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INTERCHROMOSOMAL FIBRES IN HUMAN MALE MEIOTIC CHROMOSOMES
1179 colleagues suggest that the darkly staining bands represent sequences of adenine-thymine-based pairs, whereas the unstained interbands represent guanine-cytosine-rich regions. If this hypothesis is correct it is difficult to understand why the adenine-thymine-rich distal twothirds of the Y long arm is pale-staining. Since quinacrine fluorescence followed the normal pattern in the same Y chromosomes in which Giemsa banding was reversed there can be no doubt about the presence of uninterrupted adenine-thymine sequences in the intensely fluorescing 1 part of the Y chromosome. Formation of bands or interbands by trypsinisation can be explained by cleavage of peptide bonds on the free carboxyl sites of aminoacids, with subsequent complexing of the dye with the remaining histone or D.N.A.2 If a modification of the trypsin treatment can produce interbands instead of bands and vice versa, this could speak in favour of an acidic-protein distribution being the cause of the banding,3 rather than differences in base composition. It could mean that differential removal of binding proteins may occur under certain experimental conditions, irrespective of base distribution; by exposing acidic groups which bind to the red component of the Giemsa stain, bands are being formed by molecular hybridisation with the blue component of the dye.3-5 Studies are in progress to determine the exact experimental conditions under which this reverse banding of the Y occurs.
repetitive
Department of Genetics, Basle University Children’s Hospital, Basle, Switzerland.
ERICA M. BÜHLER TAISO TSUCHIMOTO GERHARD R. STALDER.
INTERCHROMOSOMAL FIBRES IN HUMAN MALE MEIOTIC CHROMOSOMES SiR,—Dr Chen (April 14, p. 828) refers to several recent observations of interchromosomal fibres in mitotic chromosomes and reports his observation of similar structures in meiotic chromosomes, most commonly between the centromeric heterochromatin of pachytene bivalents. Observations made in this laboratory indicate that interchromosomal fibres between human male pachytene bivalents are not limited to centromeric heterochromatin, the recognised sites of repeated sequences of D.N.A., but also occur along the entire length of the bivalents, often displaying considerable symmetry. The characteristic furry outline of pachytene bivalents observed in cytological preparations6 and electronmicroscope sectionsis apparently due to numerous hairlike fibrils projecting laterally from the main body of the chromosomes. This may be analogous to amphibian " lampbrush " chromosomes, which are associated with active R.N.A. and protein synthesis during the growth period of oocytes. This lampbrush appearance may be enhanced by suspending the meiotic cells in 0-OlAf potassiumchloride solution for ly-1 hour at 37 °C, before fixation and staining with lactic-acetic orcein.6 In intact cells (i.e., cells in which the pachytene bivalents are not dispersed) many of the hairlike lateral fibrils are seen to form interconnections with similar fibrils from other bivalents. In some cells there may be a regular fibrillar network (fig. A) which shows a ladderlike effect, with the interconnecting fibrils forming " rungs " between the pachytene bivalents. 1. Ellison, J. R., Barr, H. J. Chromosoma, 1972, 36, 375. 2. Giese, A. C. Cell Physiology; chap. 16, p. 303. Philadelphia, 1962. 3. Pearson, P. J. med. Genet. 1972, 9, 264. 4. Comings, D. E. Expl Cell Res. 1971, 67, 441. 5. Clark, R. J., Felsenfeld, G. Nature New Biol. 1971, 229, 101. 6. McDermott, A. Can. J. Genet. Cytol. 1971, 13, 536. 7. Woollam, H. M. H., Ford, E. H. R. J. Anatomy, 1964, 98, 163.
A
primary spermatocyte at pachytene. (A) shows a regular network of fibrils between bivalents. (B) indicates position of fibrils and chromomere-like granules.
The interconnecting fibrils often bear small chromomerelike granules, which may occur singly at the midpoints of the fibrils or may be regularly paired on adjacent parallel fibrils (see fig. B). The nature and function of the interconnecting fibrils is not known. It is possible that they may be functionally analogous to the lateral loops of amphibian lampbrush chromosomes; alternatively, they may have a structural function related to chromosome orientation. Their general distribution along the length of the chromosomes, however, precludes any limited association with the known sites of satellite D.N.A., although it is possible that functionally and structurally different types of interchromosomal fibres exist. Department of Genetics, Infant Development Unit, Birmingham Maternity Hospital, Birmingham B15 2TG. Human
ALAN McDERMOTT.
HYSTEROTOMY AND ENDOMETRIOSIS
SIR,-Despite its comparatively higher morbidity and mortality it is unfortunate that hysterotomy is still one of the few certain approaches to a middle-trimester abortion when more sophisticated methods fail. Recent emphasis by Dr Higginbottom (April 28, p. 937) and Sir John Stallworthy (May 12, p. 1057) that up to 2% of these patients could subsequently have wound implantation endometriosis prompt a suggestion for a possible prophylactic
measure.
During inspected
the for
operation the uterus and appendages are conditions, such as fibroids, that might
repetitive
Department of Genetics, Basle University Children’s Hospital, Basle, Switzerland.
ERICA M. BÜHLER TAISO TSUCHIMOTO GERHARD R. STALDER.
INTERCHROMOSOMAL FIBRES IN HUMAN MALE MEIOTIC CHROMOSOMES SiR,—Dr Chen (April 14, p. 828) refers to several recent observations of interchromosomal fibres in mitotic chromosomes and reports his observation of similar structures in meiotic chromosomes, most commonly between the centromeric heterochromatin of pachytene bivalents. Observations made in this laboratory indicate that interchromosomal fibres between human male pachytene bivalents are not limited to centromeric heterochromatin, the recognised sites of repeated sequences of D.N.A., but also occur along the entire length of the bivalents, often displaying considerable symmetry. The characteristic furry outline of pachytene bivalents observed in cytological preparations6 and electronmicroscope sectionsis apparently due to numerous hairlike fibrils projecting laterally from the main body of the chromosomes. This may be analogous to amphibian " lampbrush " chromosomes, which are associated with active R.N.A. and protein synthesis during the growth period of oocytes. This lampbrush appearance may be enhanced by suspending the meiotic cells in 0-OlAf potassiumchloride solution for ly-1 hour at 37 °C, before fixation and staining with lactic-acetic orcein.6 In intact cells (i.e., cells in which the pachytene bivalents are not dispersed) many of the hairlike lateral fibrils are seen to form interconnections with similar fibrils from other bivalents. In some cells there may be a regular fibrillar network (fig. A) which shows a ladderlike effect, with the interconnecting fibrils forming " rungs " between the pachytene bivalents. 1. Ellison, J. R., Barr, H. J. Chromosoma, 1972, 36, 375. 2. Giese, A. C. Cell Physiology; chap. 16, p. 303. Philadelphia, 1962. 3. Pearson, P. J. med. Genet. 1972, 9, 264. 4. Comings, D. E. Expl Cell Res. 1971, 67, 441. 5. Clark, R. J., Felsenfeld, G. Nature New Biol. 1971, 229, 101. 6. McDermott, A. Can. J. Genet. Cytol. 1971, 13, 536. 7. Woollam, H. M. H., Ford, E. H. R. J. Anatomy, 1964, 98, 163.
A
primary spermatocyte at pachytene. (A) shows a regular network of fibrils between bivalents. (B) indicates position of fibrils and chromomere-like granules.
The interconnecting fibrils often bear small chromomerelike granules, which may occur singly at the midpoints of the fibrils or may be regularly paired on adjacent parallel fibrils (see fig. B). The nature and function of the interconnecting fibrils is not known. It is possible that they may be functionally analogous to the lateral loops of amphibian lampbrush chromosomes; alternatively, they may have a structural function related to chromosome orientation. Their general distribution along the length of the chromosomes, however, precludes any limited association with the known sites of satellite D.N.A., although it is possible that functionally and structurally different types of interchromosomal fibres exist. Department of Genetics, Infant Development Unit, Birmingham Maternity Hospital, Birmingham B15 2TG. Human
ALAN McDERMOTT.
HYSTEROTOMY AND ENDOMETRIOSIS
SIR,-Despite its comparatively higher morbidity and mortality it is unfortunate that hysterotomy is still one of the few certain approaches to a middle-trimester abortion when more sophisticated methods fail. Recent emphasis by Dr Higginbottom (April 28, p. 937) and Sir John Stallworthy (May 12, p. 1057) that up to 2% of these patients could subsequently have wound implantation endometriosis prompt a suggestion for a possible prophylactic
measure.
During inspected
the for
operation the uterus and appendages are conditions, such as fibroids, that might