Variation in the ribosomal internal transcribed spacers and 5.8S rDNA among five species of Acropora (Cnidaria; Scleractinia): patterns of variation consistent with reticulate evolution

The ITS sequences of Acropora spp. are the shortest so far identified in any metazoan and are among the shortest seen in eukaryotes; ITS1 was 70-80 bases, and ITS2 was 100-112 bases. The ITS sequences were also highly variable, but base composition and secondary structure prediction indicate that divergent sequence variants are unlikely to be pseudogenes. The pattern of variation was unusual in several other respects: (1) two distinct ITS2 types were detected in both A. hyacinthus and A. cytherea, species known to hybridize in vitro with high success rates, and a putative intermediate ITS2 form was also detected in A. cytherea; (2) A. valida was found to contain highly (29%) diverged ITS1 variants; and (3) A. longicyathus contained two distinct 5.8S rDNA types. These data are consistent with a reticulate evolutionary history for the genus Acropora.

Successful treatment of established relapsing experimental autoimmune encephalomyelitis in mice with a monoclonal natural autoantibody

We postulated that humoral autoimmunity can play a beneficial role in CNS demyelinating diseases such as multiple sclerosis. We previously demonstrated that monoclonal natural autoantibody SCH94.03 suppresses CNS inflammation and promotes remyelination in a virus-induced model of chronic progressive multiple sclerosis. To further investigate the relationship between natural autoimmunity and CNS demyelination, we examined the effect of SCH94.03 treatment on clinical relapses and pathological disease in SJL/J mice with established adoptive-transfer relapsing experimental autoimmune encephalomyelitis. Treatment with SCH94.03 after recovery from the initial episode of clinical disease reduced relapse rates by half, prolonged relapse onset by 6 days and reduced spinal cord demyelination and meningeal inflammation by 40%. These results are consistent with the hypothesized immunomodulatory function of natural autoantibodies, and are the first direct demonstration that natural humoral autoimmunity can be beneficial in an autoimmune T-cell-mediated CNS demyelinating disease.

Sperm plasma membrane remodeling during spermiogenetic maturation in men: relationship among plasma membrane beta 1,4-galactosyltransferase, cytoplasmic creatine phosphokinase, and creatine phosphokinase isoform ratios

Sperm creatine phosphokinase (CK) concentrations and the synthesis of the CK-M isoform reflect normal spermiogenesis and predict maturity and fertilizing potential of ejaculated human spermatozoa. Immature spermatozoa, characterized by cytoplasmic retention and low CK-M to CK-B isoform ratios, are deficient in zona binding and fail to cause pregnancies. Because these sperm lack zona-binding ability, we examined in this study whether beta 1,4-galactosyltransferase (GalTase), a key element of sperm-zona interactions in mice, is diminished in immature human sperm. Unexpectedly, GalTase was overexpressed in immature sperm relative to mature sperm: the levels of cytoplasmic CK and plasma membrane GalTase were positively correlated (r = 0.78, p < 0.001, n = 88). Sperm populations with various levels of cellular maturity, prepared by Percoll gradients, had different CK and GalTase concentrations, but within each subpopulation the relationship between CK and GalTase was maintained (p < 0.01-0.001). GalTase activities in intact and vortex-disrupted sperm fractions were similar, showing that GalTase is present on the surface membrane of human sperm--similar to the situation in all other species assayed. The changes previously reported by our laboratory in zona-binding ability and lipid peroxidation rates (which occur simultaneously with cytoplasmic extrusion), decline in CK activity, and increased expression of the CK-M isoform are suggestive of a remodeling of the sperm surface concomitant with cytoplasmic maturation. The changes reported here in GalTase expression on the surface of maturing spermatozoa prove this hypothesis.

Internal and external relationships of the Cnidaria: implications of primary and predicted secondary structure of the 5'-end of the 23S-like rDNA

Since both internal (class-level) and external relationships of the Cnidaria remain unclear on the basis of analyses of 18S and (partial) 16S rDNA sequence data, we examined the informativeness of the 5'-end of the 23S-like rDNA. Here we describe analyses of both primary and predicted secondary structure data for this region from the ctenophore Bolinopsis sp., the placozoan Trichoplax adhaerens, the sponge Hymeniacidon heliophila, and representatives of all four cnidarian classes. Primary sequence analyses clearly resolved the Cnidaria from other lower Metazoa, supported sister group relationships between the Scyphozoa and Cubozoa and between the Ctenophora and the Placozoa, and confirmed the basal status of the Anthozoa within the Cnidaria. Additionally, in the ctenophore, placozoan and sponge, non-canonical base pairing is required to maintain the secondary structure of the B12 region, whereas amongst the Cnidaria this is not the case. Although the phylogenetic significance of this molecular character is unclear, our analyses do not support the close relationship between Cnidaria and Placozoa suggested by previous studies.

Genomes of diploblastic organisms contain homeoboxes: sequence ofeveC, aneven-skippedhomologue from the cnidarianAcropora formosa

We report the nucleotide sequence of eveC, a cnidarian eve-class homeobox; this is the first homeobox to be identified in any diploblastic organism, and is only the second eve-class in an invertebrate. Similarity between the predicted amino acid sequence of the eveC homeodomain and its insect and vertebrate equivalents was approximately 75-80% but, in the case of eveC, a role in segmentation can be ruled out. Our findings thus support the 'co-option' hypothesis: homeoboxes were an early feature of metazoan genomes, corresponding to the DNA-binding domains of more general transcription factors.

Treatment and prevention of porcine proliferative enteropathy with oral tiamulin

The effect of an oral treatment or prevention programme, incorporating the antibiotic tiamulin, on the development of proliferative enteropathy in experimentally challenged pigs was studied. Twenty weaner pigs were challenged orally with a virulent inoculum of Lawsonia intracellularis strain LR189/5/83, a British isolate of the causative agent of porcine proliferative enteropathy, and seven control pigs were dosed with a buffer solution. Seven of the 20 challenged pigs were left untreated; they gained less weight than the controls and three of them developed mild to moderate diarrhoea two weeks after the challenge. All seven developed lesions, six visible grossly, of proliferative enteropathy, and numerous intracellular L intracellularis were detected in sections of the intestines examined three weeks after the challenge. To test a 'prevention' dosing strategy for tiamulin, six of the challenged pigs were dosed orally with 50 ppm tiamulin, incorporated in a 2 per cent stabilised premix, given from two days before the challenge until they were euthanased. To test a 'treatment' strategy, the remaining group of seven challenged pigs were dosed orally with 150 ppm tiamulin given in the premix from seven days after challenge until they were euthanased. All the control pigs and the 13 pigs treated with tiamulin, either before or after challenge, remained clinically normal and had no specific lesions of proliferative enteropathy in sections of the intestines examined post mortem.

Nucleotide sequence of ub52 from the cnidarian Acropora millepora reveals high evolutionary conservation

We report the cDNA sequence encoding Ub52 from the cnidarian Acropora millepora. As in other eukaryotes, the N-terminal region of the deduced amino-acid sequence is a ubiquitin moiety and the C-terminal region CEP52, a protein component of the large ribosomal subunit. A millepora Ub52 is highly homologous (> 95% identical) with the corresponding Drosophila and vertebrate sequences, the cnidarian sequence having higher identity with these 'higher' metazoan homologs than does the corresponding Caenorhabditis elegans protein. However, the cnidarian sequence contains two unique substitutions in the ubiquitin moiety, Ser22 and Thr28. Northern analysis indicates that A. millepora Ub52 is encoded by a small (< 800 nt) mRNA present in eggs and is first expressed after the early gastrula stage in embryonic development.

Enhanced SR function in saponin-treated ventricular trabeculae from rabbits with heart failure

Cardiac sarcoplasmic reticulum (SR) Ca(2+)-loading ability was assessed in a coronary artery ligation model of heart failure. Heart failure was produced in New Zealand White rabbits by ligation of the left marginal coronary artery. Sham-operated animals were used as controls. After hemodynamic and echocardiographic assessment 8 wk after coronary ligation, a free-running trabecula was isolated from the left or right ventricle, mounted for isometric tension measurement, and permeabilized with the chemical skinning agent saponin, leaving the SR functionally intact. The SR was Ca2+ loaded by exposure of the preparation to a mock intracellular solution with a Ca2+ concentration ([Ca2+]) of 150-300 nM. The amplitude of the caffeine-induced contracture was used as a measure of Ca2+ loaded by the SR. The same preparation was then treated with Triton X-100 to disrupt all cell membranes, and Ca2+ sensitivity {expressed as [Ca2+] required to produce 50% of maximal activation (pCa50)} of isometric tension production and maximum Ca2+ activated force (Cmax) were measured. Ligated animals demonstrated enhanced SR Ca(2+)-loading ability that correlated with the degree of left ventricular dysfunction. Enhanced SR Ca2+ loading was associated with evidence of SR Ca2+ overload revealed as spontaneous tension oscillations. Cmax and pCa50 were not significantly different from controls. Increased SR Ca(2+)-loading ability may predispose the SR to Ca2+ overload and could contribute to both contractile dysfunction and arrhythmogenesis in heart failure.

The dipeptide carnosine constricts rabbit saphenous vein as a zinc complex apparently via a serotonergic receptor

1. The endogenous dipeptide carnosine (beta-alanyl-L-histidine), at 0.1-10 mM, provokes sustained contractures in rabbit saphenous vein rings with greater efficacy than noradrenaline (NA). 2. The effects of carnosine are specific; anserine and homocarnosine are ineffective, as are carnosine's constituent amino acids histidine and beta-alanine. 3. Maximum carnosine-induced tension is enhanced by Zn ions (e.g. to 127.5 +/- 13.1% of control at 10 microM total Zn concentration, Zntot) and the sensitivity to carnosine potentiated (mean [carnosine] required for half-maximal tension, K1/2, reduced from 1.23 mM to 17.0 microM carnosine with 15 microM Zntot). 4. The dipeptide apparently acts as a zinc-carnosine complex. The effects of carnosine at concentrations of 1 microM to 10 mM in the presence of 1-100 microM Zntot, can be described as a unique function of the concentration of Zn-carnosine, with an apparent K1/2 for the complex of 7.4 x 10(-8) M. 5. Contractures are reduced at low [Ca2+], unaffected by adrenoceptor antagonists, but can be blocked by serotonergic receptor antagonists including ketanserin and methiothepin. 6. Competition between albumin and carnosine for Zn ions, as might occur in plasma, can be demonstrated experimentally. 7. The mode of action of carnosine is virtually unique: a vascular muscle receptor apparently transduces the action of a dipeptide in the form of a metal chelate.

Multi-organ reactivity of a monoclonal natural autoantibody that promotes remyelination in a mouse model of multiple sclerosis

A contemporary view of autoimmunity suggests that self-reactivity is a normal phenomenon, in contrast to the classical association between autoimmunity and immunopathology. We have previously demonstrated that monoclonal antibody SCH94.03, a natural autoantibody with polyreactivity towards several purified protein and hapten antigens, promotes central nervous system remyelination when passively transferred to SJL/J mice chronically infected with Theiler's murine encephalomyelitis virus, an established experimental model of multiple sclerosis. In this study we characterized the autoreactivity of SCH94.03 with endogenous mouse tissue using immunoperoxide and multiple-color immunofluorescence staining techniques on frozen tissue sections. Within the nervous system, SCH94.03 labeled fibrous astrocytes, ependymal cells, ganglion satellite cells, and a sub-population of microglia, oligodendrocytes, and peripheral nervous system neurons. Outside the nervous system, SCH94.03 labeled gastrointestinal tract smooth muscle and luminal epithelium, erythrocytes, and interdigitating dendritic cells in peripheral lymphoid organs. These data indicate that SCH94.03 is a multi-organ reactive autoantibody and support the hypothesis that autoantibodies can have a beneficial rather than a pathogenic function in central nervous system demyelinating diseases.

Breastfeeding practices among resident physicians

OBJECTIVE

To determine how employment as a resident physician (resident) affects breastfeeding practices and experiences.

DESIGN

Cross-sectional questionnaire survey.

SETTING

US resident physicians in the second half of their postgraduate year three (PGY3).

PARTICIPANTS

1500 questionnaires were mailed at random to female 1990 graduates of American medical schools. After eliminating unusable surveys, an adjusted response rate of 45% produced 450 surveys; 60 delivered a child during residency.

INTERVENTIONS

None. MEASUREMENT/MAIN RESULTS: Forty-eight (80%) of 60 residents who delivered initiated breastfeeding, and continued for the duration of their maternity leave (mean, 7 weeks). With a return to residency half (24) of those who had initiated breastfeeding discontinued breastfeeding. The breastfeeding rate dropped to 15% (9/60) at 6 months. Residency work schedule was the most common reason (80%) for discontinuing breastfeeding. Of the 24 residents who continued breastfeeding while working, 83% pumped breast milk during their work shifts; 79% felt there was insufficient time during work, and 42% reported no appropriate place at work to express milk. Only 54% who continued felt supported by their attending physicians for their efforts to breastfeed; 67% felt colleagues were supportive.

CONCLUSIONS

The breastfeeding initiation rate for resident mothers was in compliance with the Healthy People 2000 guidelines, but the rate at infant age 6 months fell well below the goal of 50%. Modifiable factors in residents' work sites include both physical and emotional accommodations to encourage resident mothers to breastfeed.

cDNAs from Onchocerca sp. encoding members of the MRS3/MRS4 class of mitochondrial solute carriers

cDNA clones from the parasitic nematodes Onchocerca volvulus and Onchocerca gibsoni encode homologs of the yeast proteins MRS3 and MRS4. Together with an uncharacterised ORF on chromosome III of Caenorhabditis elegans, these constitute a new class of proteins belonging to the mitochondrial solute carrier protein superfamily. So far, five other members of this protein family have been identified in C. elegans, but levels of identity between these and the Onchocerca proteins were considerably lower. Consideration of cysteine content and overall charge implies that the natural substrates of the nematode proteins are small ions.

Central nervous system remyelination clinical application of basic neuroscience principles

Studies in both humans and experimental animals have demonstrated that myelin repair in the CNS is a normal physiological response to myelin damage, similar to tissue injury elsewhere in the body. The unanswered question is why myelin repair is incomplete in multiple sclerosis patients. In this paper we review the morphological characteristics of remyelination, discuss the available animal models of CNS demyelination and their usefulness to identify the molecular, cellular, and morphological events involved in CNS myelin repair, examine the use of immunosuppression, immunoglobulins, protein growth factors, and glial cell transplantation at the primary experimental therapies designed to promote CNS remyelination, and address the potential electrophysiological and clinical benefits of myelin repair in the CNS.

Spontaneous central nervous system remyelination in strain A mice after infection with the Daniel's (DA) strain of Theiler's virus

Intracerebral infection of susceptible SJL/J (H-2s) mice with the Daniel's strain of Theiler's murine encephalomyelitis virus produces chronic, progressive, inflammatory central nervous system demyelination, with minimal spontaneous remyelination. To assess the role of host genetic factors in spontaneous myelin repair following chronic infection with the Daniel's strain of Theiler's virus, we examined demyelination and spontaneous remyelination in strain A mice after infection with Theiler's virus. We found that A.BY/SnJ (H-2a), and A.SW/SnJ (H-2s) mice all developed chronic demyelination with substantial spontaneous remyelination 90 days after infection. In the spinal cords of both A/J and A/WySnJ mice, one quarter of the total lesion area showed spontaneous remyelination, whereas in A.SW/SnJ mice, the extent of remyelination increased to two thirds of the total lesion area. The spontaneous remyelination seen in strain A mice was consistent with myelin repair by oligodendrocytes and Schwann cells, and occurred despite the presence of persistent virus antigen. These results indicate that host-pathogen interactions play an important role in myelin regeneration after virus-induced demyelination, and suggest that host genetic factors influence spontaneous remyelination.

Monoclonal autoantibody SCH94.03, which promotes central nervous system remyelination, recognizes an antigen on the surface of oligodendrocytes

A monoclonal antibody SCH94.03, made in syngeneic mice by injection of spinal cord homogenate, promotes central nervous system remyelination when injected into SJL/J mice chronically infected with Theiler's virus. To elucidate the mechanism of antibody-mediated remyelination, SCH94.03 was investigated by immunocytochemistry, flow cytometry, immunoelectron microscopy, Western blotting, and immuno-thin layer chromatography. All cell types investigated in vitro showed strong cytoplasmic staining with a pattern resembling a cytoskeletal protein. In contrast, among the primary cultured cells studied, only oligodendrocytes showed strong surface reactivity. Other cell types, including astrocytes, microglia, Schwann cells, myoblasts, and T and B lymphocytes, were negative. Mouse and rat oligodendrocytes which showed strong surface reactivity exhibited a well-differentiated morphology, and approximately 50% expressed myelin basic protein. Since oligodendrocyte progenitors were negative for surface staining, the expression of the antigens recognized by this monoclonal antibody appears to be developmentally regulated, i.e., transiently expressed on younger, terminally differentiating oligodendrocytes. Among the cell lines studied, only two rat oligodendrocyte lineage cell lines showed surface reactivity with SCH 94.03. Western blotting of secondary isolated oligodendrocytes lysates revealed reactivity with multiple protein bands of 27, 32, 50, 100, and 106 kDa, whereas there was no reactivity to lipid antigens by immuno-thin layer chromatography. These results raise the possibility that SCH94.03 recognizes a novel oligodendrocyte-specific surface antigen, and may act directly on oligodendrocytes to promote remyelination.

Immunoglobulins reactive with myelin basic protein promote CNS remyelination

We tested the hypothesis that immunoglobulins directed against a CNS autoantigen, myelin basic protein, may promote remyelination in the course of a chronic, immune-mediated demyelinating disease. SJL/J mice infected chronically with Daniel's strain of Theiler's virus served as an experimental model of MS. The spinal cords of these mice exhibit extensive primary demyelination and inflammation with minimal spontaneous remyelination. Treatment with whole antiserum or affinity-purified mouse immunoglobulins directed against rat or rabbit myelin basic protein increased new myelin synthesis as measured by quantitative morphometry. Electron microscopy revealed numerous oligodendrocytes in remyelinated CNS lesions and a relative lack of inflammatory cells. Viral antigen persisted in the spinal cord despite enhanced CNS-type remyelination. These findings indicate that immunoglobulins reactive with myelin autoantigens have the potential to promote myelin repair.

A monoclonal natural autoantibody that promotes remyelination suppresses central nervous system inflammation and increases virus expression after Theiler's virus-induced demyelination

We have used an established experimental model of multiple sclerosis to investigate the potential beneficial relationship between natural autoimmunity and remyelination after central nervous system (CNS) demyelination. Intracerebral infection of SJL/J mice with Theiler's murine encephalomyelitis virus (TMEV) produces chronic, progressive, inflammatory CNS demyelination. Chronically infected SJL/J mice show minimal spontaneous remyelination, which is in part due to a T cell-mediated immune response inhibiting myelin repair. We previously identified a monoclonal natural autoantibody, designated SCH94.03, that promotes remyelination when passively transferred to chronically infected SJL/J mice. The mechanism whereby SCH94.03 promotes remyelination is unknown, although previous reports suggest that natural autoantibodies can modulate immune system function. In this report we demonstrate that treatment with SCH94.03 reduced by 2- to 3-fold the number of CD4(+) and CD8(+) cells infiltrating the CNS of SJL/J mice chronically infected with TMEV, in the absence of global lymphocyte depletion. Associated with the decreased inflammation was a 2- to 3-fold increase in virus antigen expression without a significant increase in viral RNA or virus titers. Treatment with SCH94.03 also suppressed the humoral immune response to a T cell-dependent antigen in chronically infected mice. Immunohistochemical staining showed that SCH94.03 labeled MHC class II-positive dendritic cells in peripheral lymphoid organs. These results are consistent with the proposed immunomodulatory function of natural autoantibodies and suggest that one mechanism whereby SCH94.03 promotes CNS remyelination in chronically infected SJL/J mice is through inhibition of a pathogenic immune response.

Oligodendrocyte-reactive O1, O4, and HNK-1 monoclonal antibodies are encoded by germline immunoglobulin genes

Natural or physiologic autoantibodies are present normally in serum, are polyreactive, are frequently of the IgM subtype, and are encoded by unmutated germline genes. We tested whether the oligodendrocyte-reactive O1, O4, A2B5, and HNK-1 IgM kappa monoclonal antibodies are natural autoantibodies by sequencing immunoglobulin (Ig) cDNAs and comparing these with published germline sequences. O1 VH was identical with unrearranged VH segment transcript A1 and A4. O4 VH had three and HNK-1 VH had six nucleotide differences from germline VH101 in the VH coding region. The D segment of O1 was derived from germline SP2 gene family. The D segments of O4 and HNK-1 were derived from DFL16 gene family. O4 JH and HNK-1 JH were encoded by unmutated germline JH4, whereas O1 JH was encoded by germline JH1 with one silent nucleotide change. O1 and O4 light chains were identical with myeloma MOPC21 except for one silent nucleotide change. HNK-1 V kappa was identical with germline V kappa 41 except for two silent nucleotide changes. O1 J kappa, O4 J kappa and HNK J kappa were encoded by unmutated germline J kappa 2. In contrast, A2B5 VH showed seven nucleotide differences from germline V1, whereas no germline sequence encoding A2B5 V kappa was identified. O1 and O4, but not A2B5 were polyreactive against multiple antigens by direct ELISA. Therefore, O1, O4 and HNK-1 Igs are encoded by germline genes, and have the genotype and phenotype of natural autoantibodies.

Characterization of a novel non-muscle myosin-related protein from Onchocerca gibsoni

A cDNA library was constructed in lambda gt11 using poly(A)+ mRNA from early larvae of Onchocerca gibsoni. Screening of the library using serum from a single onchocerciasis patient yielded several strongly immunoreactive clones, one of which (OGK2) was found to encode a novel myosin-related protein. cDNA clone OGK2 contained an insert of 2017 bp, consisting of continuous open reading frame in frame with the vector, hence this clone encodes 671 amino acid residues of a larger protein. A fragment (619 nt) of the OGK2 cDNA was subcloned into the expression vector pGEX-1N to generate a glutathione S-transferase fusion protein. Polyclonal antiserum raised to this fusion protein strongly recognised an O. gibsoni protein of approximately 220 kDa. Immunolocalization studies indicated that this protein was associated predominantly with the hypodermis and a number of other specific membrane layers in the adult parasite. Myosin-related proteins are frequently immunodominant parasite antigens and in a number of studies have been shown to confer a degree of protective immunity against the corresponding parasite. Evaluation of the protective potential of the OGK2 protein, therefore, appears to be warranted.

Spontaneous CNS remyelination in beta 2 microglobulin-deficient mice following virus-induced demyelination

Animal models with selective genetic immunodeficiencies are useful tools to identify pathogenic mechanisms of disease. Resistant (C57BL/6F 129/J) (H-2b) mice are rendered susceptible to Theiler's murine encephalomyelitis virus-induced demyelination by genetic disruption of the beta 2 microglobulin gene [beta 2 m(-l-)]. The absence of beta 2 m prevents the expression of major histocompatibility complex class I molecules and normal levels of functional CD8+ T cells. We tested whether genetic depletion of beta 2 m would permit CNS remyelination after chronic demyelination induced by the Daniel's strain of Theiler's virus. In contrast to the minimal spontaneous remyelination observed in SJL/J mice after infection with the Daniel's strain of Theiler's virus, chronically infected beta 2 m(-I-) mice showed extensive and progressive spontaneous CNS remyelination at 6, 12, and 18 months after infection. Spontaneous remyelination by both oligodendrocytes and Schwann cells occurred despite the presence of persistent virus antigen and RNA, but was associated with diminished virus-specific humoral and delayed-type hypersensitivity responses. These experiments support the hypothesis that the immune response inhibits myelin regeneration after virus-induced CNS demyelination.

Spontaneous and induced remyelination in multiple sclerosis and the Theiler's virus model of central nervous system demyelination

Remyelination in the central nervous system, originally thought to occur rarely, if ever, is now an established phenomena in multiple sclerosis patients. However, the extent of myelin repair is incomplete and limited. Experimental models of central nervous system demyelination provide an opportunity to study the cellular and molecular events involved in remyelination. These models may provide some clue to why remyelination in multiple sclerosis is incomplete as well as suggest potential methods to stimulate central nervous system repair. In this review we examine the morphological aspects of central nervous system remyelination and discuss both spontaneous and induced remyelination in multiple sclerosis and experimental models of central nervous system demyelination. We give special emphasis to the Theiler's virus model of central nervous system demyelination and its usefulness to identify therapeutic agents to promote remyelination. The role of immunoglobulins in promoting remyelination in both the Theiler's model system and in multiple sclerosis is discussed. Finally, we examine the potential physiological role of demyelination and remyelination and its relationship with clinical manifestations of central nervous system disease.

Activation of a G protein complex by aggregation of beta-1,4-galactosyltransferase on the surface of sperm

Fertilization is initiated by the species-specific binding of sperm to the extracellular coat of the egg. One sperm receptor for the mouse egg is beta-1,4-galactosyltransferase (GalTase), which binds O-linked oligosaccharides on the egg coat glycoprotein ZP3. ZP3 binding induces acrosomal exocytosis through the activation of a pertussis toxin-sensitive heterotrimeric guanine nucleotide-binding protein (G protein). The cytoplasmic domain of sperm surface GalTase bound to and activated a heterotrimeric G protein complex that contained the Gi alpha subunit. Aggregation of GalTase by multivalent ligands elicited G protein activation. Sperm from transgenic mice that overexpressed GalTase had higher rates of G protein activation than did wild-type sperm, which rendered transgenic sperm hypersensitive to their ZP3 ligand. Thus, the cytoplasmic domain of cell surface GalTase appears to enable it to function as a signal-transducing receptor for extracellular oligosaccharide ligands.