Deletion mapping by immunoselection against the H-Y histocompatibility antigen further resolves the Sxra region of the mouse Y chromosome and reveals complexity of the Hya locus

Pregnancy environment, and not preconception, leads to fetal growth restriction and congenital abnormalities associated with diabetes

Maternal diabetes can lead to pregnancy complications and impaired fetal development. The goal of this study was to use a mouse model of reciprocal embryo transfer to distinguish between the preconception and gestational effects of diabetes. To induce diabetes female mice were injected with a single high dose of streptozotocin and 3 weeks thereafter used as oocyte donors for in vitro fertilization (IVF) and as recipients for embryo transfer. Following IVF embryos were cultured to the blastocyst stage in vitro or transferred to diabetic and non-diabetic recipients. Diabetic and non-diabetic females did not differ in regard to the number of oocytes obtained after ovarian stimulation, oocytes ability to become fertilized, and embryo development in vitro. However, diabetic females displayed impaired responsiveness to superovulation. Reciprocal embryo transfer resulted in similar incidence of live fetuses and abortions, and no changes in placental size. However, fetuses carried by diabetic recipients were smaller compared to those carried by non-diabetic recipients, regardless hyperglycemia status of oocyte donors. Congenital abnormalities were observed only among the fetuses carried by diabetic recipients. The findings support that the diabetic status during pregnancy, and not the preconception effect of diabetes on oogenesis, leads to fetal growth restriction and congenital deformities.

UTX Mutations in Human Cancer

Ubiquitously transcribed tetratricopeptide repeat on chromosome X (UTX, encoded by KDM6A) is a histone demethylase that targets di- and tri-methylated histone H3 lysine 27 (H3K27). UTX function has been linked to homeotic gene expression, embryonic development, and cellular reprogramming. UTX and its protein interactors within the COMPASS family, including the MLL3 and MLL4 lysine methyltransferases, are frequently mutated in multiple human cancers; however, the molecular basis of how these mutations contribute to oncogenesis remains unclear. Here, we discuss catalytic-dependent and -independent functions of UTX and its partners MLL3 and MLL4 as part of the COMPASS family during development and in oncogenesis.

Two genes substitute for the mouse Y chromosome for spermatogenesis and reproduction

The mammalian Y chromosome is considered a symbol of maleness, as it encodes a gene driving male sex determination, Sry, as well as a battery of other genes important for male reproduction. We previously demonstrated in the mouse that successful assisted reproduction can be achieved when the Y gene contribution is limited to only two genes, Sry and spermatogonial proliferation factor Eif2s3y. Here, we replaced Sry by transgenic activation of its downstream target Sox9, and Eif2s3y, by transgenic overexpression of its X chromosome-encoded homolog Eif2s3x. The resulting males with no Y chromosome genes produced haploid male gametes and sired offspring after assisted reproduction. Our findings support the existence of functional redundancy between the Y chromosome genes and their homologs encoded on other chromosomes.

The male sterility and histoincompatibility (mshi) mutation in mice is a natural variant of microtubule-associated protein 7 (Mtap7)

Males homozygous for the mouse male sterility and histoincompatibility (mshi) mutation exhibit small testes and produce no sperm. In addition, mshi generates an "antigen-loss" histoincompatibility barrier, such that homozygous mutants reject skin grafts from wild type co-isogenic BALB/cByJ donors. To facilitate the molecular characterization of the pleiotropic mshi mutation, we genetically mapped mshi into a 0.68 megabasepair region which contains fewer than 10 candidate genes. Complementation testing showed that one of these, Mtap7, is disrupted in mshi mice. Sequence analysis has revealed a 13 kilobasepair deletion in BALB/cByJ-mshi/J mice that begins in Intron 10-11 of Mtap7, and ends less than 2000 base pairs downstream of the wild type gene. Analysis of the mutant cDNA predicts that Mtap7(mshi) encodes a 457 amino acid protein, the first 423 of which are identical to wild type, and the last 34 of which are due to aberrant mRNA splicing with two cryptic exons in the Mtap7 to P04Rik intergenic region. This molecular assignment for the mshi mutation further supports an essential role for microtubule stabilization in spermatogenesis and indicates a new role in allograft transplantation.

DDX3Y encodes a class I MHC-restricted H-Y antigen that is expressed in leukemic stem cells

The Y chromosome encodes male-specific minor histocompatibility (H-Y) antigens that stimulate T- and B-lymphocyte responses after sex-mismatched allogeneic hematopoietic cell transplantation (HCT). A CD8(+) cytotoxic T lymphocyte (CTL) clone that recognizes a novel HLA-B*2705-restricted H-Y antigen encoded by the DDX3Y gene was isolated from a male who had received a hematopoietic cell graft from his human leukocyte antigen (HLA)-identical sister. The antigenic peptide is a decamer that differs from the homologous DDX3X-encoded peptide at 4 positions. Expression of DDX3Y and of the H-Y epitope that it encodes was examined by quantitative polymerase chain reaction (PCR) and by CTL recognition assays. Expression of DDX3Y is detected in all myeloid and lymphoid leukemic cells that carry an intact Y chromosome. Moreover, the DDX3Y-encoded H-Y epitope is presented on the surface of both myeloid and lymphoid leukemic cells from male HLA-B*2705(+) patients. DDX3Y-specific CTLs prevent engraftment of human acute leukemia in nonobese diabetic/severe combined immune deficient mice, demonstrating that the DDX3Y-encoded H-Y antigen is also expressed in leukemic stem cells. These results demonstrate that CD8(+) T-cell responses against DDX3Y have the potential to contribute to graft-versus-leukemia (GVL) activity after female into male allogeneic HCT. This study is registered at http://clinicaltrials.gov as NCT00107354.

Role of immunoproteasomes in cross-presentation

The evidence that proteasomes are involved in the processing of cross-presented proteins is indirect and based on the in vitro use of proteasome inhibitors. It remains, therefore, unclear whether cross-presentation of MHC class I peptide epitopes can occur entirely within phagolysosomes or whether it requires proteasome degradation. To address this question, we studied in vivo cross-presentation of an immunoproteasome-dependent epitope. First, we demonstrated that generation of the immunodominant HY Uty(246-254) epitope is LMP7 dependent, resulting in the lack of rejection of male LMP7-deficient (LMP7(-/-)) skin grafts by female LMP7(-/-) mice. Second, we ruled out an altered Uty(246-254)-specific T cell repertoire in LMP7(-/-) female mice and demonstrated efficient Uty(246-254) presentation by re-expressing LMP7 in male LMP7(-/-) cells. Finally, we observed that LMP7 expression significantly enhanced cross-priming of Uty(246-254)-specific T cells in vivo. The observations that male skin grafts are not rejected by LMP7(-/-) female mice and that presentation of a proteasome-dependent peptide is not efficiently rescued by alternative cross-presentation pathways provide strong evidence that proteasomes play an important role in cross-priming events.

In vivo role of ER-associated peptidase activity in tailoring peptides for presentation by MHC class Ia and class Ib molecules

Endoplasmic reticulum (ER)-associated aminopeptidase (ERAP)1 has been implicated in the final proteolytic processing of peptides presented by major histocompatibility complex (MHC) class I molecules. To evaluate the in vivo role of ERAP1, we have generated ERAP1-deficient mice. Cell surface expression of the class Ia molecules H-2Kb and H-2Db and of the class Ib molecule Qa-2 was significantly reduced in these animals. Although cells from mutant animals exhibited reduced capacity to present several self- and foreign antigens to Kb-, Db-, or Qa-1b-restricted CD8+ cytotoxic T cells, presentation of some antigens was unaffected or significantly enhanced. Consistent with these findings, mice generated defective CD8+ T cell responses against class I-presented antigens. These findings reveal an important in vivo role of ER-associated peptidase activity in tailoring peptides for presentation by MHC class Ia and class Ib molecules.

Cysteine-tailed class I-binding peptides bind to CpG adjuvant and enhance primary CTL responses

Immunostimulatory CpG motifs in synthetic oligonucleotides can be effective adjuvants for the priming of CTLs. We first observed that a single male-specific peptide (KCSRNRQYL) (HY2) was more efficient than another male-specific peptide (WMHHNMDLI) (HY1) at priming IFN-gamma-secreting CTLs in vivo when combined with lipid A and CpG and that it also visibly precipitated CpG. The addition of the six N-terminal residues (KCSRNR) from HY2 to HY1 yielded a peptide, KCSRNR-HY1, that both precipitated CpG and primed increased numbers of HY1-specific CTLs. We refer to this type of peptide as a primotope that includes a class I binding peptide tailed with amino acids that increase priming. Ala residues were substituted for the Arg/Lys residues (ACSANA-HY1), and these substitutions did not reduce in vivo priming potential. However, the substitution of Ala for Cys (KASRNR-HY1) resulted in the complete loss of priming, demonstrating the importance of Cys for in vivo priming when mixed with CpG. This result suggested that increased priming was based in disulfide bonding between Cys residues and internal phosphorothioate groups of synthetic CpG. The addition of Cys-bearing primotopes to radiolabeled CpG with a single thioate group resulted in the appearance of a new band that was inhibited by 1) Cys > Ala substitution and 2) reduction and alkylation of CpG. These results reveal a novel mechanism for complexing class I binding peptides and CpG adjuvant for development of new peptide-adjuvant combinations for vaccines for cancer and infectious diseases.

X-ray-induced deletion complexes in embryonic stem cells on mouse chromosome 15

Chromosomal deletions have long been used as genetic tools in dissecting the functions of complex genomes, and new methodologies are still being developed to achieve the maximum coverage. In the mouse, where the chromosomal deletion coverage is far less extensive than that in Drosophila, substantial coverage of the genome with deletions is strongly desirable. This article reports the generation of three deletion complexes in the distal part of mouse Chromosome (Chr) 15. Chromosomal deletions were efficiently induced by X rays in embryonic stem (ES) cells around the Otoconin 90 (Oc 90), SRY-box-containing gene 10 (Sox 10), and carnitine palmitoyltransferase 1b (Cpt 1 b) loci. Deletions encompassing the Oc 90 and Sox 10 loci were transmitted to the offspring of the chimeric mice that were generated from deletion-bearing ES cells. Whereas deletion complexes encompassing the Sox 10 and the Cpt 1 b loci overlap each other, no overlap of the Oc 90 complex with the Sox 10 complex was found, possibly indicating the existence of a haploinsufficient gene located between Oc 90 and Sox 10. Deletion frequency and size induced by X rays depend on the selective locus, possibly reflecting the existence of haplolethal genes in the vicinity of these loci that yield fewer and smaller deletions. Deletions induced in ES cells by X rays vary in size and location of breakpoints, which makes them desirable for mapping and for functional genomics studies.

Modification of an existing chromosomal inversion to engineer a balancer for mouse chromosome 15

Chromosomal inversions are valuable genetic tools for mutagenesis screens, where appropriately marked inversions can be used as balancer chromosomes to recover and maintain mutations in the corresponding chromosomal region. For any inversion to be effective as a balancer, it should exhibit both dominant and recessive visible traits; ideally the recessive trait should be a fully penetrant lethality in which inversion homozygotes die before birth. Unfortunately, most inversions recovered by classical radiation or chemical mutagenesis techniques do not have an overt phenotype in either the heterozygous or the homozygous state. However, they can be modified by relatively simple procedures to make them suitable as an appropriately marked balancer. We have used homologous recombination to modify, in embryonic stem cells, the recessive-lethal In(15)21Rk inversion to endow it with a dominant-visible phenotype. Several ES cell lines were derived from inversion heterozygotes, and a keratin-14 (K14) promoter-driven agouti minigene was introduced onto the inverted chromosome 15 in the ES cells by gene targeting. Mice derived from the targeted ES cells carry the inverted chromosome 15 and, at the same time, exhibit lighter coat color on their ears and tails, making this modified In(15)21Rk useful as a balancer for proximal mouse chromosome 15.

Escape from immune surveillance does not result in tolerance to tumor-associated antigens

Despite expression of tumor-associated or tumor-specific antigens by most tumors, evasion of protective T-cell immunity is the rule rather than the exception. Understanding whether tumor immune escape primarily represents T-cell neglect, anergy/tolerance, or quantitative limits of an existent immune response is central to developing new strategies to enhance antitumor immunity. The authors studied the immune response to MB49, a tumor that naturally expresses HY. Immune surveillance was effective following low-dose tumor inocula, since normal female mice showed a diminished incidence and slower growth rate of MB49 compared with T-cell-depleted female mice and male mice. Following high-dose tumor inoculation, females developed large, progressive tumors but continued to demonstrate immune responses to class I and class II restricted HY epitopes. The HY reactive T cells remained capable of executing HY immune responses since T cells adoptively transferred from MB49-bearing animals mediated accelerated HY skin graft rejection compared with those taken from naive mice. Thus, MB49 does not induce immune tolerance to HY but rather escapes immune surveillance largely due to quantitative limits of the immune response. Treatment of tumor-bearing animals with rhIL7 significantly increased the number of T cells responding to HY but did not alter tumor growth rate. These results demonstrate that escape from immune surveillance does not necessarily imply immune tolerance to tumor antigens and that immunotherapy need not overcome tumor-induced tolerance per se, and suggest that substantial opportunities remain in tumor-bearing hosts to amplify weak but persistent antitumor immune responses.

A new deletion of the mouse Y chromosome long arm associated with the loss of Ssty expression, abnormal sperm development and sterility

The mouse Y chromosome carries 10 distinct genes or gene families that have open reading frames suggestive of retained functionality; it has been assumed that many of these function in spermatogenesis. However, we have recently shown that only two Y genes, the testis determinant Sry and the translation initiation factor Eif2s3y, are essential for spermatogenesis to proceed to the round spermatid stage. Thus, any further substantive mouse Y-gene functions in spermatogenesis are likely to be during sperm differentiation. The complex Ssty gene family present on the mouse Y long arm (Yq) has been implicated in sperm development, with partial Yq deletions that reduce Ssty expression resulting in impaired fertilization efficiency. Here we report the identification of a more extensive Yq deletion that abolishes Ssty expression and results in severe sperm defects and sterility. This result establishes that genetic information (Ssty?) essential for normal sperm differentiation and function is present on mouse Yq.

Flt3 ligand enhances thymic-dependent and thymic-independent immune reconstitution

Despite recent progress in our understanding of the biology of T-cell homeostasis, clinically available therapies to substantially improve immune reconstitution in patients sustaining T-cell depletion are lacking. T cells are regenerated via a dynamic interplay between thymopoiesis and thymic-independent homeostatic peripheral expansion (HPE). Using athymic mice subjected to T-cell depletion, we observed that HPE is critically dependent on dendritic cells (DCs) for presentation of antigen, raising the possibility that the availability of DCs might be limiting in vivo for HPE to occur efficiently. Indeed, flt3 ligand (flt3L) treatment of athymic mice subjected to T-cell depletion (without DC depletion) substantially enhanced HPE and improved immune competence. Following bone marrow transplantation (BMT) in athymic hosts, both dendritic cells and T cells were profoundly depleted and flt3L therapy restored DC numbers and enhanced HPE. In addition, thymus-bearing BMT recipients treated with flt3L regenerated increased numbers of thymic-dependent progeny with increased numbers of T-cell receptor excision circle (TREC)-positive T cells, indicating increased thymopoiesis. Therefore, flt3L is a potent immunorestorative agent that enhances both thymic-dependent and thymic-independent pathways of T-cell regeneration.

Duration of Alloantigen Presentation and Avidity of T Cell Antigen Recognition Correlate with Immunodominance of CTL Response to Minor Histocompatibility Antigens

CD8 T lymphocytes (CTL) responsive to immunodominant minor histocompatibility (minor H) Ags are thought to play a disproportionate role in allograft rejection in MHC-identical solid and bone marrow transplant settings. Although many studies have addressed the mechanisms underlying immunodominance in models of infectious diseases, cancer immunotherapy, and allograft immunity, key issues regarding the molecular basis of immunodominance remain poorly understood. In this study, we exploit the minor H Ag system to understand the relationship of the various biochemical parameters of Ag presentation and recognition to immunodominance. We show that the duration of individual minor H Ag presentation and the avidity of T cell Ag recognition influence the magnitude and, hence, the immunodominance of the CTL response to minor H Ags. These properties of CTL Ag presentation and recognition that contribute to immunodominance have implications not only for tissue transplantation, but also for autoimmunity and tumor vaccine design.

A New Deletion of the Mouse Y Chromosome Long Arm Associated With the Loss of Ssty Expression, Abnormal Sperm Development and Sterility

The mouse Y chromosome carries 10 distinct genes or gene families that have open reading frames suggestive of retained functionality; it has been assumed that many of these function in spermatogenesis. However, we have recently shown that only two Y genes, the testis determinant Sry and the translation initiation factor Eif2s3y, are essential for spermatogenesis to proceed to the round spermatid stage. Thus, any further substantive mouse Y-gene functions in spermatogenesis are likely to be during sperm differentiation. The complex Ssty gene family present on the mouse Y long arm (Yq) has been implicated in sperm development, with partial Yq deletions that reduce Ssty expression resulting in impaired fertilization efficiency. Here we report the identification of a more extensive Yq deletion that abolishes Ssty expression and results in severe sperm defects and sterility. This result establishes that genetic information (Ssty?) essential for normal sperm differentiation and function is present on mouse Yq.

Bone marrow mesenchymal stem cells inhibit the response of naive and memory antigen-specific T cells to their cognate peptide

Mesenchymal stem cells (MSCs) have been recently shown to inhibit T-cell proliferation to polyclonal stimuli. We characterized the effect of MSCs of bone marrow origin on the T-cell response of naive and memory T cells to their cognate antigenic epitopes. The immune response to murine male transplantation antigens, HY, was selected because the peptide identity and major histocompatibility complex (MHC) restriction of the immunodominant epitopes are known. C57BL/6 female mice immunized with male cells were the source of memory T cells, whereas C6 mice transgenic for HY-specific T-cell receptor provided naive T cells. Responder cells were stimulated in vitro with male spleen cells or HY peptides in the presence or absence of MSCs. MSCs inhibited HY-specific naive and memory T cells in a dose-dependent fashion and affected cell proliferation, cytotoxicity, and the number of interferon gamma (IFN-gamma)-producing HY peptide-specific T cells. However, the MSC inhibitory effect did not selectively target antigen-reactive T cells. When MSCs were added to the T-cell cultures in a Transwell system or MSCs were replaced by MSC culture supernatant, the inhibitory activity was abrogated. T-cell reactivity was also restored if MSCs were removed from the cultures. The expression of MHC molecules and the presence in culture of antigen-presenting cells (APCs) or of CD4(+)/CD25(+) regulatory T cells were not required for MSCs to inhibit. We conclude that MSCs inhibit naive and memory T-cell responses to their cognate antigens. Overall our data suggest that MSCs physically hinder T cells from the contact with APCs in a noncognate fashion.

An X-encoded alloantigenicity between BALB/c and C57BL/6 strains of mice

To detect minor barriers to histocompatibility that might be encoded on the X chromosome in mice, we grafted reciprocal sets of (C57BL/6xBALB/c)F1, (C57BL/6xDBA/2)F1, and (BALB/cxDBA/2)F1 mice with tail skin from the respective paternal inbred strain. Our histogenic analysis suggests that, compared with the C57BL/6 mouse strain, the BALB/c strain generates X-linked antigen loss. In contrast, we detected no X-linked histogenic differences between strains C57BL/6 and DBA/2, or DBA/2 and BALB/c. To localize this X-linked barrier to histocompatibility, we produced a panel of 25 [(BALB/cxC57BL/6)F1xC57BL/6]N2 males that were grafted with C57BL/6 skin to determine which carried the BALB/c-derived component(s) necessary for graft rejection. DNA marker analysis showed one region of overlapping BALB/c-derived X-chromosomal segments among the graft rejecters, suggesting that this antigen-loss haplotype ( H-hix(c), for histoincompatibility on the X chromosome, c haplotype) may be restricted within the DXMit55 to the Xq telomere interval (which excludes only the centromeric tip of the X). Further backcrossing of H-hix(c) to C57BL/6 resulted in fewer rejecter mice than expected by the N4 generation, suggesting that a second, unlinked locus is also involved in this X-linked alloantigenicity. The vigorous rejection of male (C57BL/6xBALB)F1 and female (B6.C- H2(d)xC57BL/6)F1 skin by (BALB/cxC57BL/6)F1 males, as well as the assessment of markers on Chromosome 17 among N2 and N4 graft-recipient males, suggests that this second locus is H2, and that H-hix(b)-encoded alloantigens require both H2(b) and H2(d)-encoded presentation molecules for efficient graft rejection.

The complementary roles of deletion and regulation in transplantation tolerance

Neonatal tolerance of alloantigens was described in mice nearly half a century ago, but unfortunately, the translation of these early findings into the clinical arena proved to be much more challenging than was first anticipated. However, the past decade has seen considerable progress in our understanding of the mechanisms that contribute to transplantation tolerance in experimental models. This review outlines our current understanding of the mechanisms of allograft tolerance, emphasizing the complementary roles of deletion and regulation of alloreactive T cells.

Real-time T-cell profiling identifies H60 as a major minor histocompatibility antigen in murine graft-versus-host disease

Although CD8 T cells are thought to be a principal effector population of graft-versus-host disease (GVHD), their dynamics and specificity remain a mystery. Using a mouse model in which donor and recipient were incompatible at many minor histocompatibility antigens (minor H Ags), the CD8 T-cell response was tracked temporally and spatially through the course of GVHD. Donor CD8 T cells in the circulation, spleen, lung, and liver demonstrated virtually identical kinetics: rapid expansion and then decline prior to morbidity. Remarkably, up to one fourth of the CD8 T cells were directed against a single minor antigen, H60. Extreme H60 immunodominance occurred regardless of sampling time, site, and genetic background. This study is the first to analyze the T cells participating in GVHD in "real-time," demonstrates the exceptional degree to which immunodominance of H60 can occur, and suggests that such superdominant minor H Ags could be risk factors for GVHD.

Efficient chromosomal mapping of a methylcholanthrene-induced tumor antigen by CTL immunoselection

It has been difficult to genetically map the genes encoding tumor Ags because they arise as a consequence of somatic mutational events. CTL-mediated immunoselection can impose potent immunoselective pressure against tumor cells, resulting in the survival of rare tumor Ag-loss variants. We subjected a heterozygous 3-methylcholanthrene-induced murine sarcoma cell line to CTL immunoselection, selecting for the loss of a tumor-specific Ag, recognized antigen from MCA-induced tumor 1 (Ram1). Several variants eluded CTL recognition by genetic loss of the hemizygously expressed tumor-specific Ag epitope. A frequently observed genetic escape mechanism was spontaneous mitotic recombination resulting in loss of heterozygosity on chromosome 4. Higher density genetic analyses along with functional confirmation with an independently produced chromosome 4 loss of heterozygosity variant positioned the Ram1 locus to a distal 7.1 cM interval on chromosome 4. This region of the mouse genome is rich in tumor-modifier genes and this positioning of Ram1 may thus provide insight into the genetic basis of 3-methycholanthrene-induced tumor Ags.

Examination of HY response: T cell expansion, immunodominance, and cross-priming revealed by HY tetramer analysis

We have applied MHC class I tetramers representing the two H2(b) MHC class I-restricted epitopes of the mouse male-specific minor transplantation Ag, HY, to directly determine the extent of expansion and immunodominance within the CD8+ T cell compartment following exposure to male tissue. Immunization with male bone marrow (BM), spleen, dendritic cells (DCs) and by skin graft led to rapid expansion of both specificities occupying up to >20% of the CD8+ T cell pool. At a high dose, whole BM or spleen were found to be more effective at stimulating the response than BM-derived DCs. In vivo, immunodominance within the responding cell population was only observed following chronic Ag stimulation, whereas epitope immunodominance was established rapidly following in vitro restimulation. Peptide affinity for the restricting MHC molecule was greater for the immunodominant epitope, suggesting that this might be a factor in the emergence of immunodominance. Using tetramers, we were able to directly visualize the cross-primed CD8+ HY response, but we did not find it to be the principal route for MHC class I presentation. Immunization with female spleen or DCs coated with the full complement of defined HY peptides, including the A(b)-restricted CD4+ Th cell determinant, failed to induce tetramer-reactive cells.

Modulation of CD8+ T cell response to antigen by the levels of self MHC class I

The response of H-Y-specific TCR-transgenic CD8(+) T cells to Ag is characterized by poor proliferation, cytolytic activity, and IFN-gamma secretion. IFN-gamma secretion, but not cytotoxic function, can be rescued by the B7.1 molecule, suggesting that costimulation can selectively enhance some, but not all, effector CD8(+) T cell responses. Although the H-Y epitope binds H-2D(b) relatively less well than some other epitopes, it can induce potent CTL responses in nontransgenic mice, suggesting that the observed poor responsiveness of transgenic CD8(+) T cells cannot be ascribed to the epitope itself. Previously reported reactivity of this TCR to H-2A(b) is also not the cause of the poor responsiveness of the H-Y-specific CD8(+) T cells, as H-Y-specific CD8(+) T cells obtained from genetic backgrounds lacking H-2A(b) also responded poorly. Rather, reducing the levels of H-2(b) class I molecules by breeding the mice to (C57BL/6 x B10.D2)F(1) or TAP1(+/-) backgrounds partially restored cytotoxic activity and enhanced proliferative responses. These findings demonstrate that the self MHC class I gene dosage may regulate the extent of CD8(+) T cell responsiveness to Ag.

Quantitative analysis of the immune response to mouse non-MHC transplantation antigens in vivo: the H60 histocompatibility antigen dominates over all others

Minor histocompatibility Ags (minor H Ags) are substantial impediments to MHC-matched solid tissue and bone marrow transplantation. From an antigenic standpoint, transplantation between MHC-matched individuals has the potential to be remarkably complex. To determine the extent to which the immune response is simplified by the phenomenon of immunodominance, we used peptide/MHC tetramers based on recently discovered minor H Ags (H60, H13, and HY) and monitored in vivo CD8 T cell responses of female C57BL/6 mice primed with MHC-matched, but background-disparate, male BALB.B cells. CD8 T cells against H60 overwhelmed responses to the H13 and HY throughout primary and secondary challenge. H60 immunodominance was an inherent quality, overcoming a lower memory precursor frequency compared with that of H13 and evoking a T cell response with diverse TCRV beta usage. IFN-gamma staining examining congenically defined minor H Ags extended H60 dominance over additional minor H Ags, H28, H4, and H7. These four minor H Ags accounted for up to 85% of the CD8 T cell response, but H60 stood out as the major contributor. These findings show that immunodominance applies to antigenically complex transplantation settings in vivo and that the responses to the H60 minor H Ag dominates in this model. We suggest that immunodominant minor H Ags are those that result from the absence of a self analog.

The role of human and mouse Y chromosome genes in male infertility

It was suggested by Ronald Fisher in 1931 that genes involved in benefit to the male (including spermatogenesis genes) would accumulate on the Y chromosome. The analysis of mouse Y chromosome deletions and the discovery of microdeletions of the human Y chromosome associated with diverse defective spermatogenic phenotypes has revealed the presence of intervals containing one or more genes controlling male germ cell differentiation. These intervals have been mapped, cloned and examined in detail for functional genes. This review discusses the genes mapping to critical spermatogenesis intervals and the evidence indicating which are the most likely candidates underlying Y-linked male infertility.

Evidence that sex chromosome asynapsis, rather than excess Y gene dosage, is responsible for the meiotic impairment of XYY mice

There is extensive evidence for the existence of a meiotic checkpoint that acts to eliminate spermatocytes that fail to achieve full sex chromosome synapsis at the pachytene stage of the first meiotic prophase. XYY mice are nearly always sterile, with clear signs of meiotic impairment, and sex chromosome asynapsis has been proposed to underlie this impairment. However, a study of XYY*(X) mice (mice having three sex chromosomes but only a single dose of Y genes) revealed that these mice are fertile, and thus implicated Y gene dosage as a major factor in the sterility of XYY mice. To address this question further, sex chromosome synapsis and spermatogenic proficiency were compared between XYY*(X) and XYY mice generated in the same litters. This established that differences in spermatogenic proficiency within and between the two genotypes correlated with the frequency of radial trivalent formation (full sex chromosome synapsis); XYY*(X) males, as a group, had double the radial trivalent frequency of XYY males. This observation provides strong support for the view that sex chromosome asynapsis (or some consequence thereof), rather than Y gene dosage, is the major factor leading to the meiotic impairment of XYY mice.

Dendritic cells permit identification of genes encoding MHC class II-restricted epitopes of transplantation antigens

Minor or histocompatibility (H) antigens are recognized by CD4+ and CD8+ T lymphocytes as short polymorphic peptides associated with MHC molecules. They are the targets of graft versus host and graft versus leukemia responses following bone marrow transplantation between HLA-identical siblings. Several genes encoding class I-restricted minor H epitopes have been identified, but approaches used for these have proved difficult to adapt for cloning class II-restricted minor H genes. We have combined the unique antigen-presenting properties of dendritic cells and high levels of episomal expression following transfection of COS cells to identify a Y chromosome gene encoding two HY peptide epitopes, HYAb and HYEk.

DFFRY codes for a new human male-specific minor transplantation antigen involved in bone marrow graft rejection

Graft rejection after histocompatibility locus antigen (HLA)-identical stem cell transplantation results from the recognition of minor histocompatibility antigens on donor stem cells by immunocompetent T lymphocytes of recipient origin. T-lymphocyte clones that specifically recognize H-Y epitopes on male target cells have been generated during graft rejection after sex-mismatched transplantation. Previously, 2 human H-Y epitopes derived from the same SMCY gene have been identified that were involved in bone marrow graft rejection. We report the identification of a new male-specific transplantation antigen encoded by the Y-chromosome-specific gene DFFRY. The DFFRY-derived peptide was recognized by an HLA-A1 restricted CTL clone, generated during graft rejection from a female patient with acute myeloid leukemia who rejected HLA-phenotypically identical bone marrow from her father. The identification of this gene demonstrates that at least 2 genes present on the human Y-chromosome code for male-specific transplantation antigens.

Crooked tail (Cd) models human folate-responsive neural tube defects

Genetic correlation of human neural tube defects (NTDs) with NTD genes identified in mouse may unravel predisposing complex traits for assessment of individual risk and treatment in clinical settings. Folic acid (FA) can reduce the recurrence of NTDs in human populations by as much as 50-70%, though the mechanism of this rescue is unknown. We examined whether Crooked tail ( Cd ), a mouse strain prone to exencephaly, could provide a genetic animal model for folate-responsive NTDs. The Cd locus was localized to a 0.2 cM interval of the Mouse Genome Database genetic map, identifying tightly linked markers for genotyping prior to phenotypic expression. In a controlled diet study, Cd was found to mimic closely the clinical response to FA. FA supplementation reduced the recurrence risk of Cd exencephaly by as much as 55%. This rescue was dose dependent and did not require subjects to be inherently folate deficient. Like the female predominance of NTDs in humans, female Cd embryos were most likely to display exencephaly and were more responsive than males to the FA rescue. Importantly, FA supplementation shifted the severity of Cd phenotypic expression from early embryonic lethality to longer survival, and reduced the incidence of NTDs. The Cd locus is distinct from the known genes associated with neurulation defects, and isolation of this gene will assist identification of biochemical, genetic and gender-dependent factors contributing to folate-responsive NTDs.

Stochastic Acquisition of Qa1 Receptors During the Development of Fetal NK Cells In Vitro Accounts in Part But Not in Whole for the Ability of These Cells to Distinguish Between Class I-Sufficient and Class I-Deficient Targets

Fetal mouse NK cells are grossly deficient in the expression of Ly49 molecules yet show a limited ability to distinguish between wild-type and MHC class I-deficient target cells. In this paper we report that during their development in vitro from immature thymic progenitors, a proportion of C57BL/6 fetal NK cells acquires receptors for a soluble form of the nonclassical class I molecule Qa1b associated with the Qdm peptide, but not for soluble forms of the classical class I molecules Kb and Db. The acquisition of these Qa1 receptors occurs in a stochastic manner that is strictly controlled by cytokines, and in particular is strongly inhibited by IL-4. All fetal NK clones tested, including those that lack detectable Qa1 receptors, express mRNA for CD94 and for both inhibitory and noninhibitory members of the NKG2 family. Fetal NK cells lacking receptors for Qa1 (and also for classical class I molecules) cannot distinguish between wild-type and class I-deficient blasts but, surprisingly, distinguish efficiently between certain wild-type and class I-deficient tumor cells. A variant line that lacks several members of the NKG2 family kills both types of tumor cell equally well, suggesting the existence of NKG2-containing inhibitory receptors that recognize as yet undefined nonclassical class I molecules of restricted distribution.

Biochemical and Immunogenetic Analysis of an Immunodominant Peptide (B6dom1) Encoded by the Classical H7 Minor Histocompatibility Locus

Of the many minor histocompatibility (H) Ags that have been detected in mice, the ability to induce graft vs host disease (GVHD) after bone marrow transplantation is restricted to a limited number of immunodominant Ags. One such murine Ag, B6dom1, is presented by the H2-Db MHC class I molecule. We present biochemical evidence that the natural B6dom1 peptide is indistinguishable from AAPDNRETF, and we show that this peptide can be isolated from a wide array of tissues, with highest levels from the lymphoid organs and lung. Moreover, we employ a novel, somatic cell selection technique involving CTL-mediated immunoselection coupled with classical genetics, to show that B6dom1 is encoded by the H7 minor H locus originally discovered ∼40 years ago. These studies provide a molecular genetic framework for understanding B6dom1, and exemplify the fact that mouse minor H loci that encode immunodominant CTL epitopes can correspond to classical H loci originally identified by their ability to confer strong resistance to tumor transplantation. Additionally, these studies demonstrate the utility of somatic cell selection approaches toward resolving H Ag immunogenetics.

Positional cloning and molecular characterization of an immunodominant cytotoxic determinant of the mouse H3 minor histocompatibility complex

Immune responses to minor histocompatibility antigens are poorly understood and present substantial barriers to successful solid tissue and bone marrow transplantation among MHC-matched individuals. We exploited a unique positional cloning approach relying on the potent negative selection capability of cytotoxic T cells to identify the H3a gene responsible for immunodominant H2-Db-restricted determinants of the classically defined mouse autosomal H3 complex. The allelic basis for reciprocal H3a antigens is two amino acid changes within a single nonamer H2-Db-binding peptide. The H3a gene, now called Zfp106, encodes a 1888-amino acid protein with three zinc fingers and a beta-transducin domain consistent with DNA/protein binding. A region of ZFP106 is identical to a 600-amino acid sequence implicated in the insulin receptor signaling pathway.

Characterization of genes encoding translation initiation factor eIF-2gamma in mouse and human: sex chromosome localization, escape from X-inactivation and evolution

The Delta Sxrb interval of the mouse Y chromosome is critical for spermatogenesis and expression of the male-specific minor transplantation antigen H-Y. Several genes have been mapped to this interval and each has a homologue on the X chromosome. Four, Zfy1 , Zfy2 , Ube1y and Dffry , are expressed specifically in the testis and their X homologues are not transcribed from the inactive X chromosome. A further two, Smcy and Uty , are ubiquitously expressed and their X homologues escape X-inactivation. Here we report the identification of another gene from this region of the mouse Y chromosome. It encodes the highly conserved eukaryotic translation initiation factor eIF-2gamma. In the mouse this gene is ubiquitously expressed, has an X chromosome homologue which maps close to Dmd and escapes X-inactivation. The coding regions of the X and Y genes show 86% nucleotide identity and encode putative products with 98% amino acid identity. In humans, the eIF-2gamma structural gene is located on the X chromosome at Xp21 and this also escapes X-inactivation. However, there is no evidence of a Y copy of this gene in humans. We have identified autosomal retroposons of eIF-2gamma in both humans and mice and an additional retroposon on the X chromosome in some mouse strains. Ark blot analysis of eutherian and metatherian genomic DNA indicates that X-Y homologues are present in all species tested except simian primates and kangaroo and that retroposons are common to a wide range of mammals. These results shed light on the evolution of X-Y homologous genes.

The mouse Y chromosome interval necessary for spermatogonial proliferation is gene dense with syntenic homology to the human AZFa region

The Delta Sxrb deletion interval of the mouse Y chromosome contains Spy, a spermatogenesis factor gene(s) whose expression is essential for the postnatal development of the mitotic germ cells, spermatogonia. The boundaries of Delta Sxrb are defined by the duplicated genes Zfy1 and Zfy2 and four further genes have previously been mapped within the interval: Ube1y and Smcy, linked with Zfy1 on a contig of 250 kb, and Dffry and Uty, which were unanchored. The interval was estimated to be >450 kb. In order to identify any further gene(s) that may underlie Spy, systematic exon trapping was performed on an extended contig, anchored on Zfy1, which covers 750 kb of the Delta Sxrb interval. Exons from two novel genes were isolated and placed together with Dffry and Uty on the contig in the order Dffry-Dby-Uty-Tspy-Eif2gammay-Smcy- Ube1y-Zfy1. All the genes, with the double exception of Tspy, are X-Y homologous and produce putatively functional, spliced transcripts. The tight linkage and order of Dffry, Dby and Uty was shown to be conserved in deletion intervals 5C/5D of the human Y chromosome by the construction of a contig of human PAC and YAC clones; this represents the first example of syntenic homology between Y chromosomes from two distinct mammalian orders. Interval 5C/5D contains the distal boundary of the AZFa interval, which, like Delta Sxrb, is believed to be necessary for spermatogonial development in the prepubertal testis. Our results therefore show that AZFa and Spy may be encoded by homologous genes.

Transposition of RhoA to the murine Y chromosome

In an effort to produce a more complete transcription map of the short (approximately 5 Mb) arm of the mouse Y chromosome, we have initiated exon trapping from Yp-derived YACs. Sequence analysis of the trapped products has identified exons of previously cloned mouse Y-located genes Zfy and SSty and potential exons homologous to the human Y-located Tspy gene family. In addition, a family of three Yp-located transcripts that show close homology to human RHOA (locus designation ARHA), a member of the Ras family of small GTPases, has been identified. To determine whether these Yp sequences had been transposed from an autosomal ancestor, we used this trapped product to isolate a full-length autosomal mouse RhoA cDNA that is 80% identical at the nucleotide level and 98% identical at the amino acid level to human RHOA and maps to mouse Chromosome 2 (locus designation ArhA). Sequence analysis indicates that the Y-linked copies have diverged from the autosomal form, with small deletions precluding maintenance of a significant open reading frame in all Yp copies. Yet RT-PCR analysis indicates that two of these pseudogenes, RhoAy1 and 3, are expressed in a testis-specific manner, in sharp contrast to the nearly ubiquitous expression pattern of the autosomal ancestor. The data indicate that the Y copies of RhoA have been transposed from an autosome, followed by subsequent duplication, sequence divergence, and acquisition of a testis-specific promoter/enhancer.

Spectratyping of TCR Expressed by CTL-Infiltrating Male Antigen (HY)-Disparate Allografts

Minor histocompatibility Ags (HA) play prominent roles in stimulating allograft rejection and are recognized by CTLs that mediate this process. There is limited information regarding the sequences of minor HA peptides and the diversity of minor HA-specific TCRs. In the case of the male minor HA (HY), a peptide presented by H2Db molecules has been sequenced. We have used spectratyping to study the diversities of Vβ usage and β complementarity-determining region 3 (CDR3) lengths of TCRs expressed by CTLs that infiltrate HY-disparate skin allografts during rejection. Spectratyping of RNA from second- and third-set male allografts on CD4-depleted, female recipients showed a reduction in Vβ usage and β CDR3 length diversity with prominent representation of Vβ8 genes. CDR3 sequences, as a group, were characterized by net negative charges resulting from negatively charged residues at positions 5–6 and 10–11. The effects of in vivo anti-Vβ8 Ab treatment on rejection of second-set male allografts were investigated. This Ab treatment had no effect on allograft rejection time and resulted in increased Vβ7 usage in recipients with complete Vβ8 depletion. More interestingly, the net charges of β CDR3s derived from Vβ8-depleted recipients were altered by the inclusion of positively charged and polar residues at positions 4–6. These results indicate that Vβ-specific T cell depletion has no effect on HY-disparate allograft survival, but it alters Vβ usage and changes the characteristics of β CDR3s that facilitate class I:peptide recognition.

Protamine-Cre recombinase transgenes efficiently recombine target sequences in the male germ line of mice, but not in embryonic stem cells

The production of subtle or conditional mutations in mice through the combined use of site-specific and homologous recombination has become an increasingly widespread experimental paradigm in mammalian genetics. Embryonic stem cells containing recombinase transgenes that were expressed in the male germ line, but not in other tissues or in the embryonic stem cells themselves, would substantially simplify the production of such alleles. Here we show that transgenes comprised of the mouse protamine 1 promoter and the Cre recombinase coding sequence mediate the efficient recombination of a Cre target transgene in the male germ line, but not in other tissues. Embryonic stem cell lines generated from one of these transgenic strains were transfected with targeting vectors that included loxP-flanked selectable markers, and homologously recombined alleles containing the marker and functional loxP sites were isolated. These results establish the potential of the system for substantially reducing the time, effort, and resources required to produce homologously recombined alleles in mice that have been secondarily rearranged by a site-specific recombinase.

Minor histocompatibility antigens

The existence of transplantation antigens, in addition to those encoded by genes in the MHC, has been known for over half a century. The molecular identification of these additional minor histocompatibility (H) antigens lagged behind that of their MHC counterparts, largely because minor H antigens are recognised by T cells and not by antibodies. In the past year, however, new minor H antigens have been identified at both the genetic and protein level and include Uty, a second novel gene encoding a male-specific epitope in mice, a novel autosomal gene encoding each of the H-13 alleles of mice, and a second male-specific epitope encoded by the SMCY gene.

Minors held by majors: the H13 minor histocompatibility locus defined as a peptide/MHC class I complex

The products of minor histocompatibility (H) loci are serious barriers to tissue transplantation even among major histocompatibility complex (MHC) identical individuals, frequently causing chronic graft rejection and graft versus host disease. Over 50 minor H loci map to mouse autosomal chromosomes but none are known at the molecular level. By expression cloning, we identified the H13 locus, a classical minor H locus first detected 30 years ago by the trait of graft rejection. The H13a allele is located on chromosome 2 and encodes a novel protein that yields the rare naturally processed nonapeptide SSVVGVWYL (SVL9) for presentation by the Db MHC class I molecule. The SVL9 peptide binds Db MHC despite the absence of the consensus binding motif, and a conservative methyl group substitution (Valine 4 <--> Isoleucine) explains why reciprocal T cell responses are elicited in H13a and H13b congenic strains.

Human minor histocompatibility antigens: new concepts for marrow transplantation and adoptive immunotherapy

Bone marrow transplantation (BMT) is the present treatment for hematological malignancies. Two major drawbacks of allogeneic BMT are graft-versus-host disease (GVHD) and leukemia relapse. The use of HLA-matched siblings as marrow donors results in the best transplant outcome. Nonetheless, the results of clinical BMT reveal that the selection of MHC-identical donors' bone marrow (BM) is no guarantee for avoiding GVHD or ensuring disease-free survival even when donor and recipient are closely related. It is believed that non-MHC-encoded so-called minor histocompatibility antigens (mHag) are involved in both graft-versus-host and graft-versus-leukemia activities. The recent new insights into the chemical nature of mHag not only reveal their physiological function but, more importantly, provide insights into their role in BMT. Together with the information on the human mHag genetics and tissue distribution gathered in the past, we may now apply this knowledge to the benefit of human BMT. Directly relevant is the utility of mHag molecular typing for diagnostics in BM donor selection. Most promising is the use of mHag-specific cytotoxic T cells for adoptive immunotherapy of leukemia.

The HLA-A*0201-restricted H-Y antigen contains a posttranslationally modified cysteine that significantly affects T cell recognition

A peptide recognized by two cytotoxic T cell clones specific for the human minor histocompatibility antigen H-Y and restricted by HLA-A*0201 was identified. This peptide originates from SMCY, as do two other H-Y epitopes, supporting the importance of this protein as a major source of H-Y determinants in mice and humans. In naturally processed peptides, T cells only recognize posttranslationally altered forms of this peptide that have undergone modification of a cysteine residue in the seventh position. One of these modifications involves attachment of a second cysteine residue via a disulfide bond. This modification has profound effects on T cell recognition and also occurs in other class I MHC-associated peptides, supporting its general importance as an immunological determinant.

The male-specific histocompatibility antigen, H-Y: a history of transplantation, immune response genes, sex determination and expression cloning

H-Y was originally discovered as a transplantation antigen. In vivo primary skin graft responses to H-Y are controlled by immune response (Ir) genes mapping to the MHC. In vitro T cell responses to H-Y are controlled by MHC class I and II Ir genes, which-respectively, restrict CD8 and CD4 T cells: These can be isolated as T cell clones in vitro. T cell receptor (TCR) transgenic mice have been made from the rearranged TCR genes of several of these, of which that specific for H-Y/Db is the best studied. Non-MHC Ir genes also contribute to the control of in vitro CTL responses to H-Y. The Hya/HYA gene(s) encoding H-Y antigen have been mapped using translocations, mutations, and deletions to Yq in humans and to the short arm of the Y chromosome in mice, where they lie in the deletion defined by the Sxrb mutation between Zfy-1 and Zfy-2. Hya/HYA has been separated from the testis-determining gene, Sry/SRY, in both humans and mice and in humans the azoospermia factor AZF has been separated from HYA. In mice transfection of cosmids and cDNAs mapping to the Sxrb deletion has identified two genes encoding H-Y peptide epitopes. Two such epitopes, H-Y/K(k) and H-Y/D(k), are encoded within different exons of Smcy and a third, H-Y/D(b), by a novel gene, Uty. Peptide elution approaches have isolated a human H-Y epitope, H-Y/HLA-B7, and identified it as a product of SMCY. Each of the Hya genes in mice is ubiquitously expressed but of unknown function. Their X chromosome homologues do not undergo X inactivation.

An H-YDb epitope is encoded by a novel mouse Y chromosome gene

Rejection of male tissue grafts by genotypically identical female mice has been explained by the existence of a male-specific transplantation antigen, H-Y (ref. 1), but the molecular nature of H-Y antigen has remained obscure. Hya, the murine locus controlling H-Y expression, has been localized to delta Sxrb, a deletion interval of the short arm of the Y chromosome. In mice, H-Y antigen comprises at least four distinct epitopes, each recognized by a specific T lymphocyte clone. It has recently been shown that one of these epitopes, H-YKk, is a peptide encoded by the Y-linked Smcy gene, presented at the cell surface with the H-2Kk major histocompatibility complex (MHC) molecule. However, deletion mapping and the analysis of variable inactivation of H-Y epitopes has suggested that the Hya locus may be genetically complex. Here we describe a novel mouse Y chromosome gene which we call Uty (ubiquitously transcribed tetratricopeptide repeat gene on the Y chromosome). We identify the peptide WMHHNMDLI derived from the UTY protein as an H-Y epitope, H-YDb. Our data formally demonstrate that H-Y antigen is the product of more than one gene on the Y chromosome.

Simultaneous immunoselection in vitro for H-Y or H-2D antigen-loss variants of a mouse-derived B cell line

Cytotoxic T lymphocytes (CTL) specifically reactive with the male transplantation antigen (H-Y) were used to immunoselect in vitro for antigen loss among cells from an Abelson murine leukemia virus (AbMuLV) transformed lymphoblastoid cell line. Numerous variant cell clones were recovered that had lost expression of either H-Y or the restricting major histocompatibility class I molecule, H-2D. In all experiments, low-level gamma-irradiation applied prior to immunoselection increased the frequency of antigen loss, but when different time intervals between mutagenesis and immunoselection were used, the proportion of H-Y to H-2D antigen loss was affected, suggesting that the antigens selected against remain on the surface of the cell for differing amounts of time following allele loss.

H-Y antigens

H-Y antigen is defined as a male histocompatibility antigen that causes rejection of male skin grafts by female recipients of the same inbred strain of rodents. Male-specific, or H-Y antigen(s), are also detected by cytotoxic T cells and antibodies. H-Y antigen appears to be an integral part of the membrane of most male cells. In addition, H-Y antibodies detect a soluble form of H-Y that is secreted by the testis. The gene (Smcy/SMCY) coding for H-Y antigen detected by T cells has been cloned. It is expressed ubiquitously in male mice and humans, and encodes an epitope that triggers a specific T-cell response in vitro. Additional epitopes coded for by different Y-chromosomal genes are probably required in vivo for the rejection of male grafts by female hosts. The molecular nature of H-Y antigen detected by antibodies on most male cells is not yet known. Testis-secreted, soluble H-Y antigen, however, was found to be identical to Müllerian-inhibiting substance (MIS). MIS cross-reacts with H-Y antibodies and identical findings were obtained for soluble H-Y antigen and MIS, i.e., secretion by testicular Sertoli and, to a lesser degree, ovarian cells, binding to a gonad-specific receptor, induction of gonadal sex reversal in vitro and, in cattle, in vivo. H-Y antisera also detect a molecule or molecules associated with the heterogametic sex in nonmammalian vertebrates. Molecular data on this antigen or antigens are not yet available.

Human H-Y: a male-specific histocompatibility antigen derived from the SMCY protein

H-Y is a transplantation antigen that can lead to rejection of male organ and bone marrow grafts by female recipients, even if the donor and recipient match at the major histocompatibility locus of humans, the HLA (human leukocyte antigen) locus. However, the origin and function of H-Y antigens has eluded researchers for 40 years. One human H-Y antigen presented by HLA-B7 was identified as an 11-residue peptide derived from SMCY, an evolutionarily conserved protein encoded on the Y chromosome. The protein from the homologous gene on the X chromosome, SMCX, differs by two amino acid residues in the same region. The identification of H-Y may aid in transplantation prognosis, prenatal diagnosis, and fertilization strategies.

Identification of a mouse male-specific transplantation antigen, H-Y

The male-specific transplantation antigen, H-Y, causes rejection of male tissue grafts by genotypically identical female mice and contributes to the rejection of human leukocyte antigen-matched male organ grafts by human females. Although first recognized 40 years ago, the identity of H-Y has remained elusive. T cells detect several distinct H-Y epitopes, and these are probably peptides, derived from intracellular proteins, that are presented at the cell surface with major histocompatibility complex (MHC) molecules. In the mouse, the gene(s) controlling H-Y expression (Hya) are located on the short arm of the Y chromosome between the zinc-finger genes Zfy-1 and Zfy-2. We have recently identified Smcy, a ubiquitously expressed gene, in this region and its X-chromosome homologue, Smcx. Here we report that Smcy encodes an H-YKk epitope that is defined by the octamer peptide TENSGKDI: no similar peptide is found in Smcx. These findings provide a genetic basis for the antigenic difference between males and females that contributes towards a tissue transplant rejection response.