In a large collaborative screening project, 370 men with idiopathic azoospermia or severe oligozoospermia wereanalysed for deletions of 76 DNA loci in Yq11. In 12 individuals, we observed de novo microdeletions involvingseveral DNA loci, while an additional patient had an inherited deletion. They were mapped to three differentsubregions in Yq11. One subregion coincides to the AZF region defined recently in distal Yq11. The second andthird subregion were mapped proximal to it, in proximal and middle Yq11, respectively. The different deletionsobserved were not overlapping but the extension of the deleted Y DNA in each subregion was similar in eachpatient analysed. In testis tissue sections, disruption of spermatogenesis was shown to be at the same phasewhen the microdeletion occurred in the same Yq11 subregion but at a different phase when the microdeletionoccurred in a different Yq11 subregion. Therefore, we propose the presence of not one but three spermatogenesisloci in Yq11 and that each locus is active during a different phase of male germ cell development. As the mostsevere phenotype after deletion of each locus is azoospermia, we designated them as: AZFa, AZFb and AZFc.Their probable phase of function in human spermatogenesis and candidate genes involved will be discussed. INTRODUCTIONGenes for male germ cell development are present on the Ychromosome in different species groups (1–3). In men, theposition of a spermatogenesis locus was mapped in theeuchromatic part of the long Y arm (Yq11). It was called‘azoospermia factor’ (AZF), as the first six men observed withterminal deletions in Yq were azoospermic (4). Mature spermcells were not detectable in their seminal fluid. In all cases, the Ydeletions included the large heterochromatin block of the long Yarm (Yq12) and an undefined amount of the adjacent euchromatin(Yq11). Subsequently, the presence of AZF in Yq11 wasconfirmed by numerous studies at both cytogenetic (5) andmolecular level (6–8). However, the genetic complexity of AZFcould not be revealed by these analyses.This first became possible by the detection of sterile patientswith small interstitial deletions (i.e. microdeletions) in Yq11. Ina study with 13 sterile men suffering from idiopathic azoospermiatwo different microdeletions in Yq11 were observed (9). Theywere mapped to two non overlapping positions in Yq11 interval6 (10). However, further studies of Yq11 microdeletionsassociated to the phenotype of male sterility, only confirmed theposition of an AZF locus in distal Yq11 (11,12). The mostextensive study was performed by Reijo et al. (13) on 89 sterile

Human Y Chromosome Azoospermia Factors (AZF) Mapped to Different Subregions in Yq11

▪ Abstract Meiotic chromosomes have been studied for many years, in part because of the fundamental life processes they represent, but also because meiosis involves the formation of homolog pairs, ...

Meiotic chromosomes: integrating structure and function.

Cloning and characterization of the

http://www.gs.washington.edu/academics/courses/braun/55105/readings/ahmad.pdf

The histone variant H3.3 marks active chromatin by replication-independent nucleosome assembly.

Structures in Other Domains The methodology of structural analysis discussed in this article has been applied beyond the narrow realm of natural language syntax that we have discussed in this article. Within the study of language, similar methods of analysis have been pervasively applied to the study of sounds (phonology), words (morphology), and meanings (semantics), yielding a range of of abstract structural representations whose properties bear considerable explanatory burden. There are a wealth of cases in each of these domains analogous to those discussed here, though space prevents us from going in these (see Akmajian, Demers, Farmer and Harnish 1995 for a traditional overview, and Jackendo 1994 for one more focused on connections with cognitive science). Additionally, these representations have shed substantial light on the processes of language acquisition and language change. It has been found that variation in the types of sentences that are used, whether during the course of children's acquisition of their native languages or in the centuries-long periods of linguistic change, are best characterized not as super cial and haphazard alterations, but rather in terms of parametric modi cations to the fundamental underlying grammatical rules and constraints. Moving outside the domain of language, one application of these same methods has been in the study of music cognition. Just as the representations of linguistic theory arise out of an attempt to model speakers' intuitions about well-formedness and possible meanings of the sentences of their

Structural analysis

The polytenization of rRNA cistrons in Drosophila species is studied in an attempt to follow the course of under-representation of heterochromatic compared with euchromatic chromosome regions.

Reduced polyteny of ribosomal RNA cistrons in giant chromosomes of Drosophila hydei.

It is shown by isopycnic density gradient centrifugation that the DNAs of the sibling species Drosophila hydei, Drosophila neohydei and Drosophila pseudoneohydei differ regarding the numbers and proportions of satellite DNA bands. An overwhelming proportion of all repetitive nucleotide sequences of the DNA is contained in these satellite fractions. The majority of the satellites are species specific despite the close phylogenetic and cytological relationship between the three species studied. — By in situ hybridization experiments it is demonstrated that the various satellite sequences occupy different positions within the chromosomes. All types of localization patterns, from a wide spread occurrence in all chromosomes to an apparent restriction to kinetochore regions of single chromosomes, have been observed. Main band DNA, on the other hand, in its hybridization behavior reflects the DNA distribution according to the banding pattern in giant chromosomes. Generally satellite sequences seem to be included in α-heterochromatic chromosome regions but no relation to the heterochromatin of the Y-chromosome was found. — Renaturation studies support various evidence that satellite sequences occur in tandemly repetitious units. At least some of this repetitious material seems to be linked to non-satellite DNA sequences or to DNA of other satellites.

Repeated sequences in the DNA of Drosophila and their localization in giant chromosomes.

1.

Die Strukturdifferenzierungen des Y-Chromosoms in den primaren Spermatocyten von Drosophila hydei enthalten nach histochemischen und autoradiographischen Befunden DNS. In bestimmten Bereichen der Y-Strukturen wird RNS synthetisiert. Sie entsprechen damit strukturell und funktionell den Schleifen von Amphibien-Lampenburstenchromosomen.




2.

In den Y-Strukturen wird neusynthetisierte RNS angereichert. Diese unterliegt einem Austausch innerhalb von 20 bis 30 Std, obgleich die Y-Strukturen uber 120 Std hinweg unverandert bestehen. Vermutlich handelt es sich bei der angereicherten RNS um in situ synthetisiertes Material. Von der nicht-nukleolaren RNS-Synthese in den Spermatocytenkernen entfallt etwa 50% auf die autosomale RNS-Synthese.




3.

Eine Proteinsynthese ist in den Spermatocytenkernen autoradiographisch nicht nachweisbar, obwohl die Y-Strukturdifferenzierungen nach histochemischen Befunden uberwiegend aus Proteinen bestehen.

Nach Inkubation in markierten Aminosauren kommt es aber zu einer Anreicherung markierter Proteine in den Spermatocytenkernen, die aus dem Nukleolus oder dem Cytoplasma stammen. Auch diese Proteine sind nur fur einige Stunden im Kern vorhanden und werden nicht fur langere Zeit in den Strukturdifferenzierungen des Y-Chromosoms angereichert. Da man auch nach Langzeitinkubationen bis zu 40 Std keine markierten Y-Strukturen findet, scheinen deren Proteine zum grosten Teil nicht-stationar zu sein und einem standigen Austausch zu unterliegen.




4.

Aufgrund der Wirkung von Inhibitoren der RNS- und der Proteinsynthese, die zu einem Abbau und unter bestimmten Bedingungen zu einer Neubildung der Y-Strukturen fuhren, werden die Y-Strukturen als dynamische Strukturen interpretiert, deren Form durch ein Gleichgewicht zwischen dem Abflus von Material und der Ansammlung neuer Strukturbestandteile aufrecht erhalten wird: Der strukturelle Bestand wird nicht allein durch die RNS-Synthese gewahrleistet, auch ein ungestorter Proteinstoffwechsel ist Voraussetzung fur die volle Ausbildung der Y-Strukturen.




5.

Da eine RNS-Synthese nur bis zur Diakinese der I. Reifeteilung autoradiographisch nachweisbar ist, mus Information fur die Spermiohistogenese im primaren Spermatocytenstadium bereitgestellt werden. Wahrscheinlich liegt diese Information in Form stabiler „messenger“-RNS-Molekule vor, da markierte RNS sich bis in junge Spermien verfolgen last und eine Proteinsynthese wahrend der gesamten Spermiohistogenese ablauft. Die mogliche Bedeutung der Y-Strukturdifferenzierungen in den Spermatocytenkernen fur diese Bereitstellung von Information wird diskutiert.

Untersuchungen zur Struktur und Funktion des Lampenbürsten-Y-Chromosoms in der Spermatogenese von Drosophila

A short summary on the present knowledge on spermatogenesis in Drosophila is given which also points out particular questions of interest in the context of this morphogenetic process. Such points of interest are the formation of lampbrush loops in primary spermatocytes, the chromosomal events during meiosis, the occurrence of chromatin rearrangements and the regulation of gene activities at the posttranscriptional level. The activities and some major conclusions from my laboratory are subsequently described. They include studies of the expression of histone variants, the structure and function of lampbrush loops and the expression of genes participating in sperm morphogenesis.

/pdf/spermatogenesis-in-drosophila-4f34j4i7g9.pdf

Spermatogenesis in Drosophila.

Transcribing ribosomal RNA genes in primary spermatocyte nucleoli of Drosophila hydei have been visualized by electron microscopy using a microspreading technique. The length of the transcribing unit is in agreement with the length of the ribosomal RNA precursor as determined by acrylamide gel electrophoresis (2.6×106 daltons). The length of the non-transcribed spacer is approximately 1.0×106 daltons. The maximum number of active cistrons in wild type (XY) males only approaches one half the estimated number of ribosomal cistrons of the replicated diploid genome (∼300) of D. hydei and is found to vary between 120 and 320 cistrons in different developmental stages of spermatocytes. There is also some variation between different males. In a few cases a variation in the transcriptional activity of different cistrons has been observed. The synthesis of ribosomal RNA therefore seems to be regulated primarily by the activation or inaetivation of varying numbers of ribosomal cistrons. Groups of adjacent cistrons seem to be under coordinated control. Inhibition of RNA synthesis by actinomycin, in contrast, follows a random pattern. The frequent observation of a bipartite nucleolus indicates that the nucleolus organizer regions of the two sex chromosomes are both active in transcription. The number of active ribosomal eistrons found in some X-Y translocation stocks and in XO males deviates considerably from that expected on the basis of DNA/RNA hybridization data. We conclude that, in agreement with the observations of other authors, a mechanism adjusting the number of ribosomal cistrons may be operating in these cases.

Wolfgang Hennig

Papers

Reduced polyteny of ribosomal RNA cistrons in giant chromosomes of Drosophila hydei.

Repeated sequences in the DNA of Drosophila and their localization in giant chromosomes.

Untersuchungen zur Struktur und Funktion des Lampenbürsten-Y-Chromosoms in der Spermatogenese von Drosophila

Spermatogenesis in Drosophila.

The nucleolus in primary spermatocytes of Drosophila hydei.