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Biomedical subjects

M Fellous

Publications and source records attributed to M Fellous.

At least 73 records · Page 4Linked to original sources
PubMed1997

Gene sequence, localization, and evolutionary conservation of DAZLA, a candidate male sterility gene.

We have isolated the human homologue of the mouse germ cell-specific transcript Tpx2, which we had previously mapped to mouse chromosome 17. Sequence analysis shows that the human gene is part of the DAZ (Deleted in Azoospermia) family, represents the human homologue of the mouse Dazla and Drosophila boule genes, and is termed DAZLA. Like Dazla and boule, DAZLA is single copy and maps to 3p25. This defines a new region of synteny between mouse chromosome 17 and human chromosome 3. Unlike DAZ, which has multiple DAZ repeats, DAZLA encodes a putative RNA-binding protein with a single RNA-binding motif and a single DAZ repeat. DAZLA is more closely related to Dazla in the mouse than to the Y-linked homologue DAZ (88% identity overall with mouse Dazla compared to 76% identity with the human DAZ protein sequence). Southern blot analysis showed that DAZLA is autosomal in all mammals tested and that DAZ has been recently translocated to the Y chromosome, sometime after the divergence of Old World and New World primates. To investigate the evolutionary relatedness of DAZLA and DAZ further, their partial genomic structures were obtained and compared. This revealed that the genomic organization of both genes in the 5' region is highly conserved. DAZLA is a new member of the DAZ family of genes, which is associated with spermatogenesis and male sterility. Familial cases of male infertility in humans show an autosomal recessive mode of inheritance. It is possible that some of these families may carry mutations in the DAZLA gene.

Amino Acid Sequence↗
PubMed1997

Deletions of distal 9p associated with 46,XY male to female sex reversal: definition of the breakpoints at 9p23.3-p24.1.

Monosomy of distal 9p is associated in rare cases with abnormalities of testicular determination, which can lead to male to female sex reversal in a 46,XY genetic background. We present two 46,XY individuals partially monosomic for 9p who were raised as females. Definition of the breakpoints using somatic cell hybrids containing only the rearranged chromosome 9 indicated that in the first patient the breakpoint was located between markers D9S256 and D9S144 and in the second patient, the breakpoint was distal to the marker D9S144. In both cases this corresponds to the cytogenetic position 9p23.3-p24.1. Analysis of highly polymorphic microsatellite markers demonstrated a paternal origin of the rearranged chromosome 9 in both patients. These studies define the minimum region associated with male to female sex reversal as 9p24.1-pter.

Child, Preschool↗
PubMed1997

Hypertelorism and hypospadias associated with a de novo apparently balanced translocation between 8q22.3-23 and 20p13.

A de novo apparently balanced translocation involving chromosomes 8 and 20 was found in a 14-year-old boy with minor anomalies, mild skeletal abnormalities and ambiguous external genitalia including perineoscrotal hypospadias, rudimentary fused labioscrotal folds, bilateral cryptorchidism, and small penis. The karyotype was 46,XY, t(8;20)(q22.3-23;p13). No signs of other conditions known to be associated with structural anomalies of either chromosome 8 or 20 were present and incomplete masculinisation of the external genitalia appears to be the main component of the phenotype. Clinical and biological studies showed apparently normal testicular function in utero and after birth. Examinations excluded 5 alpha-reductase deficiency or a block in any enzymatic steps of testosterone, glucocorticoid and mineralocorticoid biosynthesis. Coding sequences of the sex-determining gene (SRY) and androgen receptor gene (AR) were found to be identical to those of a normal male excluding their role in the cause of the present condition. Since several other reports describe the association of hypospadias and hypertelorism with deletions or translocations involving 8q, we suggest that a locus necessary for male sex differentiation is located at distal 8q.

Abnormalities, Multiple↗
PubMed1997

Isolation of a B-cell-specific promoter for the human class II transactivator.

The class II transactivator (CIITA) is essential for the expression of major histocompatibility complex (MHC) class II antigens. The tissular patterns of CIITA and MHC class II gene expression are tightly correlated: CIITA mRNA is highly expressed in B cells, and is induced by interferon gamma (IFN-gamma) in macrophage and epithelial cell lines. We first isolated two overlapping cosmids encoding human CIITA which, when co-transfected, are able to restore MHC class II expression in a B-lymphoblastoid cell line (B-LCL) defective for CIITA. Subsequently, a 1.8 kilobase (kb) fragment of the CIITA promoter was isolated and sequenced. A motif presenting a strong similarity to an initiator was detected, as well as putative binding sites for Sp1, GATA-2, LyF-1, ets-1, AP1, and MZF1 transcription factors, and two GAS motifs. When introduced in front of a luciferase reporter gene, this promoter is able to direct a high luciferase activity in a human B-LCL. In contrast, luciferase expression was not stimulated after IFN-gamma treatment when the construct was transfected in macrophage or in epithelial cell lines. However, an induction of the human CIITA gene was observed in mouse macrophage and fibrosarcoma cell lines, when the cells were transfected with a cosmid containing the human CIITA gene, but lacking the 1.8 kb promoter described above. Taken together, these data suggest the existence of an intragenic promoter driving an IFN-gamma-inducible expression of CIITA.

B-Lymphocytes↗
PubMed1997

Mutations and sequence variants in the testis-determining region of the Y chromosome in individuals with a 46,XY female phenotype.

The testis-determining gene SRY (sex determining region, Y) is located on the short arm of the Y chromosome and consists of a single exon, the central third of which is predicted to encode a conserved motif with DNA binding/bending properties. We describe the screening of 26 patients who presented with 46,XY partial or complete gonadal dysgenesis for mutations in both the SRY open reading frame (ORF) and in 3.8 kb of Y-specific flanking sequences. DNA samples were screened by using the fluorescence-assisted mismatch analysis (FAMA) method. In two patients, de novo mutations causing complete gonadal dysgenesis were detected in the SRY ORF. One was a nonsense mutation 5' to the HMG box, whereas the other was a missense substitution located at the C terminus of the conserved motif and identical to one previously detected in an unrelated patient. In addition, two Y-specific polymorphisms were found 5' to the SRY gene, and a sequence variant was identified 3' to the SRY polyadenylation site. No duplications of the DSS region in 20 of these patients were detected.

Amino Acid Sequence↗
PubMed1997

Donor splice-site mutations in WT1 are responsible for Frasier syndrome.

Frasier syndrome (FS) is a rare disease defined by male pseudo-hermaphroditism and progressive glomerulopathy. Patients present with normal female external genitalia, streak gonads and XY karyotype and frequently develop gonadoblastoma. Glomerular symptoms consist of childhood proteinuria and nephrotic syndrome, characterized by unspecific focal and segmental glomerular sclerosis, progressing to end-stage renal failure in adolescence or early adulthood. No case of Wilms' tumour has been reported, even in patients with extended follow-up. In contrast with FS patients, most individuals with Denys-Drash syndrome (DDS; refs 6,7) have ambiguous genitalia or a female phenotype, an XY karyotype and dysgenetic gonads. Renal symptoms are characterized by diffuse mesangial sclerosis, usually before the age of one year, and patients frequently develop Wilms' tumour. Mutations of the Wilms'-tumour gene, WT1, cause different pathologies of the urogenital system, including DDS. WT1 is composed of ten exons and encodes a protein with four zinc-finger motifs and transcriptional and tumour-suppressor activities. Alternative splicing generates four isoforms: the fifth exon may or may not be present, and an alternative splice site in intron 9 allows the addition of three amino acids (KTS) between the third and fourth zinc fingers of WT1 (ref. 17). Here we demonstrate that FS is caused by mutations in the donor splice site in intron 9 of WT1, with the predicted loss of the +KTS isoform. Examination of WT1 transcripts indeed showed a diminution of the +KTS/-KTS isoform ratio in patients with FS.

Adult↗
PubMed1997

True hermaphroditism: clinical aspects and molecular studies in 16 cases.

Although true hermaphroditism (TH) accounts for less than 10% of intersex patients, it stands as a diagnostic challenge and has allowed a better understanding of the mechanisms involved in sexual differentiation. In this paper we review the clinical and laboratory data as well as molecular biology findings on 16 TH patients followed up at the Pediatric Endocrine Unit, Instituto da Criança, Hospital das Clínicas. São Paulo University Medical School. They were of a mean age of 3 years 8 months and nine of them were black. All the patients had ambiguous external genitalia as the main complaint. The 46,XX karyotype accounted for 50% of the cases and the ovotestis was the most frequent gonad found (59%). In the eight TH patients with a 46,XX karyotype, the sex-determining region of the Y chromosome (SRY) was negative, posing an intriguing question about the testicular differentiation mechanisms involved in these cases. In 7/19 ovotestes, the ovarian portion of the gonad has been preserved, keeping open the possibility of fertility. The female sex option was made in 10/16 cases (62.5%) and three patients exhibited spontaneous puberty. The mechanism through which testicular tissue develops without SRY has not yet been completely clarified, suggesting the involvement of the X chromosome as well as autosomal genes in the process.

Child↗
PubMed1996

Interferon-alpha-dependent activation of Tyk2 requires phosphorylation of positive regulatory tyrosines by another kinase.

Tyk2 and JAK1, members of the Janus kinase (JAK) family of protein tyrosine kinases, are required for interferon-alpha/beta binding and signaling. Both enzymes are associated with the interferon-alpha/beta receptor, and upon ligand binding, they undergo tyrosine phosphorylation and catalytic activation in an interdependent manner. To identify residues involved in Tyk2 regulation and to understand the basis of the interdependence of Tyk2 and JAK1, six mutated versions of Tyk2 bearing single or multiple point mutations in the tyrosine kinase domain were studied in a cell line lacking endogenous Tyk2. The Y1054F/Y1055F substitutions in the putative activation loop prevented ligand-dependent activation of Tyk2, without abolishing its catalytic potential. The K930R mutation in the ATP binding site generated a kinase-negative protein, which however, still became phosphorylated upon interferon-alpha treatment. The Y1054F/Y1055F substitutions in this kinase-negative Tyk2 abolished the induced phosphorylation. These results indicate that Tyk2 is activated by phosphorylation on Tyr-1054 and/or Tyr-1055 and that this phosphorylation requires another kinase, most likely JAK1. While the Tyk2 forms mutated on Tyr-1054 and Tyr-1055 or on Lys-930 allowed some inducible gene expression, the combination of the three point mutations totally abolished signaling.

Amino Acid Sequence↗
PubMed1996

Loss of sequences 3' to the testis-determining gene, SRY, including the Y pseudoautosomal boundary associated with partial testicular determination.

The condition termed 46,XY complete gonadal dysgenesis is characterized by a completely female phenotype and streak gonads. In contrast, subjects with 46,XY partial gonadal dysgenesis and those with embryonic testicular regression sequence usually present ambiguous genitalia and a mix of Müllerian and Wolffian structures. In 46,XY partial gonadal dysgenesis gonadal histology shows evidence of incomplete testis determination. In 46,XY embryonic testicular regression sequence there is lack of gonadal tissue on both sides. Various lines of evidence suggest that embryonic testicular regression sequence is a variant form of 46,XY gonadal dysgenesis. The sex-determining region Y chromosome gene (SRY) encodes sequences for the testis-determining factor. To date germ-line mutations in SRY have been reported in approximately 20% of subjects with 46,XY complete gonadal dysgenesis. However, no germ-line mutations of SRY have been reported in subjects with the partial forms. We studied 20 subjects who presented either 46,XY partial gonadal dysgenesis or 46,XY embryonic testicular regression sequence. We examined the SRY gene and the minimum region of Y-specific DNA known to confer a male phenotype. The SRY-open reading frame (ORF) was normal in all subjects. However a de novo interstitial deletion 3' to the SRY-ORF was found in one subject. Although it is possible that the deletion was unrelated to the subject's phenotype, we propose that the deletion was responsible for the abnormal gonadal development by diminishing expression of SRY. We suggest that the deletion resulted either in the loss of sequences necessary for normal SRY expression or in a position effect that altered SRY expression. This case provides further evidence that deletions of the Y chromosome outside the SRY-ORF can result in either complete or incomplete sex reversal.

Base Sequence↗
PubMed1996

[46,XX karyotype males, based on a specific case].

Individuals with 46,XX karyotype and testicular tissue are known as XX males. They either have male phenotype or sexual ambiguity. SRY (testis determining factor) is present in 80% of the reported cases. In our patient the presence of SRY was verified by polymerase chain reaction, explaining the sex reversal.

Adult↗
PubMed1996

The RAG cell line defines a new complementation group of MHC class II deficiency.

We previously described RAG, a mouse adenocarcinoma cell line, as deficient for the induction of major histocompatibility (MHC) class II antigens by IFN-gamma, but responding normally for MHC class I antigen stimulation and anti-viral protection. We had established that the fusion of RAG with various human cell lines restored the induction of MHC class II antigens, whenever the human chromosome 16 was present in somatic cell hybrids. Here we show that the RAG cell line does not exhibit any induction by IFN-gamma of DMA, DMB, and the invariant chain (Ii) mRNAs, and that the induction is restored in somatic cell hybrids containing human chromosome 16. In order to define the gene (designated F16) affected in the RAG cells, we performed a complementation analysis by fusing RAG with previously described human cell lines defective for MHC class II antigen expression (e.g., BLS cell lines), and which belong to five different complementation groups. Our data show that the resulting somatic cell hybrids present an inducible expression of mouse MHC class II antigens, Ii, DMA, and DMB. Therefore, the RAG cell line represents a yet undescribed cellular mutant affected in the expression of MHC class II antigens. In addition, we demonstrate that MHC class II antigens can be constitutively expressed in the RAG cell line when transfected with the cDNA encoding human CIITA driven by the RSV LTR promoter. Since the complementation analysis assessed that F16 and CIITA are distinct, our data suggest that F16 is required for the expression of CIITA.

Animals↗
PubMed1996

Genetic mapping of the autosomal region involved in XX sex-reversal and horn development in goats.

Contrary to other genetic disorders, the genetic study of sex determination anomalies in humans stumbles over the difficulty in observing large pedigrees. In goats, abnormalities in sex determination are intimately linked to a dominant Mendelian gene coding for the "polled" (hornless) character, which could render this species an interesting animal model for the rare human cases of SRY-negative XX males. In this report, we describe genetic linkage between the polled/intersex synchome (PIS) and four microsatellite markers of the distal region of goat Chromosome 1 (CHI1), quite distinct from the bovine "polled" region. According to comparative mapping data, no sex-determining gene has been described so far in homologous regions in the human. This genetic localization constitutes a first step towards identifying a new autosomal sex-determining gene in mammals.

Animals↗
PubMed1996

A duplication of distal Xp associated with hypogonadotrophic hypogonadism, hypoplastic external genitalia, mental retardation, and multiple congenital abnormalities.

An unusual familial case of three sibs with a partial duplication of distal Xp sequences is described. The proband, an 18 year old boy, showed mental retardation, severe dysmorphic features, hypogonadotrophic hypogonadism (HHG), and hypoplastic external genitalia. His karyotype was 46,Y,inv dup(X) (p22.11-->p 22.32). The proband has two sisters each with the same inv dup(Xp) chromosome. Both sisters presented with short stature but were otherwise phenotypically normal. The abnormal X chromosome was inactive in the majority of cells examined. Southern blot dosage analysis indicated a duplication of distal Xp sequences. The proximal breakpoint is located between DXS28 and DXS41, and is therefore at least 2 Mb distal to the DSS locus. The relationship between the phenotype and the Xp duplication is discussed.

Abnormalities, Multiple↗
PubMed1996

A novel mutation in the putative DNA helicase XH2 is responsible for male-to-female sex reversal associated with an atypical form of the ATR-X syndrome.

We describe a pedigree presenting X-linked severe mental retardation associated with multiple congenital abnormalities and 46,XY gonadal dysgenesis, leading in one family member to female gender assignment. Female carriers are unaffected. The dysmorphic features are similar to those described in the alpha-thalassemia and mental retardation (ATR-X) syndrome, although there is no clinical evidence of alpha-thalassemia in this family. In addition, the family had other clinical features not previously observed in the ATR-X syndrome, including partial optic-nerve atrophy and partial ocular albinism. Mutations in a putative DNA helicase, termed XH2, have been reported to give rise to the ATR-X syndrome. We screened the XH2 gene for mutations in affected members of the family and identified a 4-bp deletion at an intron/exon boundary that removes an invariant 3' splice-acceptor site. The mutation cosegregates with the syndrome. The genomic deletion causes missplicing of the pre-mRNA, which results in the loss of 8 bp of coding sequence, thereby generating a frameshift and a downstream premature stop codon. Our finding increases the range of clinical features associated with mutations in the XH2 gene.

Abnormalities, Multiple↗