Structural Basis of Non-Latent Signaling by the Anti-Müllerian Hormone Procomplex

Most TGFβ family ligands exist as procomplexes consisting of a prodomain noncovalently bound to a growth factor (GF); Whereas some prodomains confer latency, the Anti-Müllerian Hormone (AMH) prodomain maintains a remarkably high affinity for the GF yet remains active. Using single particle EM methods, we show the AMH prodomain consists of two subdomains: a vestigial TGFβ prodomain-like fold and a novel, helical bundle GF-binding domain, the result of an exon insertion 450 million years ago, that engages both receptor epitopes. When associated with the prodomain, the AMH GF is distorted into a strained, open conformation whose closure upon bivalent binding of AMHR2 displaces the prodomain through a conformational shift mechanism to allow for signaling.

Anti-Müllerian Hormone Signal Transduction involved in Müllerian Duct Regression

Over seventy years ago it was proposed that the fetal testis produces a hormone distinct from testosterone that is required for complete male sexual development. At the time the hormone had not yet been identified but was invoked by Alfred Jost to explain why the Müllerian duct, which develops into the female reproductive tract, regresses in the male fetus. That hormone, anti-Müllerian hormone (AMH), and its specific receptor, AMHR2, have now been extensively characterized and belong to the transforming growth factor-β families of protein ligands and receptors involved in growth and differentiation. Much is now known about the downstream events set in motion after AMH engages AMHR2 at the surface of specific Müllerian duct cells and initiates a cascade of molecular interactions that ultimately terminate in the nucleus as activated transcription factors. The signals generated by the AMH signaling pathway are then integrated with signals coming from other pathways and culminate in a complex gene regulatory program that redirects cellular functions and fates and leads to Müllerian duct regression.

The anti-Müllerian hormone prodomain is displaced from the hormone/prodomain complex upon bivalent binding to the hormone receptor

Noncovalent complexes of transforming growth factor-β family growth/differentiation factors with their prodomains are classified as latent or active, depending on whether the complexes can bind their respective receptors. For the anti-Müllerian hormone (AMH), the hormone-prodomain complex is active, and the prodomain is displaced upon binding to its type II receptor, AMH receptor type-2 (AMHR2), on the cell surface. However, the mechanism by which this displacement occurs is unclear. Here, we used ELISA assays to measure the dependence of prodomain displacement on AMH concentration and analyzed results with respect to the behavior expected for reversible binding in combination with ligand-induced receptor dimerization. We found that, in solution, the prodomain has a high affinity for the growth factor (GF) (K_d = 0.4 pM). Binding of the AMH complex to a single AMHR2 molecule does not affect this K_d and does not induce prodomain displacement, indicating that the receptor binding site in the AMH complex is fully accessible to AMHR2. However, recruitment of a second AMHR2 molecule to bind the ligand bivalently leads to a 1000-fold increase in the K_d for the AMH complex, resulting in rapid release of the prodomain. Displacement occurs only if the AMHR2 is presented on a surface, indicating that prodomain displacement is caused by a conformational change in the GF induced by bivalent binding to AMHR2. In addition, we demonstrate that the bone morphogenetic protein 7 prodomain is displaced from the complex with its GF by a similar process, suggesting that this may represent a general mechanism for receptor-mediated prodomain displacement in this ligand family.

Most Cleaved Anti-Müllerian Hormone Binds Its Receptor in Human Follicular Fluid but Little Is Competent in Serum

CONTEXT

Anti-Müllerian hormone (AMH) is an important clinical marker for diagnosing and assessing the reproductive status and/or disorders in men and women. Most studies have not distinguished between levels of inactive AMH precursor and the cleaved noncovalent complex that binds the AMH type II receptor (AMHRII) and initiates signaling.

OBJECTIVE

The objective of the study was to measure the levels of AMH cleavage and bioactivity in human body fluids.

DESIGN, SETTING, AND PATIENTS

AMH cleavage levels and bioactivity were measured in the serum of six boys and in the follicular fluid and serum of nine control women and 13 women with the polycystic ovary syndrome (PCOS).

MAIN OUTCOME MEASURES

AMH cleavage levels were measured by capturing AMH with an anti-AMH antibody, followed by Western blotting. The bioactivity of cleaved AMH was assessed with an ELISA that measures the levels of AMH capable of binding AMHRII.

RESULTS

PCOS women have an elevated level of AMH cleavage in their follicular fluid (24% vs 8% in control women), and most of the cleaved AMH can bind AMHRII. Higher levels of cleavage are observed in female (60%) and male (79%) serum, but very little of the cleaved AMH can bind AMHRII.

CONCLUSIONS

These results support an autocrine role for AMH in the pathophysiology of PCOS in the follicle. In addition, they indicate that AMH undergoes interactions or structural changes after cleavage that prevent receptor binding, meaning, unexpectedly, that the level of cleaved AMH in biological fluids does not always reflect the level of bioactive AMH.

Constitutive negative regulation in the processing of the anti-Müllerian hormone receptor II

The levels and intracellular localization of wild-type transforming growth factor β superfamily (TGFβ-SF) receptors are tightly regulated by endocytic trafficking, shedding and degradation. In contrast, a main regulatory mechanism of mutation-bearing receptors involves their intracellular retention. Anti-Müllerian hormone receptor II (AMHRII, also known as AMHR2) is the type-II receptor for anti-Müllerian hormone (AMH), a TGFβ-SF ligand that mediates Müllerian duct regression in males. Here, we studied AMHRII processing and identified novel mechanisms of its constitutive negative regulation. Immunoblot analysis revealed that a significant portion of AMHRII was missing most of its extracellular domain (ECD) and, although glycosylated, was unfolded and retained in the endoplasmic reticulum. Exogenous expression of AMHRII, but not of type-II TGF-β receptor (TβRII, also known as TGFR2), resulted in its disulfide-bond-mediated homo-oligomerization and intracellular retention, and in a decrease in its AMH-binding capacity. At the plasma membrane, AMHRII differed from TβRII, forming high levels of non-covalent homomeric complexes, which exhibited a clustered distribution and restricted lateral mobility. This study identifies novel mechanisms of negative regulation of a type-II TGFβ-SF receptor through cleavage, intracellular retention and/or promiscuous disulfide-bond mediated homo-oligomerization.

Quantitative analysis of receptor tyrosine kinase-effector coupling at functionally relevant stimulus levels

A major goal of current signaling research is to develop a quantitative understanding of how receptor activation is coupled to downstream signaling events and to functional cellular responses. Here, we measure how activation of the RET receptor tyrosine kinase on mouse neuroblastoma cells by the neurotrophin artemin (ART) is quantitatively coupled to key downstream effectors. We show that the efficiency of RET coupling to ERK and Akt depends strongly on ART concentration, and it is highest at the low (∼100 pM) ART levels required for neurite outgrowth. Quantitative discrimination between ERK and Akt pathway signaling similarly is highest at this low ART concentration. Stimulation of the cells with 100 pM ART activated RET at the rate of ∼10 molecules/cell/min, leading at 5-10 min to a transient peak of ∼150 phospho-ERK (pERK) molecules and ∼50 pAkt molecules per pRET, after which time the levels of these two signaling effectors fell by 25-50% while the pRET levels continued to slowly rise. Kinetic experiments showed that signaling effectors in different pathways respond to RET activation with different lag times, such that the balance of signal flux among the different pathways evolves over time. Our results illustrate that measurements using high, super-physiological growth factor levels can be misleading about quantitative features of receptor signaling. We propose a quantitative model describing how receptor-effector coupling efficiency links signal amplification to signal sensitization between receptor and effector, thereby providing insight into design principles underlying how receptors and their associated signaling machinery decode an extracellular signal to trigger a functional cellular outcome.

Mutations of the AMH type II receptor in two extended families with persistent Müllerian duct syndrome: lack of phenotype/genotype correlation

Our goal was to compare phenotype and genotype in two extended Middle-Eastern families affected by persistent Müllerian duct syndrome due to mutations of the type II anti-Müllerian hormone receptor (AMHR-II). The first, consanguineous, family consisted of 6 boys and 2 girls, the second consisted of 4 girls and 2 boys. In family I, 4 boys and 1 girl were homozygous for a stop mutation in the 9th exon of AMHR-II, removing part of the intracellular domain of the protein. In family II, 1 girl and 1 boy were homozygous for a transversion changing conserved histidine 254 into a glutamine. Both homozygous girls were normal. In the homozygous males, the degree of development of Müllerian derivatives was variable. The uterus was well developed in 2 boys of family I and in the patient from family II; however, in 1 subject from family I, Müllerian derivatives were undetectable. Taken together, the diversity of clinical symptoms within the same sibship and the lack of correlation between the development of the Müllerian derivatives and the severity of the molecular defects suggest highly variable penetrance of the abnormal alleles and/or the existence of other genetic or epigenetic modifiers of gene expression.

Processing of anti-mullerian hormone regulates receptor activation by a mechanism distinct from TGF-beta

TGF-β family ligands are translated as prepropeptide precursors and are processed into mature C-terminal dimers that signal by assembling a serine/threonine kinase receptor complex containing type I and II components. Many TGF-β ligands are secreted in a latent form that cannot bind their receptor, due to the pro-region remaining associated with the mature ligand in a noncovalent complex after proteolytic cleavage. Here we show that anti-Müllerian hormone (AMH), a TGF-β family ligand involved in reproductive development, must be cleaved to bind its type II receptor (AMHRII), but dissociation of the pro-region from the mature C-terminal dimer is not required for this initial interaction. We provide direct evidence for this interaction by showing that the noncovalent complex binds to a soluble form of AMHRII in an ELISA format and to AMHRII immobilized on Sepharose. Binding of the noncovalent complex to Sepharose-coupled AMHRII induces dissociation of the pro-region from the mature C-terminal dimer, whereas no dissociation occurs after binding to immobilized AMH antibodies. The pro-region cannot be detected after binding of the AMH noncovalent complex to AMHRII expressed on COS cells, indicating that pro-region dissociation may occur as a natural consequence of receptor engagement on cells. Moreover, the mature C-terminal dimer is more active than the noncovalent complex in stimulating Sma- and Mad-related protein activation, suggesting that pro-region dissociation contributes to the assembly of the active receptor complex. AMH thus exemplifies a new mechanism for receptor engagement in which interaction with the type II receptor promotes pro-region dissociation to generate mature ligand.

Natural mutations of the anti-Mullerian hormone type II receptor found in persistent Mullerian duct syndrome affect ligand binding, signal transduction and cellular transport

The anti-Müllerian hormone type II (AMHRII) receptor is the primary receptor for anti-Müllerian hormone (AMH), a protein produced by Sertoli cells and responsible for the regression of the Müllerian duct in males. AMHRII is a membrane protein containing an N-terminal extracellular domain (ECD) that binds AMH, a transmembrane domain, and an intracellular domain with serine/threonine kinase activity. Mutations in the AMHRII gene lead to persistent Müllerian duct syndrome in human males. In this paper, we have investigated the effects of 10 AMHRII mutations, namely 4 mutations in the ECD and 6 in the intracellular domain. Molecular models of the extra- and intracellular domains are presented and provide insight into how the structure and function of eight of the mutant receptors, which are still expressed at the cell surface, are affected by their mutations. Interestingly, two soluble receptors truncated upstream of the transmembrane domain are not secreted, unless the transforming growth factor beta type II receptor signal sequence is substituted for the endogenous one. This shows that the AMHRII signal sequence is defective and suggests that AMHRII uses its transmembrane domain instead of its signal sequence to translocate to the endoplasmic reticulum, a characteristic of type III membrane proteins.

Glial cell line-derived neurotrophic factor (GDNF) receptor alpha-1 (GFR alpha 1) is highly selective for GDNF versus artemin

To clarify whether glial cell line-derived neurotrophic factor (GDNF) receptor alpha-1 (GFRalpha1), the glycosylphosphatidylinositol (GPI)-linked coreceptor for GDNF, is also a functional coreceptor for artemin (ART), we have studied receptor binding, signaling, and neuronal survival. In cell-free binding studies, GFRalpha1-Ig displayed strong preferential binding to GDNF, though in the presence of soluble RET, weak binding to ART could also be detected. However, using GFRalpha1-transfected NB41A3 cells, ART showed no detectable competition against the binding of (125)I-labeled GDNF. Moreover, ART failed to induce phosphorylation of extracellular signal-related kinase (ERK) and Akt in these cells and was >10(4)-fold less potent than GDNF in stimulating RET phosphorylation. When rat primary dorsal root ganglion (DRG) neurons were used, only the survival promoting activity of GDNF and not that of ART was blocked by an anti-GFRalpha1 antibody. These results indicate that although ART can interact weakly with soluble GFRalpha1 constructs under certain circumstances in vitro, in cell-based functional assays GFRalpha1 is at least 10 000-fold selective for GDNF over ART. The extremely high selectivity of GFRalpha1 for GDNF over ART and the low reactivity of ART for this receptor suggest that GFRalpha1 is not likely to be a functional coreceptor for ART in vivo.

LINGO-1 is a component of the Nogo-66 receptor/p75 signaling complex

Axon regeneration in the adult CNS is prevented by inhibitors in myelin. These inhibitors seem to modulate RhoA activity by binding to a receptor complex comprising a ligand-binding subunit (the Nogo-66 receptor NgR1) and a signal transducing subunit (the neurotrophin receptor p75). However, in reconstituted non-neuronal systems, NgR1 and p75 together are unable to activate RhoA, suggesting that additional components of the receptor may exist. Here we describe LINGO-1, a nervous system-specific transmembrane protein that binds NgR1 and p75 and that is an additional functional component of the NgR1/p75 signaling complex. In non-neuronal cells, coexpression of human NgR1, p75 and LINGO-1 conferred responsiveness to oligodendrocyte myelin glycoprotein, as measured by RhoA activation. A dominant-negative human LINGO-1 construct attenuated myelin inhibition in transfected primary neuronal cultures. This effect on neurons was mimicked using an exogenously added human LINGO-1-Fc fusion protein. Together these observations suggest that LINGO-1 has an important role in CNS biology.

Mutations of the anti-mullerian hormone gene in patients with persistent mullerian duct syndrome: biosynthesis, secretion, and processing of the abnormal proteins and analysis using a three-dimensional model

Anti-Müllerian hormone (AMH), a TGF-beta family member, determines whether an individual develops a uterus and Fallopian tubes. Mutations in the AMH gene lead to persistent Müllerian duct syndrome in males. The wild-type human AMH protein is synthesized as a disulfide-linked dimer of two identical 70-kDa polypeptides, which undergoes proteolytic processing to generate a 110-kDa N-terminal dimer and a bioactive 25-kDa TGF-beta-like C-terminal dimer. We have studied the biosynthesis and secretion of wild-type AMH and of seven persistent Müllerian duct syndrome proteins, containing mutations in either the N- or C-terminal domain. Mutant proteins lacking the C-terminal domain are secreted more rapidly than full-length AMH, whereas single amino acid changes in both domains can have profound effects on protein stability and folding. The addition of a cysteine in an N-terminal domain mutant, R194C, prevents proper folding, whereas the elimination of the cysteine involved in forming the interchain disulfide bond, in a C-terminal domain mutant, C525Y, leads to a truncation at the C terminus. A molecular model of the AMH C-terminal domain provides insights into how some mutations could affect biosynthesis and function.

Multiple actions of systemic artemin in experimental neuropathy

The clinical management of neuropathic pain is particularly challenging. Current therapies for neuropathic pain modulate nerve impulse propagation or synaptic transmission; these therapies are of limited benefit and have undesirable side effects. Injuries to peripheral nerves result in a host of pathophysiological changes associated with the sustained expression of abnormal pain. Here we show that systemic, intermittent administration of artemin produces dose- and time-related reversal of nerve injury-induced pain behavior, together with partial to complete normalization of multiple morphological and neurochemical features of the injury state. These effects of artemin were sustained for at least 28 days. Higher doses of artemin than those completely reversing experimental neuropathic pain did not elicit sensory or motor abnormalities. Our results indicate that the behavioral symptoms of neuropathic pain states can be treated successfully, and that partial to complete reversal of associated morphological and neurochemical changes is achievable with artemin.

Developmental regulation of GDNF response and receptor expression in the enteric nervous system

The development of the enteric nervous system is dependent upon the actions of glial cell line-derived neurotrophic factor (GDNF) on neural crest-derived precursor cells in the embryonic gut. GDNF treatment of cultured enteric precursor cells leads to an increase in the number of neurons that develop and/or survive. Here we demonstrate that, although GDNF promoted an increase in neuron number at all embryonic ages examined, there was a developmental shift from a mitogenic to a trophic response by the developing enteric neurons. The timing of this shift corresponded to developmental changes in gut expression of GFR alpha-1, a co-receptor in the GDNF-Ret signaling complex. GFR alpha-1 was broadly expressed in the gut at early developmental stages, at which times soluble GFR alpha-1 was released into the medium by cultured gut cells. At later times, GFR alpha-1 became restricted to neural crest-derived cells. GFR alpha-1 could participate in GDNF signaling when expressed in cis on the surface of enteric precursor cells, or as a soluble protein. The GDNF-mediated response was greater when cell surface, compared with soluble, GFR alpha-1 was present, with the maximal response seen the presence of both cis and trans forms of GFR alpha-1. In addition to contributing to GDNF signaling, cell-surface GFR alpha-1 modulated the specificity of interactions between GDNF and soluble GFR alphas. These experiments demonstrate that complex, developmentally regulated, signaling interactions contribute to the GDNF-dependent development of enteric neurons.

Perturbation of RET signaling in the embryonic kidney

We have used a RET-Ig fusion protein to disrupt signaling in the rat embryonic kidney development pathway. Treatment of embryonic kidney organ cultures with RET-Ig results in a decrease in branching of the ureteric bud and a down regulation in expression of the Wnt-11, Wnt-4, and ld genes. These data suggest that Wnt-11, Wnt-4, and ld function downstream of RET signaling in normal development. Expression of BMP-7, shh, and ptc were uneffected by RET-Ig treatment, implying that these genes are regulated independently of ret. We have also performed immunohistochemistry with a GFR alpha-1 specific polyclonal antisera to localize GFR alpha-1 protein expression in the developing kidney.

Transforming growth factor-beta initiates wound repair in rat liver through induction of the EIIIA-fibronectin splice isoform

A prominent feature of the hepatic response to injury is production of a fetal isoform of fibronectin, a splice variant containing the EIIIA region, which appears very early after injury and derives from sinusoidal endothelial cells. Previous studies have shown that it is instrumental in initiating the cellular response to injury, specifically the conversion of resting stellate cells to myofibroblast-like cells. The present work describes the regulation of this change in fibronectin expression. Using sinusoidal endothelial cells from normal or injured liver in primary culture, we show that exogenous transforming growth factor beta (TGFbeta) stimulates [EIIIA]Fn expression. To assess the role of TGFbeta in vivo, we used a chimeric IgG containing the extracellular portion of the TGFbeta type II receptor as a competitive inhibitor of the cytokine. Administered to animals at the time of injury, the inhibitor reduced expression of [EIIIA]Fn mRNA by 50% as compared to controls (P < 0.01). There was a corresponding decrease in [EIIIA]Fn protein production as judged by immunohistochemistry. Cell fractionation experiments indicated that the changes observed in whole-liver extracts were localized to sinusoidal endothelial cells. We conclude that TGFbeta initiates wound repair in part by stimulating endothelial expression of [EIIIA]Fn. Results with the soluble inhibitor of the TGFbeta type II receptor suggest a novel strategy for modulating wound repair in vivo.

Expression of anti-Müllerian hormone during normal and pathological gonadal development: association with differentiation of Sertoli and granulosa cells

The ontogeny of expression of anti-Müllerian hormone (AMH) was examined by immunohistochemistry in 135 human gonadal tissue specimens of various developmental age, ranging from 6 weeks of fetal development to 38 yr of postnatal age. The series included specimens from normal testes and ovaries and from individuals either with pathological conditions affecting gonadal development or with idiopathic infertility manifested as azoospermia or severe oligozoospermia. AMH expression was found only in Sertoli and granulosa cells. A 6-week-old fetal testis at the indifferent gonad stage did not yet express AMH. The protein was first visible at 8.5 weeks of development, when sex cords have not yet been formed. Afterward, a majority of testicular specimens, including those from pathological conditions, strongly expressed AMH through fetal development and childhood until puberty. Markedly prolonged expression of AMH was observed in a 20-yr-old 46,XY female with androgen insensitivity syndrome, who retained prepubertal testicular morphology. In normal testes, the switch-off of AMH expression was usually associated with the appearance of primary spermatocytes, suggesting that their presence had an inhibitory effect on AMH. However, in adolescent boys lacking germ cells because of cancer treatment and in a majority of infertile adult men with idiopathic germ cell aplasia, AMH expression was also down-regulated despite the complete lack of spermatogenesis. The decrease in AMH expression thus reflects the terminal differentiation of Sertoli cells and is probably only partially dependent upon a regulatory factor associated with the onset of meiosis. In fetal ovaries, AMH was first detected at 36 weeks gestation in granulosa cells of preantral follicles. Thus, the onset of ovarian expression is at the end of fetal life and not in infancy as previously reported.

Kidney injury molecule-1 (KIM-1), a putative epithelial cell adhesion molecule containing a novel immunoglobulin domain, is up-regulated in renal cells after injury

We report the identification of rat and human cDNAs for a type 1 membrane protein that contains a novel six-cysteine immunoglobulin-like domain and a mucin domain; it is named kidney injury molecule-1 (KIM-1). Structurally, KIM-1 is a member of the immunoglobulin gene superfamily most reminiscent of mucosal addressin cell adhesion molecule 1 (MAdCAM-1). Human KIM-1 exhibits homology to a monkey gene, hepatitis A virus cell receptor 1 (HAVcr-1), which was identified recently as a receptor for the hepatitis A virus. KIM-1 mRNA and protein are expressed at a low level in normal kidney but are increased dramatically in postischemic kidney. In situ hybridization and immunohistochemistry revealed that KIM-1 is expressed in proliferating bromodeoxyuridine-positive and dedifferentiated vimentin-positive epithelial cells in regenerating proximal tubules. Structure and expression data suggest that KIM-1 is an epithelial cell adhesion molecule up-regulated in the cells, which are dedifferentiated and undergoing replication. KIM-1 may play an important role in the restoration of the morphological integrity and function to postischemic kidney.

Genomic structure and chromosomal localization of the human GDNFR-alpha gene

GDNFR-alpha is a glycosyl-phosphotidylinositol-linked receptor for glial cell line-derived neurotrophic factor (GDNF). GDNF binds to GDNFR-alpha and this complex, in turn, is believed to interact with the RET receptor tyrosine kinase to effect downstream signalling. GDNFR-alpha belongs to a novel gene family without strong homology to known genes. Thus, little information has been available to help predict genomic structure or location of this gene. In this study, the genomic organization of human GDNFR-alpha was delineated through a combination of PAC clone characterization, long distance PCR and sequence analyses. Exon-intron boundaries were defined by comparing the size and sequence of the genomic PCR products to those predicted by the cDNA sequence. The human GDNFR-alpha gene comprises 9 exons. GDNFR-alpha PAC clones were used for FISH analysis to map this gene to 10q26.

Sequence, genomic organization, and chromosomal location of the mouse Müllerian-inhibiting substance type II receptor gene

We have determined the sequence and structure of the mouse Müllerian-inhibiting substance (MIS) type II receptor gene. Sequence comparisons demonstrate that the mouse, rat, rabbit, and human MIS type II receptors are highly conserved. The mouse MIS type II receptor gene is encoded by 11 exons and spans approximately 9-kb. Only half of the intron/exon boundaries of its kinase domain are conserved in comparison to the kinase domain of the related activin type II receptor. Whereas the activin type II receptor gene contains large introns (> 40-kb), the largest intron of the MIS type II receptor gene is only 4.3-kb. The MIS type II receptor gene (Amhr) is closely linked to Hoxc on mouse chromosome 15. Knowledge of the sequence and genomic structure of Amhr provides important information for the genetic manipulation of the Amhr locus.

Glial cell line-derived neurotrophic factor-dependent RET activation can be mediated by two different cell-surface accessory proteins

Glial cell line-derived neurotrophic factor (GDNF)-dependent activation of the tyrosine kinase receptor RET is necessary for kidney and enteric neuron development, and mutations in RET are associated with human diseases. Activation of RET by GDNF has been shown to require an accessory component, GDNFR-alpha (RETL1). We report the isolation and characterization of rat and human cDNAs for a novel cell-surface associated accessory protein, RETL2, that shares 49% identity with RETL1. Both RETL1 and RETL2 can mediate GDNF dependent phosphorylation of RET, but they exhibit different patterns of expression in fetal and adult tissues. The most striking differences in expression observed were in the adult central and peripheral nervous systems. In addition, the mechanisms by which the two accessory proteins facilitate the activation of RET by GDNF are quite distinct. In vitro binding experiments with soluble forms of RET, RETL1 and RETL2 demonstrate that while RETL1 binds GDNF tightly to form a membrane-associated complex which can then interact with RET, RETL2 only forms a high affinity complex with GDNF in the presence of RET. This strong RET dependence of the binding of RETL2 to GDNF was confirmed by FACS analysis on RETL1 and RETL2 expressing cells. Together with the recent discovery of a GDNF related protein, neurturin, these data raise the possibility that RETL1 and RETL2 have distinctive roles during development and in the nervous system of the adult. RETL1 and RETL2 represent new candidate susceptibility genes and/or modifier loci for RET-associated diseases.

Genetic analysis of the Müllerian-inhibiting substance signal transduction pathway in mammalian sexual differentiation

Müllerian-inhibiting substance (MIS) is a member of the transforming growth factor-beta (TGF-beta) gene family. MIS expression in males causes the regression of the Müllerian ducts, an essential process in male sexual differentiation. Recently, an MIS type II receptor gene has been isolated that is expressed during embryogenesis in mesenchymal cells adjacent to the Müllerian duct epithelium and in Sertoli and granulosa cells of the fetal and adult, male and female gonads, respectively. MIS receptor mutant males develop as internal pseudohermaphrodites, possessing a complete male reproductive tract and also a uterus and oviducts, a phenocopy of MIS ligand-deficient male mice. They express both MIS mRNA and protein, showing that ligand was present, but target organs were hormone-insensitive. All produce sperm, but the majority were infertile because the presence of their female reproductive organs blocks sperm transfer into females. Focal seminiferous tubule atrophy accompanied by Leydig cell hyperplasia was observed and began as early as 2 months of age. The phenotype of MIS ligand/MIS receptor double mutant males was indistinguishable from those of each single mutant. MIS receptor/alpha-inhibin double mutant males developed testicular stromal tumors and large fluid-filled uteri that were identical in phenotype to MIS ligand/alpha-inhibin double mutant males. These studies provide in vivo evidence that MIS is the only ligand of the MIS type II receptor, in contrast to the complexity of other TGF-beta gene family signaling pathways.

Insensitivity to anti-müllerian hormone due to a mutation in the human anti-müllerian hormone receptor

Anti-Müllerian hormone (AMH) and its receptor are involved in the regression of Müllerian ducts in male fetuses. We have now cloned and mapped the human AMH receptor gene and provide genetic proof that it is required for AMH signalling, by identifying a mutation in the AMH receptor in a patient with persistent Müllerian duct syndrome. The mutation destroys the invariant dinucleotide at the 5' end of the second intron, generating two abnormal mRNAs, one missing the second exon, required for ligand binding, and the other incorporating the first 12 bases of the second intron. The similar phenotypes observed in AMH-deficient and AMH receptor-deficient individuals indicate that the AMH signalling machinery is remarkably simple, consisting of one ligand and one type II receptor.

In vivo administration of CD4-specific monoclonal antibody: effect on provirus load in rhesus monkeys chronically infected with the simian immunodeficiency virus of macaques

Since monoclonal antibodies (MAb) specific for CD4 are potent inhibitors of HIV and SIV replication in vitro, we explored their potential usefulness in vivo as an AIDS therapy. The anti-CD4 MAb 5A8 binds to domain 2 of the CD4 molecule and inhibits virus replication and virus-induced cell fusion at a postvirus binding step. Administration of this MAb to normal rhesus monkeys coats all circulating and lymph node CD4 cells and induces neither CD4 cell clearance nor measurable immunosuppression. In the present study, monkeys chronically infected with the simian immunodeficiency virus of macaques (SIVmac) had stable levels of SIVmac provirus in PBMC prior to treatment as measured by a quantitative polymerase chain reaction technique. Six infected monkeys treated with anti-CD4 MAb demonstrated a significant decrease in SIVmac provirus level after 9 days. Of these monkeys, 3 had > 800 CD4 cells/microliter and developed strong antimouse Ig responses that prevented further treatment. The remaining 3 monkeys had < 800 CD4 cell/microliter and failed to develop antimouse Ig antibody responses. When treatment was continued for 12-21 days in these monkeys, a sustained or further decrease in SIVmac provirus load occurred over the extended treatment period. Four monkeys that received a control MAb of irrelevant specificity for 9-22 days showed either no significant change or a transient increase in SIVmac provirus. Thus, the passive administration of anti-CD4 MAb may exert a specific antiviral effect in controlling immunodeficiency virus infection in vivo.

Müllerian-inhibiting substance function during mammalian sexual development

To investigate the role of Müllerian-inhibiting substance (MIS) in mammalian sexual development, we generated MIS-deficient mice. Although MIS-deficient males had testes that were fully descended and produced functional sperm, they also developed female reproductive organs, which interfered with sperm transfer into females, rendering most of these males infertile. Their testes had Leydig cell hyperplasia and, in one instance, neoplasia. The actions of the two primary hormones of male sexual differentiation were genetically eliminated using the testicular feminization (Tfm) mutation in combination with the MIS mutant allele. XY Tfm/MIS double mutants developed as females, with a uterus, coiled oviducts, and no male reproductive organs except undescended dysfunctional testes. These results suggest that eliminating the presumptive female reproductive tract in male fetuses facilitates fertility and that in testes MIS is a negative regulator of Leydig cell proliferation. Eliminating the presumptive male reproductive tract is necessary for proper oviductal morphogenesis during female mouse development.

Anti-müllerian hormone in children with androgen insensitivity

Anti-Müllerian hormone (AMH), also called Müllerian inhibiting substance or factor, is secreted in high amounts by the immature Sertoli cell; it is negatively regulated by testosterone at puberty. In the present study, we measured serum AMH in 20 patients with defects of androgen synthesis or action: 9 with complete androgen insensitivity syndrome, 9 with a partial form, 1 patient with 3 beta-hydroxysteroid dehydrogenase deficiency, and 1 with Leydig cell agenesis. AMH was also determined in 15 control patients with idiopathic male pseudohermaphroditism. The serum AMH concentration was elevated in all testosterone-insensitive or -deficient patients compared with control levels during the first year of life. From 1 yr of age to the onset of puberty, serum AMH levels in patients with androgen insensitivity returned to normal values, but after pubertal development began, AMH levels again rose to extremely high levels in the complete androgen insensitivity syndrome. These results suggest that AMH is negatively regulated by testosterone not only at puberty, but also during the postnatal period. An elevation of serum AMH appears to be an interesting marker of androgen resistance or defect of androgen production in sexually ambiguous male infants.

Anti-müllerian hormone and testosterone serum levels are inversely during normal and precocious pubertal development

Anti-Müllerian hormone (AMH), also called Müllerian inhibiting substance or factor, is produced by Sertoli cells from fetal life until puberty. In the present study, AMH, testosterone (T), LH, and FSH were measured by immunochemical methods in the serum of 50 boys with normal or delayed pubertal development, 4 patients with suspected androgen insensitivity, and 11 patients with either central (CPP) or gonadotropin-independent (GIPP) precocious puberty to investigate the hormonal regulatory mechanisms of AMH secretion at puberty. An inverse relationship between AMH and T levels was demonstrated. In boys with normal or delayed puberty with T concentrations below 6.7 nmol/L, AMH values were elevated (mean +/- SEM, 22.4 +/- 3.1 micrograms/L) and widely dispersed. In subjects with T levels over 6.7 nmol/L, AMH levels were uniformly low (3.4 +/- 0.5 micrograms/L), except in patients with suspected androgen insensitivity. No significant relationship was found between AMH and gonadotropin levels. Similar results were obtained in patients with either CPP or GIPP. Longitudinal studies were performed on four boys with CPP and two with GIPP before and after treatment. At the time of diagnosis, the T concentration was high, and AMH levels were usually low in CPP and GIPP patients alike. When appropriate treatment was initiated, the T concentration was normalized within 2-4 weeks, but restoration of prepubertal AMH levels required several months. Mature Sertoli cells were observed in testicular biopsies performed in three patients with untreated GIPP. Our results suggest that gonadotropins are not directly implicated in repression of AMH synthesis at puberty, but, rather, that the decrease in AMH production is the consequence of an androgen-mediated, long term, reversible chain of events leading to morphological and functional maturation of the Sertoli cells. Thus, the fall in serum AMH levels appears to be an excellent marker of Sertoli cell pubertal development.

Mullerian inhibiting substance requires its N-terminal domain for maintenance of biological activity, a novel finding within the transforming growth factor-beta superfamily

Mullerian inhibiting substance (MIS)/anti-Mullerian hormone is a differentiation factor that causes regression of the Mullerian duct in the developing male fetus and an apparent sex reversal of the fetal ovary when inappropriately exposed to it. The purified product is a 140-kilodalton glycoprotein composed of two identical subunits. We show that a C-terminal fragment of MIS, which shares homology with transforming growth factor-beta, causes regression of the Mullerian duct and inhibits the biosynthesis of aromatase in the fetal ovary. However, both activities are enhanced dramatically by addition of the N-terminal portion of MIS. Under conditions where potentiation occurs, the N- and C-terminal domains of MIS reassociate. These results indicate that the N-terminus of MIS, unlike that of the other members of the transforming growth factor-beta family, plays a role in maintaining the biological activity of the C-terminus.

Detection of DNA in Southern blots with chemiluminescence

The chemiluminescent detection methods described in this chapter have been successfully applied to the detection of plasmid DNA and genomic DNA in Southern and sequencing protocols. The high sensitivity and the simplicity of AMPPD are instrumental in making the chemiluminescent detection of DNA successful in hybridization assays. This detection technique has also been used to detect DNA in dot blots and in situ hybridization experiments as well as proteins in enzyme-linked immunosorbent assays (ELISAs) and Western blots.

Directed expression of an oncogene to Sertoli cells in transgenic mice using mullerian inhibiting substance regulatory sequences

Mullerian inhibiting substance (MIS) is a glycoprotein hormone expressed by Sertoli cells that induces the regression of Mullerian ducts during development of the male reproductive tract. Transgenic mice carrying a fusion gene composed of human MIS transcriptional regulatory sequences linked to the SV40 T-antigen gene specifically develop testicular tumors composed of a cell type histologically resembling the Sertoli cell. The lack of pathology at other sites suggests tissue-restricted expression of the transgene. A cell line derived from one of the testicular tumors has been established that continues to express markers associated with Sertoli cells, such as transferrin, sulfated glycoprotein-2, and inhibin-beta B. The cell line does not express detectable levels of inhibin-alpha, MIS, or FSH receptor. However, the cells have retained forskolin responsiveness. As adult Sertoli cells cannot be propagated in vitro, the availability of an immortal cell line displaying features characteristic of normal Sertoli cells should aid in subsequent analyses of the biology of this cell type.

Isolation of the rat gene for Mullerian inhibiting substance

Mullerian inhibiting substance (MIS), a testicular glycoprotein also known as anti-Mullerian hormone, plays a key role in male sexual development by causing regression of the Mullerian duct, the anlagen of the uterus, the Fallopian tubes, and part of the vagina. MIS is also expressed in the postnatal ovary, but its precise function is still not known. We report here the complete nucleotide sequence of the rat MIS gene. Rat MIS is encoded in five exons and is synthesized as a precursor of 553 amino acids, containing a 24-amino-acid leader. Based on homology with human MIS, we predict that the rat protein undergoes proteolytic processing at a site 108 amino acids from the C-terminus. Expression of the rat MIS mRNA is high in the 1-day-postnatal testis and decreases to a low level in the adult testis. In contrast, expression is not detected in the 1-day ovary, but increases to an intermediate level in the adult ovary. The rat gene should provide a good model for studying transcriptional regulation of MIS in the testis and ovary.

A quantitative and interspecific test for biological activity of anti-mullerian hormone: the fetal ovary aromatase assay

Anti-Mullerian hormone (AMH), also known as Mullerian-inhibiting substance or factor, has previously been shown to sex-reverse the steroidogenic pattern of fetal mammalian ovaries through repression of aromatase biosynthesis. Study of the ontogeny of the response of cyclic AMP-stimulated aromatase activity of rat fetal ovaries to AMH has allowed us to develop a quantitative bioassay for the hormone. Linear responses as a function of the logarithm of AMH concentration were observed over ranges of 0.2-7.5 micrograms/ml for the bovine protein and 0.15-2 micrograms/ml for the human protein, with a maximal decrease in aromatase activity of 90% for both proteins. Under the same in vitro conditions, AMH treatment did not affect cyclic AMP-stimulated fetal rat testicular aromatase activity. Partially purified chick AMH also decreased rat ovarian aromatase activity, allowing us to use this test to study AMH ontogeny in chick gonads. Analysis of the species specificity of AMH repression of ovarian aromatase activity indicated that turtle and rat fetal ovaries responded to AMH of other vertebrate classes, whereas aromatase activity of chick embryo ovaries could be repressed only by the homospecific hormone.

Developmentally regulated polyadenylation of two discrete messenger ribonucleic acids for müllerian inhibiting substance

Mullerian inhibiting substance (MIS) is a 140-kilodalton homodimeric glycoprotein that causes regression of the Mullerian ducts in male embryos, and may also have a role in both males and females in the regulation of germ cell maturation. We examined the ontogeny of MIS messenger RNA (mRNA) in rat testes from midgestation through adulthood and found two discrete MIS mRNA species that are developmentally regulated. The larger 2.0-kilobase species is abundant at embryonic day 14, then decreases in late gestation, and is barely detectable after birth. The smaller 1.8-kilobase species is first noted at embryonic day 18 and is the major species detected postnatally. Both species are abundant just prior to birth, at embryonic day 21, then decrease markedly after birth. This variation in MIS mRNA levels correlates with the developmental expression of MIS protein. A series of oligonucleotide-directed ribonuclease H mapping experiments determined that the two mRNA species differ at their 3' ends in the extent of polyadenylation. Thus, differential polyadenylation of MIS mRNA may be an additional mechanism for regulating MIS expression during fetal and postnatal development.

Insensitivity of the chick embryo müllerian duct to human recombinant müllerian-inhibiting substance

To determine whether mammalian Müllerian-inhibiting substance (MIS) is active in birds, Müllerian ducts from 7- to 8-day-old male or female chick embryos were cultured in the presence of human recombinant MIS at concentrations between 2.5 and 12.5 micrograms/ml. None of 20 ducts regressed at any concentration. In contrast, at concentrations of 2.5-5 micrograms/ml, all 12 Müllerian ducts from 13-day-old male mouse embryos and 13 out of 14 female ducts were inhibited to varying degrees. It is concluded that avian Müllerian ducts are unresponsive to mammalian MIS. There may be a difference in structure between the MIS of birds and mammals, or the signal-transduction system may be different.

Correlation of gene and protein structure of rat and human lipocortin I

Lipocortins (annexins) are a family of calcium-dependent phospholipid-binding proteins with phospholipase A2 inhibitory activity. The characteristic primary structure of members of this family consists of a core structure of four or eight repeated domains, which have been implicated in calcium-dependent phospholipid binding. In two lipocortins (I and II) a short amino-terminal sequence distinct from the core structure has potential regulatory functions which are dependent on its phosphorylation state. We have isolated the rat and the human lipocortin I genes and found that they both consist of 13 exons with a striking conservation of their exon-intron structure and their promoter and amino acid sequences. Both lipocortin I genes are at least 19 kbp in length with exons ranging from 57 to 123 bp interrupted by introns as large as 5 kbp. Each of the four repeat units of lipocortin I are encoded by two consecutive exons while individual exons code for the highly conserved putative calcium-binding domains. The promoter sequences in the rat and in human genes are highly conserved and contain nucleotide sequences characterized as enhancer sequences in other genes. The structure of the lipocortin I gene lends support to the hypothesis that the lipocortin genes arose by a duplication of a single domain.

Genomic Southern analysis with alkaline-phosphatase-conjugated oligonucleotide probes and the chemiluminescent substrate AMPPD

We have used a chemiluminescent detection method to improve both the sensitivity and the speed of detection of human genes with oligonucleotide probes. A direct chemiluminescent substrate (AMPPD) was used in combination with an alkaline-phosphatase-labeled oligonucleotide probe to detect the human tissue of plasminogen activator gene by Southern blot analysis. X-ray exposures obtained after 4 h were comparable to those obtained after 7 days with a 32P-labeled oligomer. After 16 h, the signal was 12 times greater than the 32P signal. The detection of the single-copy tissue plasminogen activator gene in 0.25 micrograms of human genomic DNA (76,000 molecules) was achieved. The improved sensitivity obtained by chemiluminescent detection should increase the usefulness of oligonucleotide probes in the direct Southern analysis of human genetic disorders.

Imaging of DNA sequences with chemiluminescence

We have coupled a chemiluminescent detection method that uses an alkaline phosphatase label to the genomic DNA sequencing protocol of Church and Gilbert [Church, G. M. & Gilbert, W. (1984) Proc. Natl. Acad. Sci. USA 81, 1991-1995]. Images of sequence ladders are obtained on x-ray film with exposure times of less than 30 min, as compared to 40 h required for a similar exposure with a 32P-labeled oligomer. Chemically cleaved DNA from a sequencing gel is transferred to a nylon membrane, and specific sequence ladders are selected by hybridization to DNA oligonucleotides labeled with alkaline phosphatase or with biotin, leading directly or indirectly to deposition of enzyme. If a biotinylated probe is used, an incubation with avidin-alkaline phosphatase conjugate follows. The membrane is soaked in the chemiluminescent substrate (AMPPD) and is exposed to film. Dephosphorylation of AMPPD leads in a two-step pathway to a highly localized emission of visible light. The demonstrated shorter exposure times may improve the efficiency of a serial reprobing strategy such as the multiplex sequencing approach of Church and Kieffer-Higgins [Church, G. M. & Kieffer-Higgins, S. (1988) Science 240, 185-188].

Abnormal sexual development in transgenic mice chronically expressing müllerian inhibiting substance

Müllerian inhibiting substance (MIS), also known as anti-Müllerian hormone, is a glycoprotein normally secreted by the Sertoli cells of the fetal and adult testis and by granulosa cells of the postnatal ovary. The production of MIS in the male fetus brings about the regression of the Müllerian ducts, the anlagen of the uterus, oviducts, and upper vagina. In addition, purified MIS induces the formation of seminiferous cord-like structures in fetal rat ovaries cultured in vitro, suggesting that MIS may influence testicular differentiation. We have produced transgenic mice chronically expressing human MIS under the control of the mouse metallothionein-1 promoter to investigate its role during sexual development. In females, chronic expression led to the inhibition of Müllerian duct differentiation, resulting in a blind vagina and no uterus or oviducts. At birth the ovaries had fewer germ cells than normal; during the next two weeks germ cells were lost and the somatic cells became organized into structures resembling seminiferous tubules. Apparently, these structures degenerate as they are undetectable in adult females. The majority of transgenic males developed normally. But in two lines with the highest levels of MIS expression, some males showed feminization of the external genitalia, impairment of Wolffian duct development, and undescended testes. These results suggest that MIS has several distinct roles in mammalian sexual development.

An immunoassay to detect human müllerian inhibiting substance in males and females during normal development

An enzyme-linked immunosorbent assay has been developed to measure human Müllerian inhibiting substance (MIS) in biological fluids. The enzyme-linked immunosorbent assay is specific for MIS, with a sensitivity in human serum to 0.5 ng/ml and does not recognize transforming growth factor-beta 1 or -beta 2, LH, or FSH. It similarly fails to recognize other proteins secreted from the cell type into which the MIS gene was cloned. MIS was detected in the serum of normal newborns, infants, children, and adults. In males the serum level of MIS is 10-70 ng/mL at birth. The level increases slightly after birth, and then decreases to a basal level of 2-5 ng/mL after the first 10 yr of life. Newborn male urine contains minimal amounts of MIS (0.5 ng/mL). In females MIS is barely detectable in serum at birth, but rises to the basal level equal to that seen in males after 10 yr of age. Similar basal levels of MIS were found in adult ovarian follicular fluid. MIS levels were high in the serum of a female patient with a sex cord tumor (3200 ng/mL), but fell to 100 ng/mL after multiple excisional operations. In addition, a serum MIS level of 20 ng/mL was detected in a patient with an ovarian granulosa cell tumor. A sensitive assay for MIS could be useful in the diagnosis of patients with congenital abnormalities of sexual development and patients with Sertoli cell and/or other MIS-producing neoplasms. Other applications may also be recognized as the biology of MIS in both males and females is further elucidated.

Minimal antiproliferative effect of recombinant müllerian inhibiting substance on gynecological tumor cell lines and tumor explants

Múllerian Inhibiting Substance (MIS) is a testicular hormone that promotes involution of the Múllerian duct during embryogenesis. The Múllerian duct gives rise to adult female reproductive ducts including the fallopian tubes, uterus, and upper vagina. Thus, testicular MIS ensures the regression of female sex organ primordia. Partially purified bovine MIS was reported to inhibit proliferation of tumor cells derived from human gynecological cancers. These observations suggest that MIS might be an effective anticancer agent for some human tumors. Recombinant human MIS (rHu-MIS) has recently become available. To assess the antiproliferative activity of rHu-MIS, we examined its effects on 11 ovarian, six endometrial, and two nongynecological human tumor cell lines. rHu-MIS had no effect on proliferation of these cell lines in five independent assays. Forty-three primary human tumor explants were also examined in human tumor colony forming assays, gel-supported primary culture assays, and subrenal capsule assays. rHu-MIS significantly inhibited the growth of five of these tumors including four ovarian and one small cell lung cancer explant. The four ovarian cancer responses include three of 13 (23%) explants tested in human tumor colony-forming assays and one of eight (12.5%) explants tested in gel-supported primary culture assays. We conclude that rHu-MIS may have antiproliferative activity against some human ovarian cancers.