Plasmacytoid cells in salivary-gland pleomorphic adenomas: evidence of luminal cell differentiation

To determine the cellular origin of plasmacytoid cells in salivary gland adenomas, immunohistochemistry was performed on sections from 12 pleomorphic adenomas rich in these cells. In normal salivary glands included in these sections, the myoepithelial cells (MECs) expressed -smooth muscle actin (SMA) and smooth muscle myosin heavy chain (SMMHC), whereas the duct luminal cells expressed keratins 19, 18 and 8. Some of the salivary duct basal cells expressed these keratins, and the acinar cells expressed keratins 18 and 8. The expression profile was similar in rat salivary glands not only after but also during development. The immature MECs never expressed the keratins nor did the immature duct cells express SMA. In seven cases, up to 60% of the plasmacytoid cells expressed keratin 19. In three of these cases, about 10% of the plasmacytoid cells expressed keratin 18. No plasmacytoid cells expressed SMA, SMMHC or keratin 8. These results indicate that plasmacytoid cells originate from luminal cells and not from MECs. Furthermore, in addition to the luminal tumor cells, the non-luminal cells could express keratins 19, 18 and 8. Therefore, it is necessary to re-evaluate the prevailing notion that non-luminal cells are modified MECs. Keratin 14, basic calponin, vimentin and p63 were bi-specific for the MECs and the duct cells. Therefore, expression of these proteins by significant numbers of the non-luminal tumor cells and the plasmacytoid cells never denied the above notion.     

Immunohistochemical distribution of S-100 protein and glial fibrillary acidic protein in normal and neoplastic salivary glands

Summary Immunohistochemical localization of S-100 protein, its and subunits, and glial fibrillary acidic protein (GFAP) in normal and neoplastic salivary glands was studied by the peroxidase-antiperoxidase method and immunoblot analysis. Positive immunostaining for S-100 protein was observed in pleomorphic adenoma, adenolymphoma, tubular adenoma, adenoid cystic carcinoma, acinic cell tumour, adenocarcinoma and carcinoma in pleomorphic adenoma. S-100 protein was localized in myoepithelial cells, epithelial cells of intercalated ducts and serous acinar cells of normal salivary gland. Both and subunits of S-100 protein showed almost identical distribution in normal and neoplastic salivary glands, but skeletal muscle cells were -positive/-negative whereas Schwann cells and fat cells were -negative/-positive in the stroma and neighbouring tissue. GFAP was only found in pleomorphic adenoma and its malignant counterpart. Immunoblot analysis showed that the GFAP-related antigen consisted of several polypeptide bands with a molecular weight ranging between 35,000 to 50,000 daltons.     

Differential expression of basement membrane type-IV collagen α1, α2, α5 and α6 chains among the histological subtypes of adenoid cystic carcinoma

Six distinct (IV) chains in the basement membrane (BM) of adenoid cystic carcinoma (ACC) of the salivary gland were immunohistochemically examined by anti-(IV) chain-specific antibodies, and their expressions were compared with the histological subtypes and the expressions of cytokeratin 19 (CK19), cytokeratin 14 (CK14) and -smooth muscle actin (-SMA) and Ki-67. In the BM of normal salivary ducts, 1(IV), 2(IV), 5(IV) and 6(IV) chains were continuously stained, but 3(IV) and 4(IV) chains were negative. In the tubular and cribriform subtypes of ACC, tubules with continuous staining of 5(IV) and 6(IV) chains showed the biphasic-staining pattern among the expressions of CK19, CK14 and -SMA. However, in cancer-cell nests with discontinuous or negative staining of 5(IV) and 6(IV) chains, the biphasic pattern was ambiguous. In the solid subtype, the staining of 1(IV) and 2(IV) chains was discontinuous, the staining of 5(IV) and 6(IV) chains was negative and the biphasic-staining pattern was unclear. The mitotic activity of cancer cells analyzed by the Ki-67 labeling index was significantly related to the expression of 5(IV) and 6(IV) chains in the cribriform subtype. These results suggest that BM irregularity with the differential expression of (IV) chains in ACC closely relates to cell proliferation, cell differentiation and histological structure.     

Immunohistochemical studies on S-100 cells in the anterior pituitary gland of Sprague Dawley rats and spontaneous dwarf rats

The S-100 cells in the pituitary glands of adult male Sprague Dawley rats (SDs) and spontaneous dwarf rats (SDRs) were immunohistochemically examined using anti-S-100 and anti-S-100 monoclonal antibodies. The immunoreactive cells against S-100 protein were divided into three subtypes on the basis of their immunore-activity against subunits of S-100 protein: S-100 dominant type (the -type cell), S-100 dominant type (the \-type cell) and immunoreactive against both S-100 and S-100 (the -type cell). In the SD, -type cells represented 26% of the total S-100 immunoreactive cells (S-100 cells) and were localized in the peripheral area of the ventral region of the pituitary gland. This type of cell was observed forming clusters, with more abundant cytoplasm than the -type cell. The proportion of -type cells was 53%. They were diffusely distributed throughout the gland, and their processes were thicker than those of the -type cell. In the SDR, the proportion of -type cells was 55%, and they were observed throughout the gland. In contrast, -type cells totalled 12% and were localized in small areas of the central and peripheral region of the gland. The proportion of -type cells was 21% in the SD and 33% in the SDR and they were observed forming small clusters in both animal groups. The proportion of -type cells compared with the total of S-100-immunoreactive cells was significantly higher (P < 0.05) in the SDR than in the SD, while the proportion of -type cells was markedly lower (P < 0.05).     

Synchronous appearance of fibronectin,integrin α5β1, vinculin and actin in epithelial cells and fibroblasts during rat tracheal wound healing

The distribution of integrin 51 (51) and associated components during wound healing was investigated in the rat trachea following mechanical injury. Under anesthesia, the ventral surface of the trachea was scratched, and tissue specimens were obtained from 6 h to 3 weeks after injury and studied using light and electron microscopy and immunohistochemistry. 51, vinculin and actin in regenerating epithelial cells and extracellular fibronectin appear virtually simultaneously after injury (from 12 h to 7 days) as do 51, vinculin and -smooth muscle actin in fibroblasts and cellular fibronectin in granulation tissue (from 3 to 10 days). Immunoelectron microscopy 2 days after injury showed that 51 and vinculin were localized on the basal and lateral surfaces of regenerating epithelial cells and fibroblast surfaces, and fibronectin was localized just under the regenerating epithelial cells, around collagen fibrils and sporadically around fibroblasts. Bromodeoxyuridine labeling showed that the appearance of these components was associated with the period of cell proliferation. The appearances of fibronectin, 51, vinculin and actin in regenerating epithelial cells and fibroblasts during tracheal wound healing are well coordinated. During the initial cell migration phase, plasma fibronectin may stimulate cell migration before cellular fibronectin is produced in situ, and regenerating epithelial cells appear to begin to migrate into the wound before cell proliferation starts.     

Alpha actinin–CapZ,an anchoring complex for thin filaments in Z-line

CapZ is a widely distributed and highly conserved, heterodimeric protein, that nucleates actin polymerization and binds to the barbed ends of actin filaments, preventing the addition or loss of actin monomers. CapZ interaction with actin filaments was shown to be of high affinity and decreased in the presence of PIP2. CapZ was located in nascent Z-lines during skeletal muscle myofibrillogenesis before the striated appearance of thin filaments in sarcomers. In this study, the stabilization and the anchorage of thin filaments were explored through identification of CapZ partners in the Z-line. Fish (sea bass) striated white muscle and its related Z-line proteins were selected since they correspond to the simplest Z-line organization. We report here the interaction between purified CapZ and -actinin, a major component of Z filaments and polar links in Z-discs. Affinity of CapZ for -actinin, estimated by fluorescence and immunochemical assays, is in the m range. This association was found to be independent of actin and shown to be weakened in the presence of phosphoinositides. Binding contacts on the -actinin molecule lie in the 55 kDa repetitive domain. A model including CapZ/-actinin/titin/actin interactions is proposed considering Luther's 3D Z-line reconstruction.     

Regional location of α1-antichymotrypsin and α1-antitrypsin genes on human chromosome 14

The human protease inhibitor genes ₁ antitrypsin (₁-PI) and ₁-antichymotrypsin (₁-ACT) are acute-phase proteins which are induced in response to inflammation. These inhibitors function to limit the activity of serine proteases in vivo. ₁-PI acts as an inhibitor of neutrophil elastase to protect the elastin fibers of the lung. Genetic deficiencies of ₁-PI result in development of chronic pulmonary emphysema. The physiologic role of ₁-ACT has not been clearly defined, but it also appears to function in the maintenance of protease-protease inhibitor equilibrium in the lung. Nucleic acid and protein sequence homologies detected between ₁-PI and ₁ t-ACT suggested an evolutionary relationship. Gene mapping experiments were performed to determine if these protease inhibitor genes reside at the same chromosomal locus in man. In situ hybridization data demonstrate that both ₁-PI and ₁-ACT map to the same region, q31–q32.3, on chromosome 14.     

An α-mating-type-specific mutation causing specific defect in sexual agglutinability in the yeast Saccharomyces cerevisiae

We have identified a recessive -mating-type-specific gene agl causing agglutinability defect without significant effects on other sexual activities. a cells carrying agl showed sexual agglutination with cells but cells carrying agl showed sexual agglutination with neither cells nor a cells. cells carrying agl produced pheromone and responded to a pheromone just like wild cells. cells carrying agl showed a little decreased but significant mating ability when tested on solid media or membrane filter. The agl mutant is different from any -specific ste mutants found so far in many sexual activities. The agl gene is recessive, and unlinked to the mating type locus. Biological significance of the mating type agglutinability is discussed based on the results obtained with the mutant.     

Bioactive 5-Reduced 16α,17α-Cyclohexanoprogesterone Derivatives Weakly Interact with Proteins of the Soluble Uterine Fraction

We studied competitive activities of 16,17-cyclohexano-5- and 5-dihydroprogesterone in replacing ₃H-progesterone and ₃H-16,17-cyclohexano-6-methylprogesterone from protein complexes. Direct binding of ₃H-5-reduced derivatives with proteins of soluble fractions from rat and rabbit uteri was also assayed. Cd values for 5-reduced derivatives were in the micro- or submicromolar range. The data suggest that biological effects of these analogues are not mediated via soluble uterine receptors.     

αv Integrins mediate adhesion and migration of breast carcinoma cell lines

Integrins with the _v subunit are involved in cell adhesion and cellular signaling. Some _v integrins have been associated with tumor progression and dissemination. The objective of this study was to assess the contribution of _v integrins to the adhesive and migratory behavior of cells derived from breast carcinoma (BCA). The expression and function of _v integrins was characterized in three BCA cell lines which exhibit different metastatic potentials. These include MCF-7 cells which metastasize inefficiently, MDA-MB-231 cells, which have a moderate metastatic potential, and MDA-MB-435 cells, which metastasize extensively. Each cell type displays a different repertoire of _v integrins on the cell surface. The complement of _v integrins on each cell type influences their ability to adhere and migrate. The most striking difference among these cell lines was the expression of the _{v3 3} integrin. The highly metastatic MDA-MB-435 cells express substantial levels of this receptor, whereas MDA-MB-231 and MCF-7 cells do not. The MDA-MB-435 cells showed a greater ability to adhere and to migrate and this functional difference can largely be attributed to the expression of _v3 integrin. This characterization is a first step toward determining the role of _v integrins in animal models of BCA metastasis, and lends support to the hypothesis that the _v3 integrin can be a contributing factor in metastatic disease. © Rapid Science 1998     

Erythrocytes carrying mutations in spectrin and protein 4.1 show differing sensitivities to invasion byPlasmodium falciparum

The role of the erythrocyte skeleton in the invasion process ofPlasmodium falciparum was evaluated using genetically variant erythrocytes containing well-defined molecular defects in spectrin (Sp) or protein 4.1 from eight unrelated families. Invasion into red cells from subjects of three black families with hereditary pyropoikilocytosis (HPP) due to inheritance of I/74 mutant spectrin was significantly reduced in cells both from the patients and from the relatives of these who carried asymptomatic hereditary elliptocytosis (HE). Like-wise, reduced invasion was also seen in red cells from two families with HE in which the I/65 variant spectrin was present. Resistance to invasion was not absolute in any sample and varied between 38% and 71% of that seen in normal cells. The decreased invasion correlated with the percentage of spectrin dimers present within the membrane of variant cells. In contrast, invasion into elliptocytes from three families that had a partial deficiency in protein 4.1 (HE/4.1⁺) but a normal percentage of spectrin dimers was either unchanged or increased. The precise mechanism and molecular basis behind the reduced invasion into HPP and HE red cells bearing SpI domain variants remains to be elucidated but might relate to alterations in merozoite/red cell-receptor interactions and/or merozoite endocytosis. The occurrence of elliptocytosis with spectrin defects (in particular, SpI/65 and SpI/46 variants in West Africa) suggests that these mutations of the Sp gene could be related to some protection against malaria.     

alpha1-acid glycoprotein possesses in vitro pro- and antiinflammatory activities

We studied the effects of ₁-acid glycoprotein on tumor necrosis factor- (TNF-) and interleukin-10 (IL-10) production and lymphocyte response to phytohemagglutinin in cultured peripheral blood mononuclear leukocytes from 6 healthy donors. We observed 2 opposite responses to ₁-acid glycoprotein: first, stimulation of TNF- and IL-10 production and inhibition of lymphocyte proliferation, and second, suppression of cytokine production and stimulation of lymphocyte proliferation. In cell cultures isolated from 4 of 6 donors, the TNF-/IL-10 ratio remained unchanged after addition of native ₁-acid glycoprotein, but some fractions isolated by chromatography on concanavalin A-Sepharose changed this parameter. These changes were most pronounced after treatment with fraction C enriched with molecules with incomplete (biantennary) carbohydrate chains. The mechanisms of ₁-acid glycoprotein-induced effects on peripheral blood mononuclear leukocytes are discussed.     

Transient expression of myosin heavy chain MHCIα in rabbit muscle during fast-to-slow transition

The expression of an -cardiac-like myosin heavy chain, MHCI, was investigated at both the mRNA and protein levels in rabbit tibialis anterior muscle undergoing fast-to-slow transition by continuous chronic low-frequency stimulation (CLFS). According to sequence analyses of the PCR product, the MHCI isoform was found to be identical to the -cardiac MHC expressed in rabbit atrium. In muscles at different degrees of transformation, the upregulation of MHCI mRNA preceded that of the MHCI mRNA. At more advanced stages of the transformation, MHCI mRNA decayed while MHCI mRNA persisted at high levels. The expression of MHCI, therefore, was transitory. Studies at the protein level were based on immunoblotting using a monoclonal antibody (F88 12F8,1), characterized to be specific to MHCI in rabbit muscle. These studies revealed a similar relationship between initial increase and successive decline of the MHCI protein as seen at themRNA level. Immunohistochemistry of 30-day stimulated muscle revealed that up to 65% of the fibres expressed the MHCI isoform in combination with other adult MHC isoforms. The most frequent patterns of coexistence were MHCIIa+MHCI + MHCI (28%), MHCI+MHCI (18%), and MHCIIa + MHCI (11%). According to these combinations, the upregulation of MHCI may be assigned as an intermediate step in the transformation of existing fibres during theMHCIIa MHCI transition. A small fraction of fibres contained, in addition to the MHCI + MHCI and MHCIIa + MHCI combinations, developmental myosin, suggesting that MHCI was also expressed in regenerating fibres originating from satellite cell-derived myotubes.     

α 2-Adrenoceptors activate dihydropyridine-sensitive calcium channels via Gi-proteins and protein kinase C in rat portal vein myocytes

The presence of functional ₂-adrenoceptors was investigated in isolated smooth muscle cells from rat portal vein using the nystatin-perforated patch-clamp technique. The free cytoplasmic calcium concentration ([Ca²⁺]_i) was estimated using emission from the dye Fura-2. Activation of ₂-adrenoceptors by clonidine (an ₂-adrenoceptor agonist) or noradrenaline (a non-selective -adrenoceptor agonist), both in the presence of 0.1 M prazosin to block ₁-adrenoceptors, caused a slow and sustained increase in [Ca²⁺]_i which was inhibited by 0.1 M rauwolscine (an ₂-adrenoceptor antagonist). A similar Ca²⁺ response was obtained with oxymetazoline (a selective _2A-adrenoceptor agonist) suggesting that the increase in [Ca²⁺]_i resulted from activation of the _2A-adrenoceptor subtype. The increase in [Ca²⁺]_i did not occur in calcium-free solution or in the presence of oxodipine (a voltage-dependent calcium channel blocker), indicating that it depended on a calcium influx. The _2A-adrenoceptor-activated calcium influx was unchanged after complete release of the stored calcium induced by applications of ryanodine and caffeine. In addition, no accumulation of inositol trisphosphate was detected in the presence of 0.1 M prazosin. Taken together, these results indicate that _2A-adrenoceptor activation does not stimulate phosphoinositide turnover and subsequent calcium release from intracellular stores. Wholecell patch-clamp experiments showed that _2A-adrenoceptor activation promoted calcium influx through voltage-dependent L-type channels. Concomitant with calcium influx, _2A-adrenoceptor activation induced a 10- to 15-mV depolarization. Similar effects on both calcium channel current and [Ca²⁺]_i were obtained with mastoparan, an activator of Gi-proteins. Activation of calcium influx by both _2A-adrenoceptors and mastoparan was reduced by treatment with pertussis toxin and GF 109203X (a protein kinase C inhibitor). These data suggest that activation of protein kinase C through a transduction pathway involving Gi-proteins phosphorylates voltage-activated L-type calcium channels and thus, increases their opening probability.     

Heterogeneity of myofibroblast phenotypic features: an example of fibroblastic cell plasticity

Granulation tissue fibroblasts (myofibroblasts) develop several ultrastructural and biochemical features of smooth muscle (SM) cells, including the presence of microfilament bundles and the expression of -SM actin, the actin isoform present in SM cells and myoepithelial cells and particularly abundant in vascular SM cells. Myofibroblasts have been suggested to play a role in wound contraction and in retractile phenomena observed during fibrotic diseases. When contraction stops and the wound is fully epithelialized, myofibroblasts containing -SM actin disappear, probably as a result of apoptosis, and the scar classically becomes less cellular and composed of typical fibroblasts with well-developed rough endoplasmic reticulum but with no more microfilaments. In contrast, -SM actin expressing myofibroblasts persist in hypertrophic scars and in fibrotic lesions of many organs, including stroma reaction to epithelial tumours, where they are allegedly involved in retractile phenomena as well as in extracellular matrix accumulation. The mechanisms leading to the development of myofibroblastic features remain to be investigated. In vivo and in vitro investigations have shown that -interferon exerts an antifibrotic activity at least in part by decreasing -SM actin expression whereas heparin increases the proportion of -SM actin positive cells. Recently, we have observed that the subcutaneous administration of transforming growth factor-1 to rats results in the formation of a granulation tissue in which -SM actin expressing myofibroblasts are particularly abundant. Other cytokines and growth factors, such as platelet-derived growth factor, basic fibroblast growth factor and tumour necrosis factor-, despite their profibrotic activity, do not induce -SM actin in myofibroblasts. In conclusion, fibroblastic cells are relatively undifferentiated and can assume a particular phenotype according to the physiological needs and/or the microenvironmental stimuli. Further studies on fibroblast adaptation phenomena appear to be useful for the understanding of the mechanisms of development and regression of pathological processes such as wound healing and fibrocontractive diseases.     

Poly ADP Ribose-Polymerase Inhibitors Prevent the Upregulation of ICAM-1 and E-selectin in Response to Th1 Cytokine Stimulation

We studied the role of poly-ADP-ribose polymerase (PARP) in the mobilization of ICAM-1, VCAM-1, and E-selectin by TNF- and IL-1 in cultured human endothelial cells. Enzyme linked immunosorbent analysis (ELISA) was used to assess if ICAM-1, VCAM-1, and E-selectin were expressed at the cell surface, and if PARP inhibition (using the selective PARP inhibitor GPI 6150) blocked the induced expression. Endothelial cell adhesion molecule expression was evaluated at 4 and at 24 h after cytokine stimulation. At 4 h ICAM-1 and E-selectin, but not VACM-1, were stimulated by both IL-1 and TNF-. Blocking PARP via GPI 6150 only affected TNF- induced E-selectin expression at 4 hours. ICAM-1, VCAM-1, and E-selectin expression were all stimulated by both IL-1 and TNF- in the 24 h assays. PARP inhibition with GPI 6150 blocked the IL-1 mediated stimulation of both ICAM-1 and E-selectin expression, and blocked TNF- stimulation of ICAM-1 expression at 24 h. These experiments suggest that specific PARP inhibition may provide a novel method of controlling leukocyte dependent inflammation through the reduction of ICAM-1 and E-selectin expression in endothelial cells in response to cytokines.     

Mechanism of modulation of single sodium channels from skeletal muscle by the β 1-subunit from rat brain

We studied the molecular mechanism of the rat skeletal muscle -subunit (_I) gating kinetics modulation by the brain ₁-subunit by heterologous expression of single sodium channels from _I and ₁ in Xenopus laevis oocytes. Coexpression of ₁ reduced mean open time at –10 mV to 21% when compared to channels expressed by _I alone. Channels formed by _I exerted multiple openings per depolarization, which occurred in bursts, in contrast to the channels formed by the _I/₁ complex that opened in average only once per depolarizing voltage pulse. Macroscopic current decay (mcd), as evidenced by reconstructed open probability vs. time , was greatly accelerated by ₁, closely resembling mcd of sodium currents from native skeletal muscle. Generally was larger for channels expressed from the pure _I subunit.From our single channel data we conclude that ₁ accelerates the inactivation process of the sodium channel complex.     

Erythromycin and cycloheximide sensitivities of protein and RNA Synthesis in sporulating cells of Saccharomyces cerevisiae: Environmentally induced modifications controlled by chromosomal and mitochondrial genes

Summary The purpose of the experiments reported below was to examine the response in sporulation medium of the three diploid cell types MAT MAT, MAT MAT (asporogenic diploids) and MAT MAT (sporogenic diploid) to erythromycin, a specific inhibitor of mitochondrial protein synthesis (MPS) in vegetative cultures, and cycloheximide, a specific inhibitor of cytosol protein synthesis (CPS) in vegetative cultures. When MAT MAT diploids are transferred to sporulation medium a significant fraction of total protein synthesis (CPS + MPS) becomes sensitive to erythromycin in contrast to the behavior of MATa MATa and MAT MAT diploids in which the resistance of CPS to erythromycin is maintained. The decompartmentalization of erythromycin sensitivity is thus cell type specific. Erythromycin stimulates total RNA synthesis of MAT MAT cells in sporulation medium but not of MAT MAT and MAT MAT cells. Cycloheximide inhibits protein synthesis and stimulates RNA synthesis in all three diploid cell types. An erythromycin resistant mutant, shown to be due to a mutation of the mitochondrial genome, exhibited only partial resistance of CPS to erythromycin in sporulation medium in the background of the MAT MAT mating type genotype. Total RNA synthesis in this mutant was not stimulated. The results reported indicate that mitochondrial functions during sporulation are not restricted to those involving respiratory metabolism.     

Neuronal nicotinic acetylcholine receptors expressed in Xenopus oocytes: role of the α subunit in agonist sensitivity and desensitization

Neuronal nicotinic acetylcholine receptors (nAChRs) were expressed in Xenopus laevis oocytes after nuclear injection of complementary deoxyribonucleic acid (cDNA) expression vectors. The two receptor subtypes 4/n1 and 3/n1 were readily distinguishable from one another by ACh sensitivity and desensitization. 3/n1 receptors showed lower ACh sensitivity and stronger desensitization than 4/n1 receptors. Furthermore, although the current/voltage relationship was very similar in both receptor subtypes, the voltage dependence of desensitization was found to be strikingly different. As the n1 subunit was unchanged, the subunits must be responsible for these functional differences. Symmetric hybrid cDNAs, 43 and 34, were constructed and functional receptors were obtained by co-injection with n1. These hybrid receptors displayed an ACh sensitivity that was mainly defined by the extracellular sequence of the subunit. In contrast, no part of the subunit was found fully to determine desensitization.     

Genetic characterization of an α-specific gene responsible for sexual agglutinability in Saccharomyces cerevisiae: mapping and gene dose effect

Summary A recessive ag1 mutation leads to specific defect in sexual agglutinability specifically in cells of the yeast Saccharomyces cerevisiae. The cryptopleurine resistance gene cry^R 1, closely linked to the mating type locus, was used to select / strains which emerged from / strains by mitotic nonreciprocal recombination, to genetically analyse ag1, since ag1 is expressed only in mating type. The ag1 gene was found to be linked to the centromere tightly, to met3 at 4.4 cM, and to ilv3 at 12 cM on chromosome X. Sexual agglutinability of cells was shown to be dependent on the dose of the AG1 gene, using / isogenic strains carrying AG1/AG1, AG1/ag1 or ag1/ag1. The sst2-1 mutation did not suppress the ag1 mutation. Based on these results, function of the AG1 gene is discussed.Abbreviations cM centimorgan - FDS first division segregation - NPD nonparental ditype - PD parental ditype - SDS second division segregation - TT tetratype