ABSTRACT
The mouse Bapx1 gene is homologous to the Drosophila homeobox containing bagpipe (bap) gene. A shared characteristic of the genes in these two organisms is expression in gut mesoderm. In Drosophila, bap functions to specify the formation of the musculature of the midgut. To determine the function of the mammalian cognate, we targeted a mutation into the Bapx1 locus. Bapx1, similar to Drosophila, does have a conspicuous role in gut mesoderm; however, this appears to be restricted to development of the spleen. In addition, Bapx1 has a major role in the development of the axial skeleton. Loss of Bapx1 affects the distribution of sclerotomal cells, markedly reducing the number that appear ventromedially around the notochord. Subsequently, the structures in the midaxial region, the intervertebral discs, and centra of the vertebral bodies, fail to form. Abnormalities are also found in those bones of the basal skull (basioccipital and basisphenoid bones) associated with the notochord. We postulate that Bapx1 confers the capacity of cells to interact with the notochord, effecting inductive interactions essential for development of the vertebral column and chondrocranium.
Subject(s)
Body Patterning/genetics , Drosophila Proteins , Homeodomain Proteins/physiology , Osteogenesis/genetics , Spleen/embryology , Animals , DNA-Binding Proteins/genetics , DNA-Binding Proteins/physiology , Homeodomain Proteins/genetics , In Situ Hybridization , Mice , Mice, Knockout , Notochord/abnormalities , Notochord/embryology , PAX2 Transcription Factor , Skull Base/embryology , Transcription Factors/genetics , Transcription Factors/physiologyABSTRACT
We have isolated mammalian homologues of the Drosophila dachshund gene. Two domains of high conservation, one of which contains an alpha-helical, coiled-coil motif, show similarity to the Ski family of genes. We therefore propose that Dachshund belongs to a superfamily including these genes. Mouse Dachshund (Dach) is expressed in the eye and limb, structures affected by the Drosophila loss-of-function mutant, and rib primordia, CNS and genital eminence. Pax6 and Dach show overlapping but non-identical expression patterns. Dach expression is unaffected in smalleye mouse brain, indicating that Pax6 is not directly activating Dach. In Drosophila eye development dachshund is a component of an interacting network of proteins. Genes homologous to many of these exist in mammals; Dach joins this expanding group.
Subject(s)
DNA-Binding Proteins/genetics , Drosophila Proteins/genetics , Drosophila melanogaster/genetics , Extremities/embryology , Eye/embryology , Fetal Proteins/genetics , Gene Expression Regulation, Developmental , Multigene Family , Nuclear Proteins/genetics , Proto-Oncogene Proteins/genetics , Proto-Oncogenes , Amino Acid Sequence , Animals , Caenorhabditis elegans Proteins/genetics , DNA, Complementary/genetics , Drosophila Proteins/biosynthesis , Drosophila melanogaster/embryology , Expressed Sequence Tags , Eye/metabolism , Eye Proteins/biosynthesis , Eye Proteins/genetics , Fetal Proteins/biosynthesis , Genitalia/embryology , Genitalia/metabolism , Homeodomain Proteins/biosynthesis , Homeodomain Proteins/genetics , Humans , In Situ Hybridization , Leg/embryology , Mice , Mice, Mutant Strains , Molecular Sequence Data , Morphogenesis , Nerve Tissue Proteins/biosynthesis , Nerve Tissue Proteins/genetics , Nervous System/embryology , Nervous System/metabolism , Nuclear Proteins/biosynthesis , Organ Specificity , PAX6 Transcription Factor , Paired Box Transcription Factors , Protein Structure, Tertiary , Proto-Oncogene Mas , Repressor Proteins , Ribs/embryology , Ribs/metabolism , Sequence Alignment , Sequence Homology, Amino Acid , Species SpecificityABSTRACT
According to the 'three signal model', the regional specification of tissue type within the mesoderm of Xenopus laevis occurs in a process called 'dorsalization'. We have studied the timing and transmission characteristics of this signal, and assessed the dorsalizing activity of the lithium ion and a panel of cytokines.The marginal zone has been fate mapped during gastrulation by colloidal gold labelling and it is shown that the ventral tissue undergoes substantial circumferential expansion. The fate map information is used to provide tissues of constant cellular composition for experiments conducted at different stages.The stage at which dorsalization can occur has been investigated by means of heterochronic dorsal-ventral combinations. The results indicate that the interaction occurs during gastrulation, with a decline in both signal strength and competence of the ventral marginal zone to respond as gastrulation proceeds.The signal is capable of passing through arrangements of membranes that exclude the possibility of cytoplasmic contact, implying that it can be carried by a diffusible morphogen.The effect on the ventral marginal zone of lithium and a number of cytokines has also been studied. While none appears to function as a dorsalizing signal, lithium acts during blastula stages to alter the response to the mesoderm-inducing signal such that the inductions are of a more dorsal character.These data confirm that the dorsalizing signal is independent of and operates later than the signal(s) from the vegetal hemisphere that induce mesoderm during the blastula stages.
Subject(s)
Body Patterning , Gastrula/embryology , Signal Transduction , Xenopus laevis/embryology , Animals , Body Patterning/drug effects , Cytokines/pharmacology , Gastrulation/drug effects , Lithium Compounds/pharmacology , Signal Transduction/drug effectsABSTRACT
Although the mesoderm itself is induced at the blastula stage, its subdivision mainly occurs in response to further inductive signals during gastrulation. In the late blastula, most of the mesoderm has a ventral-type commitment except for the small organizer region which extends about 30 degrees on each side of the dorsal midline. During gastrulation, dorsal convergence movements bring the cells of the lateroventral marginal zone up near the dorsal midline and into the range of the dorsalizing signal emitted by the organizer. This dorsalizing signal operates throughout gastrulation, can cross a Nuclepore membrane, and is not mimicked by lithium, FGFs or activin. Anteroposterior specification also takes place during gastrulation and is probably controlled by a dominant region at the posterior end of the forming axis. We have studied the expression patterns in Xenopus of three members of the FGF family: bFGF, int-2 and a newly discovered species, eFGF. These all have mesoderm inducing activity on isolated animal caps, but are likely also to be involved with the later interactions. RNAase protections and in situ hybridizations show that the int-2 and eFGF mRNAs are concentrated at the posterior end, while bFGF is expressed as a posterior to anterior gradient from tailbud to head. Studies of embryos in which bFGF is overexpressed from synthetic mRNA show that biological activity is far greater when a functional signal sequence is provided. This suggests that int-2 and eFGF, which possess signal sequences, are better candidates for inducing factors in vivo than is bFGF.
Subject(s)
Gastrula/physiology , Mesoderm/cytology , Morphogenesis/physiology , Xenopus/embryology , Activins , Animals , Fibroblast Growth Factors/physiology , Inhibins/physiology , Microscopy, FluorescenceABSTRACT
An influenza B virus nucleoprotein (BNP) peptide, residues 82-94, defined by limited sequence homology with an HLA-A2-restricted peptide from influenza A matrix protein, was recognized by HLA-A2-restricted CTL. Reciprocal inhibition of T cell recognition by the two peptides suggest that the BNP peptide may have lower avidity for HLA-A2 molecules than the matrix peptide. The interaction between this peptide and HLA-A2 was explored by studying the CTL recognition of BNP 82-94 presented by mutant HLA-A2 molecules. Mutations at residues 9, 99, 70, 74, 152 and 156 were found to abolish T cell recognition of the BNP peptide. These results were compared with results previously obtained with the influenza A matrix peptide and suggest that the two peptides bind differently in the peptide binding site.
