Expression of mouse and human fibronectin in mouse-human somatic cell hybrids

Using antisera to the human and mouse fibronectin (Large External Transformation Sensitive (LETS) protein), we studied the expression of mouse and human fibronectin in mouse-human somatic cell hybrids segregating either human or mouse chromosomes. The results of this study show that, in such somatic cell hybrids, mouse and human fibronectin are coexpressed. In addition, activation of the synthesis of mouse fibronectin was observed in somatic cell hybrids between mouse peritoneal macrophages, which do not produce detectable amounts of fibronectin, and either SV40-transformed human cells or cells derived from a human fibrosarcoma.     

Suppression of replication of SV40 and polyoma virus in mouse-human hybrids.

Mouse-human heterokaryons are permissive for the replication of both SV40 virus and polyoma virus. If the hybrids which develop from these heterokaryons segregate human chromosomes (mouse greater than human hybrids), the hybrids are permissive for replication of polyoma virus but not for replication of SV40 virus. If the subsequent hybrids segregate mouse chromosomes (human greater than mouse hybrids), such hybrids support the replication of SV40 virus but not the replication of polyoma virus, even when the hybrids contain at least one copy of each mouse chromosome. This indicates that during the transition from heterokaryon to hybrid cell, suppression of expression of species-specific function(s) required for the replication of these species-specific viruses occurs in parallel with the direction of chromosome loss and suppression of nucleolus organizer activity.     

Gene mapping in the rat by mouse-rat somatic cell hybridization: synteny of the albumin and alpha-fetoprotein genes and assignment to chromosome 14

The methods of somatic cell genetics and molecular hybridization were applied to a panel of mouse X rat hepatocyte hybrids segregating rat chromosomes to assign the rat genes coding for two serum proteins, albumin and alpha-fetoprotein (Alb and Afp). The molecular hybridization of DNAs from different hybrids with cloned DNA probes showed that all the hybrid clones possessing the rat Alb gene and expressing it also retained the rat Afp locus, which is not expressed in these hybrids. So the Alb and Afp genes are syntenic in the rat, as in the mouse. Furthermore, the cytogenetic analysis allowed the assignment of these two loci to rat chromosome 14.     

Conserved autosomal syntenic group on mouse (MMU) chromosome 15 and human (HSA) chromosome 22: assignment of a gene for arylsulfatase A to MMU 15 and regional mapping of DIA1, ARSA, and ACO2 on HSA 22

We have utilized a panel of Chinese hamster x mouse somatic cell hybrids segregating mouse chromosomes to assign a gene for arylsulfatase A (ARSA) to mouse chromosome 15. Considering our previous assignment of a gene for diaphorase-1 (DIA1) to the same mouse chromosome, we have evidence for another syntenic relationship that has been conserved, since the homologous loci for human ARSA and DIA1 are both located on human chromosome 22. Because MMU 15 and HSA 22 are quite dissimilar in size and banding patterns, we have attempted to identify the conserved portion by regional mapping of human DIA1 and ARSA using somatic cell hybrids segregating a human chromosome translocation t(15;22)(q14;q13.31). The results assign human DIA1 and ARSA to the distal sub-band of 22q13 (region 22q13.31 leads to qter). The locus for mitochondrial aconitase (ACO2) has been separated by the breakpoint from DIA1 and ARSA and is located more proximally.     

Chinese hamster X mouse hybrid cells segregating mouse chromosomes and isozymes.

Hybrid cells are readily formed by fusing clonal Chinese hamster cells to fresh, noncultured, adult mouse spleen cells followed by isolation in selective medium. The vast majority of such hybrids retain Chinese hamster chromosomes and isozymes while segregating mouse chromosomes and isozymes. The growth, plating efficiency, ease of karyology, and rapid segregation of mouse markers allows linkage tests in primary clones. Analysis of 13 isozymes showed 12 to be asyntenic and on epair (PGD-PGM2) to be syntenic This system will allow extensive somatic cell hybrid gene mapping in the mouse and permit a comparison of human and mouse linkage relationships.     

Histone gene expression and chromatin structure in mammalian cell hybrids

DNA isolated from mammalian cell nuclear reveals discrete size patterns when partially digested with micrococcal nuclease. The DNA repeat lengths from different tissues within a species or from different species may vary. These differences have been attributed to the presence of different species of histone H1. To examine the nature of regulation of DNA repeat lengths and their possible relationship to histone H1, we have selected several mouse and human cell lines that differ in their DNA repeat lengths and examined them and their cell hybrids. 24 mouse X human and five mouse X mouse hybrid cell lines were analyzed. All the interspecific hybrids exhibited the repeat pattern characteristic of the murine parent. The mouse intraspecific hybrids had a repeat pattern of only one of the parents. We conclude that the partial human chromosome complements retained in the hybrids assume the repeat lengths exhibited by the mouse cells. Because H1 histones have been implicated in the determination of DNA repeat lengths, we also investigated the regulation of H1 histone expression in these cell hybrids. Purified H1 histones were radioactively labeled in vitro, and individual subfractions were subjected to proteolysis followed by gel electrophoresis. The resulting partial peptide maps off H1 histone subfractions A and B were distinguishable from one another and from different cell lines. In the mouse X human hybrids analyzed, only the mouse H1 histones were detected. These observations were extended to H2b by analysis of the hybrid cell histone by Triton-acid-urea gels. Neither the DNA repeat length nor histone expression is affected by the presence of any specific human chromosome. The fact that human genes are expressed in these hybrids suggests that the H1 histones of one species is able to interact with the chromatin of another species in a biologically funtional conformation. Analysis of the intraspecific PG19 X B82 (mouse X mouse) hybrids reveals the presence of H1 histone subfractions of the B82 mouse cells. Because these hybrids exhibit the nucleosome repeat length only of the PG19 cells, it appears that if histone H1 plays a role in determining the repeat length it does so in consort with other nonhistone chromosomal proteins.     

Human salivary proline-rich protein genes on chromosome 12.

A DNA probe (PRP1) for the proline-rich protein (PRP) genes was used to analyze the segregation of human PRP genes in human X mouse somatic cell hybrids. Endonuclease restriction analysis of 22 independent hybrid clones segregating human chromosomes demonstrated that PRP genes segregate with human chromosome 12 only and were therefore assigned to that chromosome. The PRP1 probe should prove useful for further mapping studies of human chromosome 12.     

The use of cell surface antigens to characterize and select for fragments of human chromosomes retained by interspecies hybrids

We have used a mouse cell transformant generated by human chromosome-mediated gene transfer (CMGT) to explore the use of cell surface antigens in the identification of fragments of human chromosomes retained by somatic cell hybrids. The transformed line, 21-30b, contained an intact rear-ranged human chromosome, and could be shown by isozyme analysis to contain genetic material from chromosomes 9 and X. By using the transformant as an immunogen in mice, it was also possible to produce antiserum to human-specific surface antigens. Using genetically characterized human X rodent hybrid lines, the genes controlling expression of these antigens could be localized to 11per----11p13, segregating concordantly with surface antigen S3. These conclusions were possible despite the fact that the presence of chromosome 11 in the transformant was not detectable by the presence of chromosome specific isozyme LDH-A or surface antigens W6/34 and 4F2. Finally, the fluorescence-activated cell sorter (FACS) was used to fractionate the transformant cells into antigen positive and negative subpopulations. This resulted in the isolation and characterization of four additional chromosome rearrangements involving interspecies chromosome translocations. This work demonstrates the value of chromosome-specific surface antigens and the FACS in the evaluation of human chromosome fragments retained by interspecies hybrids.     

Translation is required for regulation of histone mRNA degradation

When DNA synthesis is inhibited, the mRNAs coding for the replication-dependent histone proteins are selectively destabilized. The histone genes have been altered and reintroduced into tk- mouse L cells by cotransfection with the herpesvirus thymidine kinase gene. Two features of the mRNA are necessary for regulation of degradation: first, the hairpin loop must be present at the 3' end of the histone mRNA; and second, the histone mRNA must be capable of being translated to within 300 nucleotides of the 3' end of the RNA. Polyadenylated histone mRNAs are stable, as are histone mRNAs that contain in-frame termination codons early in the coding region or 500 nucleotide 3' untranslated regions with a normal hairpin loop at the 3' end.     

Amino acid accumulation in mouse-human parental hybrid cells

Cell membrane function during hybridization was assessed by examining the accumulation of four representative amino acids and a sugar in mouse-human hybrid cells, parental mouse cells and human cells. Qualitatively, accumulation in the hybrids was found to resemble the accumulation in parental mouse more than the human cells. In particular, the steady-state uptake of leucine and glycine in hybrids was similar to that in parental mouse cells and different than that observed in the human cells. The findings suggest that hybrids retain transport properties of mouse rather than human cells. These results are in keeping with our previous observation that the human mouse hybrids conserve most of the mouse chromosomes and the membrane proteins of the hybrids are very likely of mouse parental origin.