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R Krumlauf

Publications and source records attributed to R Krumlauf.

125 records · Page 7Linked to original sources
PubMed1987

Diversity of alpha-fetoprotein gene expression in mice is generated by a combination of separate enhancer elements.

The 5' flanking region of the mouse alpha-fetoprotein (AFP) gene contains a tissue-specific promoter and three upstream regulatory elements that behave as classical enhancers. At least one of these enhancers is now shown to be required for the tissue-specific expression of the AFP gene when it is introduced into the mouse genome by microinjection of cloned DNA fragments into fertilized eggs. Each enhancer can direct expression in the appropriate tissues, the visceral endoderm of the yolk sac, the fetal liver, and the gastrointestinal tract, but each exerts different influence in these three tissues. These differences may explain the tissue-specific diversity in the levels of expression characteristic of the AFP gene. The postnatal repression of transcription of the AFP gene in both liver and gut, as well as the reinitiation of its transcription during liver regeneration, is mimicked by the introduced gene when it is linked to the enhancer domains together or singly. Thus, the DNA sequence elements responsible for directing the activation of AFP transcription, its repression, and reinduction are contained in a limited segment of DNA within or 5' to the gene (or both) and are operative in the absence of the closely linked albumin gene.

Animals↗
PubMed1987

Developmental and spatial patterns of expression of the mouse homeobox gene, Hox 2.1.

The Hox 2.1 gene forms part of a cluster of homeobox-containing genes on mouse chromosome 11. Analysis of Hox 2.1 cDNAs isolated from an 8 1/2-day p.c. mouse embryo library predicts that the gene encodes a 269 amino acid protein (Mr, 29,432). This deduced protein contains a homeobox 15 amino acids from the carboxy terminus and is very rich in serine and proline. A second partially conserved region present in several other genes containing homeoboxes, the hexapeptide Ile-Phe-Pro-Trp-Met-Arg, is located 12 amino acids upstream of the homeodomain and is encoded by a separate exon. Analysis of Hox 2.1 gene expression reveals a complex and tissue-specific series of RNA transcripts in a broad range of fetal tissues (lung, spinal cord, kidney, gut, spleen, liver and visceral yolk sac). Comparison of the temporal patterns of gene expression during development and in the adult suggests that Hox 2.1 is regulated independently in different tissues. Evidence is also presented that transcripts from other loci have extensive homology to the Hox 2.1 gene in sequences outside of the homeobox. In situ hybridization shows that Hox 2.1 transcripts are regionally localized in the spinal cord in an apparent anterior-posterior gradient extending from the hind brain. The distribution of RNA also displays a cell-type specificity in the lung, where mesodermal cells surrounding the branching epithelial cell layer accumulate high levels of Hox 2.1 transcripts.

Amino Acid Sequence↗
PubMed1985

Developmental regulation of alpha-fetoprotein genes in transgenic mice.

The mouse alpha-fetoprotein gene is activated in embryonic development in the visceral endoderm of the extraembryonic yolk sac and the fetal liver and gut. Transcription of the gene is subsequently repressed in the neonatal liver. To ask whether the DNA sequence elements required for tissue-specific activation are the same or different from those required for postnatal developmental regulation of the gene, modified copies of the alpha-fetoprotein gene were microinjected into fertilized mouse eggs. Those animals which developed to term and carried integrated copies of the modified gene were analyzed for expression. In approximately 50% of such animals, the introduced gene was active only in the three cell lineages which expressed the authentic alpha-fetoprotein gene. Furthermore, its expression was repressed in the neonatal liver. Thus, we conclude that the modified genes, which included either 7 or 14 kilobase pairs of 5'-flanking DNA, contained the DNA sequence information to direct both tissue-specific expression and developmental regulation. The observation that 50% of the mice which carried the modified gene did not express it in any tissue, combined with the fact that the level of expression was highly variable between expressing transgenic animals, suggested that the gene was susceptible to its site of integration in the mouse genome.

Animals↗
PubMed1984

Use of a chromosome 21 cloned DNA probe for the analysis of non-disjunction in Down syndrome.

A recombinant clone was isolated containing a sequence which occurs only on human chromosome 21 and defines a two-allele restriction fragment length polymorphism showing Mendelian inheritance. Forty seven percent of the London population are heterozygous for the polymorphism. The chromosomal location of the DNA sequence homologous to the probe was confirmed using rodent-human somatic cell hybrids. DNA from persons with Down syndrome and from their parents was analysed. It was possible to confirm trisomy 21 by dosage hybridisation to Southern blots, and to determine the origin of the supernumerary chromosome. The technique will be of use for determination of the paternal or maternal origin of nondisjunction in cases of Down syndrome which are not informative using existing markers.

Adult↗
PubMed1982

Cloning and characterisation of the abundant cytoplasmic 7S RNA from mouse cells.

A cDNA library has been prepared from mouse embryo small RNAs and screened for the presence of clones complementary to the highly abundant cytoplasmic 7S RNA. One clone (pA6) was selected which hybridized exclusively with 7S RNA on a Northern blot prepared from cytoplasmic RNA run on high resolution polyacrylamide/urea gels. Sequence analysis of this clone has shown that at least 65 nucleotides at the 5' end of 7S RNA are extensively homologous with the highly repeated mouse B1 family. Heterologous hybridisations between the cloned mouse 7S sequence and RNAs prepared from rat, human and chick cells have shown that the non-B1 part of the 7S RNA molecule has been highly conserved during recent eucaryotic evolution. There are multiple copies of 7S RNA genes in the genomes of mouse, human, rat and chick cells, but substantial differences exist in copy number and genomic organisation in these organisms.

Animals↗
PubMed1982

Construction and characterization of genomic libraries from specific human chromosomes.

Highly purified fractions of human chromosomes 21 and 22 were isolated from a suspension of metaphase chromosomes stained with ethidium bromide by using a fluorescence-activated cell sorter (FACS II). Two recombinant DNA libraries, representing chromosomes 21 and 22, were constructed by complete digestion of DNA from these fractions with EcoRI and insertion into the vector lambda gtWES lambda B. Twenty clones selected at random from the chromosome 22 library hybridized to EcoRI-digested human DNA, and five of these clones hybridized to single bands identical in size to the phage inserts. These five single-copy sequences and a clone coding for an 8S RNA isolated by screening the chromosome 22 library for expressed sequences were characterized in detail. Hybridization of all six clones to a panel of sorted chromosomes and hybrid cell lines confirmed the assignment of the sequences to chromosome 22. The sequences were localized to regions of chromosome 22 by hybridization to translocated chromosomes sorted from a cell line having a balanced translocation t(17;22)(p13;q11) and to hybrid cell lines containing the various portions of another translocation t(X;22)(q13;q112). Five clones reside on the long arm of chromosome 22 between q112 and pter, while one clone and an 18S rRNA gene isolated from the chromosome 22 library reside pter and g112. The construction of chromosome-specific libraries by this method has the advantage of being direct and applicable to nearly all human chromosomes and will be important in molecular analysis of human genetic diseases.

Cell Line↗
PubMedDate not supplied

Differential expression of alpha-fetoprotein genes on the inactive X chromosome in extraembryonic and somatic tissues of a transgenic mouse line.

During development of the female mouse embryo, one of the two X chromosomes is inactivated in a random manner in most cell lineages. However, in the extraembryonic trophectoderm and primary endoderm lineages there is preferential inactivation of the paternally derived X chromosome. The inactivated X chromosomes of the extraembryonic and somatic tissues appear equally inactive at the level of the expression of X-linked genes. However, there are differences in the timing of their replication and the extent of DNA modification as determined by gene transfer. The identification of transgenic animals carrying X-linked modified alpha-fetoprotein (AFP) genes allowed us to examine whether the inactivation process extends to an autosomal gene which is normally expressed at high levels in specific extraembryonic and somatic cells, and if so, whether the inactivation process is different in these two tissues. Our results demonstrate that the X-linked AFP genes were expressed on the inactive X chromosome in the visceral endoderm of the yolk sac but not in fetal liver. Thus, the transcriptional activity of the AFP minigene on the inactive X chromosome is dependent on the tissue in which it resides, and most probably reflects differences in the nature of the maintenance of the inactive state of the extraembryonic and embryonic X chromosomes.

Animals↗
PubMedDate not supplied

Retinoic acid alters hindbrain Hox code and induces transformation of rhombomeres 2/3 into a 4/5 identity.

It has been suggested that Hox genes play an important part in the patterning of limbs, vertebrae and craniofacial structures by providing an ordered molecular system of positional values, termed the Hox code. Little is known about the nature of the signals that govern the establishment and regulation of Hox genes, but retinoic acid can affect the expression of these genes in cell lines and in embryonic tissues. On the basis of experimental and clinical evidence, the hindbrain and branchial region of the head are particularly sensitive to the effects of retinoic acid but the phenotypes are complex and hard to interpret, and how and if they relate to Hox expression has not been clear. Here we follow the changes induced by retinoic acid to hindbrain segmentation and the branchial arches using transgenic mice which contain lacZ reporter genes that reveal the endogenous segment-restricted expression of the Hox-B1 (Hox-2.9), Hox-B2(Hox-2.8) and Krox-20 genes. Our results show that these genes rapidly respond to exposure to retinoic acid at preheadfold stages and undergo a progressive series of changes in segmental expression that are associated with specific phenotypes in hindbrain of first branchial arch. Together the molecular and anatomical alterations indicate that retinoic acid has induced changes in the hindbrain Hox code which result in the homeotic transformation of rhombomeres (r) 2/3 to an r4/5 identity. A main feature of this rhombomeric phenotype is that the trigeminal motor nerve is transformed to a facial identity. Furthermore, in support of this change in rhombomeric identity, neural crest cells derived from r2/3 also express posterior Hox markers suggesting that the retinoic acid-induced transformation extends to multiple components of the first branchial arch.

Animals↗
PubMedDate not supplied

Altered segmental identity and abnormal migration of motor neurons in mice lacking Hoxb-1.

Segmentation of the vertebrate hindbrain into rhombomeres is important for the anterior-posterior arrangement of cranial motor nuclei and efferent nerves. Underlying this reiterated organization, Hox genes display segmentally restricted domains of expression, such as expression of Hoxb-1 (refs 5, 6) in rhombomere 4 (r4). Here we report that absence of Hoxb-1 leads to changes in r4 identity. In mutant mouse embryos, molecular markers indicate that patterning of r4 is initiated properly but not maintained. Cellular analysis by DiI tracing reveals that the r4-specific facial branchiomotor (FBM) and contralateral vestibuloacoustic efferent (CVA) neurons are incorrectly specified. In wild-type mice CVA neurons migrate from r4 into the contralateral side, and we found in lineage analysis that FBM neurons migrate from r4 into r5. In mutants, motor neurons differentiate but the CVA and FBM neurons fail to migrate into their proper positions. Instead, they form a motor nucleus which migrates atypically, and there is a subsequent loss of the facial motor nerve. These results demonstrate that, as a part of its role in maintaining rhombomere identity, Hoxb-1 is involved in controlling migratory properties of motor neurons in the hindbrain.

Animals↗