Linkage of the murine steroid sulfatase locus, Sts, to sex reversed, Sxr: a genetic and molecular analysis

We present genetic and molecular data demonstrating linkage of the gene for steroid sulfatase (Sts) to the mutation sex reversed (Sxr) definitively showing the existance of a functional allele for Sts mapping to the pseudoautosomal region of the mouse Y chromosome. Thus, in mouse, functional Sts genes are present in the pseudoautosomal region of both the X and Y chromosomes. This is in contrast to man where Sts has been mapped to the short arm of the X just centromeric to the pseudoautosomal region. Only a single recombinant separating Sts and Sxr was found out of 103 male meioses analyzed; double recombinants were not found between sex (Tdy), Sts and Sxr. If the rate of recombination in the pseudoautosomal region in male mice is equivalent to that in man and thus 7-10X higher than normal, then our data suggest that the distance between Sts and Sxr (or the telomere of the Y) is approximately 100-200 kb in length. Our data is in contrast to a recent report of a recombination frequency separating Sts and Sxr of as high as 6.2-9.8%.

The use of specific DNA probes to analyse the Sxr mutation in the mouse

The mouse Y chromosome plays a fundamental role in the control of primary sex determination and fertility. Both genetic and molecular biological evidence has shown that much of the necessary information is contained in a minute piece of the Y (the Sxr region) which has arisen by a duplication of the pericentric region of the normal Y and the transposition of one copy to the distal pseudoautosomal region. The present article describes the isolation of random Y-chromosome probes and their use to investigate this Sxr region at the molecular level. Total mouse Y-chromosome libraries were constructed from flowsorted material and a Sxr regional library after specific microdissection and cloning. Transcription has been detected in the testis using both Sxr-specific and non Sxr-located genomic probes taken from these libraries. In addition, we have been able to confirm the presence of an active steroid sulphatase gene on the mouse Y. This gene is located in the distal portion of the pseudoautosomal region and is tightly linked to Sxr. Finally, using an Sxr-specific probe we can define multiple Y-chromosome haplotypes in the mouse showing that the region is evolving very rapidly.

Chromosomal localization of muscle nicotinic acetylcholine receptor genes in the mouse

The chromosomal localization of the genes encoding the four subunits of muscle nicotinic receptor was determined by analyzing restriction fragment length polymorphisms between two mouse species Mus musculus domesticus (DBA/2) and Mus spretus (SPE). Analysis of the progeny of the interspecies mouse backcross (DBA/2 X SPE) X DBA/2 showed that the alpha-subunit gene cosegregates with the alpha-cardiac actin gene on chromosome 17, that the beta-subunit gene is located on chromosome 11, and that the gamma- and delta-subunit genes cosegregate and are located on chromosome 1.

Murine primary in vivo response to TNP-Ficoll: multigenic control involving H-2

Since the primary PFC response to TNP-Ficoll, a thymus-independent type 2 antigen, displays an important variability in vivo among diverse inbred mouse strains, we used, in the present report, H-2 congenic strains possessing different genetic backgrounds to show that the amplitude of this response is governed by MHC genes, with one regulating locus situated in or near the centromeric part of the I-A subregion. In addition, this H-2 control was largely modulated by gene(s) located outside MHC and IgH haplotypes, as evidenced by the response of recombinant inbred strains (BXH) between the high responder C3H/HeJ and the low responder C57BL/6J. Our results are discussed in terms of humoral regulations and the requirement for self-recognition in cellular interactions which lead to activation of B lymphocytes in the in vivo primary response towards TI-2 antigens.

Mta, the maternally transmitted antigen, is determined jointly by the chromosomal Hmt and the extrachromosomal Mtf genes

Mus spretus from four stocks, originating in Spain, Portugal, and Morocco, were tested for the maternally transmitted antigen, Mta. All expressed a variant form not found in other species of mice. Analysis of appropriate crosses with inbred mice showed that the spretus form of Mta is determined by a new allele, c, of the Hmt gene. The Hmtc allele has been isolated in coupling with four different H-2 haplotypes. It is possible to raise CTL specific for the spretus form of Mta. The maternally transmitted factor, Mtf alpha s, of spretus mice determines, in conjunction with the Hmta allele of C57BL/6, an Mta that is indistinguishable from the common form found in C57BL/6 and most other inbred mice. Our experiments show that the specificity of the cell surface antigen Mta is governed jointly by the cytoplasmic gene Mtf and the chromosomal gene Hmt. We propose that Hmt encodes a class I histocompatibility antigen that acts as a restricting element for the Mtf gene product, thus meeting the requirements of T killer cell recognition.

The differentiation of repeated epilation (Er/Er) mouse mutant skin in organ culture and in grafts

The homozygous repeated epilation (Er/Er) mouse mutant dies at birth and shows a variety of malformations, one of which is a skin defect. The developmental abilities of skin fragments from these Er/Er mouse embryos were studied in organ culture and in grafts performed either under the renal capsule of young mouse hosts or under the skin of mouse fetuses. In organ culture, the skin fragments differentiated in accordance with their genetic origin. The most characteristic feature was the abnormally thickened spinous layer and the formation of numerous epidermal nodules in Er/Er skin pieces removed from 13- to 16-day-old embryos, and cultured for 4 to 6 days, whereas the normal skin showed a constant layered organization. As in normal skin, keratin fibers developed within 4 to 6 days of culture. However, in contrast to normal skin, where keratin sheaths developed all over the surface of the epidermis, the Er/Er skin exhibited keratin masses inside the nodules. Combinations of mutant Er/Er epidermis with normal dermis resulted in abnormal skin differentiation, with formation of nodules similar to those observed for unseparated Er/Er skin fragments, whereas the reciprocal combination (normal epidermis with Er/Er dermis) produced normal skin differentiation. Cornified layers developed in both types of explants. Grafts of Er/Er and, for comparison, of normal skin fragments under the renal capsule or under a fetus's skin showed that the development of Er/Er skin in a normal or Er/+ host was similar to that of a normal skin. Thus, if isolated from the mutant organism, and inserted into a normal environment, the skin recovered within 6 to 7 days after transplantation and then developed normally. Our experiments suggest that the abnormal skin development of the Er/Er mutant might be caused by environmental influences.

Genes for skeletal muscle myosin heavy chains are clustered and are not located on the same mouse chromosome as a cardiac myosin heavy chain gene

Myosin heavy chain (MHC) genes are expressed as several distinct isoforms in a tissue- and stage-specific manner; three skeletal muscle MHC isoforms appear sequentially during development. We have isolated cDNA clones, identified by RNA blot hybridization and by nucleotide sequence determination as coding for portions of the embryonic (pMHC2.2), perinatal (pMHC16.2A), and alpha(V1) cardiac (pMHC141 and pMHC101) MHC isoforms. These four probes and the adult skeletal MHC probe (pMHC32) have been used on Southern blots of genomic DNA to detect restriction fragment length polymorphisms defining the alleles for these genes in mouse species Mus musculus and Mus spretus. In this way, we followed the segregation of skeletal and cardiac MHC genes in 42 offspring resulting from an interspecies backcross. We found that the embryonic, perinatal, and adult skeletal MHC genes are clustered on chromosome 11 near the locus nude, the skeletal and cardiac MHC genes do not cosegregate, and the alpha(V1) cardiac MHC gene is located on chromosome 14 close to Np-1. This result is in contrast to that for other contractile protein genes such as the alkali myosin light chain and the actin multigene families, which are dispersed in the genome.

The myosin alkali light chains of mouse ventricular and slow skeletal muscle are indistinguishable and are encoded by the same gene

We have isolated a cDNA recombinant plasmid (pA29) identified as encoding part of the ventricular muscle myosin light chain MLC1v. This cDNA contains a 300-base pair fragment which under conditions of moderate stringency shows specific hybridization to MLC1v mRNA with no detectable cross-hybridization with the mRNAs encoding the fast skeletal muscle isoforms MLC1F and MLC3F, or the atrial muscle isoform MLC1A. Under these conditions hybridization is seen with an abundant mRNA present in slow skeletal muscle (soleus) which is indistinguishable from ventricular MLC1V mRNA on the basis of size and of thermal stability of hybrids formed with plasmid pA29. The mouse MLC1V and MLC1S proteins are found to co-migrate on two-dimensional gels. We therefore conclude that these isoforms are the same and are encoded by the same mRNA. Analysis of mouse DNA has identified a single region of the genome which hybridizes to this same fragment of pA29. This region has been isolated in a recombinant phage and has been shown to contain a single gene showing homology with MLC1V mRNA by R-loop analysis. We therefore conclude that MLC1V and MLC1S are encoded by a single gene. The pattern of segregation of a restriction fragment length polymorphism identified for this gene between Mus musculus and Mus spretus has been followed in an F1 backcross between these two mouse species. The results show the MLC1V/MLC1S gene to be closely linked to a marker at the distal end of mouse chromosome 9.

Investigation of genetic linkage between myosin and actin genes using an interspecific mouse back-cross

The introduction of cloned probes to follow the segregation of DNA restriction fragment length polymorphisms (RFLPs) has led to a revival of mendelian genetics in attempts to map the human genome. In the mouse, however, it has often proved difficult to detect an RFLP with a DNA probe between different inbred strains of the laboratory mouse. To circumvent this problem, we have used two species, Mus musculus domesticus and Mus spretus which interact as sympatric species but can be interbred under laboratory conditions. Because of the relative evolutionary distance between these species, they exhibit polymorphism at many more loci than do different strains of the usual M. m. domesticus laboratory mouse. This is also observed at the DNA level when the sizes of restriction fragments encoding a specific gene are compared. We have used these RFLPs between M. m. domesticus and M. spretus to follow the segregation of genes encoding different isoforms of myosin alkali light chains in the backcross progeny between these species and to compare this with that of other contractile protein genes. No linkage between these genes was observed.

Rheumatoid factors in 129XB recombinant inbred strains. Igh-1-linked control of allotypic and isotypic specificities

To examine the role of autologous IgG in the induction of murine rheumatoid factors (RF) we have analyzed the allotypic specificity of anti-IgG2a RF in recombinant inbred strains derived from 129/Sv (Igh-1a) and C57BL/6 (Igh-1b) mice. In five of six Igh-1a strains, anti-IgG2a RF reacted with IgG2aa but failed to react with IgG2ab. In contrast, isotype-specific RF, which reacted equally well with a and b allotypes of IgG2a, represented the major RF species in one Igh-1a and all five Igh-1b strains tested. An additional form of RF specific for IgG2ab and not reactive with IgG2aa was detected in one Igh-1b strain. RF specific for a give allotype was thus only found in the presence of that allotype, which strongly suggests the involvement of autologous IgG in the induction of mouse RF synthesis. The specificity of RF was apparently further controlled by genes linked to but different from the Igh-C locus, as indicated by the absence of IgG2aa-specific RF in one of the 6 Igh-1a strains tested. Because this strain, 129XBG, has been shown to express idiotypic markers characteristic of Igh-1b mice, it is likely that the genes, which in the presence of a given allotype induce the production of isotype rather than allotype-specific RF, are identical to those that control the expression of idiotypes. Evidence was also obtained to indicate that Igh-1-linked genes influence the isotypic specificity and the isotype of RF itself: IgA anti-IgG2a predominated in Igh-1a strains and IgM anti-IgG1 in Igh-1b strains. Interestingly enough, total IgA and IgG2a levels also were higher in Igh-1a than in Igh-1b strains.

Recombination between two mouse t-haplotypes (tw12tf and tLub-1): segregation of lethal factors relative to centromere and tufted (tf) locus

Recombination between two mouset–haplotypes,tw12tfandtLub-1, was investigated by screening the tailless progeny of the cross ♀tw12tf/tLub-1+ × ♂Ttf/+tffor the segregation of tufted phenotype,tw12andtLub-1lethal factors, and metacentric chromosome (sincetLub-lhaplotype is associated with a Robertsonian fusion involving chromosomes 4 and 17). The results give a 17% estimate of the recombination frequency between centromere andtf, withtLub-llethal factor mapping about two-thirds of the distance from centromere totfand thetw12lethal factor behaving as if closely linked totf. This further extends the findings of Silver & Artzt (1981) and of Artzt, McCormick & Bennett (1982), and shows that twot–haplotypes with quite independent laboratory histories recombine at a normal level, supporting the notion that allt–haplotypes basically share the same structure.

Number and organization of actin-related sequences in the mouse genome

Recombinant plasmids containing cDNA sequences complementary to the two mouse striated-muscle actin messenger RNAs (pAF81, pAM91) and to a non-muscle actin mRNA (pAL41) have been used to examine the number and organization of actin-related sequences in the mouse genome. A large number (greater than 20) of actin-related sequences are detected on Southern blots of restricted mouse DNA, the majority of which hybridize to both the 5' and 3' ends of the actin-coding sequence, even under conditions revealing only sequences greater than 80% homologous to the actin cDNA probes. More stringent washing of these blots indicates that the two striated muscle actins are each encoded by single genes, and that a non-muscle (beta or gamma) actin cDNA detects one homologous and two closely related sequences in mouse DNA. The segregation of the two striated-muscle actin genes in recombinant inbred mouse strains shows that these genes are not closely linked (greater than 1 centimorgan), and that the skeletal muscle actin gene is not linked to a non-muscle actin gene. Screening a bank of mouse genomic DNA, cloned in Charon 4A, indicates that the number of actin-related sequences in the mouse genome is much higher than 20. In particular, five phages have been isolated representing part of a sub-family of 20 to 50 similar but non-identical sequences, only weakly homologous to actin cDNA probes (probably a family of actin pseudogenes), which are the result of a recent amplification of a greater than 17 X 10(3) base region of mouse DNA.

Altered circulation of lymphocytes mediating delayed-type hypersensitivity when primed in Wf/Wf mice

When mice were homozygous for the Wf allele at W locus, the delayed-type hypersensitivity (DTH) reaction observed in mice primed i.v. or s.c. with optimal doses of sheep red blood cells was greatly decreased. The number of sensitized splenic cells able to transfer a delayed-type hypersensitivity reaction was identical in +/+ and Wf/Wf primed mice. At site of local transfer of +/+ sensitized cells and antigen, the recruitment of monocytes was identical in +/+ and Wf/Wf mice. In contrast, the number of blood cells able to transfer a DTH reaction was decreased by a factor 40 in Wf/Wf primed mice compared to +/+ ones. This decreased number of sensitized cells in blood of Wf/Wf mice revealed a specific defective circulation of Wf/Wf DTH mediating cells whatever the genotypes (+/+ or Wf/Wf) of recipients used to measure this property of circulation.