Chromosome studies of Cebus apella The standard karyotype of Cebus apella paraguayanus Fischer 1829.код для вставкиСкачать
American Journal of Primatology 10:185-193 (1986) BRIEF REPORT Chromosome Studies of Cebus apella: The Standard Karyotype of Cebus apella paraguayanus, Fischer, 1829 TETSUJI MATAYOSHI, EDGARDO HOWLIN, NORA NASAZZI, CARLOS NAGLE, ENRIQUE GADOW, AND HECTOR N. SEUANEZ* Seccwn Genktica, Departamento de Ginecologia y Obstetriciq Centro de Educacion Mkdica e Investigaciones Clinicas (CEMIC), Buenos Aires, Argentina;* Department of Genetics, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil Chromosome studies were performed on 40 specimens identified as Cebus apella paraguayanus, Fischer, 1829, which had been wild-caught in Santa Catalina (Republic of Paraguay). Elongated chromosome spreads obtained from lymphocyte cultures were sequentially stained with different techniques, and a constant pattern of 382 bands was identified in all specimens. A standard karyotype based on the measurements of the total chromosome length and the G-Q banding pattern is proposed. Key words: Cebus apella, chromosomes, standardization INTRODUCTION Cebus apella is a platyrrhine species extensively distributed in the tropical forests of South America and commonly used in biomedical research. Feral populations of Cebus apella, ranging from 5" north to some 30" south of the equator line, are subdivided into different subspecies on the basis of their gross morphological characteristics and geographic distribution [Napier & Napier, 19671. Chromosome studies of Cebus apella subspecies are scarce and fragmentary because the geographical origin andlor the phenotypic characteristics of the specimens under study are rarely mentioned. Moreover, the karyological characterization of this species has been based so far on very few specimens [Bender & Chu, 1963; Chiarelli & Barberis, 1966; de Boer, 1974; Garcia et al, 1976, 1978; Cambefort & Moro, 19781 without a common criterion of chromosome nomenclature and ordination and with different techniques of chromosome analysis. None of these previous reports refers specifically to Cebus apella paraguayanus, Fischer, 1829, also known as Cebus apella cay, Illiger, 1815, a subspecies which was originally described in the Chaco forests of the Republic of Paraguay in a clearly delimited region between the Parana and Paraguay rivers. More recent studies of Cebus apella subpopulations, such as the report of Freitas and Seuanez , are restricted to specimens from three different regions of Brazil on the Atlantic coast. Furthermore, the only report on Cebus apella cay [Mudry de Pargament et al, 19841 is based on specimens captured outside the limits of their original distribution in the northern provinces of Argentina, across the Parana river, where the range of Cebus apella cay partially overlaps with that of Cebus apella nigritus and crossbreeding between them has not been excluded. Received May 20,1985; revision accepted October 6, 1985. Address reprint requests to T. Matayoshi, Seccion Genetica, CEMIC, Galvan 4102, 1431-Buenos Aires, Argentina. 0 1986 Alan R. Liss, Inc. 186 I Matayoshi et a1 Fig. 1. The arrow shows the area where the specimens were wild-caught. Santa Catalina (Republic of Paraguay) latitude 26" 30' S, longitude 57" 44'W. Herewith we present our studies on the chromosome complement of a large number of Cebus apella paraguayanus which had been wild-caught within the boundaries of their natural habitat, a region where this subspecies is not sympatric with any other subspecies of Cebus apella. Well spread, elongated chromosomes were sequentially stained with different procedures. The level of resolution at the chromosome band level allowed us to standardize the karyotype of this subspecies, which can be used as a reference karyotype for other Cebus apella subspecies. METHODS Subjects Forty specimens (20 males and 20 females) of Cebus apella paraguayanus were studied. The animals had been wild-caught in Santa Catalina (Republic of Paraguay), a region included in the Paraguayan Chaco forest between the Parana and Paraguay rivers (Fig. 1).All specimens were unequivocally identified following the descriptive criterion of Hill  for the identification and distinction of Cebus apella subspecies [see also Napier & Napier, 19671. Procedure Blood cultures were grown in TC 199 or Hams' F-10 media with 2%PHA (Difco) supplemented with fetal calf serum (15%)for 70 hours a t 37°C. Colcemid (0.2 wg/ml) was added for the last 60 minutes of incubation before harvesting. Well-spread preparations showing elongated chromosomes were sequentially stained with quinacrine [Caspersson et al, 19701 and conventional Giemsa staining (Fig. 2). Following Q-band identification, conventionally stained chromosomes were photographed, and Cebus apella paraguayanus Karyotype f 187 their relative chromosome length (RCL) was estimated as the ratio between chromosome length of each homologue x100 and the total haploid chromosome length including the X chromosome. For karyotyping, autosomes were divided into two groups on the basis of their morphological attributes (biarmed or acrocentric). Within each of these groups, homologue pairs were ordered in decreasing size (Table I). Gbanding was done following the procedure of Seabright . An idiogram was constructed on the basis of the morphometric characteristics and the specific Q-Gband pattern of each homologue pair. RESULTS All animals had a diploid chromosome number of 54 chromosomes consisting of ten biarmed (numbers 1-10) and 16 acrocentric autosome pairs (numbers 11-26); of the sex chromosomes, the X was biarmed and the Y was a n acrocentric chromosome (see Fig. 3). A standard karyotype of this subspecies was constructed on the basis of the Q-G-banding of each homologue pair, both techniques producing basically the same pattern of staining. Within each autosome group, pairs were ordered in decreasing size on the basis of the measurements shown in Table number I. Chromosome band resolution in elongated chromosomes allowed for the precise identification and characterization of 382 chromosome subregions that were numbered similarly to the High Resolution Human Karyotype (see “An International System for Human Cytogenetics Nomenclature, ISCN” ). TABLE I. Relative Chromosome Length (RCL) Group Biarmed Acrocentric Sex Chromosome pair 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 X Y RCL 6.08 5.58 5.07 4.72 4.42 4.26 3.67 3.17 2.29 2.29 5.95 5.00 4.51 4.34 4.23 3.88 3.82 3.56 2.95 2.92 2.43 2.35 2.29 1.96 1.55 1.55 4.54 1.35 188 I Matayoshi et a1 Fig. 2. Metaphase sequentially stained with quinacrine [Caspersson et al, 19701 and conventional Giemsa staining. Fig. 3. See page 191 for legend 190 I Matayoshi et a1 Figure 3. Cebus apella paraguayanus Karyotype I 191 Fig. 3. Ideogram illustrating the G-banding pattern of the Cebus apella paraguayanus chromosomes arranged according to the proposed standardization. 192 I Matayoshi et a1 DISCUSSION Banding techniques are the only reliable procedures for the precise and unequivocal identification of chromosomes and of subregions within them. High-resolution patterns can be obtained in enlongated chromosomes, which permits better characterization of subregions. This analysis when applied to Cebus apella paraguayanus has allowed identification of 382 different subregions and unequivocal identification of each chromosome pair with a higher degree of resolution than that of any previous report on the chromosomes of this species. Moreover, a morphometric analysis of individual chromosome pairs has permitted us to order them precisely in decreasing size order within each autosome group. By carrying out measurements on conventionally stained chromosomes, we have, moreover, eliminated possible errors in length estimations which result from the appearance of G-negative regions on the telomeres or from other distorting effects produced by trypsin digestion on chromosome structure. Two aspects deserve a special comment with respect to the proposed standardization. One is that it represents a set of karyotypic characteristics of one subspecies of Cebus apella which might not be necessarily extrapolated to the whole species level. Partial evidence suggests that several Cebus apella subpopulations share the same basic karyotype [Freitas & Seuanez, 19821, implying that Cebus apella might comprise a rather karyotypically uniform group. However, this report does not include every subspecific group within the species, and the possibility that some of the variant chromosome types described could actually be subspecies-specific cannot be ruled out. More recently, Seuanez et a1 (in press) have shown that a t least one subspecies (Cebus apella xanthosternos, Wied, 1820) can be distinguished by the presence of a n intercalar heterochromatic region in one autosome pair (number 11 in our standard karyotype). For this reason, extrapolations of findings from the subspecies to the whole species level can only be tentative until more population studies are carried out, with a comparable level of technical resolution, to analyze the degree of chromosome variation within Cebus apella. The second point that is worth mentioning is that chromosome ordination and nomenclature have followed, in our study, very strict morphological and morphometric criteria regardless of the presumptive chromosome similarities between these species and others of the same genus. For this reason, our standardization criterion differs from that of Torres de Caballero et a1 , by which the chromosomes of Cebus apella were ordered as in Cebus capucinus. Since presumed morphological homologies between different primate species might not always be coincident with syntenic homologies, a n independent criterion of karyotypic standardization is preferable. Anthropocentric criteria are further biased by the fact that nonhuman primates must contain several gene loci which are absent in humans and vice versa. The use of a n anthropocentric criterion for Cebus apella chromosomes would require an indirect extrapolation with Cebus capucinus chromosomes for which a comparative gene assignment chart exists with respect to the genetic map [Creau-Goldberg et al, 19811. Finally, we wish to emphasize that our findings are based on the largest number of Cebus apella specimens studied in the literature; the karyotype standardization of this subspecies might be valuable for further comparisons at the chromosome level of different Cebus apella subspecies or populations and for the establishment of a potential correlation between karyological and phenotypic characteristics in relation to their geographic distribution. CONCLUSIONS 1. Cytogenetic studies of Cebus apella paraguayanus, with different staining techniques sequentially applied, allowed precise identification of each chromosome pair. Cebus apella paruguayanus Karyotype I 193 2. The Q-G-banding showed a constant pattern of 382 chromosome subregions in the 40 specimens. 3. The karyotype standardization we have proposed might be valuable for comparisons with other Cebus apella subspecies. ACKNOWLEDGMENTS This work was supported in part by grants from the Subsecretaria de Estado de Ciencia y Tecnica 192, 1982 (Argentina), UNESCO Regional Programme for PostGraduate Training in Biological Sciences RLA 78/028, and FINEP (Brazil) grant number 4384073400. The authors thank Mr. Armando Gette from the primate colony for technical assistance and Miss Irene Spinadel for typing this manuscript. REFERENCES Bender, M.A.; Chu, E.H.I. The chromosomes of primates, pp 261-310 in EVOLUTIONARY AND GENETIC BIOLOGY OF PRIMATES, Vol. 1. Buettner-Janush, ed. New York, Academic Press, 1963. Cambefort, Y.; Moro, F. Cytogenetics and taxonomy of some South Bolivian monkeys. FOLIA PRIMATOLOGICA 29:307-314, 1978. Caspersson, T.; Zech, L.; Johansson, C; Modest, E.J. 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