Distribution of androgen receptor immunoreactivity in the spinal cord of wild-type,androgen-insensitive and gonadectomized male rats

The polyclonal antiserum PG21 was used to detect androgen receptor (AR) protein in three motoneuronal pools of the male rat lumbar spinal cord. In gonadally intact, wild-type males, the spinal nucleus of the bulbocavernosus (SNB), dorsolateral nucleus (DLN), and retrodorsolateral nucleus (RDLN) all displayed immunolabeling of cell nuclei. The percentage of motoneurons displaying such labeling was highest in the SNB and lowest in the RDLN. This pattern of AR immunocytochemical labeling agrees well with previous steroid autoradiographic studies of androgen accumulation in the rat spinal cord. In contrast, virtually no motoneurons in any of the three pools displayed nuclear AR immunostaining in long-term gonadectomized males or in gonadally intact males carrying the Tfm mutation, which renders the AR incompetent. In gonadectomized males, labeling was restored in the SNB and DLN, but not the RDLN, 30 min after an injection of replacement testosterone. Eight hours of testosterone exposure restored immunolabeling in all three motor nuclei. Apparent cytoplasmic staining was seen in SNB motoneurons of untreated castrates and Tfm rats, but not intact rats, suggesting that AR residing in the cytoplasm translocates to the nucleus on binding to androgen in these motoneurons. © 1995 John Wiley & Sons, Inc.     

Ciliary neurotrophic factor arrests muscle and motoneuron degeneration in androgen-insensitive rats

Steroid hormones and neurotrophic factors exert profound and widespread effects on the developing nervous system, including regulation of the size, connectivity, and survival of neurons. Androgenic control of the survival of motoneurons in the spinal nucleus of the bulbocavernosus (SNB) of rats has been well documented. We previously found that ciliary neurotrophic factor (CNTF) mimics many effects of androgen on the developing SNB. Whether effects of CNTF depend on the presence of a functional androgen receptor was evaluated in the present study. Androgen-insensitive male rats bearing the testicular feminization mutation, Tfm, and female littermates were treated with CNTF or with vehicle alone from embryonic day 22 through postnatal day 3. On postnatal day 4 SNB cell number was elevated in both groups receiving CNTF. Volumes of the bulbocavernosus (BC) and levator ani (LA) muscles, targets of SNB motoneurons, were also markedly increased by CNTF. Since the BC appears to degenerate completely in untreated females, these results indicate that CNTF can delay or prevent muscle fiber death. The relative sparing of muscles and motoneurons did not differ for Tfm males and females, demonstrating that effects of CNTF on the SNB neuromuscular system do not require functional androgen receptors. © 1995 John Wiley & Sons, Inc.     

β-Glucuronidase activity is present in the microscopic epididymis of the Tfm/Y mouse

The sex-linked recessive gene Tfm in the mouse produces a condition of testicular feminization (androgen insensitivity syndrome, AIS) in hemizygotes, comparable to the condition of the same name in humans. The murine mutant was originally believed to have no derivatives of the mesonephric duct system (MDS), and this absence was ascribed to dependence of these derivatives on androgens for survival. However, microscopical epi-didymides, retia testes, and vasa deferentia were identified in these animals in our laboratory. These micro-organs may play a role in meiosis induction in Tfm/Y animals. The present study was designed to determine whether survival of these organs is due to retention of an ability to respond to androgens, or whether they are unique amongst MDS derivatives in being independent of androgens. Previous studies in our laboratory demonstrated that the enzyme β-glucuronidase (βG) is androgen sensitive in the epididymis of the normal mouse. In the present investigation we used this enzyme as a marker to study androgen sensitivity in the microscopical epididymides of Tfm/Y hemizygotes and in the epididymides of control +/Y litter-mate brothers. Both mutant and control animals were studied with and without exogenous androgen stimulation. Tfm/Y hemizygotes demonstrated low levels of diffuse, cytoplasmic βG activity that appears to be unresponsive to exogenous androgen stimulation. In light of our previous studies, this distribution of βG reaction products suggests some degree of androgen sensitivity. The survival of these micro-organs and their partial androgen sensitivity may be related to the role of the MDS in inducing meiosis.     

Effect of the mouse mutants testicular feminization and sex reversal on hormone-mediated induction and repression of enzymes

The mouse mutants testicular feminization and sex reversal have been used to investigate hormone-mediated induction and repression of enzymes. Tfm/Y animals were already known to be androgen insensitive, rendering the androgeninducible enzymes ADH and -glucuronidase noninducible becuase of an inherited deficiency of a cytosol androgen-receptor complex. The animals display female secondary sexual characteristics. Sxr/+,XX animals display male primary and secondary sexual characteristics with small testes. We demonstrate (1) that the Tfm mutation is pleiotropic, preventing repression of an androgenrepressible enzyme (ornithine aminotransferase) as well as induction of androgen-inducible enzymes, (2) that an estrogen-inducible enzyme (histidine decarboxylase) is not affected by the Tfm mutation, and (3) that Sxr/+,XX animals produce enough androgen for malelike activities of androgen-sensitive enzymes. It was also discovered that histidine decarboxylase repressed by androgen in normal animals, rather than being unaffected by it in Tfm/Y animals, is in fact induced. This unexpected phenomenon is discussed and an explanation is suggested for it.This work was supported by a grant from the MRC.     

Putative androgen receptors distinguished in wild-type and testicular-feminized (Tfm) mice.

The reduced level of putative androgen receptor in the mouse mutant, testicular feminization (Tfm), chromatographs on DNA-cellulose differently from the bulk of wild-type receptors. While the elution maximum for extracts of Tfm/Y kidney is in the 180–190 mM NaCl range, wild-type kidney extracts exhibit two maxima of elution at 140–150 mM NaCl and 180–190 mM NaCl, respectively. For hypothalamus-preoptic area, Tfm/Y has one elution maximum at approximately 180 mM NaCl, while the wild-type exhibits a major elution maximum at 140–150 mM NaCl, with a minor peak at approximately 180 mM NaCl. Mixing experiments between wild-type and Tfm/Y cytosols reveal that the different characteristic elution patterns are intrinsic to the binding complexes and are not conveyed simply by other soluble factors. The distinctive pattern for Tfm indicates that the mutation does not cause merely a reduced level of wild-type receptor. Rather the residual receptor of the mutant may be either an abnormal protein or a minor form of wild-type receptor, not readily seen in wild-type tissue due to the presence of more preponderant species. Differences in the elution profiles of androgen receptor species of wild-type kidney with the two bound androgens, testosterone and dihydrotestosterone, are also presented. A model of the androgen receptor system is proposed which includes several binding classes for androgen ligands and metabolites. In light of aromatization of androgens to estrogens and its probable role in some androgenic responses, we include the “estrogen receptor” in this mechanism.     

Androgen Spares Androgen-Insensitive Motoneurons from Apoptosis in the Spinal Nucleus of the Bulbocavernosus in Rats

The spinal nucleus of the bulbocavernosus (SNB) is a sexually dimorphic motor nucleus in the rat lumbar spinal cord. The sex difference arises through the androgenic sparing of the motoneurons and their target muscles from ontogenetic cell death. Indirect evidence suggests that androgen acts on the target muscles rather than directly on SNB motoneurons to spare them from death. The testicular feminization mutation (Tfm), a defect in the androgen receptor (AR), blocks androgenic sparing of SNB motoneurons and their targets. The pattern of AR immunocytochemistry was previously found to be different in adultTfmand wild-type rats: immunostaining was nuclear in most SNB cells of wild-type rats, but very few SNB cells display nuclear AR immunostaining in affectedTfmrats. Because theTfmmutation is carried on the X chromosome, random X inactivation during development makes female carriers ofTfm(+/Tfm) genetic mosaics for androgen sensitivity.Tfmcarriers, their wild-type sisters, and affectedTfmmales were treated with perinatal testosterone and immunocytochemistry was used to detect androgen receptor in the SNB when the rats reached adulthood. Mosaic females could be distinguished from their wild-type sisters by external morphology. In such perinatally androgenized mosaics, adult SNB cells were equally divided between wild-type andTfmgenotype, as indicated by AR immunocytochemistry. In contrast, the pattern of AR immunocytochemistry in target muscles of mosaics appeared similar to that of wild-type females. These results indicate that early androgen spared both androgen-sensitive and -insensitive motoneurons from cell death, confirming a site of androgen action other than the motoneurons themselves.     

Adaptive mutation inEscherichia coli strain FC40

Mutations can arise in static populations of cells that are subjected to nonlethal selective pressure, a phenomenon that has been called ‘adaptive mutation’. This phenomenon has been extensively studied in FC40, a strain ofEscherichia coli that cannot metabolize lactose (Lac⁻) but that reverts to lactose utilization (Lac⁺) when lactose is its sole energy and carbon source. The adaptive Lac⁺ mutations arise by two mutational processes: a recombination-dependent process that is highly active on the episome carrying the Lac⁻ allele, and an unknown process that affects the whole genome. Most of the Lac⁺ mutations are due to the first process, which also produces nonselected mutations on the F′ episome. However, about 10% of the Lac⁺ mutations arise in a subpopulation of cells that experience a period of transient hypermutation. Although minor contributors to any one type of mutation, the hypermutators account for nearly all cases of multiple mutations. The evolutionary implications of these results are: (i) DNA synthesis associated with recombination may be an important source of spontaneous mutation, particularly in cells that are not actively growing; (ii) the efficient mutational mechanism that occurs on the episome could result in the horizontal transfer of new alleles among species that carry and exchange conjugal plasmids; and (iii) a subpopulation of transient hypermutators could be a source of multiple mutations that would allow for rapid adaptive evolution under adverse conditions.     

Cytosol androgen receptor from kidney of normal and testicular feminized (Tfm) mice

Steroid binding has been studied in cytoplasmic extracts of normal mouse kidney, an androgen sensitive organ, and of kidney from mice affected with testicular feminization (Tfm mutant) that have inherited androgen resistance. Macromolecules that bind ³H-5α-dihydrotestosterone (DHT, the presumed active androgen in most testosterone target organs) and sediment in glycerol gradient at 8–9S can be observed in cytosol from kidney of mice of different sex, age, and hormonal history. The 8–9S component from normal females is heat labile, pronase sensitive, and dissociated by high salt to a lower molecular weight entity. The apparent equilibrium dissociation constant (K_d) for the DHT-receptor complex is 1.4 × 10^?9M, and there are about 1500 binding sites per testosterone-sensitive kidney proximal tubule cell. Cytosol from Tfm/Y ^ animals also shows a sharp peak of ³H-DHT-binding activity at 8–9S. The Tfm protein, however, has reduced affinity for DHT and binds only 10–25% as much ³H-DHT as wild-type receptor at ³H-DHT concentrations from 5 × 10^?11M to 1.2 × 10^?8M. Scatchard analysis, and studies involving competition with unlabeled steroids, relative binding of various androgens, and dissociation of the ³H-DHT-binding protein complex after extensive dialysis have led to the conclusion that Tfm kidney contains very little, if any, androgen receptor with properties similar to that found in normal kidney.     

Mutability and importance of a hypermutable cell subpopulation that produces stress-induced mutants in Escherichia coli

In bacterial, yeast, and human cells, stress-induced mutation mechanisms are induced in growth-limiting environments and produce non-adaptive and adaptive mutations. These mechanisms may accelerate evolution specifically when cells are maladapted to their environments, i.e., when they are are stressed. One mechanism of stress-induced mutagenesis in Escherichia coli occurs by error-prone DNA double-strand break (DSB) repair. This mechanism was linked previously to a differentiated subpopulation of cells with a transiently elevated mutation rate, a hypermutable cell subpopulation (HMS). The HMS could be important, producing essentially all stress-induced mutants. Alternatively, the HMS was proposed to produce only a minority of stress-induced mutants, i.e., it was proposed to be peripheral. We characterize three aspects of the HMS. First, using improved mutation-detection methods, we estimate the number of mutations per genome of HMS-derived cells and find that it is compatible with fitness after the HMS state. This implies that these mutants are not necessarily an evolutionary dead end, and could contribute to adaptive evolution. Second, we show that stress-induced Lac⁺ mutants, with and without evidence of descent from the HMS, have similar Lac⁺ mutation sequences. This provides evidence that HMS-descended and most stress-induced mutants form via a common mechanism. Third, mutation-stimulating DSBs introduced via I-SceI endonuclease in vivo do not promote Lac⁺ mutation independently of the HMS. This and the previous finding support the hypothesis that the HMS underlies most stress-induced mutants, not just a minority of them, i.e., it is important. We consider a model in which HMS differentiation is controlled by stress responses. Differentiation of an HMS potentially limits the risks of mutagenesis in cell clones.     

A DNA-binding fraction of mouse kidney 3-ketosteroid reductase: Comparison with androgen receptors

Since approximately 1% of 3-ketosteroid reductase (which metabolizes dihydrotestosterone [17β-hydroxy-5α-androstan-3-one] to 5α-androstane-3α,17β-diol or 5α-androstane-3α,17β-diol) from mouse kidney cytosol adheres to DNA under conditions that allow virtually complete androgen receptor binding, these two DNA-binding activities were compared in cytosol extracts of mouse kidney and hypothalamus-preoptic area. This DNA-binding fraction of 3-ketosteroid reductase was distinguished from androgen receptor in several ways: (1) its pattern of elution from DNA-cellulose with steps of increasing NaC1 concentration differed from that for receptors from wild-type kidney; (2) it was influenced differently by the mutation Tfm, both in level and in DNA-cellulose elution pattern; (3) in mouse kidney cytosol it was relatively stable at moderate (25°C) temperatures which rapidly inactivated ligand-free androgen receptors in the same cytosols; (4) the DNA-binding was not proportional to androgen receptor levels between two wild-type tissues, the hypothalamus-preoptic area and kidney. By these criteria, a simple relationship of androgen receptors and a DNA-binding fraction of 3-ketosteroid reductase activity is unlikely.     

Effect of the recC gene in Escherichia coli on frequencies of ultraviolet-induced mutants

UV induction of Lac^? mutations was compared with UV induction of Mal⁺ mutations in E. coli B/r strains differing in the recC gene. The frequency of Lac^? mutants per survivor induced by the same dose was not significantly affected by the recC gene but the percentage of pure rather than sectored Lac^? colonies was greater when the recC gene was present. On the other hand, as reported previously, frequencies of Mal⁺ mutants induced by the same UV dose were lower when the strain was recC. The reduction factor was the same as for spontaneous Mal⁺ mutants. The difference in the effect of the recC gene on the yields of Lac^? and Mal⁺ mutants can be explained by taking into account the influence of lethal sectoring, which introduces an artifact when mutants arising in the recC strain are scored selectively as in the case for Mal⁺ mutants, but not when the scoring is non-selective as for Lac^? mutants. Lethal sectoring as indicated by a discrepancy between total cell counts and numbers of colony-formers, was observed for the recC strain growing in liquid minimal medium corresponding to the agar medium used to score Mal⁺ mutants but was not observed for the rec⁺ strain. Both strains showed lethal sectoring in the liquid medium corresponding to the agar medium to score Lac^? mutants. The hypothesis concerning the role of lethal sectoring in the selective scoring of mutants arising in a recC background is supported by evidence concerning the UV induction of mutants in a polA1 background. Like the recC gene, the polA1 gene did not affect yields of Lac^? mutants. However, unlike the recC gene, the polA1 gene has previously been shown not to influence UV yields of prototrophic mutations (scored selectively) and not to cause lethal sectoring except under irrelevant conditions.     

Androgen receptors are required for full masculinization of nitric oxide synthase system in rat limbic-hypothalamic region

The neuronal nitric oxide synthase (nNOS) is involved in the control of male and female sexual behavior and its distribution in several regions of the limbic–hypothalamic system, as well as its coexistence with gonadal hormones' receptors, suggests that these hormones may play a significant role in controlling its expression. However, data illustrating the role of gonadal hormones in controlling the nNOS expression are, at present, contradictory, even if they strongly suggest an involvement of testosterone (T) in the regulation of nNOS. The action of T may be mediated through androgen (AR) or, after aromatization to estradiol (E₂), through estrogen receptors.To elucidate the role of AR on nNOS expression, we compared male and female rats with a non-functional mutation of AR (Tfm, testicular feminization mutation) to their control littermates. We investigated some hypothalamic and limbic nuclei involved in the control of sexual behavior [medial preoptic area (MPA), paraventricular (PVN), arcuate (ARC), ventromedial (VMH) and stria terminalis (BST) nuclei]. In BST (posterior subdivision), VMH (ventral subdivision), and MPA we detected a significant sexual dimorphism in control animals and a decrease of nNOS positive elements in Tfm males compared to their littermate. In addition, we observed a significant increase of nNOS positive elements in BST (posterior) of Tfm females. No significant changes were observed in the other nuclei. These data indicate that, contrary to current opinions, androgens, through the action of AR may have a relevant role in the organization and modulation of the nNOS hypothalamic system.     

Preferential mutagenesis of lacZ integrated at unique sites in the Escherichia coli chromosome

To study the variation in spontaneous mutation frequencies in different chromosomal domains, a mini-Mu-kan-lacZ ⁻transposable element was constructed to insert the lacZ ⁻(Trp570 → Opal) allele into many different loci in the Escherichia coli chromosome. Papillation on MacConkey lactose plates was used to screen for mini-Mu insertion mutants with elevated levels of spontaneous mutagenesis of lacZop → LacZ⁺ candidates were then screened for normal mutation frequencies in other genes. Two different insertion mutants with this enhanced mutagenesis phenotype were isolated from 14 000 colonies, and named plm-1 (preferential lacZmutagenesis) and plm-2. The frequency of LacZ⁻→ LacZ⁺ mutations in these plm mutants was over 400-fold higher than that in isogenic strains containing mini-Mu-kan-lacZop insertions at other loci. Six Lac⁺ reversion (or suppression) mutations obtained from each of the two plm mutants were mapped by P1 transduction and all were found to be linked to the Kan^r gene in the mini-Mu-kan-lacZop, suggesting that a localized mutagenic event is responsible for the preferential mutagenesis. Furthermore, both the LacZ⁺→ LacZ⁻and Kan^r→ Kan^s mutant frequencies of these Lac⁺ revertants were in the range of 10⁻³ to 10⁻², indicating that this putative localized mutagenesis is neither allele nor gene specific. To identify the plm loci, the chromosomal regions flanking the mini-Mu insertion sites were cloned and sequenced. A computer-assisted database search of homologous sequences revealed that the plm-1 locus is identical to the mutS gene; the mini-Mu insertion most probably results in the production of a truncated MutS protein. We suggest that the enhanced lacZ mutation frequency in plm-1 may be associated with an active process involving the putative truncated MutS protein. The DNA sequence of the plm-2 locus matched a putative malate oxidoreductase gene located at 55.5 min of the E. coli chromosome. Received: 1 August 1996 / Accepted: 3 April 1997     

Mutations Affecting Synthesis of β-Galactosidase Activity in the Yeast KLUYVEROMYCES LACTIS

Fifty-one mutants of Kluyveromyces lactis that cannot grow on lactose (Lac^-) were isolated and characterized. All of the mutations are in nuclear genes, are recessive in their wild-type allele and define seven complementation groups, which we designate lac3 through lac9. Strains bearing mutations in lac3, lac5, lac7, lac8 and lac9 are also unable to grow on galactose (Gal^-). Since the Gal^- and Lac^- phenotype co-segregate, they are probably due to a single mutation. Strains bearing mutations in any of the seven complementation groups grow normally on glucose. However, strains bearing mutations in lac3, lac5 and lac6 do not grow on glucose if lactose is also present in the medium. Likewise, strains bearing mutations in lac3 and lac5 do not grow on glucose in the presence of galactose. Complementation groups lac4 and lac5 are loosely linked and map within a cluster of auxotrophic mutations on a chromosome that we designate chromosome 2. The remaining five groups are unlinked. Thus, there is no evidence for clustering of Lac genes into an operon-like regulatory unit.——To further characterize the nature of the Lac^- phenotype, the basal and inducible level of β-galactosidase activity were measured. All mutants had nearly normal basal enzyme levels, except those in lac4, which had barely detectable levels. Inducible enzyme levels varied from barely detectable levels in mutants bearing lac4 mutations up to four-fold inducible levels in strains bearing mutations in other complementation groups. In all cases, however, induction levels were below the 30-fold level obtained in wild-type cells. Three strains bearing lac5 mutations contain increased enzyme activity in the absence of inducer, indicating constitutive synthesis of β-galactosidase. In summary, these data indicate that several genes are necessary for synthesis of β-galactosidase activity.     

Conditional lysis ofEscherichia coli by the fusion of extracellular (STA) to periplasmic (LTB) enterotoxins: Apparent phenotypic suppression of lactose permease

The expression of a methanol-soluble, heat-stable enterotoxin (ST_A) fused to the B subunit of the heat-labile enterotoxin (LT_B) at 35°C or higher temperatures caused strains ofEscherichia coli deficient in lactose permease to behave on indicator media as Lac⁺; however, at 33°C or lower temperatures the original Lac^– phenotype of the host strains was maintained. The apparent phenotypic suppression oflacY was shown to be due to lysis of a fraction of the bacteria and the consequent release of active-galactosidase to the culture supernatant. After incubation at 37°C for 1 h, the cultures were committed to lyse. Plasmid and chromosomal mutants that do not show this phenotype were isolated by selecting Lac^– colonies at the unpermissive temperature. The mutations on the plasmids were localized in both the heat-stable and the heat-labile enterotoxin genes. Chromosomal mutants that show normal levels of-galactosidase and fused toxins have also been isolated.     

Binding of calmodulin to Nuf1p is required for karyogamy in<Emphasis Type="Italic"> Saccharomyces cerevisiae</Emphasis>

The role of calmodulin (CaM) during mating in Saccharomyces cerevisiae was examined by using a set of Phe-to-Ala substitutions. We identified ten CaM mutants that exhibited significantly reduced mating efficiencies when crossed to a strain of the opposite mating type harboring the same CaM mutation. Most of the mating-defective CaM mutants were bilateral, i.e., they also exhibited mating defects, albeit minor ones, when crossed to the wild type. When strains carrying different bilateral CaM mutations were mated, the mating efficiencies recovered dramatically. We termed this phenomenon "intragenic mating complementation", and classified the mating-defective CaM mutations into two intragenic mating complementation groups. Two mutant alleles belonging to different groups showed minor defects in cell adhesion and cell fusion, but exhibited severe defects in karyogamy. CaM is known to bind to the essential spindle pole body component Nuf1p. This binding appears to be important for karyogamy because the nuf1 ^C911R mutation, which impairs CaM-Nuf1p binding, resulted in a severe defect in karyogamy. Indeed, the two mating-defective CaM mutations were found to compromise formation of the CaM/Nuf1p complex, and the mating defects of these two CaM mutants were suppressible by a dominant, CaM-independent, mutation in NUF1. Taken together, these results suggest that loss of CaM binding to Nuf1p causes a defect in karyogamy, thereby inhibiting productive mating.Communicated by C. P. Hollenberg     

Genetic and endocrine control of renin activity in the submaxillary gland of the mouse

Basal activity of submaxillary gland (SMG) renin is high in female mice that carry the Rnr ^s allele and is induced to higher levels by treatment with dihydrotestosterone (DHT). To determine whether the difference in basal activity between high (Rnr ^s/Rnr^s) and low (Rnr ^b/Rnr^b) strains is due to enhanced sensitivity of Rnr ^s/Rnr^s strains to endogenous androgen, we first studied the effect of several types of endocrine ablation on SMG renin in young female mice, and second, we removed normal androgen receptor protein by introducing the X-linked Tfm gene. Adrenalectomy with or without castration had no effect on basal SMG renin; hypophysectomy decreased basal renin activity 400-fold but did not abolish responsiveness to DHT. Loss of androgen receptor did not affect basal renin activity but did prevent enhancement by DHT. Basal and induced renin activities in L.AKR(Alll)/Cy, a congenic strain homozygous for Rnr ^s introduced from AKR/J into the background of C57L/J, an Rnr ^b/Rnr^b type strain, are intermediate between levels observed in the original strains. We conclude that (1) the basal level of SMG renin is regulated directly or indirectly by some pituitary hormone(s) but not by androgen, (2) androgen induction of renin activity requires a normal androgen receptor, and (3) major gene(s) that regulate basal as well as induced SMG renin are in a circumscribed region of chromosome 1.This work has been aided by Grants GM26414 and AM03892 from the National Institutes of Health, a grant from the Texas affiliate of the American Heart Association, and by research contract NO1-CP33255 from the Division of Cancer Cause and Prevention, the National Cancer Institute. The Jackson Laboratory is fully accredited by the American Association for Accreditation of Laboratory Animal Care.     

Carbohydrate Accumulation and Metabolism in Escherichia coli: Characteristics of the Reversions of ctr Mutations

The reversion behavior of pleiotropic carbohydrate mutants, previously designated as ctr, was studied. The mutants revert to complete restoration of the wild-type phenotype, as well as to a spectrum of partial wild-type phenotypes. Lac⁺ reversions were found in the lac region (11 min) and some Mal⁺ reversions occurred at malB (79 min), at a distance from the site of the ctr mutations (46 to 47 min). About one-third of Lac⁺ and Mal⁺ revertants were constitutive for uptake of their respective substrates, and one-third modified for inducibility. The remaining third were not distinguishable from wild type. Induction of a ctr mutation in a lac constitutive strain, either operator or repressor mutant, did not affect lactose metabolism. A polar-like ctr mutant, deficient in both enzyme I and heat-stable protein of the phosphoenolpyruvate-dependent phosphotransferase strain was also described. Partial revertants of ctr were still found to lack enzyme I.     

Nuclei in testicular feminization (Tfm) are not activated by intact testosterone receptor complexes: A morphometric study in striated urethral muscle of mosaic mice

Summary Sex reversed mice heterozygous for the X-linked Tfm mutation are mosaics with respect to the Tfm locus. In the androgen-dependent striated urethral muscle, nuclei coding for the intact testosterone receptor protein and nuclei coding for the defective Tfm receptor protein are incorporated in the same multinucleate muscle fibres. The intact testosterone receptor complex can thus be expected to enter the Tfm nuclei. Our measurements show that the fibre diameters of the mosaic muscle form a homogeneous population, intermediate in size between induced male and non-inducible Tfm phenotypes. By contrast, the nuclear size shows a bimodal distribution, the subpopulations corresponding to Tfm and wild type nuclei. The results indicate that the Tfm nuclei are not activated by the intact testosterone receptor complex.