Robertsonian chromosome polymorphism of Akodon molinae (Rodentia: Sigmodontinae): analysis of trivalents in meiotic prophase

Akodon molinae (with 2n = 42-43-44 and an FN = 44) shows a remarkable polymorphism of chromosome 1 in natural and laboratory populations. Specimens 2n = 42, named single homozygotes (SH), have a chromosome pair 1 formed by two large metacentric chromosomes. Specimens 2n = 3, heterozygotes (Ht), have...

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Autores principales:	FERNÁNDEZ-DONOSO,RAÚL, BERRÍOS,SOLEDAD, PAGE,JESUS, MERANI,MARÍA S, LIZARRALDE,MARTA S, VIDAL-RIOJA,LIDIA, BIANCHI,NESTOR O
Lenguaje:	English
Publicado:	Sociedad de Biología de Chile 2001
Materias:	Akodon molinae Sigmodontinae Robertsonian chromosome polymorphism trivalents synaptonemal complex
Acceso en línea:	http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0716-078X2001000000016
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spelling	oai:scielo:S0716-078X20010000000162001-06-27Robertsonian chromosome polymorphism of Akodon molinae (Rodentia: Sigmodontinae): analysis of trivalents in meiotic prophaseFERNÁNDEZ-DONOSO,RAÚLBERRÍOS,SOLEDADPAGE,JESUSMERANI,MARÍA SLIZARRALDE,MARTA SVIDAL-RIOJA,LIDIABIANCHI,NESTOR O Akodon molinae Sigmodontinae Robertsonian chromosome polymorphism trivalents synaptonemal complex Akodon molinae (with 2n = 42-43-44 and an FN = 44) shows a remarkable polymorphism of chromosome 1 in natural and laboratory populations. Specimens 2n = 42, named single homozygotes (SH), have a chromosome pair 1 formed by two large metacentric chromosomes. Specimens 2n = 3, heterozygotes (Ht), have one chromosome 1 and two medium-sized subtelocentric chromosomes, 1a and 1b, which are homologous with the long and short arms of chromosome 1 respectively. Specimens 2n = 44 are double homozygotes (DH), with just two pairs of medium-sized subtelocentric chromosomes, 1a and 1b. Analysis of meiotic metaphases I and II showed that anomalous segregation occurs more frequently in spermatocytes carrying the 1a and 1b chromosomes. This would disturb gametogenesis and other reproductive and developmental processes, producing a marked decrease in viability of DH individuals. There is, as yet, no satisfactory explanation for these phenomena. To investigate structural elements which might explain such segregational anomalies, we have studied bivalent and trivalent synapsis in pachytene spermatocytes from SH, Ht and DH specimens. Of a total of 80 spermatocyte nuclei microspreads, the following results were obtained: of 16 microspreads from two SH individuals, 20 autosomic bivalents plus the XY bivalent were observed; of 48 microspreads from three Ht individuals, 19 autosomic bivalents, 1 trivalent and an XY bivalent were seen; and of the 16 microspreads from two DH individuals, 21 autosomic bivalents plus the XY bivalent were found. Trivalents analysed showed complete pairing between the short arms of 1a and 1b, and having an apparently normal synaptonemal complex (SC) with lengths of 1 and 2.8 µm. The trivalent SC showed three telomeric ends, corresponding to arms: q1 and q1a; p1 and q1b; and p1a and p1b, with attachment plates to the nuclear envelope of normal organisation. None of the trivalents showed asynapsis or desynapsis between p1a and p1b, nor an association with the XY bivalent. In 70 % of spermatocytes studied, the XY bivalent showed complete pairing between X and Y, with SC formation along the whole length of the Y chromosome. The remaining 30 % showed partial pairing, with an SC length which varied from the common end. Based on these findings and those of previous studies, we discuss: 1.- that the obliged configuration of the trivalent, with SC formation between the short arms of 1a and 1b, helps to assure a quasi normal segregation between 1, 1a and 1b in anaphase I of Ht meiosis; and 2.- that co-existence in trivalents of chromosomes 1, 1a and 1b in Ht individuals, breaks down the structural and functional integrity of the short arms of 1a and 1b, producing an accumulative damage which would also explain the decreased viability of individuals bearing these chromosomesinfo:eu-repo/semantics/openAccessSociedad de Biología de ChileRevista chilena de historia natural v.74 n.1 20012001-03-01text/htmlhttp://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0716-078X2001000000016en10.4067/S0716-078X2001000000016
institution	Scielo Chile
collection	Scielo Chile
language	English
topic	Akodon molinae Sigmodontinae Robertsonian chromosome polymorphism trivalents synaptonemal complex
spellingShingle	Akodon molinae Sigmodontinae Robertsonian chromosome polymorphism trivalents synaptonemal complex FERNÁNDEZ-DONOSO,RAÚL BERRÍOS,SOLEDAD PAGE,JESUS MERANI,MARÍA S LIZARRALDE,MARTA S VIDAL-RIOJA,LIDIA BIANCHI,NESTOR O Robertsonian chromosome polymorphism of Akodon molinae (Rodentia: Sigmodontinae): analysis of trivalents in meiotic prophase
description	Akodon molinae (with 2n = 42-43-44 and an FN = 44) shows a remarkable polymorphism of chromosome 1 in natural and laboratory populations. Specimens 2n = 42, named single homozygotes (SH), have a chromosome pair 1 formed by two large metacentric chromosomes. Specimens 2n = 3, heterozygotes (Ht), have one chromosome 1 and two medium-sized subtelocentric chromosomes, 1a and 1b, which are homologous with the long and short arms of chromosome 1 respectively. Specimens 2n = 44 are double homozygotes (DH), with just two pairs of medium-sized subtelocentric chromosomes, 1a and 1b. Analysis of meiotic metaphases I and II showed that anomalous segregation occurs more frequently in spermatocytes carrying the 1a and 1b chromosomes. This would disturb gametogenesis and other reproductive and developmental processes, producing a marked decrease in viability of DH individuals. There is, as yet, no satisfactory explanation for these phenomena. To investigate structural elements which might explain such segregational anomalies, we have studied bivalent and trivalent synapsis in pachytene spermatocytes from SH, Ht and DH specimens. Of a total of 80 spermatocyte nuclei microspreads, the following results were obtained: of 16 microspreads from two SH individuals, 20 autosomic bivalents plus the XY bivalent were observed; of 48 microspreads from three Ht individuals, 19 autosomic bivalents, 1 trivalent and an XY bivalent were seen; and of the 16 microspreads from two DH individuals, 21 autosomic bivalents plus the XY bivalent were found. Trivalents analysed showed complete pairing between the short arms of 1a and 1b, and having an apparently normal synaptonemal complex (SC) with lengths of 1 and 2.8 µm. The trivalent SC showed three telomeric ends, corresponding to arms: q1 and q1a; p1 and q1b; and p1a and p1b, with attachment plates to the nuclear envelope of normal organisation. None of the trivalents showed asynapsis or desynapsis between p1a and p1b, nor an association with the XY bivalent. In 70 % of spermatocytes studied, the XY bivalent showed complete pairing between X and Y, with SC formation along the whole length of the Y chromosome. The remaining 30 % showed partial pairing, with an SC length which varied from the common end. Based on these findings and those of previous studies, we discuss: 1.- that the obliged configuration of the trivalent, with SC formation between the short arms of 1a and 1b, helps to assure a quasi normal segregation between 1, 1a and 1b in anaphase I of Ht meiosis; and 2.- that co-existence in trivalents of chromosomes 1, 1a and 1b in Ht individuals, breaks down the structural and functional integrity of the short arms of 1a and 1b, producing an accumulative damage which would also explain the decreased viability of individuals bearing these chromosomes
author	FERNÁNDEZ-DONOSO,RAÚL BERRÍOS,SOLEDAD PAGE,JESUS MERANI,MARÍA S LIZARRALDE,MARTA S VIDAL-RIOJA,LIDIA BIANCHI,NESTOR O
author_facet	FERNÁNDEZ-DONOSO,RAÚL BERRÍOS,SOLEDAD PAGE,JESUS MERANI,MARÍA S LIZARRALDE,MARTA S VIDAL-RIOJA,LIDIA BIANCHI,NESTOR O
author_sort	FERNÁNDEZ-DONOSO,RAÚL
title	Robertsonian chromosome polymorphism of Akodon molinae (Rodentia: Sigmodontinae): analysis of trivalents in meiotic prophase
title_short	Robertsonian chromosome polymorphism of Akodon molinae (Rodentia: Sigmodontinae): analysis of trivalents in meiotic prophase
title_full	Robertsonian chromosome polymorphism of Akodon molinae (Rodentia: Sigmodontinae): analysis of trivalents in meiotic prophase
title_fullStr	Robertsonian chromosome polymorphism of Akodon molinae (Rodentia: Sigmodontinae): analysis of trivalents in meiotic prophase
title_full_unstemmed	Robertsonian chromosome polymorphism of Akodon molinae (Rodentia: Sigmodontinae): analysis of trivalents in meiotic prophase
title_sort	robertsonian chromosome polymorphism of akodon molinae (rodentia: sigmodontinae): analysis of trivalents in meiotic prophase
publisher	Sociedad de Biología de Chile
publishDate	2001
url	http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0716-078X2001000000016
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Robertsonian chromosome polymorphism of Akodon molinae (Rodentia: Sigmodontinae): analysis of trivalents in meiotic prophase

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