Is ZFY the sex-determining gene on the human Y chromosome?

The sex-determining region of the human Y chromosome contains a gene, ZFY, that encodes a zinc-finger protein. ZFY may prove to be the testis-determining factor. There is a closely related gene, ZFX, on the human X chromosome. In most species of placental mammals, we detect two ZFY-related loci: one on the Y chromosome and one on the X chromosome. However, there are four ZFY-homologous loci in mouse: Zfy-1 and Zfy-2 map to the sex-determining region of the mouse Y chromosome, Zfx is on the mouse X chromosome, and a fourth locus is autosomal.     

Regional assignments of the zinc finger Y-linked gene (ZFY) and related sequences on human and mouse chromosomes

Recent chromosome walking experiments have identified a candidate gene (ZFY) for the testis-determining factor on the human Y chromosome (Page et al., 1987). We report here the regional assignments of the ZFY gene and related sequences in the human and the mouse. By in situ hybridization, we assigned ZFX and ZFY to human chromosome bands Xp21 and Yp11.3, respectively. Although the mouse harbors two Zfy genes, only one site at band A1 of its Y chromosome was significantly labeled. The mouse Zfx gene and the Zfa gene on chromosome 10 were assigned to bands XD and 10B5, respectively. These assignments of the ZFX gene in human and mouse add another marker to the conserved syntenic group for evaluating the evolutionary relationship of the human and mouse X chromosomes.     

Linkage studies do not confirm the cytogenetic location of incontinentia pigmenti on Xp11

Summary Linkage studies have been performed in 5 incontinentia pigmenti (IP) families totaling 29 potentially informative meioses. Ten probes of the Xp arm were used, six of them were precisely localized on the X chromosome, using hamster x human somatic cell hybrids containing a broken X chromosome derived from an incontinentia pigmenti patient carrying an X;9 translocation [46,XX,t(X;9)(p11.21;q34)]. The following order for probes is proposed: pter-(DXS7, DXS146, DXS255)-IP1-(DXS14, DXS90)-DXS106-qter. The negative lod scores obtained exclude the possibility that in the families studied, the gene for IP is located in Xp11 or in the major part of the Xp arm.     

An Xp22 microdeletion associated with ocular albinism and ichthyosis: approximation of breakpoints and estimation of deletion size by using cloned DNA probes and flow cytometry.

Ocular albinism of the Nettleship-Falls type (OA1) and X-linked ichthyosis (XI) due to steroid sulfatase (STS) deficiency are cosegregating in three cytogenetically normal half-brothers. The mother has patchy fundal hypopigmentation consistent with random X inactivation in an OA1 carrier. Additional phenotypic abnormalities that have been observed in other STS "deletion syndromes" are not present in this family. STS is entirely deleted on Southern blot in the affected males, but the loci MIC2X, DXS31, DXS143, DXS85, DXS43, DXS9, and DXS41 are not deleted. At least part of DXS278 is retained. Flow cytometric analysis of cultured lymphoblasts from one of the XI/OA1 males and his mother detected a deletion of about 3.5 million bp or about 2% of the X chromosome. Southern blot and RFLP analysis in the XI/OA1 family support the order tel-[STS-OA1-DXS278]-DXS9-DXS41-cen. An unrelated patient with the karyotype 46,X,t(X;Y) (p22;q11) retains the DXS143 locus on the derivative X chromosome but loses DXS278, suggesting that DXS278 is the more distal locus and is close to an XI/OA1 deletion boundary. If a contiguous gene deletion is responsible for the observed XI/OA1 phenotype, it localizes OA1 to the Xp22.3 region.     

Duplication of an Xp segment that includes the ZFX locus causes sex inversion in man

Summary Two 46,XY females with tandem duplications of an X short arm segment were studied by cytogenetic and Southern blot analysis. The results show that the duplicated segment in each case included the Xp21.2–Xp22.2 interval, resulting in a double dose of ZFX on the single active X chromosome. The results from our two cases, in conjunction with those reported by other workers, lead us to conclude that the duplication is the reason for the sex inversion. If ZFY and ZFX are indeed sex-determining gene loci, these findings favour a model of sex determination characterized by antagonistic interaction between these genes.     

Localization of a gene that escapes inactivation to the X chromosome proximal short arm: implications for X inactivation.

The process of mammalian X chromosome inactivation results in the inactivation of most, but not all, genes along one or the other of the two X chromosomes in females. On the human X chromosome, several genes have been described that "escape" inactivation and continue to be expressed from both homologues. All such previously mapped genes are located in the distal third of the short arm of the X chromosome, giving rise to the hypothesis of a region of the chromosome that remains noninactivated during development. The A1S9T gene, an X-linked locus that complements a mouse temperature-sensitive defect in DNA synthesis, escapes inactivation and has now been localized, in human-mouse somatic cell hybrids, to the proximal short arm, in Xp11.1 to Xp11.3. Thus, A1S9T lies in a region of the chromosome that is separate from the other genes known to escape inactivation and is located between other genes known to be subject to X inactivation. This finding both rules out models based on a single chromosomal region that escapes inactivation and suggests that X inactivation proceeds by a mechanism that allows considerable autonomy between different genes or regions on the chromosome.     

Genes on the short arm of the human X chromosome are not shared with the marsupial X.

Eight genes located on the short arm of the human X chromosome (MAOA, SYN1, OAT, OTC, CYBB, DMD, ZFX, POLA) have been mapped in several marsupial species by cell hybrid analysis and/or in situ hybridization using probes derived from human cDNA. Seven appear to be autosomal in all marsupial species examined. The eighth, CYBB, detected a site on the X, as well as major autosomal sites. Although these genes are not conserved on the X chromosome in marsupials, at least some of them are arranged together in autosomal clusters. The autosomal location of human Xp genes in marsupials could mean that this region either was lost from a large ancestral X chromosome in the marsupial lineage or was acquired by a small ancestral X (and perhaps Y) in the eutherian lineage. Either explanation demands that the region was not subject to X chromosome inactivation in a common ancestor 120-150 MyrBP.     

Genetic mapping of the Wiskott-Aldrich syndrome with two highly-linked polymorphic DNA markers

The Wiskott-Aldrich syndrome (WAS) is an X-linked recessive genetic disease in which the molecular defect is unknown. In 15 families with WAS, seven restriction fragment length polymorphic loci from the X chromosome were used to map the disease locus. Of the eight intervals studied, the likelihood of the WAS gene lying between DXS7 (Xp11.3) and DXS14 (Xp11) was at least 128 times higher than that for any other interval. The most likely gene order is DXS84-OTC-DXS7-WAS-DXS14-DXS1-PGK-DXYS1. Close genetic linkage to DXS7 and DXS14 permits accurate prenatal diagnosis and carrier detection with greater than 98% confidence in fully informative WAS families.     

人Xp21．1－p21．3上3．5MbYAC重叠群构建及物理图谱分析

用Ａｌｕ－ＰＣＲ指纹图谱法分析了人Ｘｐ２１．１－ｐ２１．３上一系列的酵母人工染色体（ｙｅａｓｔａｒｔｉｆｉｃｉａｌｃｈｒｏｍｏｓｏｍｅ,ＹＡＣ）克隆,发现其中的两个ＹＡＣ克隆构成包含ＤＸＳ１６６位点的重叠群,而且这一重叠群与以前构建的包含ＤＭＤ基因全序列的ＹＡＣ重叠群相连接,ＹＡＣ克隆末端探针交叉杂交证实了这一重叠,使这一ＹＡＣ重叠群至少延伸至ＤＸＳ１６６位点,形成一个跨度为３．５Ｍｂ的ＹＡＣ重叠群。基于这些重叠的ＹＡＣ克隆绘制了这一区域的大尺度限制酶切图谱,并在这一图谱上定位了ＤＸＳ１６６位点,从而确定了ＤＸＳ１６６位点与ＤＭＤ基因的物理关系。这一工作为ＤＭＤ基因的５＇远端调控作用研究及该区域未知基因的克隆奠定了基础。     

Genetic and physical mapping around the properdin P gene.

A CA repeat has been found on the human X chromosome within 16 kb of the gene encoding properdin P factor (PFC) and has been shown to be a highly informative marker. Two more polymorphic CA repeats were found in a cosmid containing DXS228. The CA repeats, and other markers from proximal Xp, were mapped genetically in CEPH families and the likely order of markers was established as Xpter-(DXS7, MAO-A, DXS228)-(PFC, DXS426)-(TIMP, OATL1)-DXS255-Xcen. This places PFC in the region Xp11.3-Xp11.23, thus refining previous in situ hybridization data. Two yeast artificial chromosomes (YACs) (440 and 390 kb) contain both PFC and DXS426, and one of them (440 kb) also contains TIMP. This confirms the genetic order TIMP-(PFC, DXS426). PFC and TIMP are located on the same 100-kb SalI/PvuI fragment of the 440-kb YAC. Given the genetic orientation of TIMP and (PFC, DXS426), this YAC can now serve as a starting point for directional walking toward disease genes located in Xp11.3-Xp11.2 such as retinitis pigmentosa (RP2) and Wiskott-Aldrich syndrome.     

DXS26 (HU16) is located in Xq21.1

Summary We have localized a single-copy DNA probe, HU16 (locus DXS26), to Xq21.1. The probe was isolated from a human-mouse hybrid X;13 library and mapped with human-mouse hybrids containing different portions of the human X chromosome and DNA from male patients with different X-chromosomal deletions. The following order of loci is proposed: Xcen-(DXS72, DXS169)-(DXS232,DXS26)-DXS121-DXS233-DXS165 TCD-DXS95-DXYSl-Xqter. HU16 will be useful in the study of the putative genes that reside in Xq21 and whose defects lead to deafness and mental retardation.     

Exclusion mapping of the gene for X-linked neural tube defects in an Icelandic family

Various polymorphic markers with a random distribution along the X chromosome were used in a linkage analysis performed on a family with apparently Xlinked recessive inheritance of neural tube defects (NTD). The lod score values were used to generate an exclusion map of the X chromosome; this showed that the responsible gene was probably not located in the middle part of Xp or in the distal region of Xq. A further refining of these results was achieved by haplotype analysis, which indicated that the gene for X-linked NTD was located either within Xp21.1-pter, distal from the DMD locus, or in the region Xq12–q24 between DXS106 and DXS424. Multipoint linkage analysis revealed that the likelihood for gene location is highest for the region on Xp. The region Xq26–q28, which has syntenic homology with the segment of the murine X chromosome carrying the locus for bent tail (Bn), a mouse model for X-linked NTD, is excluded as the location for the gene underlying X-linked NTD in the present family. Thus, the human homologue of the Bn gene and the present defective gene are not identical, suggesting that more than one gene on the X chromosome plays a role in the development of the neural tube.     

Fine structure mapping of the hypoxanthine-guanine phosphoribosyltransferase (HPRT) gene region of the human X chromosome (Xq26).

The Xq26-q27 region of the X chromosome is interesting, as an unusually large number of genes and anonymous RFLP probes have been mapped in this area. A number of studies have used classical linkage analysis in families to map this region. Here, we use mutant human T-lymphocyte clones known to be deleted for all or part of the hypoxanthine-guanine phosphoribosyltransferase (hprt) gene, to order anonymous probes known to map to Xq26. Fifty-seven T-cell clones were studied, including 44 derived from in vivo mutation and 13 from in vitro irradiated T-lymphocyte cultures. Twenty anonymous probes (DXS10, DXS11, DXS19, DXS37, DXS42, DXS51, DXS53, DXS59, DXS79, DXS86, DXS92, DXS99, DXS100d, DXS102, DXS107, DXS144, DXS172, DXS174, DXS177, and DNF1) were tested for codeletion with the hprt gene by Southern blotting methods. Five of these probes (DXS10, DXS53, DXS79, DXS86 and DXS177) showed codeletion with hprt in some mutants. The mutants established the following unambiguous ordering of the probes relative to the hprt gene: DXS53-DXS79-5'hprt3'-DXS86-DXS10-DXS177 . The centromere appears to map proximal to DXS53. These mappings order several closely linked but previously unordered probes. In addition, these studies indicate that rather large deletions of the functionally haploid X chromosome can occur while still retaining T-cell viability.     

The molecular evolution of ZFY-related genes in birds and mammals

Summary We report the isolation and nucleotide sequence determination of clones derived from five ZFY-related zinc-finger genes from birds and mammals. These sequences are analyzed with reference to the previously published human genes, ZFX and ZFY, and mouse genes, Zfx, Zfa, Zfy-1, and Zfy-2. The analysis indicates that ZFY-related genes are highly conserved in birds and mammals, and that the rate of nucleotide substitution in the Y-linked genes is not as high as predicted. However, the mouse Zfy-1 and Zfy-2 genes are markedly divergent members of the ZFY gene family; we suggest this relates to X-inactivation of the mouse gene Zfx.     

A multipoint linkage map of the distal short arm of the human X chromosome.

The distal portion of the short arm of the human X chromosome (Xp) exhibits many unique and interesting features. Distal Xp contains the pseudoautosomal region, a number of disease loci, and several cell-surface markers. Several genes in this area have also been observed to escape X-chromosomal inactivation. The characterization of new polymorphic loci in this region has permitted the construction of a refined multipoint linkage map extending 15 cM from the Xp telomere. This interval is known to contain the loci for the diseases X-linked ichthyosis, chondrodysplasia punctata, and Kallmann syndrome, as well as the cell-surface markers Xg and 12E7. This region also contains the junction between the pseudoautosomal region and strictly X-linked sequences. The locus MIC2 has been demonstrated by linkage analysis to be indistinguishable from the pseudoautosomal junction. The steroid sulfatase locus has been mapped to an interval adjacent to the DXS278 locus and 6 cM from the pseudoautosomal junction. The polymorphic locus (STS) DXS278 was shown to be informative in all families studied, and linkage analysis reveals that the locus represents a low-copy repeat with at least one copy distal to the STS gene. The generation of a multipoint linkage map of distal Xp will be useful in the genetic dissection of many of the unique features of this region.