Evidence for a highly differentiated sex chromosome heteromorphism in the salamander Necturus maculosus (Rafinesque)

The mitotic chromosomes of the neotenic (sensu Gould, 1977, and Alberch et al., 1979) salamander Necturus maculosus (Rafinesque) have been examined using a C-band technique to demonstrate the distribution of heterochromatin. The C-banded mitotic chromosomes provide evidence of a highly differentiated XY male/XX female sex chromosome heteromorphism, in which the X and Y chromosomes differ greatly in size and morphology, and in the amount and distribution of C-band heterochromatin. The X chromosome represents one of the largest biarmed chromosomes in the karyotype and is indistinguishable from similar sized autosomes on the basis of C-band heterochromatin. The Y chromosome, on the other hand, is diminutive, morphologically distinct from all other chromosomes of the karyotype, and is composed almost entirely of C-band heterochromatin. The discovery of an X/Y chromosome heteromorphism in this species is consistent with the observation by King (1912) of a heteromorphic spermatogenic bivalent. Karyological and phylogenetic implications are discussed.     

Differential Uptake of Tritiated Thymidine into Hetero- and Euchromatin in Melanoplus and Secale

Grasshoppers of the species Melanoplus differentialis were injected with tritium-labelled thymidine. At intervals thereafter autoradiographic stripping film was applied over Feulgen squashes and sections. In this species during early prophase of meiosis the sex chromosome forms a heterochromatic block large enough to be resolved in tritium autoradiographs. A study of the squash preparations reveals that the sex chromosome is synthesizing DNA at a different period of time from the euchromatic autosomes. Since there is a developmental sequence of spermatocyte cysts along the testicular tubes it is possible from the sections to show that the heterochromatin synthesizes DNA later than does the euchromatin. To find out whether the results obtained in Melanoplus were characteristic of heterochromatin in general, young seedlings of rye were grown in a tritiated thymidine solution and Feulgen squashes were made as for Melanoplus. In rye leaf nuclei there is a large block of heterochromatin constituted by the proximal regions of the chromosomes and a euchromatic one formed by the median and distal regions of the same chromosomes. Here also the heterochromatin synthesizes DNA at a different period of time from the euchromatin. It is concluded that in rye the asynchrony of synthesis occurs within each chromosome. Counts of silver grains over the two types of chromatin in nuclei of Melanoplus and Secale disclosed that the number of grains per unit area was two to three times higher over the heterochromatin. To check the DNA content, Feulgen photometric measurements were made of Melanoplus nuclei at the same stage. The Feulgen and grain counts agree in showing that the heterochromatin contains two to three times more DNA per unit area than the euchromatin.     

The karyotype of the South American rodent Kunsia tomentosus (Lichtenstein, 1830).

Chromosomal analysis of Kunsia tomentosus showed a karyotype with 2n = 44, constituted by 21 pairs of acrocentric autosomes. The X chromosome was a median acrocentric, between pairs 3 and 4 in size, and the Y chromosome was a small acrocentric (between pairs 19 and 20). Five pairs with nucleolus organizer regions were located at the short arms. C-banding showed blocks of constitutive heterochromatin occurring in the centromeres of all autosomes and of the X chromosome. The Y chromosome was entirely heterochromatic. In order to identify possible homologies, karyotypes of Kunsia and Scapteromys, the phyletically related taxa, were compared. No autosome shared by either genus was found by G-band comparisons. The C-band patterns and those produced by Alu I, Mbo I, Rsa I and Hae III restriction endonucleases were also different. The results of FISH indicated a different composition of the telomeric regions of the chromosomes of both taxa, since in Scapteromys the probes hybridized in both telomeres, and in Kunsia this hybridization only occurred in one of the telomeres. These differences also occurred in the localization and number of nucleolus organizer regions.     

中国刺猬的染色体研究

本文采用全血培养和骨髓染色体制片法,对分布于我国南京市郊和济南市郊的刺猬染色体进行了组型、C-带、G-带和银染色的观察分析,并与东欧、西欧两种刺猬比较,它们之间的核型及带型差异显著;又将南京、济南及金清波(1985)报道的河南新乡三地分布的刺猬进行比较,它们的核型及带型也显示出一定差异,这种多态性在分类和进化上有一定的意义。     

水貂的染色体研究

采用复制带、C带和硝酸银染色等分带技术研究了水貂的核型和带型。结果表明,2n=30,枝型为10（M）＋16（SM）＋2（A）,XX（M）。C-带显示该水貂的一些染色体的结构异染色质比较丰富,从着丝粒区域延伸到两臂上,No.5染色体着丝粒结构异染色质有些弱化;X染色体的结构异染色质较常染色体的丰富。Ag-NORs有3个,分布在No.8染色体的次缢痕区域和一条No.2染色体长臂接近着丝粒的区域。     

Chromosome numbers, sex determining systems, and patterns of the C-heterochromatin distribution in 13 species of lace bugs (Heteroptera, Tingidae).

The karyotypes, sex chromosome systems, and male meiotic patterns in 13 species belonging to 10 genera of the family Tingidae were studied. Data on eleven species, one subgenus, and 5 genera are presented for the first time, and the chromosome formula of Acalypta parvula is revised. Karyotypes of all species included six pairs of autosomes. Most of the species displayed an XY sex chromosome system, in four species, belonging to genera of Acalypta and Kalama, the X0 system was found. Male meiosis is chiasmatic for autosomes. Sex chromosomes are achiasmatic and undergo pre-reductional meiosis. Using C-banding technique, for the first time constitutive heterochromatin was localized on chromosomes in all the species studied. The heterochromatin was found either in telomeres or in some species in interstitial locations, evidencing that a quite substantial redistribution of chromosome material within chromosomes might occur without fragmentations or fusions. In two species, a supernumerary (B) chromosome was found. In addition, the male reproductive system of four species was examined and the number of testicular follicles was determined as two per testis.     

白颊长臂猿染色体的研究

本文对我国云南南部的白须长臂猿（Ｈ．ｌｅｕｃｏｇｅｎｙｓ）染色体的Ｇ带、Ｃ带、晚复制带及Ａｇ－ＮＯＲｓ进行了较为详细的研究。它的２ｎ＝５２,核型公式为４４（Ｍ或ＳＭ）＋６（Ａ）,ＸＹ（Ｍ,Ａ）。Ｃ带表明一些染色体着丝点Ｃ带弱化;有的染色体出现插入的和端位的Ｃ带;Ｘ染色体两臂有端位Ｃ带,Ｙ染色体是Ｃ带阳性和晚复制的。Ａｇ－ＮＯＲｓ的数目,雌体有４个,雄体有５个,Ｙ染色体上具ＮＯＲ。本文对白颊长臂猿与其它长臂猿间的亲缘关系、核型进化的可能途径进行了讨论。     

白眉长臂猿(Hylobates hoolock leuconedys)的染色体研究

本文对两只雄性白眉长臂猿的染色体的C带、G带及Ag-NORs分布进行了较详细的分析,证实染色体数2n=38,并对该种的分类地位提出了一些新看法。     

Heterogeneity of constitutive heterochromatin in somatic Syrian hamster chromosomes.

Syrian hamster constitutive heterochromatin was analyzed for C-band distribution and for BrU late-replication pattern. Characteristic for this species is relatively large amounts of sex-chromosome and autosomal heterochromatin. The distribution of constitutive heterochromatin was determined. The long term of the X chromosome, the whole Y, the short arms of 8 autosomal pairs, the long arm of the smallest metacentric pair, and the centromeric regions of 12 pairs stained intensely dark on C-band preparations. In contrast to the heterochromatin in the centromeric regions, the autosomal short-arm heterochromatin has an increased susceptibility to the denaturation process, as indicated by prolonged exposure to NaOH or Ba(OH)2. Such further exposure to denaturing agents results in an intense dark stain only on the sex-chromosome heterochromatin and centromeric regions of the autosomes. The BrdU late-replication pattern demonstrated that the late-replicating regions correspond to C-bands. Centromeric regions replicate late in the S phase; however, no centromeric region is among the latest replicating segments of the complement. Centromeric and noncentromeric heterochromatin are two distinct categories of constitutive heterochromatin.     

Genomic organization and chromosomal localization of a new repeat MS7, specific for heterochromatin of sex chromosomes in Microtus species voles of the arvalis group

The tandemly arranged MS4 repeat with monomeric units of 4.1 kb is species-specifically distributed in heterochromatin of sex chromosomes of four common vole species of genus Microtus, group arvalis [1, 2]. In this work, we studied the genomic organization of the MS4 homolog in euchromatin of the X chromosome of M. arvalis. It has been shown by analyzing the phage genomic clones that one MS4 copy makes a part of a monomeric unit exceeding 8.5 kb that also includes a new MS7 repeat and, possibly, LINE fragments. MS7 is located together with MS4 in heterochromatin of common vole sex chromosomes, but in a substantially lesser amount. Probably, as a result of an evolutionary transition of an original repeat from euchromatin of the X chromosome to heterochromatin of the Y chromosome, MS4 underwent multiple amplification, and MS7 spread throughout heterochromatin, being surrounded by the MS4 tandem arrays.     

Location,structure and behaviour of C-heterochromatin during meiosis in Dichroplus silveiraguidoi (Acrididae-Orthoptera)

The constitutive heterochromatin of Dichroplus silveiraguidoi, a species which shows an exceptionally low chromosome number (2n=8), was studied at meiosis with a staining technique on normal and hypotonically treated specimens. The results showed: 1) an unusual behaviour of the heterochromatic blocks located in the so-called synaptic region of the sex bivalent (Neo Y-Neo X), which remains paired from early prophase through metaphase I; 2) in normal or in hypotonically treated cells a heterogeneous configuration of the C-heterochromatic blocks was observed. This configuration is characterized by the existence of small positive granules interconnected by euchromatic filaments and is enhanced by treatment with a low ionic strength solution; 3) A weakly positive stained (intermediate) material was demonstrated in the Neo X chromosome; 4) A large amount of heterochromatin is distributed in the form of granular material along the length of the autosomes and as telomeric and centromeric blocks in all chromosomes. The possible evolutionary mechanisms involved and the significance of the C-band heterochromatin demonstrated in this species are discussed.     

C-bands on chromosomes of four beetle species (Coleoptera: Carabidae, Silphidae, Elateridae, Scarabaeidae)

The C-banding pattern of Bembidion geniculatum, Silpha atrata, Prosternon tesselatum, and Epicometis hirta are presented. All analysed species have pracentromeric C-bands on autosomes and chromosome X but the widest ones are visible in the karyotype of B. geniculatum. In S. atrata, P. tesselatum, and E. hirta sex chromosome y is heterochromatic, only B. geniculatum having the Y chromosome wholly euchromatin. The results indicate that on the chromosomes of the investigated species do not have a terminal and an intercalar segments of heterochromatin.     

石貂的染色体研究

本文对分布在我国的石貂北方亚种染色体进行了较详细的研究。结果表明２ｎ＝３８,核型为１４（Ｍ）＋４（ＳＭ）＋１８（ＳＴ）,ＸＹ（Ｍ,Ａ）。Ｃ－带显示该亚种的一些染色体着丝粒区域结构异染色质弱化或消失。Ｎｏ,９染色体的短臂完全异染色质化;Ｘ染色体长臂丰出现插入杂色质带;Ｙ为完全结构异染色质组成。     

Cytogenetics of the South American Akodont rodents (Cricetidae) X. Akodon mollis: a species with XY females and B chromosomes

The morphology, G- and C-banding pattern of the Akodon mollis chromosome complement is analysed. Over a total of 14 males and 10 females studied, 8 males and 7 females had a modal chromosome number of 22, while 6 males and 3 females showed a modal number of 23 chromosomes. In the animals with 23 chromosomes the odd element was considered a B chromosome on the basis of: (a) its small size, (b) the lack of an homologous chromosome and the subsequent formation of univalents at diakinesis and metaphase I from testes, (c) the weak or null genetic action as evidenced by the lack of any obvious variation in the phenotype of carriers.Four females exhibited a sex-pair dimorphism indistinguishable from that observed in males. The G-banding analysis showed homology between the pattern found in the Y chromosome and that detected in the short arm of the X. The study of C-band distribution showed that several autosome pairs and the X chromosomes had small masses of centromeric heterochromatin. On the other hand, the Y and B chromosomes were C-band negative. The Y-like chromosome in females with dimorphism of the sex pair was also C-band negative. Accordingly these females were considered to be XY and not Xx (the x being an extensively deleted X chromosome).This work was supported by grants from UNESCO, OEA, CONICET and CIC. Requests for reprints should be addressed to N.O. Bianchi.     

中国两种波腿蝗（蝗总科：癞蝗科）染色体C带核型研究

报道中国两种波腿蝗的染色体C带核型,结果表明：红胫波腿蝗Asiotmethis zacharjini (Bei-Bienko, 1926) 2n ♂ =18, neo-X为亚中着丝粒染色体,其他均为近端着丝粒染色体,染色体除强染的着丝粒C带,S8染色体具强染端部C带带纹,neo-Y染色体还具有一条宽的弱染的近着丝粒端居间C带,性别决定机制是neo-XY ♂型,该种染色体组成和性别决定机制在我国癞蝗中为首次报道,蓝胫波腿蝗Asiotmethis jubatus (Uvarov, 1926) 2n＝19♂,均为近端着丝粒染色体,仅具有明显强染的着丝粒C带,性别决定机制是XO ♂型;两种波腿蝗的异染色质含量存在显著性差异（α=0.05）。     

A Novel MS7 Repeat Specific for Heterochromatin of Sex Chromosomes in Voles of Genus Microtus, Group arvalis: Genomic Organization and Chromosomal Localization

The tandemly arranged MS4 repeat with monomeric units of 4.1 kb is species-specifically distributed in heterochromatin of sex chromosomes of four common vole species of genus Microtus, group arvalis. In this work, we studied the genomic organization of the MS4 homolog in euchromatin of the X chromosome of M. arvalis. It has been shown by analyzing the phage genomic clones that one MS4 copy makes a part of a monomeric unit exceeding 8.5 kb that also includes a new MS7 repeat and, possibly, LINE fragments. MS7 is located together with MS4 in heterochromatin of common vole sex chromosomes, but in a substantially lesser amount. Probably, as a result of an evolutionary transition of an original repeat from euchromatin of the X chromosome to heterochromatin of the Y chromosome, MS4 underwent multiple amplification, and MS7 spread throughout heterochromatin, being surrounded by the MS4 tandem arrays.     

Banding analysis of the somatic chromosomes of the domestic dog (Canis familiaris).

The chromosomes of the domestic dog (Beagle) were investigated by several different staining techniques. G-banding, Q-banding, and the bis-benzimidazol derivative Hoechst 33258, make possible the identification of all 39 chromosome pairs. Constitutive heterochromatin (C-bands) was present on a few chromosomes as distinctive, large stained areas; on the other autosomes there was little or no heterochromatin detectable.     

Karyotype and heterochromatin pattern of the field mouse,Apodemus argenteus Temminck

The field mouse,Apodemus argenteus Temminck, has 46 chromosomes. The autosomes comprise 20 pairs of acrocentrics and 2 pairs of metacentrics. The X chromosome is represented by an outstandingly large submetacentric element, while the Y is an acrocentric corresponding in size to the 5th or 6th pair of autosomes. All of the autosomes and gonosomes can be unequivocally identified by their characteristic Q-band or G-band patterns. The constitutive heterochromatin, as revealed by C-banding, is localized at the centromeric regions of all autosomes, the short arm and the proximal 1/3 of the long arm of the X chromosome, and the entire Y chromosome. The C-band-positive segments which constitute 33.5% of the genome exhibit dark fluorescence after Q-banding, late DNA replication, faint or positive staining reaction to G-banding, fast reassociation of DNA revealed by AO staining, and allocyclic behavior of the sex-bivalent in male meiosis. An exception to the above is the distal segment of the Y which is positive to both C- and Q-banding. The giant X chromosome occupies 13.1% of the genome, leaving 5.6% of euchromatic segments, the latter value being equivalent to that of the original type X.     

Cytogenetic analysis of some Brazilian marsupials (Didelphidae: Marsupialia)

Three species of marsupials from the Amazon region (Marmosa cinerea, Caluromys lanatus, and Didelphis marsupialis) and two from the region of S?o Paulo (Didelphis marsupialis and Didelphis albiventris) were studied. The G-banding pattern of the species with 2n = 14 (M. cinerea and C. lanatus) was very similar, as well as the pattern of G-bands in the species with 22 chromosomes (Didelphis). All of the autosomes of M. cinerea and D. albiventris have centromeric C-bands and the Y chromosome is totally C-band positive. The long arm of the M. cinerea X chromosome is completely C-band positive except for a negative band close to the centromeric region. In D. albiventris the long arm of the X chromosome is C-band positive except for a negative band close to the telomeric region. In M. cinerea the silver-stained nucleolar organizer regions (Ag-NORs) are found in the acrocentric chromosomes, being located in the telomeric region of one pair and in the centromeric region of the other pair. Caluromys lanatus has centromeric Ag-NORs in one acrocentric and in one submetacentric chromosome pairs. Didelphis marsupialis has three chromosome pairs with telomeric Ag-NORs. In D. albiventris the Ag-NORs are terminal and located in both arms of one pair and in the long arm of two pairs of chromosomes.     

Scanning Electron Microscopy of Heterochromatin in Chromosome Spreads of Male Germ Cells in Schistocerca gregaria (Acrididae, Orthoptera) after Trypsinization

Chromosome spreads, prepared from testes of the desert locust Schistocerca gregaria, were analyzed using scanning electron microscopy (SEM) after varying periods of preincubation in trypsin. The emphasis of the study was on the appearance of heterochromatin. A trypsin pretreatment of 5 sec resulted in a smooth surface on the chromatin throughout and the heterochromatin was highly electron-emissive. The facultatively heterochromatic X chromosome was clearly visible in interphase spermatogonia and in pachytene and late prophase I spermatocytes. Chromomeres of autosomal bivalents could be recognized in pachytene cells. Centromeric heterochromatin segments were very prominent in autosomes of late prophase I spermatocytes and some chromosomes showed interstitial and telomeric bands. Longer trypsin treatment (10 sec) resulted in a fine globular surface on the chromatin; however, the electron emission of heterochromatic chromosome segments was lower under these conditions. The result of trypsin pretreatment of euchromatin differed only slightly from that of the heterochromatin. Extensive trypsin treatment (20 sec) did not alter further the relative electron emission of heterochromatin and euchromatin, but the regular globular appearance was lost, apparently owing to damage on the chromatin surface. The loss of electron emission from the centromeric heterochromatin of the autosomes and the facultatively heterochromatic X chromosome after extended trypsin treatment suggests a central role of proteins in mediating the heterochromatic status in meiotic chromo somes of the locust. Information obtained using scanning electron microscopy of chromosome spreads is complementary to that obtained by C-banding in that facultative heterochromatin is visualized with particular clarity.