Sex chromosome associated satellite DNA: evolution and conservation

A Bkm-associated human y-chromosomal DNA is conserved and transcribed in the testis of mouse

Y chromosome associated genes and repetitive sequences are continually viewed from the point of view of their possible involvement in sex determination and in the evolution of such a mechanism, thus sustaining an interest in the identification of novel sequences to gain newer insights. Here we have used the highly conserved class of Bkm repeats to isolate its associated sequences from the Y chromosome under the assumption that these sequences could be involved in sex determination and might also reflect the evolutionary status of the Y chromosome. Towards this end we have screened a genomic library enriched with human Y chromosome DNA with Bkm. One of the positive clones, C65, has a pericentromeric location on the Y chromosome and is present in a number of human sex-reversed XX males. The 10.5kb insert of clone C65 has been further subcloned (pFI, pFII, pFIII, pFIV). The subclone pFIII is present in both sexes in human and mouse, whereas pFIV is primate specific and present in both sexes. pFII contains sequences homologous to Bkm. pFI is conserved in mouse and man, but is Y specific only in primates. Although present in both sexes in mouse, pFI is transcribed specifically in the male testis suggesting that it may be involved in the process of sex determination or testis differentiation and spermatogenesis.

DNA fingerprinting in silkworm Bombyx mori using banded krait minor satellite DNA-derived probe

The genomic DNA from thirteen different ecotypes and inbred lines of silkworm, Bombyx mori, were analyzed by digesting with BstNI and HinfI restriction enzymes followed by hybridization with banded krait minor satellite DNA (Bkm)-2(8) minisatellite probe. The DNA fingerprinting revealed 9-31 discrete intense bands, some of which were ecotype/inbred line-specific. Individual specific DNA fingerprints in two representative genotypes and their F1 hybrid offspring were also obtained. Individuals of a given parental line showed very similar profiles and the hybrid offspring showed the combined profile of both parents. The presence of bands specific to diapausing and nondiapausing strains and to particular genotypes indicate their potential use for marker-assisted breeding and varietal identification.

Microdissection of the Y chromosome and fluorescence in situ hybridization analysis of the sex chromosomes of lake trout, Salvelinus namaycush

Lake trout, Salvelinus namaycush, is one of the few salmonids with morphologically differentiated sex chromosomes. Genetic analysis suggested that the sex-determining region of this species lies on the short arm of the Y chromosome. The differential arm of the Y chromosome was microdissected and the resulting DNA amplified in a sequence-independent manner. Amplified DNA was biotin labeled as a probe for fluorescence in situ hybridization (FISH). Strong hybridization signals were seen covering defined regions of both the Y and X chromosomes. Homeologous chromosomes of the ancestrally tetraploid genome were not identified by FISH with the Y probe, indicating diploidization of this region of the genome.

DNA fingerprinting of Musa cultivars with oligodeoxyribonucleotide probes specific for simple repeat motifs

Using synthetic oligodeoxyribonucleotide probes against restriction-digested genomic DNA, we have established DNA fingerprinting of Musa cultivars. Of all the enzymes used, Eco RI and Hin dIII were found to be most informative, giving rise to individual specific band patterns with oligonucleotide probes of 15- to 18-base residues. Of the several probes and enzyme combinations used, the 15mer GACA probe with Eco RI and Hin dIII digests revealed a maximal level of polymorphism, and the probability of obtaining an identical band pattern between any two random genotypes was calculated to be 1.50 x 10(-9) and 1.59 x 10(-9), respectively. Oligonucleotide probes longer than 22 residues were also used but did not hybridize. The present approach is useful for cultivar identification and for overall genome analysis to establish relatedness among the various accessions of the Musa germplasm originating from different geographic locations. The relevance of using synthetic oligonucleotide probes based on simple repeat motifs for achieving DNA fingerprinting pattern is discussed.

Amplification of DNA markers from evolutionarily diverse genomes using single primers of simple-sequence repeats

The abundance and scattered distribution of simple-sequence repeats (SSR) in eukaryotic genomes prompted us to explore the use of SSR-based oligonucleotide primers in single primer amplification reactions. In a pilot experiment, 23 primers were used across a panel of evolutionarily diverse eukaryotic genomes, including grapes, lettuce, tomato, pine, maize, salmon, chicken, Holstein cows and humans. The primers were 16-20 bases in length and represented SSRs of di-, tri-, tetra-, and pentanucleotide repeats. The results showed that tetranucleotide repeat primers were most effective in amplifying polymorphic patterns. Of 11 such primers tested, 70% produced polymorphic patterns from the DNA of one or more species. Primers representing a combination of two tetranucleotide repeats, or compound microsatellites, were equally effective. The polymorphisms contained in such fingerprints were able to identify individuals of vertebrate species as well as lines or varieties of plants. Inheritance of the polymorphic bands was studied in a maize recombinant inbred population, DE811 x B73. Thirty-two polymorphic bands, derived from two amplification patterns, were mapped as dominant markers on an existing RFLP map of the same population. The bands were distributed across nine of the ten chromosomes.

Banded krait minor-satellite (Bkm)-associated Y chromosome-specific repetitive DNA in mouse

The mouse Y chromosome remains highly condensed in all somatic tissues but decondenses extensively in testis. We have isolated a mouse Y chromosome-specific repeat M34 (11.5 kb) and shown that this is distributed along the Y chromosome except the sex-determining region (the Y short arm) in which GATA repeats are predominantly concentrated. It has 32 copies of GATA repeats in a 2.7 kb fragment. About 200-300 copies of M34 on the Y chromosome are interspersed among other sequences. A 1.2 kb fragment (p3) of M34, containing GATA repeats, also has scaffold attachment region (SAR) motifs which bind to nuclear matrices. A strong affinity of histone H1 to SAR motifs is implicated in maintaining the condensed state of the Y chromosome in somatic tissues. The probable significance of molecular organization of the Y chromosome is discussed.

Banded krait minor satellite (Bkm) contains sex and species-specific repetitive DNA

A novel class of repetitive DNA was isolated from a Bkm DNA library by exclusion hybridization. This sequence was mapped to the short arm of the W chromosome of banded krait, Bungarus fasciatus. Southern blot hybridization showed that these sequences are sex and species specific. Sequence analysis of a 206 bp long clone, BR87, revealed the presence of a tandem array of two internal repeat units of 18-19 bp alternating with each other with a gap of 1, 2 of 3 nucleotides. To our knowledge, this is the first report of an exclusively W chromosome- and species-specific repeat isolated from any reptile. The functional significance of this sequence based on its organisation is discussed.

Individualization and estimation of relatedness in crocodilians by DNA fingerprinting with a Bkm-derived probe

Individual-specific DNA fingerprints of crocodilians were obtained by the use of Bkm-2(8) probe. Pedigree analyses of Crocodylus palustris, C. porosus and Caiman crocodilus revealed that the multiple bands (22-23 bands with Aludigest) thus obtained were inherited stably in a Mendelian fashion. Unique fingerprints permitted us to identify individuals, assign parentage, and reconstruct the DNA profile of a missing parent. Average band sharing between unrelated crocodiles was found to be 0.37. Band sharing between animals of known pedigrees increased predictably with relatedness and provided a basis for distinguishing relatives from non-relatives. Similar results obtained in other species/genera, using the same probe, suggest that this approach may be applicable to all species of crocodilians, and could facilitate genetic studies of wild and captive populations.

Cloning and expression analysis of two ZFY-related zinc finger genes from Alligator mississippiensis, a species with temperature-dependent sex determination

In order to investigate the molecular mechanism of temperature-dependent sex determination, a human zinc finger gene (ZFY), known to be highly conserved amongst other species, was used to isolate homologues from the genome of the American alligator, Alligator mississippiensis. ZFY was originally a candidate for the primary testis-determining gene in man, but is now thought to function further down the sex-determining cascade. Two alligator genes are described, Zfc and Znc6. Both code for zinc finger proteins and exhibit amino acid (aa) homologies to ZFY of 91% and 73%, respectively. Znc6 shows aa homology of 88% to the protein encoded by the zinc finger exon of the human ZFY-related gene, ZNF6, recently found on the X chromosome. Analysis of Zfc and Znc6 expression during embryonic development identified two major transcripts of 5.9 kb and 2.7 kb coding for Zfc, whilst only one transcript of 4.8 kb was detected for Znc6. Both genes are transcribed at all stages tested, from day 3 (post egg laying) throughout gestation. The expression level of all transcripts appears to decline towards the time of hatching (65-72 days). No sex-specific differences in the expression were observed. The extensive sequence conservation of the genes between reptiles and humans suggests major functional constraints. The expression patterns indicate that these genes do not play a primary role in temperature-dependent sex determination.

Code domains in tandem repetitive DNA sequence structures

Traditionally, many people doing research in molecular biology attribute coding properties to a given DNA sequence if this sequence contains an open reading frame for translation into a sequence of amino acids. This protein coding capability of DNA was detected about 30 years ago. The underlying genetic code is highly conserved and present in every biological species studied so far. Today, it is obvious that DNA has a much larger coding potential for other important tasks. Apart from coding for specific RNA molecules such as rRNA, snRNA and tRNA molecules, specific structural and sequence patterns of the DNA chain itself express distinct codes for the regulation and expression of its genetic activity. A chromatin code has been defined for phasing of the histone-octamer protein complex in the nucleosome. A translation frame code has been shown to exist that determines correct triplet counting at the ribosome during protein synthesis. A loop code seems to organize the single stranded interaction of the nascent RNA chain with proteins during the splicing process, and a splicing code phases successive 5' and 3' splicing sites. Most of these DNA codes are not exclusively based on the primary DNA sequence itself, but also seem to include specific features of the corresponding higher order structures. Based on the view that these various DNA codes are genetically instructive for specific molecular interactions or processes, important in the nucleus during interphase and during cell division, the coding capability of tandem repetitive DNA sequences has recently been reconsidered.

A highly repetitive interspersed sequence isolated from genomic DNA of the Medaka, Oryzias latipes, is conserved in three other related species within the genus Oryzias

A highly repeated interspersed sequence (OLR1) was isolated from a genomic DNA library of the Medaka, Oryzias latipes. The OLR1 was about 160 base pairs (bp) in length. As judged from the results of colony hybridization experiments, OLR1 is one of the major repeated DNA sequences in the Medaka genome and is present in every 136 kb on average. Results of Southern and colony-hybridization analyses indicate that OLR1 is a small interspersed repetitive element (SINE). OLR1-related sequences were conserved in other three species (O. luzonensis, O. curvinotus, and O. mekongnensis) within the genus Oryzias as a repetitive sequence. These results lend support at the DNA level to the hypothesis that these four species form one group in the genus Oryzias, as has been suggested from an analysis of their karyotypes (Magtoon and Uwa, '85, Proc. Jpn. Acad., Ser. B, 61:157-160).

Nucleotide sequence analysis of a mouse Y chromosomal DNA fragment containing Bkm and LINE elements

The strong suppression of crossing-over between the X and Y chromosomes permits rapid accumulation of repetitive sequences in the Y chromosome. To gain insight into the mechanism responsible for the sequence amplification, it is essential to characterize Y chromosomal repetitive sequences at the molecular level. Here, we report the entire nucleotide sequence (3,902bp) of AC11, a mouse sequence that is repeated 300 times in the Y chromosome. AC11 is AT rich (32.8% GC), and contains many short poly(A) sequences. In addition, it has Bkm and LINE sequences as well as a Y chromosome-specific sequence. The Bkm sequence consists of typical (GATA) and (GACA) repeating units, whereas the LINE sequence deviates considerably from other mouse LINE sequences (71-76% identity) and may be considered atypical. The Y chromosome-specific region seems to be unique and does not identify similar sequences in the GenBank library. The information obtained from the nucleotide sequence should form the foundation to study the evolutionary processes through which AC11-related sequences have accumulated in the mouse Y chromosome.

DNA fingerprinting in domestic animals

DNAs of several species of domestic animals digested with the restriction endonucleases HinfI, AluI and HaeIII were hybridized with different synthetic probes. DNA fingerprint patterns were found in each investigated species by at least two of these probes. Furthermore, two probes gave sex-specific banding patterns in the chicken. Some applications of DNA fingerprinting in domestic animals are discussed.

The evolution of heteromorphic sex chromosomes

The facts and ideas which have been discussed lead to the following synthesis and model. 1. Heteromorphic sex chromosomes evolved from a pair of homomorphic chromosomes which had an allelic difference at the sex-determining locus. 2. The first step in the evolution of sex-chromosome heteromorphism involved either a conformational or a structural difference between the homologues. A structural difference could have arisen through a rearrangement such as an inversion or a translocation. A conformational difference could have occurred if the sex-determining locus was located in a chromosomal domain which behaved as a single control unit and involved a substantial segment of the chromosome. It is assumed that any conformational difference present in somatic cells would have been maintained in meiotic prophase. 3. Lack of conformational or structural homology between the sex chromosomes led to meiotic pairing failure. Since pairing failure reduced fertility, mechanisms preventing it had a selective advantage. Meiotic inactivation (heterochromatinization) of the differential region of the X chromosome in species with heterogametic males and euchromatinization of the W in species with heterogametic females are such mechanisms, and through them the pairing problems are avoided. 4. Structural and conformational differences between the sex chromosomes in the heterogametic sex reduced recombination. In heterogametic males recombination was reduced still further by the heterochromatinization of the X chromosome, which evolved in response to selection against meiotic pairing failure. 5. Suppression of recombination resulted in an increase in the mutation rate and an increased rate of fixation of deleterious mutations in the recombination-free chromosome regions. Functional degeneration of the genetically isolated regions of the Y and W was the result. In XY males this often led to further meiotic inactivation of the differential region of the X chromosome, and in this way an evolutionary positive-feedback loop may have been established. 6. Structural degeneration (loss of material) followed functional degeneration of Y or W chromosomes either because the functionally degenerate genes had deleterious effects which made their loss a selective advantage, or because shorter chromosomes were selectively neutral and became fixed by chance. 7. The evolutionary routes to sex-chromosome heteromorphism in groups with female heterogamety are more limited than in those with male heterogamety. Oocytes are usually large and long-lived, and are likely to need the products of X- or Z-linked genes. Meiotic inactivation of these chromosomes is therefore unlikely. In the oocytes of ZW females, meiotic pairing failure is avoided through euchromatinization of the W rather than heterochromatinization of the Z chromosome.(ABSTRACT TRUNCATED AT 400 WORDS)

A novel avian W chromosome DNA repeat sequence in the lesser black-backed gull (Larus fuscus)

The phenol emulsion reassociation technique was used to isolate and clone a female specific, repetitive DNA sequence from Larus fuscus. The repeat, designated P2000-17, is restricted to the W chromosome, although related sequences occur elsewhere in the genome of L. fuscus. Similar sequences were detected in the genome of six other bird species from outside the genus Laridae, but the sequence occurs less frequently and to a similar extent in both sexes. The 298 bp DNA sequence of P2000-17 was determined and found to have extensive sequence identity to the rabbit dihydropyridine (DHP) receptor calcium channel. P2000-17 is represented once within a larger 8.6 kb tandem repeat (LfW-1), which has a complex internal DNA sequence. LfW-1 is highly conserved between repeat motifs and may comprise 3% of the female genome. The possible evolutionary origin of LfW-1 is discussed in relation to the repeat types found on the W and Y chromosomes of other species.

Potential genetic functions of tandem repeated DNA sequence blocks in the human genome are based on a highly conserved "chromatin folding code"

This review is based on a thorough description of the structure and sequence organization of tandemly organized repetitive DNA sequence families in the human genome; it is aimed at revealing the locus-specific sequence organization of tandemly repetitive sequence structures as a highly conserved DNA sequence code. These repetitive so-called "super-structures" or "higher-order" structures are able to attract specific nuclear proteins. I shall define this code therefore as a "chromatin folding code". Since locus-specific superstructures of tandemly repetitive sequence units are present not only in the chromosome centromere or telomere region but also on the arms of the chromosomes, I assume that their chromatin folding code may contribute to, or even organize, the folding pathway of the chromatin chain in the nucleus. The "chromatin folding code" is based on its specific "chromatin code", which describes the sequence dependence of the helical pathway of the DNA primary sequence (i.e., secondary structure) entrapping the histone octamers in preferential positions. There is no periodicity in the distribution of the nucleosomes along the DNA chain. The folding pathway of the nucleosomal chromatin chain is however still flexible and determined by e.g., the length of the DNA chain between the nucleosomes. The fixation and stabilization of the chromatin chain in the space of the nucleus (i.e., its "functional state") may be mediated by additionally unique DNA protein interactions that are dictated by the "chromatin folding code". The unique DNA-protein interactions around the centromeres of human chromosomes are revealed for example by their "C-banding". I wish to stress that it is not my aim to relate each block of repetitive DNA sequences to a specific "chromatin folding code", but I shall demonstrate that there is an inherent potential for tandem repeated sequence units to develop a locus-specific repetitive higher order structure; this potential may create a specific chromatin folding code whenever a selection force exists at the position of this repetitive DNA structure in the genome.

Sex determination and the Y chromosome: the application of molecular genetic technique to behavioral genetics

In mammals, the Y chromosome mediates both gonadogenesis and spermatogenesis. It is also known to influence such traits as histocompatibility, sperm head morphology, pubertal (but not adult) testosterone level, sexual behavior, and aggressive behavior. An immediate goal in my laboratory is the isolation and characterization of the Y chromosomal gene responsible for initiating differentiation of the primitive bipotential gonads to become testes: the Y chromosomal gonadogenesis gene. Function of this gene initiates a cascade of events involving large numbers of other genes scattered throughout the genome, but it is not responsible for initiating development of all of the male phenotype; where : is XXSxr karyotype males, bearing the Sxr region of the Y chromosome which includes this gene, are sterile. It is not known if this gene influences those behaviors known to be influenced by the Y chromosome. If animals with an XXSxr karyotype, transgenic for specific Y chromosomal genes, could be produced, questions such as this could be answered. The developmental biology of the testis, molecular genetics of the Sxr region of the Y chromosome, and isolation of the testis determination gene from DNA of XXSxr males are discussed. Also discussed are the production of transgenic mice and the prospects for using such animals as coisogenic strains, differing by precisely known DNA sequences, in behavior genetic analysis. Such animals could be used both to test for behavioral phenotype and to dissect out biochemical and neurological mechanisms responsible for the behavior.

Schistosoma mansoni: chromosomal localization of DNA repeat elements by in situ hybridization using biotinylated DNA probes

Localization of the SM alpha family of repeated DNA and the rDNA repeat on the chromosomes of Schistosoma mansoni by in situ hybridization is presented. Biotinylated DNA was hybridized to target chromosomes and hybridization was detected using either alkaline phosphatase-labeled avidin or fluorescein-labeled avidin and biotinylated anti-avidin antibody. Hybridization detection using a fluorescein conjugate was more specific and sensitive with less background noise than detection with alkaline phosphatase conjugates. SM alpha hybridizing sequences were found dispersed throughout the genome, hybridizing to the sex chromosomes and autosomes. The SM alpha probe showed specific hybridization to the euchromatic gap region within the large heterochromatic block of the short arm of the W chromosome. This specific hybridization coupled with the lack of chiasma formation in this region of the ZW bivalent (presumably due to the heterochromatinization of this region) may explain the pattern of sex-specific hybridization reported for the SM alpha family. The rDNA repeat was localized to the secondary constriction of the short arm of chromosome 3. Specifically, the rDNA probe hybridized with the stalk of the secondary constriction and with parts of both side regions, the satellite and the short arm proper.

Variable evolutionary stability of Y chromosomal repeated sequences in the genus Mus

The study reported here is an examination of the organization and evolution of three Y chromosomal repeated sequences, designated pBC10-0.6, pBC15-1.1, and pBA33-1.8, in five closely related species of the genus Mus. The species distributions of major restriction fragment length polymorphisms produced with a panel of restriction enzymes is used to develop the phylogenetic relationships between the five species studied. However, the apparent degree of relatedness among these species varied a great deal with each of the three probes and was also highly dependent on the particular restriction enzyme used. The usefulness for phylogenetic studies of closely associated sequences varying in evolutionary stability is discussed.

A DNA probe from Schistosoma mansoni allows rapid determination of the sex of larval parasites

A DNA clone representing a 0.4 kb degenerative repeat has been isolated. The DNA sequence is present only in the genome of female Schistosoma mansoni at different stages of the life cycle, at a frequency of approximately 75 copies per adult female genome. The sequence is not expressed and probably represents satellite DNA in the heterochromatin region of the W chromosome. It is demonstrated that the DNA clone may be used for the rapid determination of the sex of cercariae without the need for DNA isolation or Southern blotting.

Structural and evolutionary comparisons of four alleles of the mouse immunoglobulin kappa chain gene, Igk-VSer

The mouse Igk-VSer gene encodes an immunoglobulin kappa light chain variable region which gives rise to two phenotypic polymorphisms of mouse kappa chains. The nucleotide sequences of coding and flanking regions of the Igk-VSerc and Igk-VSerd alleles found in recently inbred strains of wild mice are compared with those of the Igk-VSera and Igk-VSerb alleles described previously. Results suggest that the gene is evolving randomly and that framework 2 and complementarity determining region 2 are preserved, presumably for overall light chain structure. Results indicate that all four alleles have an octamer motif upstream of the gene which should be functional and allow prediction of whether or not the product of the germ line gene will be detectable as either the IB-peptide or Ef1a phenotypic polymorphism. Southern hybridization of genomic DNA using as probe a 1-kb Xba I-Xba I fragment located approximately 4 kb upstream of the BALB/c Igk-VSerb coding region demonstrated the presence of homologous DNA in mice bearing the Igk-VSera allele and absence from mice bearing the Igk-VSerc and Igk-VSerd alleles. Nucleotide sequence comparison of BALB/c and SK/CamRk (Igk-VSerd) DNA in this region demonstrated that BALB/c contained an insertion 2.4 kb in length which was absent from SK/CamRk. Both strains contain DNA homologous to the reverse complement of the mouse Bam5 repetitive element at the point of the insertion, with BALB/c containing approximately 70 nucleotides more of the element than SK/CamRk. Surprisingly, the strains containing DNA related to the Xba I-Xba I probe are not those determined to be the most similar by nucleotide sequence comparisons and by the Phylogenetic Analysis Using Parsimony program. The evolutionary relationship of the alleles and a possible basis for the inconsistency presented by the Xba I-Xba I fragment-related DNA are discussed.

Northern analyses using single-stranded probes do not support a role for GATA/GACA repeats in sex determination in mice and men

The possible role of GATA/GACA repeated sequences in mammalian sex determination was investigated using Northern analyses of mouse and human RNA. Brain, liver, and gonadal RNA from three developmental stages of mice of both sexes and also human fetal RNA from various tissues were hybridized to both sense and antisense Bkm riboprobes as well as to the synthetic oligonucleotide (GATA)5. At low levels of stringency, putative transcripts of various sizes were observed in all tissue samples with all probes. At high stringency, only a putative transcript of approximately 12 kb was observed, but this was later shown to consist of contaminating DNA. No sex-specific differences were observed in any tissue or developmental stage. Thus, we find no evidence that the GATA/GACA repeated sequences are specifically expressed in quantities detectable by Northern analyses in a manner important to mammalian sex determination.

Bkm sequences from the human X chromosome contain large clusters of GATA/GACA repeats

In order to determine whether the regional localizations of Bkm repeats detected on the human X chromosome consisted of typical GATA/GACA repeats, clones were isolated, mapped, and sequenced. Nine Bkm-hybridizing clones from Kunkel's fluorescent-activated, cell-sorted X-chromosome library were all unique. Five were mapped in detail with restriction enzymes and the Bkm-hybridizing segments were localized. Confirmation of X chromosomal homology was obtained for 2 of the clones and Bkm segments from these 2 clones were sequenced. Seventeen contiguous GATA repeats were found in each clone and the overall repeat arrangement showed relatively few differences from previously sequenced Bkm sequences. These are the first sequences of human Bkm repeats. The results, when compared with previously published results, suggest that there may be significant differences between the organization of Bkm repeats on the human X and on the human Y chromosome.

Simple GATCA repeats characterize the X chromosomal heterochromatin of Microtus agrestis, European field vole (Rodentia, Cricetidae)

The sex chromosomes of Microtus agrestis are extremely large due to the accumulation of constitutive heterochromatin. We have identified two prominent satellite bands of 2.0 and 2.8 kb in length after HaeIII and HinfI restriction enzyme digestion of genomic DNA, respectively. These satellites are located on the heterochromatic long arm of the X chromosome as shown using Microtus x mouse somatic cell hybrids. By in-gel hybridization with oligonucleotide probes, the organization of the two satellites was studied: among the many copies of the simple tandem tetranucleotide repeat GATA are interspersed rare single GACA tetramers. One of the satellites also harbours related GGAT simple tandem repeats. In situ hybridizations with plasmid-carried or oligonucleotide GATCA probes show clustered silver grains on the long and short arm of the X chromosome. Interspersion of differently organized (GATA)n elements is also demonstrable in the autosomal complement and on the Y chromosome. These results are discussed in the context of the evolution of vertebrate sex chromosomes in relation to heterochromatin and simple repetitive DNA sequences.

GATA tandem repeats detect minisatellite regions in blowfly DNA (Diptera: Calliphoridae)

A DNA probe containing GATA tandem repeats detected numerous dispersed minisatellite regions in the genomes of the blowflies Chrysomya rufifacies and Calliphora erythrocephala. These regions seemed to be actively transcribed into poly(A)+ RNA in a tissue-specific manner. When genomic DNA of blastoderm embryos was compared with adult genomic DNA some loci hybridizing to GATA displayed a marked stage-specific variation in length. In Calliphora, a small sex-linked dimorphism of GATA mini-satellite-associated restriction fragments was observed.

A human Y-chromosomal DNA sequence expressed in testicular tissue

Clone pJA36B (DYS14) was isolated from a human Y chromosome enriched cosmid library. Southern blot analysis revealed a male-specific hybridization pattern. Deletion mapping with patients' DNA localized pJA36B to the median region of Yp, being present in the DNA of nine of fifteen XX-males tested so far and therefore localized in the region neighbouring the TDF-locus. Northern blot analysis showed a transcription signal in poly(A)+ RNA of human testis. Sequence analysis of the genomic DNA sequence revealed an open reading frame of 522 basepairs in the absence of control or signal sequences for the regulation of transcription or polyadenylation. This suggests that only one exon of a translatable sequence is present in clone pJA36B. A computer aided search revealed no significant homologies with known DNA or protein sequences.

A DNA sequence which shows genomic variation in a, alpha and HO strains of Saccharomyces cerevisiae

HindIII digested DNA from various mutant strains of Saccharomyces cerevisiae probed with a 340 bp nucleotide sequence in M13mp8 derived from a mouse liver cDNA clone p1581 showed strong hybridization to a 4.1 kb DNA fragment class. This was limited to the DNA of cells of alpha mating type but the fragments concerned apparently do not originate from chromosome III. The pattern of hybridization was modified in strains carrying the HO gene consistent with there being extra copies of the Bkm-homologous sequence in these cells. Northern analysis of RNA from cells synchronised in various stages of the mitotic and meiotic cell cycle probed with M13mp8/p1581 indicated related transcripts in meiotic cells.

Testis development in a mouse with 10% of XY cells

Two mouse Y-chromosome-related DNA probes were used to show that an aspermic sterile male mouse with small testes contained only approximately 10% of normal XY cells dispersed among normal XX cells. Examination of testis sections by in situ hybridization revealed that XY cells were nonrandomly concentrated in the testis tubules when compared with the interstitial cell population. These observations are discussed in the context of primary sex determination and histological differentiation of the testis.

Multiple forms of male-specific simple repetitive sequences in the genus Mus

Previous reports indicate that in laboratory strains of mice, males are distinct from females in possession of repetitive DNA, notably devoid of Eco RI and Hae III sites and rich in the simple tetranucleotides GATA/GACA. We report here that such sequences originated in an ancestor common to laboratory mice, Mus hortulanus, M. spretus, and possibly also M. cookii. Interestingly, other male-specific satellite sequences were detected in M. caroli, M. cookii, M. saxicola, and M. minutoides. This novel satellite is also likely to be composed of simple repetitious sequences, but does not contain GATA and GACA. Thus, the Y chromosome appears to contain a disproportionately large amount of simple repetitious DNA. An attractive explanation for these results is that long tandem arrays of simple repeated sequences are generated at high frequency throughout the genome and that they are retained for a longer time on the Y chromosome due to the absence of homologous pairing at meiosis.

The behavior and morphology of the X and Y chromosomes during prophase I in the Sitka deer mouse (Peromyscus sitkensis)

Surface-spread, silver-stained primary spermatocytes from individuals of the Sitka deer mouse (Peromyscus sitkensis) were analyzed by electron microscopy. Pairing of the X and Y chromosomes is initiated at early pachynema and is complete by mid pachynema. The pattern of sex chromosome pairing is unique in that it is initiated at an interstitial position, with subsequent synapsis proceeding in a unidirectional fashion towards the telomeres of the homologous segments. One-third the length of the X and two-thirds the length of the Y are involved in the synaptonemal complex of the sex bivalent. Various morphological complexities develop in the heteropycnotic (unpaired) segments as pachynema progresses, but desynapsis is not initiated until diplonema. Analysis of C-banded diakinetic nuclei indicated that sex chromosome pairing involves the heterochromatic short arm of the X and the long arm of the heterochromatic Y. An interstitial chiasma between the X and Y was observed in the majority of the diakinetic nuclei. The observation of a substantial pairing region and chiasma formation between the sex chromosomes of these deer mice is interpreted as indicating homology between the short arm of the X and the long arm of the Y.

Clustered GATA repeats (Bkm sequences) on the human Y chromosome

Sixty eight individual clones of a human Y chromosome cosmid library were screened for the presence of GATA repeats, the major component of Bkm-related DNA sequences. Nine cosmid clones were found to cross-hybridize. The sequence organization of the repetitive base quadruplet GATA was analyzed using synthetic oligonucleotide probes. Subclones of GATA-positive cosmid clones were used for chromosomal localization of the Y-derived DNA sequences thus revealing male-specificity or male-female homology.

Bkm sequences are polymorphic in humans and are clustered in pericentric regions of various acrocentric chromosomes including the Y

Probes of uncloned Bkm satellite DNA and a Drosophila clone 2 (8), consisting mainly of GATA repeats related to a major sequence component in Bkm, have been used to probe Southern blots of human male and female DNAs obtained from a Caucasian and an Australian aboriginal population and to human chromosomes in situ. Hybridization was observed to a distinct and an indistinct series of bands against a smeared background. The same distinct bands are identified in the DNA samples with both probes, but are most readily detected using the uncloned Bkm probe. Most restriction bands are common to both populations and some are polymorphic. However, certain bands appear to be characteristic of the Australian aboriginal samples. There are no distinct sex-linked patterns. However all of the small acrocentric human chromosomes, including the Y chromosome show hybridization to uncloned Bkm in situ.