for N-CAM and consistently found defective organization of spinal nerves over the affected region.

XlHbox 8: a novel Xenopus homeo protein restricted to a narrow band of endoderm

We report the isolation of a new homeobox gene from Xenopus laevis genomic DNA. The homeodomain sequence is highly diverged from the prototype Antennapedia sequence, and contains a unique histidine residue in the helix that binds to DNA. The homeodomain is followed by a 65 amino acid carboxyterminal domain, the longest found to date in any vertebrate homeobox gene. We have raised specific antibodies against an XlHbox 8-beta-gal fusion protein to determine the spatial and temporal expression of this gene. The nuclear protein first appears in a narrow band of the endoderm at stage 33 and develops into expression within the epithelial cells of the pancreatic anlagen and duodenum. Expression within the pancreatic epithelium persists into the adult frog. This unprecedented restriction to an anteroposterior band of the endoderm suggests that vertebrate homeobox genes might be involved in specifying positional information not only in the neuroectoderm and mesoderm, but also in the endoderm. Our data suggest that XlHbox 8 may therefore represent the first member of a new class of position-dependent transcription factors affecting endodermal differentiation.

Vertebrate homeodomain proteins: families of region-specific transcription factors

Vertebrate homeodomain proteins are transcription factors whose genes can be isolated via a conserved DNA-binding domain called the homeobox. We review recent studies suggesting that one function of these genes is the early subdivision of the embryo along the antero-posterior axis into 'fields' of cells with different developmental potential.

Duplicated homeobox genes in Xenopus

Multiple kinds of clones and restriction fragment polymorphisms are frequently encountered when analyzing genes of the tetraploid frog Xenopus laevis. Two types of cDNA clone have been isolated for homeobox gene 2. Analysis of their corresponding genomic clones confirmed the existence of clearly distinct restriction maps; in addition the nearby presence of two additional homeoboxes suggests that this region is homologous to the Hox 2 gene complex of mammals. We asked whether the genetic polymorphism in Xenopus results from increased allelic differences due to tetraploidy or from having duplicated Hox 2 complexes. Using X. laevis/Xenopus borealis interspecies hybrids we show that the two types of X. laevis homeobox gene 2 transcripts result from two different genetic loci. They cannot represent alleles of the same gene because they do not segregate independently in the F1 hybrid progeny. Most other X. laevis homeobox genes studied so far are also found in two versions. Thus X. laevis seems to have two homeobox genes, both of which are expressed, for each one present in mammals or other vertebrates.

A gradient of homeodomain protein in developing forelimbs of Xenopus and mouse embryos

The expression of the homeodomain protein XIHbox 1 in developing Xenopus limbs was analyzed using specific antibodies. In the forelimb bud mesoderm XIHbox 1 shows a clear antero-posterior gradient that is strongest in the anterior and proximal region of the forelimb. Hindlimb bud mesoderm is devoid of XIHbox 1, indicating an early molecular difference between arm and leg. The innermost ectodermal cell layer is positive throughout the forelimb and hindlimb bud ectoderm, but no other areas of the skin. Similar results are obtained in developing mouse limbs, suggesting that XIHbox 1 participates in forelimb development in a variety of tetrapods. In early tadpoles analyzed at stages preceding limb bud formation, the lateral plate mesoderm is positive in the region corresponding to the earliest "field" of forelimb information, but not in the hindlimb field. These results suggest a molecular link between morphogenetic fields, gradients, and homeobox genes in vertebrate development.

Differential antero-posterior expression of two proteins encoded by a homeobox gene in Xenopus and mouse embryos

The X.laevis XlHbox 1 gene uses two functional promoters to produce a short and a long protein, both containing the same homeodomain. In this report we use specific antibodies to localize both proteins in frog embryos. The antibodies also recognize the homologous proteins in mouse embryos. In both mammalian and amphibian embryos, expression of the long protein starts more posteriorly than that of the short protein. This difference in spatial expression applies to the nervous system, the segmented mesoderm and the internal organs. This suggests that each promoter from this gene has precisely restricted regions of expression along the anterior-posterior axis of the embryo. Because the long and short proteins share a common DNA-binding specificity but differ by an 82 amino acid domain, their differential distribution may have distinct developmental consequences.

Differential utilization of the same reading frame in a Xenopus homeobox gene encodes two related proteins sharing the same DNA-binding specificity

Xenopus XlHbox 1 produces two transcripts during early development. One encodes a long open reading frame (ORF) and the other a short ORF sharing the same homeodomain, but differing by an 82 amino acid domain at the amino terminus. The long protein amino terminus is conserved with many other homeodomain proteins, and its absence from the short protein could have functional consequences. Some viral genes also utilize a single ORF to encode transcription factors of antagonistic functions. The overall organization of the homologous genes in frog and man is similar, supporting the notion that both transcripts are of functional significance. Studies on XlHbox 1 function show that the region common to the long and short proteins has a sequence-specific DNA-binding activity, and that microinjection of specific antibodies into embryos results in the loss of structures derived from cells normally expressing XlHbox 1.

A Xenopus laevis gene encodes both homeobox-containing and homeobox-less transcripts

A cDNA clone (p52) that contains all the protein-coding region from the maternally expressed XlHbox 2 locus of the frog Xenopus laevis has been isolated and sequenced. A probe containing the exon preceding the homeobox detected transcripts which arise from a splicing event in which the homeobox-containing exon is replaced by another exon lying 5' to it in the genome. Both the homeobox-containing and homeobox-less splicing event occur in the same tissues, with the homeobox-less RNA representing the minority of mRNA from this gene. There may therefore be a function for two types of transcript, and hence protein, from this locus. This phenomenon may not be exclusive to the XlHbox 2 gene of Xenopus, but might occur more generally in other homeobox-containing genes. The protein deduced from the homeobox-containing cDNA is significantly similar to the yeast mating type factor a1 (MAT-a1) gene product. In addition to the previously described homology of the homeodomains, the amino-terminal domains of XlHbox 2 and MAT-a1 are similar to each other; thus essentially all of the MAT-a1 protein corresponds to some part of the XlHbox 2 protein. In the case of XlHbox 2, the protein coded for by the homeoboxless mRNA would contain all of the non-homeobox homology to yeast MAT-a1.

Reconstructive surgery of hydrosalpinx with and without the carbon dioxide laser

Pregnancy rates and surgery-conception intervals were determined in 91 women operated on for bilateral terminal tubal occlusion with different techniques. The intrauterine pregnancy rate following salpingostomy utilizing the CO2 laser was 21.7% (n = 23) and following salpingostomy with the microdiathermy needle was 22.7% (n = 22) at 1 year's follow-up. The pregnancy rate following conventional surgery was 17.4% (n = 46) at 5 years' follow-up. The surgery-conception interval was shorter in the laser group than in the other two groups. This preliminary report suggests that there is no difference between the pregnancy rate following salpingostomy with CO2 laser or microdiathermy needle; however, the surgery-conception interval is shorter. This might reflect the rapid healing of the tube after laser surgery.

Injection of partially purified estrogen receptor protein from Xenopus liver nuclei into oocytes activates the silent vitellogenin locus

Injection of extracts from Xenopus liver nuclei that are enriched 2000 times in estradiol receptor into Xenopus oocytes induces transcription of the silent vitellogenin locus, which is activated in liver by estradiol, but not of the albumin locus, which is active in liver but suppressed by high levels of estradiol. Transcription initiates within the 5'-end region of the gene we have studied and probably continues into the 3' third. The activation seems to be very efficient, but most of the primary transcripts are probably rapidly and inaccurately processed. New proteins are also made and secreted by the oocytes.

Partial purification of estradiol receptor from Xenopus laevis liver and levels of receptor in relation to estradiol concentration

We have used ammonium sulphate precipitation followed by affinity chromatography to partially purify the estrogen receptor from Xenopus laevis liver which may control the genes for vitellogenin, the precursor of the egg yolk proteins. The rate at which receptor binds estradiol explains the kinetics of the induction of vitellogenin synthesis by estradiol, and the dissociation constant (0.5 X 10(-9) M) explains the concentration dependence of the response, which has a threshold of 10(-9) M estradiol, when 67% of the receptor is bound to estradiol. The estradiol concentration in male liver, which does not make vitellogenin, is 0.18 X 10(-9) M, sufficient to saturate 26% of the receptor, while in female liver, which makes vitellogenin continuously, the estradiol concentration is 3.5 X 10(-9) M, giving 88% saturation of receptor, suggesting that the proportion of occupied receptor decides whether or not the vitellogenin genes are active. In the physiological concentration range, estradiol modulates the level of receptor, which varies between 100 binding sites per nucleus in males and 440 in females, but artificially high concentrations of estradiol raise the level to approximately 1000 sites per nucleus. This suggests that the small increase in vitellogenin mRNA induced by physiological concentrations of estradiol is due to pre-existing receptor and that the much larger increases induced by very high concentrations depends on newly-synthesized receptor.