A mouse homeo box gene is expressed in spermatocytes and embryos

Temporal and constitutive expression of homeobox-2 gene (Hu-2), human heat shock gene (hsp-70), and oncogenes C-sis and N-myc in early human trophoblast

Recent studies of the genetic basis of animal development indicate that homeobox genes, protooncogenes, and some heat shock genes may play a role in early embryogenesis. To investigate the possibility that these genes function in early human embryonic development, we monitored the expression of a human homeobox gene (Hu-2), two human protooncogenes (C-sis and N-myc), and a human heat shock gene (hsp-70) in human trophoblasts at 7 to 13 weeks gestational age. All these genes were found to be expressed in the tissues analyzed. The hsp-70 gene was expressed at nearly constant levels throughout the development period surveyed, whereas N-myc, C-sis, and Hu-2 showed a coordinated pattern of regulated expression. These results are consistent with a functional role of these genes in the early course of human development.

Expression of a testis-specific hsp70 gene-related RNA in defined stages of rat seminiferous epithelium

Changes in the level of a testis-specific hsp70 gene-related transcript (hst70 RNA) and its cellular localization during the cycle of rat seminiferous epithelium have been investigated. Segments of seminiferous tubules at defined stages of the cycle were isolated in living condition by transillumination-assisted microdissection and the exact stages identified by phase-contrast microscopy of live cell squashes. The levels of the hst70 RNA were determined by Northern and slot blotting of whole cell lysates. High levels were found in stages XII-XIV and I to early VII of the cycle, and low levels were found in other stages, i.e., late VII (VIId) through VIII-XI of the cycle. The in situ hybridization revealed that the hst70 gene was activated in late pachytene primary spermatocytes during stage XII of the cycle, and that mRNA was then present in cells during differentiation through diakinesis, meiotic divisions, and early spermiogenesis (steps 1 through early 7). The activation of the gene coding for hst70 RNA shortly before meiotic divisions may indicate that the gene product is needed either during differentiation of late spermatocytes into spermatids or later during spermiogenesis, and that the mRNA may be stored in early spermatids.

Gene organization of murine homeobox-containing gene clusters

A chromosomal walk which links a previously described and a new homeobox to the Hox-2 murine homeobox gene cluster is described, and the nucleotide sequence of the new homeobox is presented. With these new data the Hox-2 gene cluster contains seven loci on an approximately 100-kb-long physical map. Homology comparisons reveal that a significant number of vertebrate homeoboxes are in fact analogous. We also find that the linear order of homologous homeoboxes is similar in the two murine gene complexes, Hox-1 and Hox-2, and among the human homeobox loci on chromosome 17. Conservation of the homeo-domain and the linear gene order of homeobox-containing genes in vertebrates is discussed in light of the interactions and the anteroposterior linear order of homeotic loci in insects.

Early retinoic acid-induced F9 teratocarcinoma stem cell gene ERA-1: alternate splicing creates transcripts for a homeobox-containing protein and one lacking the homeobox

Retinoic acid (RA), the natural acidic derivative of vitamin A, can modulate the expression of specific genes and can induce some cell types, such as the murine F9 teratocarcinoma stem cell line, to differentiate in culture. As an initial step toward understanding the molecular mechanism(s) by which RA exerts these effects, we previously isolated cDNA clones for a gene, ERA-1, which has the characteristics of an early, direct target for RA. We demonstrated that RA causes a rapid, dose-dependent, and protein synthesis-independent expression of the ERA-1 gene (G. J. LaRosa and L. J. Gudas, Proc. Natl. Acad. Sci. USA 85:329-333, 1988). We now report the full-length cDNA sequence and the further characterization of this gene. The data indicate that the RA-induced 2.2- to 2.4-kilobase ERA-1 RNA species that we previously detected consists of two alternately spliced messages. One mRNA encodes a protein with a predicted mass of about 36 kilodaltons (kDa) that possesses the Hox 1.6 homeobox domain. The other mRNA encodes a truncated protein of about 15 kDa which is identical to the 36-kDa protein for 114 amino acids at the amino-terminal end but which lacks the homeobox amino acid sequence. The RA-associated increase in the ERA-1 mRNA level does not appear to be due to message stabilization, suggesting that the response is at the level of transcription. By Northern (RNA) blot analysis, the usual 2.2- to 2.4-kilobase mRNA species was also rapidly expressed in P19 teratocarcinoma cells during their differentiation to fibroblastic cells in response to RA and was detected in day 10.5 and day 13.5 mouse embryos. This result indicates that the expression of this gene is not limited to the endodermal differentiation of F9 cells.

Differential expression of the homeobox gene Hox-1.3 in F9 embryonal carcinoma cells

The Hox-1.3 gene is located on mouse chromosome 6 and has been previously shown to be expressed in mouse embryos and adults. In this study, we have examined the steady-state levels of the Hox-1.3 transcripts in undifferentiated and differentiated F9 embryonal carcinoma cells. We find that there is a rapid increase of Hox-1.3 transcripts after differentiation induction of F9 cells. The level of the major 1.85-kilobase (kb) transcript peaks at 16-24 hr after differentiation induction of F9 cells. By using primer extension techniques the 5' ends of the major 1.85-kb transcript have been mapped to two sites in induced F9 cells. Cellular fractionation of RNA and transfer blot gel analysis has localized one minor transcript to the nucleus, whereas the major transcript and two additional minor transcripts appear in the nucleus and the cytoplasm of induced F9 cells. The results of nuclear run-off experiments with uninduced and induced F9 cell nuclei indicate that there is a substantial increase in the rate of Hox-1.3 transcription upon induction of F9 cells with retinoic acid.

Hox-5.1 defines a homeobox-containing gene locus on mouse chromosome 2

We have isolated a murine homeobox-containing gene, Hox-5.1, by virtue of its relatedness to the Hox-1.4 gene. In situ hybridization to metaphase spreads mapped Hox-5.1 to band D of mouse chromosome 2. Sequence comparisons indicate that Hox-5.1 is the murine homolog of the human C13 homeobox-containing gene. Hox-5.1 also bears significant similarity to the Xenopus Xhox-1A homeobox-containing gene and the Drosophila deformed homeotic gene at N-terminal and homeobox regions. Hox-5.1 transcripts were detected in mouse embryos, in adult mouse testis, kidney, heart, and intestine, and in mouse embryonal carcinoma cells treated with retinoic acid. In situ hybridization to sections from whole mouse embryos revealed Hox-5.1 expression in spinal cord and prevertebrae.

Expression of homeo box genes during mouse development: a review

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At least three human homeoboxes on chromosome 12 belong to the same transcription unit

Mammalian homeoboxes show a clustered chromosomal organization. In the mouse, at least seven homeoboxes on chromosome 6 and at least six on chromosome 11 identify the murine Hox-1 and Hox-2 loci, respectively. A number of homeoboxes on chromosome 7 define the human HOX-1 locus and homeoboxes on chromosome 17 define the human HOX-2 locus. We studied the genomic organization of three homeobox sequences of the HOX-3 locus on chromosome 12 and analyzed transcripts from this region. Structural characterization and sequencing of several cDNA clones reveal that the three homeobox sequences present in this chromosomal region identify a single transcription unit. Primary transcripts are alternatively processed to give mature messengers with a common 5' noncoding exon encoding different proteins containing one of the three homeodomains.

Characterization of a mouse multigene family that encodes zinc finger structures

The Drosophila segmentation gene Krüppel encodes multiple tandemly repeated units predicted to form DNA-binding zinc fingers. We have isolated 23 bacteriophages, containing nonoverlapping inserts from a mouse genomic DNA library, on the basis of cross-hybridization under nonstringent conditions to a probe corresponding to the Krüppel finger region. Nucleotide sequence analysis of six phage DNAs indicated that they all contained regions with similarity to Krüppel and potentially encoded zinc finger domains. Within these regions, the level of similarity to Krüppel was particularly high between successive fingers. Northern (RNA) blotting analysis suggested that the mouse sequences belonged to different genes, the expression of some of which was modulated during cell differentiation and development. Hybridization experiments suggested that the similarity between some of the genes extended outside of the finger regions. In conclusion, our data suggest that the mouse genome contains a large family of evolutionarily related genes encoding possible trans-acting factors. These genes are likely to play a regulatory role at the transcriptional level.

Expression of a murine homeobox gene precedes the induction of c-fos during mesodermal differentiation of P19 teratocarcinoma cells

The controlled expression of regulatory genes is the basis of normal mouse embryo development. Recent studies in our laboratory have revealed temporally and spatially restricted expression of homeobox-containing genes and the cellular protooncogene c-fos in developing mouse embryos. In order to gain insight into cellular control mechanisms responsible for differential expression of these potential regulatory genes during developmental processes, we set out to analyze their expression in teratocarcinoma cells as an in vitro model system for cellular differentiation. We demonstrated that the homeobox-containing gene Hox 1.3 and the c-fos protooncogene are expressed in P19 teratocarcinoma cells prior to their terminal myogenic differentiation, which is indicated by the expression of muscle-specific myosin. Using a combination of the transcriptional run-on assay and Northern analysis, we defined some of the cellular control mechanisms that are responsible for the changes in transcription pattern during P19 differentiation. The development-dependent activation of c-fos and muscle-specific myosin mRNA was found to result from an increased transcription rate. In contrast, the primary induction of Hox 1.1 (m6)-specific mRNA was controlled on the posttranscriptional level by changes in the half-life of the transcript. In addition, in situ hybridization studies revealed a characteristic spatially restricted expression of Hox 1.1 RNA in P19 aggregates, which may point to an important role of cell-cell interactions for Hox 1.1 expression in the mesodermal muscle differentiation pathway.

Molecular cloning and characterization of ovine homeo-box-containing genes

The sheep genome contains at least eleven homeo-boxes (hox). Using two hox-specific 36-mer oligodeoxynucleotides to screen a sheep genomic library, constructed in lambda Charon28, clones of nine of the hox were identified. Six of the hox clones were analysed by nucleotide sequencing, Southern-blot hybridization and Northern-blot analysis. Two of the hox appear to be cognates of the human Hu-1 (or mouse Hox 2.1) and the mouse Hox 1-3, while another is closely related to the mouse Hox 1-4. These results suggest that there is strong sequence conservation in the hox-containing genes of different mammals, and highlight the possible occurrence of an ubiquitous set of hox-containing genes in mammals. Northern-blot analysis of four sheep hox-containing genes indicates that they are all expressed during embryogenesis and that expression is temporally regulated allowing hierarchical-regulatory interaction. Interestingly, none of the cloned hox-containing sequences contain repetitive sequences.

cDNA cloning and sequencing of a new gene intensely expressed in early differentiation stages of embryonal carcinoma cells and in mid-gestation period of mouse embryogenesis

By the differential hybridization technique, we isolated a cDNA clone, MK1, whose RNA level increased in early stages of retinoic acid-induced differentiation of embryonal carcinoma cells. The amount of MK1 RNA progressively decreased in the later stages of the differentiation. In mouse embryos, MK1 RNA was abundant in mid-gestation stages (Day 8 to Day 11) and decreased thereafter. The corresponding RNA was 1.0 killobase in size. From the nucleotide sequence, MK1 gene was predicted to code a polypeptide of molecular weight 9,971, which was rich in basic amino acids.

Characterization of a mouse multigene family that encodes zinc finger structures

The Drosophila segmentation gene Krüppel encodes multiple tandemly repeated units predicted to form DNA-binding zinc fingers. We have isolated 23 bacteriophages, containing nonoverlapping inserts from a mouse genomic DNA library, on the basis of cross-hybridization under nonstringent conditions to a probe corresponding to the Krüppel finger region. Nucleotide sequence analysis of six phage DNAs indicated that they all contained regions with similarity to Krüppel and potentially encoded zinc finger domains. Within these regions, the level of similarity to Krüppel was particularly high between successive fingers. Northern (RNA) blotting analysis suggested that the mouse sequences belonged to different genes, the expression of some of which was modulated during cell differentiation and development. Hybridization experiments suggested that the similarity between some of the genes extended outside of the finger regions. In conclusion, our data suggest that the mouse genome contains a large family of evolutionarily related genes encoding possible trans-acting factors. These genes are likely to play a regulatory role at the transcriptional level.

Activation of four homeobox gene clusters in human embryonal carcinoma cells induced to differentiate by retinoic acid

We have studied the expression of nine homeobox genes from Hox 1, Hox 2, Hox 3 and Hox 5 clusters in human embryonal carcinoma (EC) cell lines analyzed as both stem cells and after exposure to the differentiation-inducing agents retinoic acid (RA), hexamethylenebisacetamide (HMBA) and bromodeoxyuridine (BUdR). None of the homeobox genes was expressed in stem cells, whereas all were activated, although with different kinetics, in cultures of the pluripotent EC cell line NTERA-2, clone D1 (NT2/D1), following differentiation induced by RA. At least some homeobox genes were stably expressed in differentiated cells several weeks after removal of RA from the culture medium. However, the length of initial exposure to RA is a critical factor in achieving stable gene expression, and differs among the different sets of genes and, at least in one case, among different transcripts from the same gene. No homeobox gene expression was detected in NT2/D1 cells induced to differentiate with HMBA or BUdR. Also, no expression was detectable in xenograft tumors generated by NT2/D1 cells in nude mice, even though tumors of this type contain mostly differentiated cells. Other human EC lines tested, i.e., 833KE, 2102Ep or 1156QE, did not differentiate in response to RA and did not express homeobox genes. No expression was detectable in xenograft tumors of 833KE and 2102Ep, containing essentially EC cells. These data indicate that homeobox-gene activation specifically accompanies RA-induced differentiation of NT2/D1 cells, thereby providing an excellent model for studying the molecular basis of homeobox-gene regulation and the possible role of the homeobox in cell differentiation.

Murine Hox-1.7 homeo-box gene: cloning, chromosomal location, and expression

A new murine homeo-box, called Hox-1.7, has been identified in a rare cDNA from F9 teratocarcinoma stem cells. The Hox-1.7 homeo-box is 68 and 72% homologous to the Drosophila antennapedia (Antp) and iab-7 homeo-boxes, respectively. A major 2.5-kilobase transcript and several minor transcripts were detected by Northern blot (RNA blot) analysis in adult tissues as well as in midgestational embryos. The posterior spinal cord was found to be a major site of Hox-1.7 expression in 12.5-day-old embryos. Somatic cell hybrids were used to map the Hox-1.7 gene to mouse chromosome 6. Restriction fragment length polymorphisms associated with either the Hox-1.7 gene or the previously known Hox-1 complex were identified. Their distribution patterns in recombinant inbred mouse strains were used to determine the linkage between the two loci as well as to other loci on chromosome 6. This maps Hox-1 and Hox-1.7 close to two mouse loci that affect morphogenesis, postaxial hemimelia (px) and hypodactyly (Hd).

Differential expression of the c-abl proto-oncogene and the homeo box-containing gene Hox 1.4 during mouse spermatogenesis

Mammalian spermatogenesis is a complex developmental process. Spermatozoa, like ova, are uniquely capable of supporting embryonic development. Our approach to understanding this process is to identify genes whose developmental pattern of expression suggests that they may play a role in spermatogenesis. Experiments on the cellular oncogene c-abl and the homeo box-containing gene Hox-1.4 indicate that these genes may be important for male germ cell development. Both genes produce testis-specific transcripts that are present in particular cellular populations of the adult testis. Their developmental specificity, however, is different: c-abl is haploid-specific, whereas Hox-1.4 is expressed in the germ cells as soon as they have entered meiosis. Future studies will focus on examining the protein products of these genes and their function in testicular cells.

Expression of the murine homeo box gene Hox 1.5 during embryogenesis

The spatial pattern of expression of the murine homeo box-containing gene Hox 1.5 was studied during embryogenesis. In situ hybridization of single-stranded RNA probes to mouse embryo sections revealed a specific spatial distribution of the Hox 1.5 transcripts in mouse embryos 8.5 to 12.5 days postcoitum (p.c.). Analysis of mouse embryos 8.5 days p.c. showed that the gene is expressed in a spatially restricted manner. Expression appears to be limited to the central nervous system with an anterior boundary in the hindbrain and extending posteriorly through caudal regions of the spinal cord. The same spatial pattern of expression was observed in embryos 9.5 to 12.5 days p.c. These results show that the murine Hox 1.5 gene is expressed in a spatially restricted manner during embryonic development similar to the patterns observed in Drosophila homeotic genes.

Post-transcriptional regulation of a murine homeobox gene transcript in F9 embryonal carcinoma cells

A 2.4 kb RNA encoded by the murine Hox 1.1 (m6) homeobox gene is induced when F9 stem cells are differentiated with retinoic acid and dibutyryl cyclic AMP. The regulation of Hox 1.1 expression was probed by using cycloheximide, an inhibitor of protein synthesis. Production of the Hox 1.1 RNA in differentiating F9 cells was not blocked by treatment with cycloheximide, indicating that new protein synthesis is not required for its induction. On the contrary, this transcript was detected in F9 stem cells treated with cycloheximide, anisomycin, or emetine alone. Nuclear transcription assays indicated that the Hox 1.1 gene was transcribed in F9 stem cells and that the rate of transcription did not change early in the differentiation of F9 cells. These observations indicate that the induction of Hox 1.1 transcripts in F9 stem cells during differentiation is not regulated at the level of transcription initiation but results from stabilization of the transcript.

Sequence analysis of the murine Hox-2.2, -2.3, and -2.4 homeo boxes: evolutionary and structural comparisons

We have determined the nucleotide sequences and deduced the amino acid sequences of three tandemly arranged murine boxes of the Hox-2 homeo box gene complex on mouse chromosome 11 (Hox-2.2, -2.3, and -2.4). The type and position of differences with other sequenced homeo boxes were analyzed. Hox-2.2 is nearly identical with its cognate human homeo box Hu-2. Hox-2.3 shares 59 of 61 amino acids with the Antennapedia homeo domain of Drosophila and the MM-3 homeo domain of Xenopus and shows 60 of 61 amino acid identity with human HuC1. Hox-2.3, MM-3, and HuC1 also share a stretch of six glutamic acid residues followed by a stop codon 15-20 amino acids 3' of the homeo domain. Hox-2.4 is relatively divergent from most of the other homeo boxes sequenced to date; however, it matches the Hox-3.1 murine homeo domain at 60 of 61 positions. Sequence comparisons with other murine homeo domains, together with previous studies of their genomic organization and chromosomal location, provide support for the hypothesis of a large-scale duplication resulting in the two major murine homeo box gene complexes Hox-1 and Hox-2.

Murine Hox-1.7 homeo-box gene: cloning, chromosomal location, and expression

A new murine homeo-box, called Hox-1.7, has been identified in a rare cDNA from F9 teratocarcinoma stem cells. The Hox-1.7 homeo-box is 68 and 72% homologous to the Drosophila antennapedia (Antp) and iab-7 homeo-boxes, respectively. A major 2.5-kilobase transcript and several minor transcripts were detected by Northern blot (RNA blot) analysis in adult tissues as well as in midgestational embryos. The posterior spinal cord was found to be a major site of Hox-1.7 expression in 12.5-day-old embryos. Somatic cell hybrids were used to map the Hox-1.7 gene to mouse chromosome 6. Restriction fragment length polymorphisms associated with either the Hox-1.7 gene or the previously known Hox-1 complex were identified. Their distribution patterns in recombinant inbred mouse strains were used to determine the linkage between the two loci as well as to other loci on chromosome 6. This maps Hox-1 and Hox-1.7 close to two mouse loci that affect morphogenesis, postaxial hemimelia (px) and hypodactyly (Hd).

Region-specific expression of mouse homeobox genes in the embryonic mesoderm and central nervous system

The homeobox is a 180-base-pair sequence characteristically found in homeotic and segmentation genes in Drosophila. Several copies of homeoboxes are also found in the mammalian genome, but it is not known whether these are components of morphogenetic loci in mammals as well. As a step toward understanding the function of mammalian homeoboxes, we have used in situ hybridization to define the spatial pattern of expression of two mouse homeobox genes in the midgestational mouse embryo. The two mouse homeoboxes studied here, Hox 1.2 and Hox 1.4, are located 20 kilobases apart on mouse chromosome 6. Our results demonstrate the following: (i) Hox 1.2 transcripts are localized mainly in the posterior myelencephalon, in the cervical central nervous system (CNS), and in several thoracic prevertebrae; (ii) Hox 1.4 transcripts are localized mainly in the posterior myelencephalon and in the cervical CNS; (iii) within the CNS region expressing Hox 1.4, the level of Hox 1.4 transcripts is higher in the mantle layer than in the ependymal layer and higher in the dorsal than in the ventral area. The specific localization of Hox 1.2 and Hox 1.4 transcripts in the embryonic CNS and the restricted pattern of expression along the rostrocaudal axis are strikingly reminiscent of the expression pattern of Drosophila homeoboxes in the fly embryo and larvae. Despite the different developmental strategies adopted by Drosophila and mammals, functional similarities may exist between Drosophila and mammalian homeobox genes.

New murine homeoboxes: structure, chromosomal assignment, and differential expression in adult erythropoiesis

The nucleotide sequence, chromosomal assignment, and preliminary transcriptional analysis of four murine homeoboxes is presented. Three of these are linked to the Hox-2 gene complex on chromosome 11, whereas the fourth, Hox-4, was assigned to mouse chromosome 12. A comparative analysis of homeobox sequences reveals that two of our sequences represent the previously described Hox-2.3 loci, whereas a third, mh19, could represent the predicted Hox-2.6 locus. Homeoboxes Hox-2.2 and Hox-2.3 are the cognates of two previously reported human homeoboxes that belong to a similar gene cluster on a closely related human chromosome (Chr 17), suggesting that homeoboxes may have been preserved as clusters during evolution. Moreover Hox-4, mh19, and the previously described Hox-1.5 homeobox form a separate subgroup of mammalian homeoboxes (90-92% amino acid and nucleotide homology). All four homeoboxes are expressed in the mouse embryo. Of special interest is the expression of mh19, a 4.2-kb transcript of which appears to be connected to the induced differentiation of Friend erythroleukemia cells.

A mouse homeobox containing gene on chromosome 11: sequence and tissue-specific expression

We have molecularly cloned a mouse homeobox containing gene by isolating cDNA and genomic clones. The gene is located in a previously described cluster on chromosome 11 (Hart et al. (1985) Cell 43, 9-18) and was identified as the Hox2.3 gene. We present the complete mRNA sequence of this gene and describe similarities to other homeobox containing genes, among which its human homologue, the cl gene. High expression of the Hox2.3 gene was found in kidney, testis, and spinal cord of adult mice, in the spinal cord of 12.5-17.5 day embryos and in differentiating EC cells depending on their treatment. Three different treatments of the pluripotent EC cell line P19, each leading to the induction of a specific differentiation pathway, resulted in all cases in induction of Hox2.3; however, major quantitative differences in this response were observed.

The mouse Hox2.3 homeobox-containing gene: regulation in differentiating pluripotent stem cells and expression pattern in embryos

Genomic and cDNA clones of the mouse Hox2.3 gene have been isolated. Expression of this gene was characterized in differentiating embryonal carcinoma (EC) and embryonic stem (ES) cells, and in the 13.5-day embryo. Hox2.3 is expressed at a very low level, if at all, in undifferentiated ES and EC cells. As previously reported for the Hox1.1 and Hox2.1 genes, differentiation of pluripotent stem cells induced by a nonchemical method is not accompanied by strong accumulation of Hox2.3 transcripts. Treatment of the stem cells with a chemical inducer like retinoic acid (RA), and also hexamethylenebisacetamide (HMBA), or 5-bromo-2'-deoxyuridine (BUdR), simultaneously accelerates differentiation and stimulates accumulation of Hox2.3 mRNA to high levels. Addition of RA several days after the cells have been induced to differentiate by a nonchemical method induces Hox2.3-transcript accumulation as well. For comparison, expression of the En-1 gene, which contains a homeobox belonging to a different class from that of the Antennapedia-related Hox1.1, Hox2.1, and Hox2.3 genes, was analyzed. The En-1 gene was found also to be sensitive to this regulation by chemical inducers of differentiation. It was observed that treatment of undifferentiated EC cells with the inhibitor of protein synthesis cycloheximide resulted in slight accumulation of Hox2.3 mRNA, suggesting the involvement of a short-lived protein in keeping the level of homeobox-gene transcription low in EC cells. The highest level of Hox2.3 transcripts in 13.5-day embryos in vivo was observed in the spinal cord. Comparison with the expression pattern of three other homeobox genes revealed overlapping gradients of mRNA along the longitudinal brain-spinal-cord axis. An important question is that of the molecular basis for such a spatially restricted accumulation of homeobox transcripts. Hox2.3 is expressed at a much lower level in rat and mouse embryonic midbrain than in spinal cord in vivo. We have shown that addition of RA to primary cultures of cells from rat embryo mesencephalon leads to strong accumulation of Hox2.3 mRNA. A possible interpretation is that RA mimics one or more spatially restricted effectors, accounting for the local accumulation of Hox2.3 transcripts in the embryonic central nervous system. Control of Hox2.3 gene expression in vivo may obey some similar mechanisms as in chemically stimulated EC and ES cells in vitro.

AvaII RFLP at the human apolipoprotein CII (APO CII) gene locus

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Differential expression of the mouse homeobox-containing gene Hox-1.4 during male germ cell differentiation and embryonic development

Hox-1.4 is a mouse homeobox-containing gene (initially identified as HBT-1), whose expression appears to be testis-specific in the adult animal. Examination of Hox-1.4 transcripts in RNA from testes of mutant mice deficient in germ cells confirms that Hox-1.4 expression within the testis is germ cell-specific. Enriched populations of spermatogenic cells were used to localize the expression of Hox-1.4 specifically to germ cells that have entered into and progressed beyond the meiotic prophase stage of differentiation and to demonstrate the presence of two different size Hox-1.4 transcripts. Examination of RNA from teratocarcinoma cell cultures and mouse embryos at 10.5-16.5 days of gestation demonstrated the presence of several Hox-1.4 transcripts, which are larger than those present in germ cells. In the midgestation fetus, Hox-1.4 expression is most abundant in the spinal cord.

Differential expression of opioid peptide genes by testicular germ cells and somatic cells

Spermatogenic cells have been previously shown to be a major site of testicular proenkephalin gene expression. Using RNA gel-blot analysis of purified mouse and hamster germ cells and of testes from prepuberal and germ cell-deficient mutant mice, we now have demonstrated that, in addition to its previously described expression by somatic (Leydig) cells, the gene for a second opioid peptide precursor, pro-opiomelanocortin (POMC), is also expressed by spermatogenic cells. Of particular significance is the finding that the RNAs for proenkephalin and POMC are differentially regulated during spermatogenesis. Two forms of POMC RNA were detected in mouse testis, a larger component 675- to 750-nucleotides (nt) in size common to somatic and spermatogenic cells and a smaller 625-nt RNA found only in pachytene spermatocytes. Two distinct, cell-specific proenkephalin RNAs were also shown to be present in mouse testis: a 1700-nt transcript previously shown to be expressed by spermatogenic cells and a 1450-nt form associated with somatic cells. These data suggest that proenkephalin- and POMC-derived peptides are produced by both somatic cells and germ cells in the testis and in germ cells these two families of opioid peptides may function at different stages of spermatogenesis.

Expression of the proto-oncogene int-1 is restricted to postmeiotic male germ cells and the neural tube of mid-gestational embryos

The int-1 proto-oncogene is transcriptionally activated in mammary tumors by mouse mammary tumor virus insertion mutations and is normally expressed only in adult mouse testes and mid-gestational embryos. We have used anatomical dissection of embryos, germ-cell fractionation, peripuberal expression studies, and spermatogenesis mutants to identify more precisely the tissues and cells that contain int-1 RNA. In the testis, int-1 RNA is detected only in postmeiotic germ cells undergoing differentiation from round spermatids into mature spermatozoa. In embryos 11-15 days after conception, expression of the gene is restricted to the developing central nervous system in regions of the neural tube other than the telencephalon. Our findings suggest that int-1 mediates developmental events at these two sites.

Expression of a homeo domain protein in noncontact-inhibited cultured cells and postmitotic neurons

The murine Hox 1.3 gene is one of six homeo box genes clustered on chromosome 6. Our analysis of Hox 1.3 cDNA and genomic clones indicates that the gene is organized into two exons and encodes a 270-amino-acid homeo domain protein. The predicted protein is rich in serine, glycine, and proline residues, and its homeo domain is identical to the Hox 2.1 domain. During embryogenesis, the gene is maximally expressed at midgestation but is also expressed to a lesser extent in many adult tissues possessing different cell lineages. Hox 1.3 transcripts are also present in cultured fibroblasts. The Hox 1.3 protein accumulates in the nuclei of nonconfluent cultured fibroblasts but is greatly diminished in contact-inhibited nongrowing cells. Thus, the expression of the Hox 1.3 gene correlates with growth in embryos and cultured cells. Paradoxically, it is also expressed in certain subsets of postmitotic, fully differentiated neurons, most notably the Purkinje neurons of the cerebellum, the pyramidal and dentate neurons of the hippocampus, and the motor neurons of the spinal cord. This complex pattern of expression suggests that Hox 1.3 may provide a function required by many cell types in addition to any role it may have in morphogenesis.

Region-specific expression of two mouse homeo box genes

Mammalian homeo box genes have been identified on the basis of sequence homology to Drosophila homeotic and segmentation genes. These studies examine the distribution of transcripts from two mouse homeo box genes, Hox-2.1 and Hox-3.1, throughout the latter third of prenatal development. Transcripts from these genes are regionally localized along the rostro-caudal axis of the developing central nervous system, yielding expression patterns very similar to patterns of Drosophila homeotic gene expression.

Expression of the caudal gene in the germ line of Drosophila: formation of an RNA and protein gradient during early embryogenesis

The caudal (cad) gene of Drosophila encodes a maternal and a zygotic transcript which have different promoters. Both mRNAs contain the same open reading frame, including a homeo box. In situ hybridization and antibody staining show that the maternal RNA and protein are localized in an anteroposterior gradient during the syncytial blastoderm stage. The protein is found mainly in the nuclei and is also present in the pole cells. Zygotic RNA and protein are localized in the primordia of the terminal abdominal segment, the hindgut, and in the posterior midgut rudiment. In third instar larvae, cad is expressed in the gut, the gonads, and parts of the genital discs. It is the first homeo box-containing gene expressed in the germ line of Drosophila.

Homeo box genes in murine development

Considerable information has accumulated on mouse homeo box gene organization and expression. Homeo box genes are expressed in a wide variety of tissues, developmental stages, and cell lines. How can this be interpreted in view of the relationship of these genes to Drosophila morphogenetic loci? One view is that homeo box genes control determinative decisions by modulating transcription of as yet unidentified target genes. Proponents of this view are faced with two tasks: to identify developmental processes that are controlled by homeo box genes, and to identify the target genes that mediate this control. Such target genes might be identified on the basis of in vitro homeo domain-DNA interactions. Candidate morphogenetic processes might be identified on the basis of the observed patterns of homeo box gene expression. It must be stressed that finding expression in a given tissue in no way demonstrates that the expression is necessary for the determination of that tissue. The role of Drosophila homeo box genes in determinative decisions is based upon analysis of mutants to demonstrate that the pattern of homeo box gene expression determines the morphogenetic outcome. To test whether the expression of a mouse homeo box gene is involved in a determinative decision, one must disrupt the normal pattern of expression of that gene and observe the resulting morphogenetic effect. In mouse this can be approached by looking for allelism with known morphogenetic loci, by isolating mutants in homeo box genes through large-scale mutagenesis screens, or by introducing altered homeo box genes into transgenic mice. One of the most intriguing possibilities is that homeo box genes are involved in regional specification along the anteroposterior axis. In situ hybridization and Northern blot analysis have demonstrated that at least four different homeo box genes display distinct regional patterns of expression along the anteroposterior axis of the developing CNS. The expression of each of these genes has a unique anterior boundary from which expression extends posteriorly within the CNS. Hox 1.5 expression has an anterior boundary within the hindbrain just posterior to the pontine flexure. The anterior boundary of Hox 2.1 expression lies more posteriorly within the medulla of the hindbrain. Weak expression of Hox 2.5 is detected in the spinal cord just posterior to the first cervical vertebra, and maximal expression is found posterior to the second cervical vertebra.(ABSTRACT TRUNCATED AT 400 WORDS)

Differential and stage-related expression in embryonic tissues of a new human homoeobox gene

The homoeobox is a 183 base-pair (bp) DNA sequence conserved in several Drosophila genes controlling segmentation and segment identity. Homoeobox sequences have been detected in the genome of species ranging from insects and anellids to vertebrates and homoeobox containing genes have been cloned from Xenopus, mouse and man. We recently isolated human homoeobox containing complementary DNA clones, that represent transcripts from four different human genes. One clone (HHO.c10) is selectively expressed in a 2.1 kilobase (kb) polyadenylated transcript in the spinal cord of human embryos and fetuses 5-10 weeks after fertilization. We report the characterization of a second cDNA clone, termed HHO.c13, that represents a new homoeobox gene. This clone encodes a protein of 255 amino-acid residues, which includes a pentapeptide, upstream of the homoeo domain, conserved in other Drosophila, Xenopus, murine and human homoeobox genes. By Northern analysis HHO.c13 detects multiple embryonic transcripts, which are differentially expressed in spinal cord, brain, backbone rudiments, limb buds and heart in 5-9-week-old human embryos and fetuses, in a striking organ- and stage-specific pattern. These observations suggest that in early mammalian development homoeobox genes may exert a wide spectrum of control functions in a variety of organs and body parts, in addition to the spinal cord.

Cognate homeo-box loci mapped on homologous human and mouse chromosomes

The homeotic genes of Drosophila, which regulate pattern formation during larval development, contain a 180-base-pair DNA sequence termed the "homeo-box." Nucleotide sequence comparisons indicate that the homeo-box motif is highly conserved in a variety of motazoan species. As in Drosophila, homeo-box sequences of mammalian species are expressed in a temporal and tissue-specific pattern during embryogenesis. These observations suggest functional homologies between dipteran and mammalian homeo-box gene products. To identify possible relationships between homeo-box genes of mice and humans, we have compared the chromosomal location of homeo-box genes in these species. Using in situ hybridization and somatic cell genetic techniques, we have mapped the chromosome 6-specific murine Hox-1 homolog to the region p14-p21 on human chromosome 7. We have also regionally mapped the murine Hox-3 locus to 15F1-3 and its human cognate to 12q11-q21. These comparative mapping data indicate that a syntenic relationship in mice and humans is maintained for all homeo-box loci examined to date. We suggest these regions represent evolutionarily conserved genomic domains encoding homologous protein products that function in regulating patterns of mammalian development.