We report on an infant with a previously undescribed chromosome 15 deletion (q26.1----qter) and compare the clinical findings with those of 7 reported patients with deletions of distal 15q, as well as ring chromosome 15 syndrome patients. Most of the patients with deletions of distal 15q, including our patient, have intrauterine growth retardation (IUGR), microcephaly, abnormal face and ears, micrognathia, highly arched palate, renal abnormalities, lung hypoplasia, failure to thrive, and developmental delay/mental retardation. Several genes have been assigned to the 15q25----qter region, including insulin-like growth factor 1 receptor (IGF1R). DNA analysis from our patient documented the loss of one IGF1R gene copy. Our study further localizes the IGF1R gene distal to the 15q26.1 band. It is interesting to speculate that the severe IUGR and postnatal growth deficiency of our patient and other patients with similar chromosome 15 deletions are related to the loss of an IGF1R gene copy which may lead to an abnormal number and/or structure of the receptors.

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28S ribosomal RNA (rRNA) (2-4), suggesting that the absence of the human rRNA may be related to the loss of human chromosomes. It is not due to the absence of the human acrocentric chromosomes, which carry the structural genes for rRNA (5, 6), because Marshall et al. (4) found no human 28S rRNA in a large series of mousehuman hybrids that contained 2 to 11 human acrocentrics.The chromosome regions that carry the rRNA genes have been identified as the nucleolus organizer regions (NORs) (7), and these regions can be stained preferentially by the Ag-AS silver staining method (8). In human diploid cell cultures the Ag-AS method stains the short arm regions of most of the acrocentric chromosomes (9, 10). The NORs of the same human acrocentric chromosomes are not stained in a mouse-human hybrid that has lost some human chromosomes (11). There is no evidence to suggest that rRNA genes are deleted from the human acrocentrics in hybrid cells. Therefore the absence.of Ag-AS stain suggests that this method detects only chromosome regions that functioned as nucleolus organizers in the preceding interphase, and, by implication, produced rRNA.Somatic cell hybrids between either mouse peritoneal macrophages or mouse cells obtained from a teratocarcinoma and HT-1080 human fibrosarcoma cells retain human chromosomes and lose mouse chromosomes (12). If preferential chromosome elimination is closely correlated with preferential suppression of nucleolus organizer activity, these hybrids should express only human nucleolus organizer activity. This appears to be the case. METHODS BALB/c mouse peritoneal macrophages were obtained according to a modification of the procedure described by Cohn and Benson (13) and were fused with HT-1080-6TG human fibrosarcoma cells deficient in hypoxanthine phosphoribosyltransferase (EC 2.4.2.8) (12) in the presence of f3-propiolactone-inactivated Sendai virus at pH 8.0 (14). The fused cultures were maintained in hypoxanthine-aminopterin-thymidine (HAT) selective medium (15). Large colonies of hybrid cells were visible 3-4 weeks after fusion. The colonies were picked and, subsequently, grown. OTT6050 mouse teratocarcinoma cells were obtained from a solid teratocarcinoma of a strain 129 mouse (16,17) by cutting in small fragments in trypsin/EDTA, resuspending in Eagle's minimal essential medium (MEM), and filtering through sterile gauze. The teratocarcinoma cells were fused with HT-1080-6TG cells in the presence of f.-propiolactone-inactivated Sendai virus. Hybrid colonies were selected in hypoxanthine-aminopterin-thymidine medium.Hybrid cells were maintained in Eagle's medium supplemented with 10% fetal calf serum. Mitotic cells were shaken from the culture flasks and transferred to a centrifuge tube containing 0.1 ml of colcemid (10 Ag/ml) for every 10 ml of medium and the tubes were centrifuged immediately at 800 rpm in an IEC clinical centrifuge for 7 min. The cell pellet was resuspended in 75 mM KCI. After 10 min the suspension was centrifuged and the cells were fixed for an hour in freshly prepa...

We report on 2 patients (3 1/2 year-old-male and 6-year-old female) with the ring 15 chromosome syndrome and speech delays and review 25 cases from the literature. The main characteristics of this syndrome include growth retardation (100%), variable mental retardation (95%), microcephaly (88%), hypertelorism (46%), and triangular facies (42%). Other frequent findings include delayed bone age (75%), brachydactyly (44%), speech delay (39%), frontal bossing (36%), anomalous ears (30%), café-au-lait spots (30%), cryptorchidism (30%), and cardiac abnormalities (30%). The average age at diagnosis was 8.1 years. The average maternal and paternal age at the time of birth was 28 and 31 years, respectively.

Nucleolus organizer regions were detected by the Ag-AS silver method in fixed metaphase chromosomes from human and primates. In the human, silver was deposited in the secondary constriction of a maximum of five pairs of acrocentric chromosomes: 13, 14, 15, 21 and 22. The chimpanzee also had five pairs of acrocentric chromosomes stained, corresponding to human numbers 13, 14, 18, 21 and 22. A gibbon had a single pair of chromosomes with a secondary constriction, which corresponded to the nucleolus organizer region. In each case the Ag-AS method detected the sites which have been shown by in situ hybridization to contain the ribosomal RNA genes. An orangutan had eight pairs of acrocentric chromosomes stained with Ag-AS, probably corresponding to human numbers 13, 14, 15, 18, 21 and 22, plus two others. Two gorillas had silver stain over two pairs of small acrocentric chromosomes and at the telomere of one chromosome 1. The larger gorilla acrocentric chromosomes had no silver stain although they all had secondary constrictions and entered into satellite associations.

Two unrelated children with a similar syndrome were found to have mosaicism for a cell line containing one chromosome 12 with an additional faintly G-banding staining region that apparently represents a duplication of the distal portion of the long arm. The homology and the other chromosomes are normal, as are the parental chromosomes. The remarkable phenotypic similarity of the 2 patients and their resemblance to 2 previously reported patients with duplication of the same chromosome region suggests that duplication 12q24 results in a clinically identifiable malformation syndrome.

Mouse-human hybrid cells were used to study the ability of simian virus 40 to regulate the expression of rRNA genes invivo. In these hybrid cells, only the rRNA genes of the dominant species are expressed; the genes for the rRNA of the recessive species are silent. Simian virus 40 infection of these hybrids led to the production of two distinct 28S rRNA species as analyzed by agarose/2.4% polyacrylamide gel electrophoresis. These species were identified as human and mouse rRNAs. This result was confirmed by histochemical studies which indicated that the nucleolus organizer regions of both mouse and human. chromosomes were actively synthesizing rRNA in the virus-infected hybrid cells. These results indicate that simian virus 40 infection can induce the expression of otherwise silent rRNA genes.Somatic cell hybrids between mouse and human cells tend to retain mouse chromosomes and -preferentially lose human chromosomes (1). At variance with these typical hybrid cells, certain hybrids between HT 1080 human fibrosarcoma cells and mouse cells derived directly from mouse tissues retain human chromosomes and lose mouse chromosomes (2). These hybrids have been studied for their capacity to express rRNA genes, in terms of production of 28S rRNA as well as-for the nucleolus organizer activity that can be visualized by the Ag-AS silver histochemical stain (3, 4). Rodent 28S rRNA migrates on polyacrylamide gels slightly faster than does human 28S rRNA (5), so that the two species can be easily distinguished. In those hybrids in which human chromosomes had preferentially been lost (mouse>human hybrids), only mouse 28S rRNA was detectable; in the mouse-human hybrids in which mouse chromosomes were preferentially lost (human>mouse), only human 28S rRNA was found (3). This occurred despite the fact that these hybrid cell lines contain the human and mouse chromosomes that are known to carry the rRNA genes. Similarly, by the Ag-AS stain, the nucleolus organizer regions (NORs) were found to be active only on mouse chromosomes in mouse> human hybrids and only in human chromosomes in those hybrids that preferentially had segregated mouse chromosomes (4). Studies by Perry et al. (6) on the expression of mouse and human 45S ribosomal precursor RNA have shown that these hybrid cells selectively suppress the transcription of the RNA genes of the recessive species. It is known that cellular RNA synthesis is stimulated after infection of mammalian cells by simian virus 40 (SV40) (7,8).Increased synthesis can also be demonstrated in isolated nuclei and nucleoli incubated in vitro with partially purified preparations of SV40 T antigen (9, 10). Both in vivo and in vitro, the species of RNA that seems to be stimulated is rRNA. Mousehuman hybrid cell lines should constitute a useful in vivo system for study of this cellular effect of SV40 because both active and inactive rRNA genes are present in the same cells. This communication presents evidence to indicate that infection with SV40 does, in fact, reactivate silent rRNA genes within...

A karyotype of the mitotic chromosomes of the house mouse has been prepared based upon quinacrine fluorescence patterns. All 19 pairs of autosomes and the X and Y chromosomes have been identified. Examination of the chromosomes of the following translocation stocks, T(11;?)lAld, T(3;?)6Ca, T(2;9)138Ca, T(2;12)163H, and T(9;13)19OCa, have led to the tentative assignments of autosomal linkage groups (LG) Meiotic studies of the house mouse, Mus musculus, have been very informative (1), but mitotic studies have been restricted by the limited variation in morphology of the chromosomes, all of which are acrocentric with small gradations in length. The only translocations that could be detected in stained preparations of mitotic chromosomes involved a marked change in length, such as the presence of a minute chromosome in the T6 (2) and one very long and one very short chromosome in the T190 (3), or the formation of a metacentric chromosome, as in the T163 (4). Bennett (3), who gives a brief review of prior cytologic studies, used the secondary constrictions in several chromosomes to help divide the complement into pairs. She was unable to detect any abnormality in T138.It was recently reported that quinacrine and quinacrine mustard are bound to the DNA of human chromosomes in such a highly specific manner that each chromosome can be identified by its pattern of quinacrine fluorescence (5). Furthermore, the fluorescence patterns of chromosomal segments do not appear to be altered by translocation (6).The accuracy of the quinacrine fluorescence technique of chromosome identification, and the availability of numerous potentially overlapping translocations in the house mouse, suggested to us the possibility of assigning the known murine linkage groups (LG) involved in these translocations to their specific chromosomes. MATERIALS AND METHODSStandard inbred and hybrid mice were purchased from The Jackson Laboratory, as were translocation stocks T(3;?)6Ca and T(2;9)138Ca. Translocation stocks T(2;12)163H,T(11;?)-lAld, and T(9;13)19OCa were obtained from the M.R.C. Primary tissue cultures were established from mice by trypsinization of 11-to 13-day embryos in saline-citrate to obtain suspensions of single cells (10). Cells were grown in HEPES-buffered Nutrient Mixture containing 10% calf serum and 5% fetal calf serum. Falcon tissue-culture flasks (75 cm2) were used and each flask was seeded with 10-12 ml of a suspension containing 5 X 105 viable cells/ml. After 2 or 3 days at 370C, cells (including a large proportion in metaphase) were collected by washing the cell surface twice with calcium-and magnesium-free phosphate-buffered saline, followed by a 5-min treatment of the surface with 3 ml per flask of 0.25% Viokase. Cells from 5-7 flasks were pooled, and Colcemid was added to a final concentration of 0.5 ,g/ml. Cells were immediately pelleted by centrifugation at 500 g for 10 min, resuspended in 10 ml of 0.032 M KCl, and incubated at 37°C for 5 min. 0.5 ml of freshly prepared fixative (methyl alcohol-glacial acet...