Several genes expressed in kidney and other tissues determine phosphate homeostasis in extracellular fluid. The major form of inherited hypophosphatemia in humans involves an X-linked locus (HPDR, Xp22.31-p21.3). It has two murine homologues (Hyp and Gy) which map to closely-linked but separate loci (crossover value 0·4%–0·8%). Both murine mutations impair Na+-phosphate cotransport in renal brush border membrane; an associated renal disorder of 1, 25-dihydroxyvitamin D3 (1, 25(OH)2D) metabolism has been characterized in Hyp mice. Whereas experiments with cultured Hyp renal epithelium indicate that the gene is expressed in kidney, studies showing the development of the mutant renal phenotype in normal mice parabiosed to Hyp mice implicate a circulating factor; these findings can be reconciled if the humoral factor is of renal origin. The gene dose effect of HPDR, Hyp and Gy on serum phosphorus values is consistently deviant and heterozygotes resemble affected hemizygotes. The deviant effect is also seen on renal phosphate transport; all mutant females (Hyp/Hyp and Hyp/+) have similar phenotypes. On the other hand, there is a normal gene dose effect of HPDR in mineralized tissue; tooth PRATIO (pulp area/tooth area) values for heterozygotes are distributed between those for affected males and normals. The tooth data imply that the X chromosome locus is expressed in both renal and non-renal cells. The polypeptide product of the X chromosome gene(s) is still unknown.

The locus for properdin (properdin factor complement, Pfc), a plasma glycoprotein, has been mapped to band A3 of the mouse X chromosome by in situ hybridization to metaphase spreads containing an X;2 Robertsonian translocation. The X-linkage of the locus has also been confirmed by analysis of Mus musculus x Mus spretus interspecific crosses. The XA3 localization for Pfc places it in the chromosomal segment conserved between man and mouse which is known to contain at least six other homologous loci (Cybb, Otc, Syn-1 Maoa, Araf, Timp).

Linkage data relative to the markers tabby and glucose-6-phosphate dehydrogenase are presented to locate X-linked cataract (Xcat) in the distal portion of the mouse X-chromosome between jimpy and hypophosphatemia. The human X-linked cataract-dental syndrome, Nance–Horan Syndrome, also maps closely to human hypophosphatemia and would suggest homology between mouse Xcat and human Nance-Horan Syndrome genes. In hemizygous males and homozygous females penetrance is complete with only slight variation in the degree of expression. Phenotypic expression in Xcat heterozygous females ranges from totally clear to totally opaque lenses. The phenotypic expression between the two lenses of a heterozygous individual could also vary between totally clear and totally opaque lenses. However, a correlation in the degree of expression between the eyes of an individual was observed. A variegated pattern of lens opacity was evident in female heterozygotes. Based on these observations, the site of gene action for the Xcat locus is suggested to be endogenous to the lens cells and the precursor cell population of the lens is concluded to be small. The identification of an X-linked cataract locus is an important contribution to the estimate of the number of mutable loci resulting in cataract, an estimate required so that dominant cataract mutagenesis results may be expressed on a per locus basis. The Xcat mutation may be a useful marker for a distal region of the mouse X-chromosome which is relatively sparsely marked and the X-linked cataract mutation may be employed in gene expression and lens development studies.

A gene, Hst-3, responsible for sterility in F1 males from crosses between Mus spretus and laboratory strains of mice such as C57BL/6, has been localized on the distal part of the X chromosome, using both DNA probes and biochemical markers on a panel of Fl(C57BL/6 × SEG) × C57BL/6 backcross males. This gene may be a model for studying mammalian hybrid sterility.

The mouse mutation hairy ears (Eh) originated in a neutron irradiation experiment at Oak Ridge National Laboratory. Subsequent linkage studies with Eh and other loci on Chr 15 suggested that it is associated with a chromosomal rearrangement that inhibits recombination since it shows tight linkage with several loci occupying the region extending from congenital goiter (cog) distal to caracul (ca). We report here (1) linkage experiments confirming this effect on recombination and (2) meiotic and mitotic cytological studies that confirm the presence of a chromosomal rearrangement. The data are consistent with the hypothesis of a paracentric inversion in the distal half of Chr 15. The effect of the inversion extends over a minimum of 30 cM, taking into account the genetic data and the cytologically determined chromosomal involvement extending to the region of the telomere.

We present data on the effects of three chromosome 17 deletions on transmission ratio distortion (TRD) and sterility of several t-haplotypes. All three deletions have similar effects on male TRD: that is, Tdel/tcomplete genotypes all transmit their t–haplotype in very high proportion. However, each deletion has different effects on sterility of heterozygous males, with Tor/t being fertile, Thp/t less fertile, and Torl/t still less fertile. These data suggest that wild-type genes on chromosomes homologous to f-haplotypes can be important regulators of both TRD and fertility in males, and that the wild-type genes concerned with TRD and fertility are at least to some extent different. The data also provide a rough map of the positions of these genes.

We previously identified a primary sex-determining locus, Tas, on mouse Chr 17 that causes ovarian tissue development in C57BL/6J Thp/ + and Torl/ + individuals if the AKR/J Y chromosome is present. We hypothesized that Tas is located within the region of Chr 17 deleted by Thp and Torl and that C57BL/6J carries a diagnostic Tas allele, based on the observation that ovarian tissue develops in XY mice when Thp is on a C57BL/6J inbred strain background, whereas normal testicular development occurs when Thp is on a C3H/HeSnJ inbred strain background. To test this hypothesis, we mated (C57BL/6J × C3H/HeSnJ)F1 females to C57BL/6J Thp/ + hermaphrodites. As expected, half of the XY Thp /+ offspring developed ovarian and testicular tissue while half developed exclusively testicular tissue. Unexpectedly, the inheritance of selected Chr 17 molecular loci was independent of gonadal development, as half of the male and hermaphroditic offspring inherited C3H/HeSnJ-derived Chr 17 loci and half inherited C57BL/6J-derived Chr 17 loci. We conclude that for ovarian tissue to develop in an XY Thp/ + or XY Tort/ + individual (1) Tas must be present in a hemizygous state, which is accomplished by heterozygosity for the Thp or Tort deletions; (2) the AKR/J-derived Y chromosome must be present; and (3) an additional locus involved in primary sex determination must be present in a homozygous C57BL/6J state. This newly identified gene may be one of the previously defined loci, tda-1 or tda-2.

Transmission ratio distortion (TRD) is a property of the complete t-haplotype which results in the preferential transmission of the t-haplotype chromosome from heterozygous t/+ males to the majority of the progeny. Available data suggest that in t/+ males, a dysfunction of the wild-type sperm within the female reproductive tract is responsible for the observed deviation from Mendelian segregation ratios. Genetically, Lyon has shown that multiple loci within the t-complex are required for maximum levels of TRD. These loci include multiple t-complex distorters (Teds) which act upon a single t-complex responder (Ter). Testis-expressed genes have been cloned which map to the same subregions of the t-complex as the Teds and Ter and are thus considered candidate genes for the products of these loci. To begin to understand how the products of these loci biochemically control TRD, the expression of three TRD-candidate genes (Tcp-1, D17Leh117c3, and D17Leh66) has been determined in populations of spermatocytes and differentiated spermatids purified to near homogeneity by unit gravity sedimentation. Fractions covering the entire gradient were analysed resulting in a more accurate picture of the precise timing of expression than previously reported. Transcription of all three genes was up-regulated in pachytene primary spermatocytes and persisted at stable levels through the haploid spermatid stages. Significantly, only levels of mRNA encoded by D17Leh66, the candidate gene for Tcr, increased from early round to elongating-stage spermatids. If this pattern of expression does, in fact, represent Tcr, these data provide the first direct evidence that wild-type and t-haplotype Tcr elements could be differentially expressed in haploid spermatids.

Mammalian genetics now allows a molecular study of genomic regions previously analysed by genetic and embryological techniques. To simplify such an analysis, we have established a number of libraries of mouse DNA in Yeast Artificial Chromosome (YAC) vectors, constructed either by partial digestion with EcoRI, or by complete digestion with enzymes which cut rarely in the mammalian genome. In this paper we report the construction of complete digest libraries prepared from mouse genomic DNA using the rare cutter enzymes NoiI and BssHII, and the detection of gene loci from the H-2 complex, the t–complex, and other loci from the mouse genome. Due to their large insert size, YAC clones simplify the cloning of extended regions of the mouse genome surrounding known developmental mutations and should, after introduction into the germ line, offer a high probability of correct expression of the genes contained within the cloned region. We hope that this will allow the use of YAC clones to scan regions of interest such as the t–complex for specific genes by testing DNA introduced into transgenic mice for the ability to complement mutations localised to this region.

Diploid mouse conceptuses lacking a paternal genome can form morphologically normal but small fetuses of up to 25 somites, but they invariably fail to develop beyond mid-gestation. Such conceptuses differ from normal most notably in the poor development of extra-embryonic tissues which are largely of trophectodermal and primitive endodermal origin. However, it is not clear whether the demise of diploid parthenogenetic (P) or gynogenetic (G) conceptuses is attributable entirely to the defective development of these two tissues or whether differentiation of the primitive ectoderm, the precursor of the foetus, extra-embryonic mesoderm and amnion, is also impaired by the absence of a paternal genome. Therefore, a new blastocyst reconstitution technique was used which enabled primitive ectoderm from P blastocysts to be combined with primitive endoderm and trophectoderm from fertilization-derived (F) blastocysts. One third of the ‘triple tissue’ reconstituted blastocysts that implanted yielded foetuses. However, all foetuses recovered on the llth or 12th day of gestation were small and, with one exception, either obviously retarded or arrested in development. The exception was a living 44 somite specimen which is the most advanced P foetus yet recorded. Foetuses were invariably degenerating in conceptuses recovered on the 13th day. In contrast, at least 16% of control reconstituted blastocysts with primitive ectoderm as well as primitive endoderm and trophectoderm of F origin developed normally on the 13th day of gestation or to term. Hence, the presence of a paternal genome seems to be essential for normal differentiation of all 3 primary tissues of the mouse blastocyst.

The P foetuses that developed from reconstituted blastocysts were so closely invested by their membranes that they often showed abnormal flexure of the posterior region of the body. Several also showed a deficiency of allantoic tissue. Therefore, the possibility that the defect in development of P primitive ectoderms resided in their extra-embryonic tissues was investigated by analysing a series of chimaeras produced by injecting them into intact F blastocysts. The foregoing anomalies were not discernible even when P cells made a large contribution to the extra-embryonic mesoderm or amnion plus umbilical cord. Furthermore, selection against P cells was no greater in extra-embryonic derivatives of the primitive ectoderm than in the foetus itself.

A null allele of the Gpi-1s structural gene, that encodes glucose phosphate isomerase (GPI-1; E.C. 5.3.1.9), arose in a mutation experiment and was designated Gpi-1sa-m1H. The viability of homozygotes has been investigated. No offspring homozygous for the null allele were produced by intercrossing two heterozygotes, so the homozygous condition was presumed to be embryonic lethal. Embryos were produced by crossing Gpi-1sa/null heterozygous females and Gpi-1sb/null heterozygous males. Homozygous null embryos were identified at different stages of development by electrophoresis and staining either for GPI-1 alone or GPI-1 plus phosphoglycerate kinase (PGK) activity. At 6½ and 7½ days post coitum homozygous null embryos were present at approximately the expected 25% frequency (37/165; 22·4% overall) although at 7½ days the homozygous null embryos tended to be small. By 8½ days most homozygous null embryos were developmentally retarded and had not developed significantly further than at 7½ days; some were dead or dying. By 9½ days the homozygous null conceptus was characterised by a small implantation site that contained trophoblast and often a small amount of extraembryonic membrane. Surviving trophoblast tissue was also detectable at 10½ days. Previous studies have shown that oocyte-coded GPI-1 persists only until 5½ or 6½ days. Survival of homozygous null embryos to 7½ or 8½ days and survival of certain extraembryonic tissue to 10½ days suggests that the homozygous null condition may not be cell-lethal although it is certainly embryo-lethal. Mutant cells that are deficient in glycolysis may use the pentose phosphate shunt to bypass the block in glycolysis created by the deficiency of glucose phosphate isomerase, and/or might be rescued by the transport, from the maternal blood, of energy sources other than glucose (such as glutamine). Either strategy may only permit slow cell growth that would not be adequate to support normal embryogenesis. Transport of maternal nutrients would be more efficient to the trophoblast and extraembryonic membranes and this may help to explain why these tissues survive for longer than the embryo itself. The morphological similarity between homozygous nulls and androgenetic conceptuses, where the trophoblast also survives better than the embryo, is discussed.

Heterozygotes for the reciprocal translocation T(7;15)9H were intercrossed, with albino (c) and underwhite (uw) as genetic markers, in order to study genetic complementation in mouse chromosome 7. Chromosome 15 is known to show normal complementation. Neither reciprocal cross in which one parent was c/c and the other wild type yielded albino progeny at birth although about 17% would be expected, but albino foetuses were recovered when the mother was c/c and father wild type. These products of maternal duplication/paternal deficiency for distal 7 were markedly retarded with small placentae. No albino foetuses were found when the father was c/c and mother wild type, which suggested earlier lethality. Equivalent crosses with uw (chromosome 15) as proximal marker gave normal underwhite progeny when the mother was uw/uw but small placentae, retardation and neonatal death of presumptive underwhites in the reciprocal cross. These abnormal newborn would have had a maternal duplication/paternal deficiency for proximal 7. These and other findings indicate that one region of defective complementation probably lies distal to the breakpoint of T(7;18)50H at 7E2-F2, while another is between the centromere and 7B3. Examination of man-mouse homologies suggests that the loci for three pathological human conditions (Beckwith-Weidemann syndrome, dystrophia myotonia and rhabdomyosarcoma) with differential parental transmission may be located in homologous regions to those affected by imprinting phenomena on mouse chromosome 7.

Glucose-6-phosphate dehydrogenase (G6PD) activity was measured in blood from heterozygotes for the normal allele G6pda and the low activity allele G6pda-m l Neu. In adult mice lower activity was found in G6pda/G6pda-m l Neu than in the reciprocal heterozygote G6pda-m l Neu/G6pda (the maternal allele being listed first). Thus, either the paternally derived allele was over-expressed or the maternally derived allele was under-expressed. By contrast, in younger mice the difference in G6PD activity in reciprocal crosses was less marked. The findings are interpreted in terms of differential imprinting of maternally and paternally inherited information. The explanation offered for age related differences is that, as a consequence of imprinting, either the paternal X-chromosome is preferentially reactivated, or cells in which the paternally derived allele is active are at a selective advantage, and proliferate better than those in which the maternally inherited allele is active.

Mouse embryo banking has become an important asset to geneticists. Individual laboratories can now maintain a far greater diversity of stocks than by conventional breeding alone. Also, many mutations that in the past would have been discarded due to lack of space, can now be preserved for future use. Recent advances in cryopreservation techniques have simplified procedures and, in certain cases, resulted in increased rates of survival.

A didelphid marsupial, the gray short-tailed opossum (Monodelphis domestica), was used as a model species to study the biochemical genetics of alcohol dehydrogenases (ADHs) and aldehyde dehydrogenase (ALDH) in corneal tissue. Isoelectric point variants of corneal ALDH (designated ALDH3) and a major soluble protein in corneal extracts were observed among eight families of animals used in studying the genetics of these proteins. Both phenotypes exhibited identical patterns following PAGE-IEF and were inherited in a normal Mendelian fashion, with two alleles at a single locus (ALDH3) showing codominant expression. The data provided evidence for genetic identity of corneal ALDH with this major soluble protein, and supported biochemical evidence, recently reported for purified bovine corneal ALDH, that this enzyme constitutes a major portion of soluble corneal protein (Abedinia et al. 1990). Isoelectric point variants for corneal ADH were also observed, with patterns for the two major forms (ADH3 and ADH4) and one minor form (ADH5) being consistent with the presence of two ADH subunits (designated γ and δ), and variant phenotypes existing for the γ subunit. The genetics of this enzyme was studied in the eight families, and the results were consistent with codominant expression of two alleles at a single locus (designated ADH3). It is relevant that a major detoxification function has been proposed for corneal ADH and ALDH, in the oxidoreduction of peroxidic aldehydes induced by available oxygen and UV-B light (Holmes & VandeBerg, 1986a). In addition, a direct role for corneal ALDH as a UV-B photoreceptor in this anterior eye tissue has also been proposed (Abedinia et al. 1990).

Peripheral blood lymphocytes from normal human volunteers or from Down syndrome patients were pre-treated with sodium butyrate (a compound which is known to induce structural modifications in the chromatin through hyperacetylation of nucleosomal core histones) and exposed to X-irradiation or treated with bleomycin in vitro in the G0 and/or G1 stage(s) of the cell cycle. The frequencies of chromosomal aberrations in the first mitosis after treatment were scored.

The results show an enhancement in the yield of aberrations in the butyrate pre-treated groups. However, the absolute frequencies of chromosomal aberrations as well as the relative increases with butyrate pre-treatment varied between blood samples from different donors suggesting the existence of inter-individual variations. There is a parallelism between the effects of X-irradiation or of combined treatments in G0 and G1 stages and between effects observed in the X-ray and bleomycin series. The increase in the yields of chromosomal aberrations in butyrate-treated and X-irradiated lymphocytes (relative to those which received X-irradiation alone) is interpreted as a consequence of the inhibition of repair of DNA damage by butyrate.