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The myb gene has been shown to be an important regulator of hematopoietic cell proliferation, differentiation and apoptosis. Activation of the myb gene into an oncogenic form has involved structural alterations to the coding sequences. Thus, the v-myb gene encoded by the Avian Myeloblastosis Virus, is truncated at both the 5' and 3' ends. Additionally, tumor cells containing rearrangements in the myb locus, such as the ABPL tumors or NFS60 tumor cell line have recently been shown to display a heterogeneity of structure. In this study, we examined the growth and differentiation properties of clonal cell lines derived from 32Dcl3 which harbor myb transgenes; derived from v-myb, and the ABPL-1, ABPL-2, ABPL-4 and NFS-60 cell lines. Retroviral vectors containing the appropriate myb cDNAs were produced, transfected into packaging cell lines, and the viruses were used to generate the 32D derivative cell clones. Abrogation of IL-3 dependence was never observed in any cell line. Expression of c-myb, ABPL-1-myb and ABPL-2-myb isoforms in 32D cells resulted in a block to their ability to terminally differentiate into granulocytes at the pro-myelocytic stage. However, expression of ABPL-4-myb or NFS60-myb in these cells failed to result in a similar effect. These cells differentiated into granulocytes in the presence of G-CSF, albeit more slowly than control 32Dcl3 cells. We also examined the ability of various Myb-isoforms to transactivate transcription of reporter genes containing Myb-binding elements in their promoter/enhancer sequences, to determine whether the phenotypic effects produced by these various isoforms correlate with their ability to transactivate transcription. Our results show that while v-myb and c-myb transactivated transcription equally well, the NFS60-myb exhibited the highest levels of transcriptional transactivation. The ABPL-1, ABPL-2 and ABPL-4-myb isoforms showed very low levels of transcriptional transactivation potential with the same reporter genes. These results suggest that the ability of various Myb-isoforms to transactivate transcription does not by itself correlate with their ability to induce a block to G-CSF-induced terminal differentiation of myeloid precursor cells.

Metaphase chromosome preparations of three male and one female Gorilla gorilla were stained to demonstrate quinacrine, Giemsa, centromeric heterochromatin, and, in one case, reverse-Giemsa bands. A standard karyotype is proposed based on chromosome banding pattern, centromeric index, and length. Three types of variation between homologous chromosomes are described: presence or absence of very bright fluorescence of the short arm or satellite region of acrocentric chromosomes, presence or absence of bright quinacrine bands at the distal ends of chromosome arms, and large differences in the size of the heterochromatic region on each of two biarmed chromosomes. At least half the chromosome pairs show polymorphisms of these types. Satellite associations were scored for each animal. In one case the two smallest pairs of chromosomes were preferentially involved in associations.

Differences in the number of chromosomes with secondary constrictions and in the size of the C-band region on certain chromosomes have been observed among the following inbred strains of Mus musculus: C57BL/10J, C57BR/cdJ, DBA/1J, CBA/J, BALB/cJ, and AKR. These differences are useful as indicators of the location of rRNA genes and as normal chromosome markers. The size of each C-band region appears to remain constant over many generations. Only one probable change in the size of a C-band region was found.

Metaphase chromosome preparations were made from leukocyte cultures of normal individuals. The cells were fixed in methanol:acetic acid (3:1 v/v), then dropped on cold, wet slides which were air-dried before storage at 4 degrees C. The slides were stained to identify the chromosomes by one of the following procedures: (1) Quinacrine. Slides were stained for 10 min in quinacrine mustard solution, rinsed in running tap water for 2 min, and mounted in Tris-maleat buffer, pH 5.6.

Quinacrine (Q-band) and centromeric heterochromatin (C-band) patterns of metaphase chromosomes of two subspecies of Mus musculus were compared. M. m. musculus (the laboratory mouse) and M. m. molossinus (a subspecies from Southeast Asia) had similar Q-band patterns along the length of the chromosomes, but differences were observed in the centromeric region of some chromosomes. The two subspecies had very different distributions of C-band material. Antibodies to 5-methylcytosine were bound to regions of the chromosome corresponding to the C-bands in each animal. These findings support the idea that satellite DNA, which is concentrated in the C-band region, changes more quickly than bulk DNA. The interfertility of these two subspecies permits the development of a musculus strain carrying normal marker chromosomes for genetic studies.

Nucleolus organizer regions (NORs) of rat chromosomes were stained by the Ag-AS method. The Ag-NORs were found on chromosomes 3, 11 and 12 in the ACI, Wistar Brown and Wistar Lewis inbred strains of rat. The size of the Ag-NOR on each pair of chromosomes varied from strain to strain. Rat-human somatic hybrid cells that retained human and lost some of the rat chromosomes had no Ag-NOR on rat chromosomes 3, 11 or 12. Since NORs can be Ag-stained only if their 18 + 28S rRNA genes are active, the activity of the rat rRNA genes must have been suppressed in the hybrid cells.

Fixed metaphase chromosomes of gorilla and chimpanzee were UV-irradiated to produce regions of single-stranded DNA and then treated with antibodies specific for the minor DNA base 5-methylcytosine (5 MeC). An indirect immunofluorescence technique was used to visualize sites of antibody binding. In the gorilla six pairs of autosomes contained major fluorescent regions, indicating localized regions of highly methylated DNA. These corresponded, with the exception of chromosome 19, to the major regions of constitutive heterochromatin as seen by C-banding. The Y chromosome also contained a highly fluorescent region which was located just proximal to the intense Q-band region. In the chimpanzee no comparable concentrations of highly methylated DNA were seen. Smaller regions of intense 5 MeC binding were present on perhaps six chimpanzee chromosomes, including the Y. Five of these corresponded to chromosomes which were highly methylated in the gorilla.--There is diversity among the human, gorilla and chimpanzee in both the size and location of concentrations of 5 MeC, supporting the idea that satellite DNA evolves more rapidly than DNA in the remainder of the chromosome.

Cells from four different mouse-human somatic cell hybrids were stained with quinacrine to identify each metaphase chromosome and with ammoniacal silver by the Ag-AS method to locate nucleolus organizer regions. Each of the hybrids contained human acrocentric chromosomes. None of these human acrocentric chromosomes was stained with silver in any hybrid cell. Diploid cells were available from the human parent of one of the hybrids. In these cells both copies of nos. 13 and 15 stained with silver; the same chromosomes in the hybrid cell were not stained. These results support earlier reports that the expression of human ribosomal RNA (rRNA) genes is suppressed in mouse-human hybrid cells. Further, they suggest that silver staining by the Ag-AS method reflects activity of rRNA genes rather than just the presence of these genes.

A human fibrosarcoma line, HT1080–6TG, with a near diploid number of chromosomes, has an average of 7.3 chromosomes with an Ag-stained nucleolus organizer region (NOR). Cells of this line with an increased number of chromosomes have an increased number of Ag-stained NORs. This cell line has been used as the human parent in constructing mouse-human and rat-human hybrids that segregate rodent chromosomes. The hybrid cell lines, which have 100 or more chromosomes per cell, show a proportionate increase in the number of Ag-stained NORs (means, 11.4–16.8). The frequency of association of acrocentric chromosomes increases in a similar fashion. There is no evidence of inactivation of human NORs in these cells.

Chromosomes of the owl monkey, Aotus trivirgatus, with 2n=54, 53, or 52, have been stained to show quinacrine (Q-) and Giemsa (G-) bands, and a karyotypic arrangement has been proposed based on lengths, centrometric index, and banding pattern. C-bands were present at the centromeric region of every chromosome and over the entire short arm of certain acrocentric chromosomes; 5-methylcytosine was concentrated in the same regions. Bright Q-bands at the telomeric ends of the short arms of some chromosomes probably represent a second type of repetitive DNA. Ag-staining showed that only the chromosomes bearing a secondary constriction are nucleolus organizer chromosomes.

THE wood lemming, Myopus schisticolor Liljeborg, is distinguished by an aberrant sex ratio, with a considerable excess of females, and by the fact that some females produce only daughters1,2. Fredga and his associates3 have provided a basis for understanding both these characteristics. They observed that 82 out of 181 female wood lemmings studied (45%) had an XY sex chromosome constitution, with chromosomal G-banding and C-banding patterns indistinguishable from those of XY males. On the other hand, the XY females were anatomically normal and indistinguishable from XX females. Furthermore, meiotic studies3 showed that the germ line in the somatically XY females was XX. The second X chromosome in the germ cells must have arisen by non-disjunction from the single X present in the XY cells. Thus all progeny from such females must have received copies of the same X chromosome. How does one reconcile these observations with the apparent function of the Y chromosome in mammalian sex determination4, or with more recent evidence that a particular Y-linked gene which controls presence of H–Y antigen is critical for differentiation of the male gonad? We have approached these questions serologically by typing male and female wood lemmings for expression of H–Y antigen, and we have found that all female wood lemmings are H–Y−.

HUMAN–mouse cell hybrids usually exhibit preferential loss of human chromosomes1,2. After a time interval, which depends in part on the cell types used, most or sometimes all the human chromosomes segregate out from the hybrid cells3. In the course of investigation of the phenomenon of preferential loss of human chromosomes from hybrids between the mouse cell line RAG and human leukocytes, we isolated and analysed sixteen human–mouse (RH) hybrids. Seven of these hybrids had retained the human Y chromosome. Five of these had only one copy per cell of Y, one had two copies per cell and one, RH-28, had four copies of the Y in many cells. We decided to study more extensively this hybrid which seemed to have lost all the human chromosomes except number 17 and the Y.

Silver staining has been used to detect active nucleolus organizer regions (NOR's). By this criterion six mouse chromosomes, numbers 12, 15, 16, 17, 18 and 19, can have an NOR. The number and distribution of chromosomes with NOR's vary among inbred strains of Mus musculus musculus (C57BL/6J, BALB/cJ, C3H/HeJ and C3H/StCr1BR) and in M. musculus molossinus. In a musculus x molossinus F1 hybrid, nucleolus organizers from each parent are silver stained.—Chromosomes which have NOR's in diploid cells also show them in tetraploid cells and in established cell lines. The BALB/cJ strain shows Ag-staining of NOR's on chromosomes 12, 15, 18 and occasionally 16. In the RAG cell line, which was derived from BALB/c, active NOR's are seen on 12, 15 and 18, even after these chromosomes have undergone structural rearrangements in the cell line. Some correlation exists between the amount of Ag-stain and the size of a secondary construction region, with a large amount of Ag-stain present on a chromosome which has a prominent secondary constriction. There is no correlation between the amount of Ag-stain and the presence or absence of C-band material.

A deletion of the albsino (c) locus on mouse chromosome 7 has been demonstrated using Q- and G-banding methods in a mouse heterozygous for the radiation-induced lethal albino allele, c 25H . The deletion, which is thought to be 1-6 cM long, represents about 7.6% of the length of the metaphase chromosome.