Early Prophase Of Meiosis Research Articles

Bi-allelic variants in DNA mismatch repair proteins MutS Homolog MSH4 and MSH5 cause infertility in both sexes.

Do bi-allelic variants in the genes encoding the MSH4/MSH5 heterodimer cause male infertility? We detected biallelic, (likely) pathogenic variants in MSH5 (4 men) and MSH4 (3 men) in six azoospermic men, demonstrating that genetic variants in these genes are a relevant cause of male infertility. MSH4 and MSH5 form a heterodimer, which is required for prophase of meiosis I. One variant in MSH5 and two variants in MSH4 have been described as causal for premature ovarian insufficiency (POI) in a total of five women, resulting in infertility. Recently, pathogenic variants in MSH4 have been reported in infertile men. So far, no pathogenic variants in MSH5 had been described in males. We utilized exome data from 1305 men included in the Male Reproductive Genomics (MERGE) study, including 90 males with meiotic arrest (MeiA). Independently, exome sequencing was performed in a man with MeiA from a large consanguineous family. Assuming an autosomal-recessive mode of inheritance, we screened the exome data for rare, biallelic coding variants in MSH4 and MSH5. If possible, segregation analysis in the patients' families was performed. The functional consequences of identified loss-of-function (LoF) variants in MSH5 were studied using heterologous expression of the MSH5 protein in HEK293T cells. The point of arrest during meiosis was determined by γH2AX staining. We report for the first time (likely) pathogenic, homozygous variants in MSH5 causing infertility in 2 out of 90 men with MeiA and overall in 4 out of 902 azoospermic men. Additionally, we detected biallelic variants in MSH4 in two men with MeiA and in the sister of one proband with POI. γH2AX staining revealed an arrest in early prophase of meiosis I in individuals with pathogenic MSH4 or MSH5 variants. Heterologous in vitro expression of the detected LoF variants in MSH5 showed that the variant p.(Ala620GlnTer9) resulted in MSH5 protein truncation and the variant p.(Ser26GlnfsTer42) resulted in a complete loss of MSH5. All variants have been submitted to ClinVar (SCV001468891-SCV001468896 and SCV001591030) and can also be accessed in the Male Fertility Gene Atlas (MFGA). By selecting for variants in MSH4 and MSH5, we were able to determine the cause of infertility in six men and one woman, leaving most of the examined individuals without a causal diagnosis. Our findings have diagnostic value by increasing the number of genes associated with non-obstructive azoospermia with high clinical validity. The analysis of such genes has prognostic consequences for assessing whether men with azoospermia would benefit from a testicular biopsy. We also provide further evidence that MeiA in men and POI in women share the same genetic causes. This study was carried out within the frame of the German Research Foundation sponsored Clinical Research Unit 'Male Germ Cells: from Genes to Function' (DFG, CRU326), and supported by institutional funding of the Research Institute Amsterdam Reproduction and Development and funds from the LucaBella Foundation. The authors declare no conflict of interest.

Sources of Chromosomal Polymorphism of Microsporocytes in Species of Lilium L. and Allium L.: Cytomixis, Extra Chromosomes, and Chromatin Diminution

Cytomixis and chromosomal polymorphism of microsporocytes in microsporogenesis of the species Lilium croceum Chaix, Allium fistulosum L., and A. cepa L. were studied. It was found that the main cytomictic events are associated with the early prophase of meiosis and are obligatory (constitutive) for the examined species. In metaphase microsporocytes, the so-called extra chromosomes, presumably of cytomictic origin, were identified. They are characterized by weakening of synapsis and/or disintegration of homologues and associations with bivalents of the basic karyotype with the formation of secondary associations of chromosomes. Extra chromosomes are present not only in hyperchromosomal but also in eu- and hypochromosomal microsporocytes. The majority of extra chromosomes seem to be a “genetic ballast” for the cell, which it gets rid of using a wide range of cellular tools, in particular, chromosomal rearrangements, chromatin diminution, asymmetry of division, cytomixis, and programmed cell death. Nevertheless, some extra chromosomes can participate in the rearrangement of the karyotype of microsporocytes and microspores.

Stage-Specific Gene Profiling of Germinal Cells Helps Delineate the Mitosis/Meiosis Transition.

In flowering plants, germ lines are induced from somatic meristems within reproductive organs. Within anthers, germinal cell initials first undergo several rounds of mitotic proliferation before synchronously entering meiosis. Our understanding of the progression and the molecular basis of this mitosis to meiosis transition is still limited. Taking advantage of the correlation between anther length and premeiotic germinal cell development in maize (Zea mays), we studied the transcriptome dynamics of germinal cells at three sequential stages, mitotic archesporial cells, enlarging pollen mother cells at the premeiosis interphase, and pollen mother cells at the early prophase of meiosis, using laser microdissection-based expression profiling. Our analysis showed that cells undergoing the mitosis-meiosis switch exhibit robust transcriptional changes. The three stages are distinguished by the expression of genes encoding transcription factor subsets, meiotic chromosome recombination proteins, and distinct E3 ubiquitin ligases, respectively. The transcription level of genes encoding protein turnover machinery was significantly higher in these three stages of germinal cells than in mature pollen, parenchyma cells, or seedlings. Our experimental results further indicate that many meiotic genes are not only transcribed, but also translated prior to meiosis. We suggest that the enlarging pollen mother cells stage represents a crucial turning point from mitosis to meiosis for developing germinal cells.

Dynamic epigenetic states of maize centromeres.

The centromere is a specialized chromosomal region identified as the major constriction, upon which the kinetochore complex is formed, ensuring accurate chromosome orientation and segregation during cell division. The rapid evolution of centromere DNA sequence and the conserved centromere function are two contradictory aspects of centromere biology. Indeed, the sole presence of genetic sequence is not sufficient for centromere formation. Various dicentric chromosomes with one inactive centromere have been recognized. It has also been found that de novo centromere formation is common on fragments in which centromeric DNA sequences are lost. Epigenetic factors play important roles in centromeric chromatin assembly and maintenance. Non-disjunction of the supernumerary B chromosome centromere is independent of centromere function, but centromere pairing during early prophase of meiosis I requires an active centromere. This review discusses recent studies in maize about genetic and epigenetic elements regulating formation and maintenance of centromere chromatin, as well as centromere behavior in meiosis.

A Wisp3 Cre-knockin Allele Produces Efficient Recombination in Spermatocytes during Early Prophase of Meiosis I

Individuals with the autosomal recessive skeletal disorder Progressive Pseudorheumatoid Dysplasia have loss-of-function mutations in WISP3, and aberrant WISP3 expression has been detected in tumors from patients with colon and breast cancer. In mice however, neither absence nor over-expression of WISP3 was found to cause a phenotype, and endogenous Wisp3 expression has been difficult to detect. To confirm that Wisp3 knockout mice have no phenotype and to identify potential sites of endogenous Wisp3 expression, we generated mice with a knockin allele (Wisp3 GFP-Cre) designed to express Green Fluorescent Protein (GFP) and Cre-recombinase instead of WISP3. Heterozygous and homozygous knockin mice were fertile and indistinguishable from their wild-type littermates, confirming that mice lacking Wisp3 have no phenotype. We could not detect GFP-expression from the knockin allele, but we could detect Cre-expression after crossing mice with the knockin allele to Cre-reporter mice; the double heterozygous offspring had evidence of Cre-mediated recombination in several tissues. The only tissue that had high levels of Cre-mediated recombination was the testis, where recombination in spermatocytes occurred by early prophase of meiosis I. As a consequence, males that were double heterozygous for a Wisp3 GFP-Cre and a floxed allele only contributed a recombined allele to their offspring. We detected no evidence of Cre-mediated recombination in the female ovary, although when double heterozygous females contributed the reporter allele to their offspring it had recombined ~7% of the time. Wisp3 GFP-Cre expression therefore occurs less frequently and most likely at a later stage of oocyte development in female mice compared to male mice. We conclude that although WISP3 is dispensable in mice, male mice with a Wisp3 GFP-Cre allele (Jackson Laboratory stock # 017685) will be useful for studying early prophase of meiosis I and for efficiently recombining floxed alleles that are passed to offspring.

MOV10L1 is necessary for protection of spermatocytes against retrotransposons by Piwi-interacting RNAs

Piwi-interacting RNAs (piRNAs) comprise a broad class of small noncoding RNAs that function as an endogenous defense system against transposable elements. Here we show that the putative DExD-box helicase MOV10-like-1 (MOV10L1) is essential for silencing retrotransposons in the mouse male germline. Mov10l1 is specifically expressed in germ cells with increasing expression from gonocytes/type A spermatogonia to pachytene spermatocytes. Primary spermatocytes of Mov10l1(-/-) mice show activation of LTR and LINE-1 retrotransposons, followed by cell death, causing male infertility and a complete block of spermatogenesis at early prophase of meiosis I. Despite the early expression of Mov10l1, germline stem cell maintenance appears unaffected in Mov10l1(-/-) mice. MOV10L1 interacts with the Piwi proteins MILI and MIWI. MOV10L1 also interacts with heat shock 70-kDa protein 2 (HSPA2), a testis-enriched chaperone expressed in pachytene spermatocytes and also essential for male fertility. These studies reveal a crucial role of MOV10L1 in male fertility and piRNA-directed retrotransposon silencing in male germ cells and suggest that MOV10L1 functions as a key component of a safeguard mechanism for the genetic information in male germ cells of mammals.

MIWI2 Is Essential for Spermatogenesis and Repression of Transposons in the Mouse Male Germline

Small RNAs associate with Argonaute proteins and serve as sequence-specific guides for regulation of mRNA stability, productive translation, chromatin organization, and genome structure. In animals, the Argonaute superfamily segregates into two clades. The Argonaute clade acts in RNAi and in microRNA-mediated gene regulation in partnership with 21-22 nt RNAs. The Piwi clade, and their 26-30 nt piRNA partners, have yet to be assigned definitive functions. In mice, two Piwi-family members have been demonstrated to have essential roles in spermatogenesis. Here, we examine the effects of disrupting the gene encoding the third family member, MIWI2. Miwi2-deficient mice display a meiotic-progression defect in early prophase of meiosis I and a marked and progressive loss of germ cells with age. These phenotypes may be linked to an inappropriate activation of transposable elements detected in Miwi2 mutants. Our observations suggest a conserved function for Piwi-clade proteins in the control of transposons in the germline.

Chromosome condensation in mitosis and meiosis of rye (Secale cereale L.)

Structural investigation and morphometry of meiotic chromosomes by scanning electron microscopy (in comparison to light microscopy) of all stages of condensation of meiosis I + II show remarkable differences during chromosome condensation in mitosis and meiosis I of rye (Secale cereale) with respect to initiation, mode and degree of condensation. Mitotic chromosomes condense in a linear fashion, shorten in length and increase moderately in diameter. In contrast, in meiosis I, condensation of chromosomes in length and diameter is a sigmoidal process with a retardation in zygotene and pachytene and an acceleration from diplotene to diakinesis. The basic structural components of mitotic chromosomes of rye are “parallel fibers” and “chromomeres” which become highly compacted in metaphase. Although chromosome architecture in early prophase of meiosis seems similar to mitosis in principle, there is no equivalent stage during transition to metaphase I when chromosomes condense to a much higher degree and show a characteristic “smooth” surface. No indication was found for helical winding of chromosomes either in mitosis or in meiosis. Based on measurements, we propose a mechanism for chromosome dynamics in mitosis and meiosis, which involves three individual processes: (i) aggregation of chromatin subdomains into a chromosome filament, (ii) condensation in length, which involves a progressive increase in diameter and (iii) separation of chromatids.

Missing oocyte encodes a highly conserved nuclear protein required for the maintenance of the meiotic cycle and oocyte identity in Drosophila.

In Drosophila, a single oocyte develops within a 16-cell germline cyst. Although all 16 cells initiate meiosis and undergo premeiotic S phase, only the oocyte retains its meiotic chromosome configuration and remains in the meiotic cycle. The other 15 cells in the cyst enter the endocycle and develop as polyploid nurse cells. A longstanding goal in the field has been to identify factors that are concentrated or activated in the oocyte, that promote meiotic progression and/or the establishment of the oocyte identity. We present the characterization of the missing oocyte gene, an excellent candidate for a gene directly involved in the differentiation of the oocyte nucleus. The missing oocyte gene encodes a highly conserved protein that preferentially accumulates in pro-oocyte nuclei in early prophase of meiosis I. In missing oocyte mutants, the oocyte enters the endocycle and develops as a polyploid nurse cell. Genetic interaction studies indicate that missing oocyte influences meiotic progression prior to pachytene and may interact with pathways that control DNA metabolism. Our data strongly suggest that the product of the missing oocyte gene acts in the oocyte nucleus to facilitate the execution of the unique cell cycle and developmental programs that produce the mature haploid gamete.

Ultrastructure of tetrasporogenesis in the red alga Osmundea spectabilis var. spectabilis (Rhodomelaceae: Ceramiales: Rhodophyta)

Tetrasporogenesis in Osmundeaspectabilis (Postels and Ruprecht) K.W. Nam var. spectabilis proceeds through three developmental stages. A uninucleate tetraspore mother cell with synaptonemal complexes depicted during early prophase of meiosis I comprises the youngest stage. Subsequently, the nuclear envelope obtains a highly irregular profile and is surrounded by perinuclear endoplasmic reticulum (ER) and numerous mitochondria. Proplastids with peripheral thylakoid and numerous straight-profiled dictyosomes are present. Dictyosome vesicles discharge their contents, initiating tetraspore wall formation. A four-nucleate tetraspore mother cell is formed prior to tetrahedral cleavage. During the second stage of tetraspore formation the nuclei are very irregular in outline and move toward the central region where they fuse. The formation of fibrous vacuoles originates from the fibrous vacuole associated organelles (FVAOs). Thylakoid formation from concentric lamellar bodies (CLBs) seems to occur in plastids. Extremely hypertrophied dictyosomes with two tightly compressed and densely laminated mid-regions produce vesicles which contribute to enlargement of the fibrous vacuoles. During the second stage of tetraspore development striated vesicles are formed and starch granule formation increases. Mature tetraspores are characterized by numerous cored vesicles and abundant starch granules. Plastids have a fully developed system of internal thylakoids, and cleavage is usually complete at this stage. Mature tetraspores are surrounded by a bi-layered wall and the tetrasporangial wall. Unbranched, tubular structures connecting the plasmalemma with the peripheral sheets of ER are possibly involved in wall deformation. A distinct blebbing nuclear envelope appears to sequester vesicles into the cytoplasm.

Asymmetry in chromosome pairing: a major factor in de novo mutation and the production of genetic disease in man.

At the outset of the meiotic pairing process in man, trial and error mismatching and misalignment, both within homologous pairs and between heterologues, can be observed cytologically. Pairing starts at...

Cellular energy levels and their effect on male cell abortion in cytoplasmically male sterile lines of Petunia hybrida

Using an HPLC method it has proved possible to follow the levels of adenine and pyridine nucleotides in the anthers of normal and cytoplasmically male sterile (CMS) lines of Petunia hybrida. Well before the appearance of any structural differences, anthers of CMS plants begin to show lower ATP/ADP ratios. In anthers, as in other non-photosynthetic plant tissues, there is a strong correlation between the ATP/ADP ratio and levels of NADPH and, when NADPH was assayed in fertile and CMS anthers, very dramatic differences were discovered. In male fertile plants, the NADPH/NADP ratio differs strikingly between somatic and reproductive tissues and reaches a peak in anthers at the early prophase of meiosis. The ratio in male sterile anthers remains largely unchanged from that normally seen in somatic tissues over this period. A cytochemical localisation technique revealed that, at the stage of development in question, the major reserves of anther NADPH are held within the tapetal cells and that levels within CMS tapeta are strikingly lower than those of normal plants. These findings are discussed in the perspective of theories proposed to explain the operation of CMS, and also in terms of the now conclusive evidence that the genetical basis of CMS lies in changes in the organisation of the mitochondrial genome.

The Ultrastructure of Tetrasporogenesis in the Marine Red Alga Chondria tenuissima (Good, et Woodw.) (Ceramiales, Rhodomelaceae)

Tetraspore development has been studied in Chondria tenuissima using light and electron microscopy. The transformation of tetrasporangial mother cells into mature tetrasporangia involves a series of structural changes, especially of dictyosomes and of the nucleus. The youngest stage of tetrasporogenesis consists of a uninucleate tetraspore mother cell with synaptonemal complexes present during early prophase of meiosis I. Mitochondria are aggregated around the nucleus, dictyosome activity is low, and proplastids occur in the peripheral cytoplasm. The cleavage furrows are initiated almost concomitantly with commencement of meiosis. When the cleavage furrows are initiated, spherical bodies bounded by two membranes are found within the cytoplasm; they develop into vacuoles with fibrillar contents (fv1), which increase in size during tetraspore development by fusing with each other and with Golgi vesicles. The Golgi vesicles and the vacuoles with fibrillar contents (fv1) contribute material to the developing tetraspore wall. During the middle stage of tetraspore formation the vacuoles with fibrillar contents (fv1) are dominant, dictyosome activity increases, as well as the number of plastids and mitochondria; starch formation also increases. Stacked cisternae of the endoplasmic reticulum are found within the peripheral part of the nucleus. The same nuclear structures are also observed in tetrasporangia of the marine red alga Gastroclonium clavalum. The final stage is characterized by the disappearance of vacuoles with fibrillar contents (fv1) and of the stacked ER within the nucleus, presence of straight, large dictyosomes which produce cored vesicles, an abundance of starch grains and by the formation of fully developed chlorqplasts. The cored vesicles contain Thiery-positive material and contribute to the formation of vacuoles with fibrous contents (fv2) as they are dominant in the tetraspores before their liberation.

Effects of gamma irradiation and pyronin-Y treatments on meiotic recombination in tomato

The recombination frequency was measured between two linked marker loci a (anthocyaninless) and hl (hairless) in control and irradiated developing buds in Cluster I on the main stem in tomato. The buds which corresponded to early prophase I of meiosis showed significant increase in recombination frequency after gamma irradiation at a stimulating dose level (72R). Besides, the response was similar for all bud development stages tested. Treatment of buds with 0.005 per cent pyronin Y during early prophase of meiosis did not produce consistent results.

The Fine Structure of the Pre-Meiotic Stages of Sporogenesis in Onoclea sensibilis

Ultrastructural features of the dividing meiocyte of Onoclea sensibilis L. were described by the author (1977), and those of the young spores arising from this cell by Marengo and Badalamente (1978). Since a light microscopic study of this species by the author (1949) showed an apparent decrease in size of cytoplasmic inclusions from the sporangium initial to the spore mother cell, it is of interest to elucidate these changes on the ultrastructural level. Individual sporangia dissected from young fertile fronds were routinely fixed in glutaraldehyde followed by osmium tetroxide and embedded in Epon (Spurr, 1969). Sections 0.5um thick were cut from individual sporangia and were examined by phase contrast microscopy without staining. From sporangia identified as containing pre-meiotic stages in sporogenesis, thin sections were cut with a diamond knife, stained with uranyl acetate and lead citrate, and examined with an Hitachi HU11A electron microscope. The sporangial initials (Fig. 1) appear to contain large, osmiophilic bodies (Fig. 1, t) which resemble closely the tannin accumulations described by Ledbetter and Porter (1970). The appearance of vacuoles (v) within these bodies is followed by their disappearance in the later stages of sporogenesis, including newly formed spores. Mitochondria (m) appear hardly larger than those in later stages and in newly formed spores. Their internal structure, however, differs from that of mitochondria in newly formed spores. Cristae appear not to be shelf-like, but rather mitochondrial material separated by internal cavities. This peculiar and distinctive internal structure persists through at least the early prophase of meiosis (Fig. 6,m), following which their cristae extend as plates, continuous across the mitochondrion (Marengo, 1977). The osmiophilic bodies are still present in early sporogenous cells (Fig. 2,t), with an occasional vacuole apparently replacing the tannin mass (Fig. 2, v). By the time the sporogenous cells approach the rounded-up meiocyte stage, the osmiophilic bodies have disappeared and lipid droplets appear in the cytoplasm (Fig. 3,L). In the dividing sporogenous cell in anaphase (Fig. 4), the mitochondria appear concentrated in the polar regions of the spindle. The distribution of mitochondria at mitotic anaphase appears to contrast markedly with that of the meiotic anaphase I, where the mitochondria are concentrated at the edge of the spindle preparatory to invading it, and form the mitochondrial plate characteristic of interphase following the first division as well as all phases of the second meiotic division (Marengo, 1949, 1977). In the early prophase of the first meiotic division (Fig. 5), spore mother cell polarity is reflected in a concentration of mitochondria at the base of a barely

Histone acetylation during meiosis in Lilium microsporocytes

Acetate incorporation into histones of Lilium microsporocytes is consistently higher in early prophase of meiosis than in later stages. The pattern of acetate incorporation into histones differs from that found for the soluble nuclear proteins. Evidence is presented that acetate incorporation reflects true acetylation, not histone synthesis. e- N-acetyllysine (eNAcLys) was released from histones by enzymatic digestion. Amino acid analysis of the digests confirm the presence of significantly higher amounts of eNAcLys in early meiotic stages. These results are consistent with the hypothesis that modulation of histone charge plays a role in the binding of histones to DNA and/or chromosome condensation. In vitro levels of histone acetylating activity remain constant throughout meiosis. The results suggest that microsporocyte histone deacetylase activity increases through meiotic prophase.

Aberration induction by mitomycin C in early primary spermatocytes of mice

MC is well known to induce dominant lethal mutations in mouse spermatocytes. Tests were done to determine whether chromosomal aberrations could be identified in spermatocytes as being responsible for the dominant lethal effects. Male mice were treated single doses of MC during DNA synthesis preceding meiosis and during early prophase of meiosis. Simultaneous labeling was performed to identify cells that were S-phase during the time of treatment. Diakineses-metaphases I were analyzed for the occurrence of univalents, gaps, fragments and rearrangements. The frequencies of cells with aberrations incrreased with dose and time after treatment. Maximal values were obtained after 12 days, indicating that MC was most effective in cells undergoing DNA replication. 95% of these cells were labeled. The majority of aberrant cells contained one or more fragments. These cells will lead to dominant lethality of the zygotes after fertilization. Cells with rearrangements occurred 11 and 12 days after treatment. These cells can develop into sperm carrying a reciprocal translocation which would then give rise to semi-sterile progeny after fertilization. Further investigations are needed to study the transmission of rearrangements observed in primary spermatocytes.

Increased meiotic recombination by incorporated tritium

Tritium applied as 3 H-orotic acid to the anthers of tomato during interphase—early prophase of meiosis increased recombination between the marker loci a and hl by approximately 50 per cent. The same amount of tritium applied as 3 H-thymidine or 3 H-water caused only small, non-significant increases. Equal parts of 3 H-orotic acid and 3 H-thymidine increased recombination by approximately 25 per cent. The 3 H-orotic acid and the 3 H-thymidine were localized in the RNA and DNA fraction respectively. The 3 H-water was not localized in nucleic acids. It is postulated that the 3 H-orotic acid is incorporated into the RNA of the synaptonemal complex during prophase of meiosis and increases recombination by localized β-irradiation.

ULTRASTRUCTURE OF TETRASPOROGENESIS IN THE PARASITIC RED ALGA LEVRINGIELLA GARDNERI (SETCHELL) KYLIN12

SUMMARYUltrastructural studies on tetraspore formation in Levringiella gardneri revealed that 3 stages may be recognized during their formation. The youngest stage consists of a uninucleate tetraspore mother cell with synaptonemal complexes present during early prophase of meiosis I. Mitochondria are aggregated around the nucleus, dictyosome activity is low, and chloroplasts occur in the peripheral cytoplasm. A 4‐nucleate tetraspore mother cell is formed prior to tetrahedral cell cleavage, and an increase in the number of chloroplasts and mitochondria occurs. Small straight‐profiled dictyosomes secrete vesicles into larger fibrous vesicles or contribute material to the developing tetraspore wall. During the second stage of tetraspore formation, striated vesicles form within endoplasmic reticulum, semicircular profiled dictyosomes secrete vesicles for fibrous vesicles or wall material, and starch formation increases. The final stage is characterized by the disappearance of striated vesicles, presence of straight, large dictyosomes which secrete cored vesicles, and an abundance of starch grains. Cleavage is usually complete at this stage and the tetraspore wall consists of a narrow outer layer of fibrillar material and an inner, electron transparent layer. These spores are surrounded by a tetrasporangial wall which was the original wall surrounding the tetraspore mother cell.

Multiple synaptinemal complexes at the region of gene amplification in Acheta

Ovaries of Acheta domesticus (house cricket) were fixed for electron microscopy at two stages of development: (1) ovaries containing mainly oocytes at interphase and early prophase of meiosis, and (2) ovaries with oocytes mainly at pachytene and diplotene. The E.M. study was accompanied by three types of light microscopy controls consisting mainly of cytochemical tests. Every oocyte contains a DNA body which at pachytene and diplotene acquires the appearance of a “puff”. In the light microscope two zones can be distinguished inside the body: (1) an inner core of DNA and (2) and outer shell of RNA. In the E. M. the inner core consists of a fibrillar material and the outer shell is composed of areas of high electron opacity consisting mainly of tightly packed particles and fibrils. At these stages synaptinemal complexes are seldom seen associated with the DNA body but are present throughout the nucleus as part of the paired chromosomes. The complexes are present as single units. — In the oocytes at interphase and early prophase of meiosis, where the DNA body is active in DNA replication, the body appears in the light microscope as a large Feulgen positive sphere containing Feulgen negative areas. In the E. M. at these stages the DNA body consists of: (a) the two components found at pachytene, (b) a third electron dense component which is more homogeneous than the other two, and (c) of large assemblies of synaptinemal complexes originating from several centers. The most significant features of the axial complexes are: (1) the circular packing of the complexes, (2) their occurrence in packages of 300 to 400 units and (3) the fact that not all of the DNA body forms complexes but only a part of it.