Müllerian inhibiting substance in sex-reversed dogs

In normal males, Müllerian Inhibiting Substance (MIS), produced by testes during an embryonic critical period, is thought to induce regression of the Müllerian duct system, including the oviducts and uterus. In XX sex-reversed dogs, an apparent contradiction has been reported: The uterus persists in the presence of testes or ovotestes. The objective of this study is to determine whether testes of XX male and ovotestes of true hermaphrodite dogs produce MIS, and to examine the anatomy of Müllerian duct derivatives of affected dogs for evidence of regression. Gonadal samples were tested for MIS activity in a bioassay. The mean MIS activity score of XX males was similar to that of normal XY males and significantly greater than that of normal XX females. The mean MIS activity score of XX true hermaphrodites was intermediate between normal XX females and XY males. Within the true hermaphrodite group, ovotestes in which the proportion of testicular tissue was greater than or equal to 1/2 had higher MIS scores than those in which the proportion of testicular tissue was less than 1/2. XX males had a well-developed epididymis adjacent to each testis, but no oviducts. In true hermaphrodites, the oviduct regressed and an epididymis was present when greater than or equal to 1/2 of the adjacent ovotestis was testicular, and MIS activity in that gonad was high. A few ovotestes with intermediate levels of MIS activity had both an oviduct and an epididymis. Regression of the oviductal portion of the Müllerian duct system was positively correlated to the amount of testicular tissue and the MIS activity of the gonad, as would be predicted by Jost's original hypothesis.(ABSTRACT TRUNCATED AT 250 WORDS)     

Müllerian mimicry in aposematic spiny plants

Müllerian mimicry is common in aposematic animals but till recently, like other aspects of plant aposematism was almost unknown. Many thorny, spiny and prickly plants are considered aposematic because their sharp defensive structures are colorful and conspicuous. Many of these spiny plant species (e.g., cacti and Agave in North American deserts; Aloe, Euphorbia and acacias with white thorns in Africa; spiny plants in Ohio; and spiny members of the Asteraceae in the Mediterranean basin) have overlapping territories, and also similar patterns of conspicuous coloration, and suffer from the evolutionary pressure of grazing by the same large herbivores. I propose that many of these species form Müllerian mimicry rings.Key words: aposematic coloration, defense, evolution, herbivory, müllerian mimicry, spines, thornsAposematic (warning) coloration is a biological phenomenon in which poisonous, dangerous or otherwise unpalatable organisms visually advertise these qualities to other animals. The evolution of aposematic coloration is based on the ability of target enemies to associate the visual signal with the risk, damage or non-profitable handling, and later to avoid such organisms as prey. Typical colors of aposematic animals are yellow, orange, red, purple, black, white or brown and combinations of these.^1–5 Many thorny, spiny and prickly plant species were proposed to be aposematic because their sharp defensive structures are usually colorful (yellow, orange, red, brown, black, white) and/or associated with similar conspicuous coloration.^5–22 Animal spines also have similar conspicuous coloration and were proposed to be aposematic.^1,5,17,23Several authors have proposed that mimicry of various types helps in plant defense, e.g.,^9,24–34 More specifically, Müllerian mimicry was already proposed to exist in several defensive plant signaling systems. The first was for several spiny species with white-variegated leaves.^8,10 The second was for some tree species with red or yellow poisonous autumn leaves.³⁵ The third cases are of a mixture of Müllerian and Batesian mimicry, of thorn auto-mimicry found in many Agave species.⁸Here I propose that many species of visually aposematic spiny plants of the following taxa: (1) Cactaceae, (2) the genus Agave, (3) the genus Aloe, (4) African thorny members of the genus Euphorbia, (5) African acacias with white thorns, (6) spiny vascular plants of southeastern Ohio, (7) spiny Near Eastern plants with white variegation on their leaves, (8) Near Eastern members of the Asteraceae with yellow spines, form Müllerian mimicry rings of spiny plants.To consider the existence of Müllerian mimicry rings in aposematic organisms, two factors are needed: (1) a similar signal, and (2) an overlapping distribution in respect to the territory of predators in animals, or herbivores in plants. I will show below that for the plant taxa proposed here to form Müllerian mimicry rings, both criteria operate.The accumulating data about the common association of plant defenses by spines with visual conspicuousness, along with the fact that many such species overlap in their habitat, raises the possibility of the broad phenomenon of existence of Müllerian mimicry rings in plants. Even from the limited number of publications proposing visual aposematism in spiny plants, the operation of vegetal Müllerian mimicry rings seems to be obvious. The phenomenon can now be traced to both the Old World (Asia, Africa and Europe) and the New World (North America). The best-studied cases include Cactaceae and the genera Agave, Aloe and Euphorbia,⁶ African acacias with white thorns,^12,15 Near Eastern spiny plants with white variegation on their leaves,^7,11 aposematic spiny vascular plants of southeastern Ohio,¹⁶ and many spiny Mediterranean species of the Asteraceae with yellow spines.²²In the four spiny taxa (Cactaceae and the genera Agave, Aloe and Euphorbia) that were the first to be proposed as visually aposematic⁶ there is a very strong morphological similarity. In cacti, there are two types of conspicuousness of spines that are typical of many plant species: (1) colorful spines, and (2) white spots, or white or colorful stripes, associated with spines on the stems. These two types of aposematic coloration also dominate the spine system of Agave, Aloe and Euphorbia. The fact that many species of three of these four spiny taxa (Agave, Aloe and Euphorbia) are also poisonous^36–38 further indicates their potential to form Müllerian mimicry rings.I propose that each of these groups for itself and some of these groups (e.g., Cactaceae and the genus Agave in North America; Aloe, Euphorbia and acacias in east and south Africa) that have overlapping distribution and share at least some of the herbivores, form Müllerian mimicry rings.The first Müllerian mimicry ring is of cacti and Agave that have an overlapping distribution over large areas in North America.^37,39 The large herbivores in North America disappeared not so long ago in evolutionary time scales and seem to have shaped the spiny defense of these plant taxa.⁴⁰The second Müllerian mimicry ring is of the spiny and thorny members of the African genera Aloe, Euphorbia and certain acacias with very conspicuous white thorns, which partly overlap in distribution and share various large mammalian herbivores.^12,15,36,41The third Müllerian mimicry ring is the outcome of the common presence of aposematic coloration in spiny vascular plants of southeastern Ohio,¹⁶ with color patterns in thorns and spines similar to those of Cactaceae and the genera Agave, Aloe and Euphorbia described in Lev-Yadun.⁶The next case of potential operation of Müllerian mimicry ring of spiny plants with overlapping territories that suffer from the same large herbivores, but on a much smaller geographical scale, has recently been proposed for several spiny species with white-variegated leaves,⁷ and later for more than 20 spiny species in the flora of Israel that have white markings associated with their spines.¹¹The last case of a probable Müllerian mimicry ring was described by Ronel et al.²² who while studying the spine system of Near Eastern spiny members of the Asteraceae, found 29 spiny species with yellow spines, and additional such species are expected to occur. Since some of these species and others with yellow spines also grow in southern Europe, it is clear that the same phenomenon is also common there.I conclude that Müllerian mimicry rings seem to be very common in plants, and that it is probable that many other spiny plants that form Müllerian mimicry rings are waiting to be studied. Such defensive rings are probably also formed by poisonous plants that share similar colors or odors.     

Persistence of müllerian ducts in male rabbits passively immunized against bovine anti-müllerian hormone during fetal life

A female rabbit was immunized against purified bovine AMH and mated. Booster injections were given at Day 8 of pregnancy to ensure a high titer of anti-AMH antibodies at the time the rabbit fetal testis begins to produce AMH. In three consecutive litters, the immunized female produced a total of 12 males, 9 of which had persistent Müllerian duct derivatives. No other significant abnormalities were detected in these animals, which were compared to the offspring of a control saline-injected female. In particular, testicular morphology was normal in most animals, and serum FSH levels did not differ from controls. This experimental model lends no support to the hypothesis that AMH controls extra-Müllerian events of male sex differentiation, nor that of the existence of a regulatory mechanism for synthesis of AMH by Sertoli cells, but it does not definitely exclude these possibilities, inasmuch as our tentative conclusions are based upon study of only one immunized female.     

Anti-Müllerian hormone in three intersex conditions.

Anti-Müllerian hormone (AMH), secreted by embryonic testicular Sertoli cells, inhibits the development of Müllerian ducts in the male. An enzyme-linked immunoassay (ELISA) for AMH was used to investigate three intersex infants. The AMH level was correlated with each patient's degree of Müllerian duct development. Complete inhibition of Müllerian structures correlated with the normal levels of AMH in the infant with testicular feminization. Detectable levels of AMH were found in the hermaphroditic infant; however, these low levels reflected Sertoli cell inadequacy of the ovotestis, which was documented by a right rudimentary Fallopian tube and a normal uterus. In the infant with persistent Müllerian duct syndrome, (PMDS), the normal Müllerian derivatives are compatible with 1) an AMH receptor defect; 2) a biologically and immunologically abnormal AMH molecule, or 3) a functional AMH deletion. The lack of detectable AMH in this infant excluded the AMH receptor abnormality and thus directed authors' search for the specific defect to the AMH gene. Thus, this ELISA for AMH is as valuable a tool to the molecular biologist studying a precise genetic error as it is to the physician making a precise clinical diagnosis.     

Contacts between Wolffian and Müllerian cells at the tip of the outgrowing Müllerian duct in rat embryos

The developing Müllerian duct was studied at the light microscopic as well as the electron microscopic level in rat embryos, especially in the section of the terminal bud and its tip, where Wolffian and Müllerian duct are enclosed by a common basal membrane. In this zone desmosomes can be found among Wolffian cells and also among Müllerian cells. In addition, we found cell contacts between Müllerian and Wolffian cells, namely short electron-dense segments on adjacent surfaces or disc-shaped thickenings within opposite plasma membranes, as well as fusions of the plasmalemmata over short distances. Until now, these cell contacts have not been described in rat embryos.     

Biochemical analysis of bovine testicular anti-Müllerian hormone

Direct biochemical analysis has been applied to bovine testicular anti-Müllerian hormone (AMH), purified from incubation medium of bovine fetal testes by immunochromatography on a monoclonal antibody. The hormone contains a high proportion of hydrophobic amino acids and 13.5% carbohydrate. The oligosaccharide composition suggests that both N- and O-glycosidically linked chains are present. The molecular extinction coefficient is 3.27 +/- 0.06. One RIA unit, defined as the amount of hormone released by 1 g fetal bovine testicular tissue incubated during 4 h, corresponds to 3.06 +/- 0.17 microgram protein.     

Mimetic gain in batesian and Müllerian mimicry

Summary Starting from field investigations and experiments on mimetic butterfly populations a model for two mimetic species is developed. The model comprises various features such as the growth rates and carrying capacities of the two species, their unpalatability to predators, the recruitment and the training of the predators and, most important, the similarity of the two mimetic species. The model ranges from pure Batesian to pure Müllerian mimicry over a spectrum of possible cases. The mimetic gain is introduced as the relative increase in equilibrium density in a mimetic situation as compared to a situation where mimicry is not present. The dependence of this quantity on parameters as growth rate, carrying capacity, unpalatability, and similarity is investigated using numerical methods.     

Anti-Müllerian Hormone Recruits BMPR-IA in Immature Granulosa Cells

Anti-Müllerian hormone (AMH) is a member of the TGF-β superfamily secreted by the gonads of both sexes. This hormone is primarily known for its role in the regression of the Müllerian ducts in male fetuses. In females, AMH is expressed in granulosa cells of developing follicles. Like other members of the TGF-β superfamily, AMH transduces its signal through two transmembrane serine/threonine kinase receptors including a well characterized type II receptor, AMHR-II. The complete signalling pathway of AMH involving Smads proteins and the type I receptor is well known in the Müllerian duct and in Sertoli and Leydig cells but not in granulosa cells. In addition, few AMH target genes have been identified in these cells. Finally, while several co-receptors have been reported for members of the TGF-β superfamily, none have been described for AMH. Here, we have shown that none of the Bone Morphogenetic Proteins (BMPs) co-receptors, Repulsive guidance molecules (RGMs), were essential for AMH signalling. We also demonstrated that the main Smad proteins used by AMH in granulosa cells were Smad 1 and Smad 5. Like for the other AMH target cells, the most important type I receptor for AMH in these cells was BMPR-IA. Finally, we have identified a new AMH target gene, Id3, which could be involved in the effects of AMH on the differentiation of granulosa cells and its other target cells.     

Anti-Müllerian hormone: Hormone or growth factor?

Anti-Müllerian hormone (AMH) is a dimeric glycoprotein member of the TGF-β family. It is synthesized by immature Sertoli cells, and, to a lesser degree, by adult Sertoli and granulosa cells. AMH is responsible for the regression of Müllerian ducts in the male fetus; it also has deleterious effects on the female fetal reproductive tract, destroying Müllerian primordia and germ cells, and masculinizing the fetal ovary on the rare occasions female fetuses become exposed to its effects. All other suggested actions for AMH—retardation of oocyte meiosis, inhibition of EGF receptor autophosphorylation, anti-cancer activity—have been reported with crude hormone preparations, and have not been confirmed using pure AMH. Its relatively limited sphere of action—the fetal genital tract—and the fact that it is secreted into the general circulation and can act at long range, imply that AMH is more like a hormone than a growth factor, but the complex interaction between hormones and growth factors make a formal distinction impossible.     

Variants of the anti-Müllerian hormone gene in a compound heterozygote with the persistent Müllerian duct syndrome and his family

Summary The human genome contains a large number of interspersed simple repeat sequences that are variable in length and can therefore serve as highly informative, polymorphic markers. Typing procedures include conventional multilocus and single locus probing, and polymerase chain reaction aided analysis. We have identified simple sequences in a cosmid clone stemming from the human Y chromosome and consisting of (gata)_n repeats. We have compared these with two equivalent simple repeat loci from chromosome 12. After amplifying the tandemly repeated motifs, we detected between four and eight different alleles at each of the three loci. Codominant inheritance of the alleles was established in family studies and the informativity of the simple repeat loci was determined by typing unrelated individuals. The polymorphisms are suitable for application in linkage studies, practical forensic case work, deficiency cases in paternity determination, and for studying ethnological questions. The mutational mechanisms that bring about changes in simple repeats located both on the autosomes and on the sex chromosomes, are discussed.Professor Dr. Otto Prokop (Humboldt-Universität Berlin) on the occasion of his 70th birthday     

Müllerian inhibiting substance in reproduction and cancer.

During embryogenesis normal male phenotypic development requires the action of Müllerian Inhibiting Substance (MIS) which is secreted by Sertoli cells of the fetal testis. As testes differentiate in genetic (XY) males, they produce MIS which causes regression of the Müllerian ducts, the anlagen of the female reproductive tract. Soon thereafter, testicular androgens stimulate the Wolffian ducts. In females, on the other hand, MIS is not produced by grandulosa cells until after birth, before which, estrogens induce Müllerian duct development, while the Wolffian ducts passively atrophy in the absence of androgenic stimulation. High serum MIS levels in males are maintained until puberty, whereupon they fall to baseline levels. In females MIS is undetectable in serum until the peripubertal period when values approach the baseline levels of males. This distinct pattern of sexual and ontogenic expression presupposes and requires tight regulation. MIS may play a role in gonadal function and development. Our laboratory has shown that an important role for ovarian MIS is to inhibit oocyte meiosis, perhaps providing maximal oocyte maturation prior to selection for ovulation and subsequent fertilization. Furthermore, Vigier et al. (Development 100:43-55) have recently obtained evidence that MIS may influence testicular differentiation, coincident with inhibition of aromatase activity. Current structure-function studies demonstrate that MIS, like other growth regulators in its protein family, requires proteolytic cleavage to exhibit full biological activity. MIS can be inhibited by epidermal growth factor. This antagonism, which is common to all MIS functions so far investigated, is associated with inhibition of EGF receptor autophosphorylation. We have provided evidence that bovine MIS can inhibit female reproductive tract tumors arising in adults.(ABSTRACT TRUNCATED AT 250 WORDS)     

Cellular mechanisms of Müllerian duct formation in the mouse

Regardless of their sex chromosome karyotype, amniotes develop two pairs of genital ducts, the Wolffian and Müllerian ducts. As the Müllerian duct forms, its growing tip is intimately associated with the Wolffian duct as it elongates to the urogenital sinus. Previous studies have shown that the presence of the Wolffian duct is required for the development and maintenance of the Müllerian duct. The Müllerian duct is known to form by invagination of the coelomic epithelium, but the mechanism for its elongation to the urogenital sinus remains to be defined. Using genetic fate mapping, we demonstrate that the Wolffian duct does not contribute cells to the Müllerian duct. Experimental embryological manipulations and molecular studies show that precursor cells at the caudal tip of the Müllerian duct proliferate to deposit a cord of cells along the length of the urogenital ridge. Furthermore, immunohistochemical analysis reveals that the cells of the developing Müllerian duct are mesoepithelial when deposited, and subsequently differentiate into an epithelial tube and eventually the female reproductive tract. Our studies define cellular and molecular mechanisms for Müllerian duct formation.     

Detection of anti-Müllerian activity in boar rete testis fluid

Boar rete testis fluid was tested for its capacity to induce Müllerian regression in 14.5-day-old rat Müllerian ducts. Weak activity was present in crude RTF, but after gel filtration 5-fold concentration, greater activity was detected in 1 our of 7 pools of the eluted fractions. The biologically active fraction (mol. wt 160 000-310 000) coincided with the elution of authentic labelled anti-Müllerian hormone, obtained from bovine fetal testes. These results indicate that a small amount of anti-Müllerian hormone is still synthesized in post-natal life.     

Evidence for a Müllerian mimetic radiation in Asian pitvipers

Müllerian mimicry, in which toxic species gain mutual protection from shared warning signals, is poorly understood in vertebrates, reflecting a paucity of examples. Indirect evidence for mimicry is found if monophyletic species or clades show parallel geographic variation in warning patterns. Here, we evaluate a hypothesis of Müllerian mimicry for the pitvipers in Southeast Asia using a phylogeny derived from DNA sequences from four combined mitochondrial regions. Mantel matrix correlation tests show that conspicuous red colour pattern elements are significantly associated with sympatric and parapatric populations in four genera. To our knowledge, this represents the first evidence of a Müllerian mimetic radiation in vipers. The putative mimetic patterns are rarely found in females. This appears paradoxical in light of the Müllerian prediction of monomorphism, but may be explained by divergent selection pressures on the sexes, which have different behaviours. We suggest that biased predation on active males causes selection for protective warning coloration, whereas crypsis is favoured in relatively sedentary females.     

Testing Müllerian mimicry: an experiment with wild birds

Experiments with wild birds feeding on pastry 'prey' were performed to test competing theories of Müllerian mimicry Conventional theories predict that all resemblances between defended prey will be mutually advantageous and, hence, Müllerian. In contrast, unconventional theories predict that, if there are inequalities in defences between mimetic species, the less well-defended prey may dilute the protection of the better defended species in a quasi-Batesian manner. This unconventional prediction follows from an assumption that birds learn about the edibilities of prey using rules of Pavlovian learning. We report on two experiments, each lasting 40 days, which showed that a moderately defended prey can dilute the protection of a better defended mimic in a quasi-Batesian fashion, but can add protection to a mimic which has the same moderate levels of defence. These results match predictions of unconventional theories of mimicry and go some way to resolving the long-running arguments over the nature of Müllerian mimicry.     

Müllerian inhibiting substance regulates its receptor/SMAD signaling and causes mesenchymal transition of the coelomic epithelial cells early in Müllerian duct regression

Examination of Müllerian inhibiting substance (MIS) signaling in the rat in vivo and in vitro revealed novel developmental stage- and tissue-specific events that contributed to a window of MIS responsiveness in Müllerian duct regression. The MIS type II receptor (MISRII)-expressing cells are initially present in the coelomic epithelium of both male and female urogenital ridges, and then migrate into the mesenchyme surrounding the male Müllerian duct under the influence of MIS. Expression of the genes encoding MIS type I receptors, Alk2 and Alk3, is also spatiotemporally controlled; Alk2 expression appears earlier and increases predominantly in the coelomic epithelium, whereas Alk3 expression appears later and is restricted to the mesenchyme, suggesting sequential roles in Müllerian duct regression. MIS induces expression of Alk2, Alk3 and Smad8, but downregulates Smad5 in the urogenital ridge. Alk2-specific small interfering RNA (siRNA) blocks both the transition of MISRII expression from the coelomic epithelium to the mesenchyme and Müllerian duct regression in organ culture. Müllerian duct regression can also be inhibited or accelerated by siRNA targeting Smad8 and Smad5, respectively. Thus, the early action of MIS is to initiate an epithelial-to-mesenchymal transition of MISRII-expressing cells and to specify the components of the receptor/SMAD signaling pathway by differentially regulating their expression.     

Spatial mosaic formation through frequency-dependent selection in Müllerian mimicry complexes

Although contemporary models of Müllerian mimicry have considered the movement of interfacial boundaries between two distinct mimetic forms, and even the possibility of polymorphisms in two patch systems, no model has considered how multiple forms of Müllerian mimics might evolve and be maintained over large geographical areas. A spatially explicit individual-based model for the evolution of Müllerian mimicry is presented, in which two unpalatable species are distributed over discrete cells within a regular lattice. Populations in each cell are capable of genetic drift and experience localized dispersal as well as frequency-dependent selection by predators. When each unpalatable prey species was introduced into a random cell and allowed to spread, then mimicry evolved throughout the system in the form of a spatial mosaic of phenotypes, separated by narrow "hybrid zones". The primary mechanism generating phenotypic diversity was the occasional establishment of new mutant forms in unoccupied cells and their subsequent maintenance (and spread) through frequency-dependent selection. The mean number of discrete clusters of the same morph that formed in the lattice was higher the higher the intensity of predation, and higher the lower the dispersal rate of unpalatable prey. Under certain conditions the hybrid zones moved, in a direction dependent on the curvature of their interfacial boundaries. However, the mimetic mosaics were highly stable when the intensity of predation was high and the rate of prey dispersal was low. Overall, this model highlights how a stable mosaic of different mimetic forms can evolve from a range of starting conditions through a combination of chance effects and localized frequency-dependent selection.     

Spatial mosaic and interfacial dynamics in a Müllerian mimicry system

Uncovering why spatial mosaics of mimetic morphs are maintained in a Müllerian mimicry system has been a challenging issue in evolutionary biology. In this article, we analyze the reaction diffusion system that describes two-species Müllerian mimicry in one- and two-dimensional habitats. Due to positive frequency-dependent selection, a local population first approaches the state where one of the comimicking patterns predominates, which is followed by slow movement of boundaries where different patterns meet. We then analyze the interfacial dynamics of the boundaries to find whether a stable cline is maintained and to obtain the wave speed if the cline is unstable. The results are: (1) In a spatially uniform habitat the morph with greater base fitness spreads both in one and two species system. (2) The strength of cross-species interaction determines whether the mimetic morph clines of model and mimic species coalesce into the same geographical region or pass through each other. The joint wave speed of clines decreases by increasing the number of comimicking species in the mimicry ring. (3) In spatial heterogeneous habitats, stable clines can be maintained due to the balance between the base fitness gradient and the biased gene flow by negative curvature of boundary. This allows the persistence of a spatial mosaic even if one of the morphs is in every place advantageous over the other. A balanced cline is also maintained if there is a gradient in the population density. (4) A new advantageous morph occurring at a local region is doomed to go to extinction in a finite time if the "radius" of initial distribution is below a threshold. Possible applications to the heliconiine butterfly mimicry ring, heterozygous disadvantage systems of chromosomal rearrangement and hybrid zone, the third phase of Wright's Shifting Balance theory, and cytoplasmic incompatibility are discussed.     

Familial Occurrence of Persistent Müllerian Structures in Otherwise Normal Males

Eight cases of males with persistent Müllerian structures are reported in four pairs of unrelated siblings. A genetically inherited failure to produce or to respond to the Müllerian-inhibiting substance elaborated by the fetal testis is postulated.