Sex determination in mammals — Before and after the evolution of SRY

Therian mammals (marsupials and placentals) have an XX female: XY male sex chromosome system, which is homologous to autosomes in other vertebrates. The testis-determining gene, SRY, is conserved on the Y throughout therians, but is absent in other vertebrates, suggesting that the mammal system evolved about 310 million years ago (MYA). However, recent work on the basal monotreme mammals has completely changed our conception of how and when this change occurred. Platypus and echidna lack SRY, and the therian X and Y are represented by autosomes, implying that SRY evolved in therians after their divergence from monotremes only 166 MYA. Clues to the ancestral mechanism usurped by SRY in therians are provided by the monotremes, whose sex chromosomes are homologous to the ZW of birds. This suggests that the therian X and Y, and the SRY gene, evolved from an ancient bird-like sex chromosome system which predates the divergence of mammals and reptiles 310 MYA. Received 4 March 2008; received after revision 22 April 2008; accepted 3 June 2008     

Distribution of sister chromatid exchanges in different types of chromatin in the X chromosome ofMicrotus cabrerae

We used the X chromosomes ofMicrotus cabrerae as a model to analyze the distribution of sister chromatid exchanges (SCEs) on different types of chromatin, because of the marked heterogeneity of the heterochromatin in the entire short arm and a portion of the long arm of this chromosome. Computer-simulated distributions, according to an algorithm that makes it possible to modify the distribution on the basis of any possible hypothesis, were compared with real distributions by log-linear models. We found that the frequency of SCEs in different types of heterochromatin was higher than that expected for a random distribution, and located an SCE hot-spot at the junction between euchromatin and heterochromatin. The possible relationship between the distribution of SCEs and base composition or chromatin accessibility are discussed.     

A 41, XYY mouse

Summary Cytogenetic analyses of bone marrow and meiotic cells in an apparently normal male mouse clearly revealed the presence of an extra Y chromosome leading to 2n=41, XYY. During meiosis the sex chromosomes formed all possible types of combinations (XYY, XY/Y, YY/X and X/Y/Y). Compared to 40, XY normal mice, the sperm count was significantly less, but the incidence of sperm head abnormality was at the normal level.Acknowledgment. The authors are grateful to Prof. G. K. Manna, Department of Zoology, Kalyani University, for his valuable comments and Prof. M. C. Dash, School of Life Sciences, Sambalpur University for providing necessary facilities. Thankful acknowledgment to CSIR, India for a SRF awarded to RNK.     

An overview of factors influencing sex determination and gonadal development in birds

The morphological development of the embryonic gonads is very similar in birds and mammals, and recent evidence suggests that the genes involved in this process are conserved between these classes of vertebrates. The genetic mechanism by which sex is determined in birds remains to be elucidated, although recent studies have reinforced the contention that steroids may play an important role in the structural development of the testes and ovaries in birds. So far, few genes have been assigned to the avian sex chromosomes, but it is known that the Z and W chromosomes do not share significant homology with the mammalian X and Y chromosomes. The commercial importance of poultry breeding has motivated considerable investment in developing physical and genetic maps of the chicken genome. These efforts, in combination with modern molecular approaches to analyzing gene expression, should help to elucidate the sex-determining mechanism in birds in the near future.     

Huygens at work: Annotations in his rediscovered personal copy of Hooke's Micrographia

It is well known that Hooke's wave theory of light, set forth in his Micrographia of 1665, is viewed as a step towards Huygens's famous theory of light. This view depends mostly on some short remarks given by Huygens in his Traité de la Lumi`ere (1690) and the earlier Projet du Contenu de la Dioptrique (1673). Huygens's personal copy of Micrographia was believed to be lost until found at Braunschweig (Brunswick) University Library by the author three years ago. It is annotated at Observ. IX (pp. 47–67) only, where Hooke deals with his wave theory of light and colours. This article provides a short review of Hooke's theory, and an interpretation of Huygens's annotations, which show clearly the first steps towards the opinions he was to express in his Traité de la lumi`ere, particularly methodological ones. Furthermore, a short comparison is here drawn with Huygens's annotations in his copy of Ango's L'optique divisée en trois livres, which show similar patterns of reasoning.     

Constitutive heterochromatin and nucleolus organizer region in the knifefish,Apteronotus albifrons (Pisces,Apteronotidae)

Summary The C-banding and silver staining of the chromosomes of the knifefishApteronotus albifrons (2n=24), demonstrated the presence of constitutive heterochromatin in the centromeric region of every chromosome, except pair 4, where the entire long arm was darkly stained, the silver stain positive nucleolus organizer region (NOR) being embedded in it.The authors are grateful to Dr Sen Pathak (University of Texas System Cancer Center at Houston, Texas, USA) and Dr Yatiyo Yassuda (Universidade de São Paulo, São Paulo, Brasil) for their suggestions. This study was supported in part by grants of the Conselho Nacional de Desenvolvimento Cientifico e Tecnológico (CNPq).     

Effect of adaptation level on maintained firing and sensitivity in receptive field center of X and Y cells

Summary Maintained firing rates of X cells and Y cells were compared at 6 adaptation levels (AL) between –2.71 log cd/m² and 2.28 log cd/m² (10 mm² pupil size). X cell maintained firing was higher at all ALs and was statistically different at medium and high ones. Changes in AL had nearly identical effects upon X and Y cell suprathreshold sensitivity to a flashing spot in the center of their receptive fields; the Weber function had a slope of 0.744 for Y cells and 0.743 for X cells. These values are not statistically different.This research is supported by Public Health Service grant no. EY 00701.     

The mitotic chromosomes of the lampreyMordacia mordax (agnatha: Petromyzonidae)

Résumé L'étude des chromosomes somatiques de la lamproie de l'hémisphère sud,Mordacia mordax (Richardson), montre que l'équipement chromosomique diploïde de cette espèce est composé de 76 chromosomes très petits. La plupart des chromosomes sont métacentrique ou bien submétacentrique. Ces chromosomes sont différents en nombre de ceux décrits pour les lamproies de l'hémisphère nord.     

Effects of ultra-violet light on nucleic acid and nucleoproteins and other biological systems

Résumé L'auteur a examiné les conséquences chimiques de l'absorption de radiations ultra-violettes par les substances présentes dans les cellules vivantes (en particulier l'acide désoxyribonucléique).Les effets observés sont dus: 1° à l'absorption directe des radiations; 2° à une action directe — ou activée photodynamiquement — sur l'oxygène présent. Les conséquences de cette dernière sont très semblables à celles produites par les rayons X.En ce qui concerne l'absorption directe des radiations U.V., il se pourrait que la rupture des chromosomes soit due à celle des liens existant entre les chaînes de DNA et l'histone.

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Lecture given to the Congrès International de Photobiologie, Amsterdam, August 1954.     

Lipopurealins,novel bromotyrosine derivatives with long chain acyl groups,from the marine spongePsammaplysilla purea

Summary Lipopurealin-A,-B and-C have been isolated from the Okinawan marine spongePsammaplysilla purea. They are inhibitors of Na, K-ATPase, and the structures have been elucidated on the basis of spectral data. They are bromotyrosine derived structures with saturated long chain acyl parts.Physiologically active marine natural products from Porifera X. Preceding paper: Nakamura, H., Wu, H., Kobayashi, J., Nakamura, Y., Ohizumi, Y., and Hirata, Y., Tetrahedron Lett.26 (1985) 4517.     

Selection of the relevant information set for predictive relationships analysis between time series

In time series analysis, a vector Y is often called causal for another vector X if the former helps to improve the k‐step‐ahead forecast of the latter. If this holds for k=1, vector Y is commonly called Granger‐causal for X . It has been shown in several studies that the finding of causality between two (vectors of) variables is not robust to changes of the information set. In this paper, using the concept of Hilbert spaces, we derive a condition under which the predictive relationships between two vectors are invariant to the selection of a bivariate or trivariate framework. In more detail, we provide a condition under which the finding of causality (improved predictability at forecast horizon 1) respectively non‐causality of Y for X is unaffected if the information set is either enlarged or reduced by the information in a third vector Z . This result has a practical usefulness since it provides a guidance to validate the choice of the bivariate system { X , Y } in place of { X , Y , Z }. In fact, to test the ‘goodness’ of { X , Y } we should test whether Z Granger cause X not requiring the joint analysis of all variables in { X , Y , Z }. Copyright © 2002 John Wiley & Sons, Ltd.     

Surface morphology of the subfornical organ: Effects of low and high sodium chloride diet

Summary Ependymal cells found in the subfornical organ of the rat were counted. Cells covered by small microvilli, small protrusions and smooth cells were frequently found. Also present were cells with long or short cilia, cels with large protrusions and supraependymal cells. High and low sodium diets reduced the number of cells with large protrusions. Microvilli-covered cells increased after a low sodium diet.Acknowledgments. We thank Dr A. C. Taquini for his helpful discussions and Servicio de Microscopía Electrónica de Barrido, Conicet, and Facultad de Odontologia for technical assistance.     

The mitotic chromosomes of the lamprey,Petromyzon marinus L.

Résumé L'étude des chromosomes somatiques de la lamproie,Petromyzon marinus L. a montré que l'équipment chromosomique diploïde de cette espèce est composé de 168 chromosomes très petits, dont queleues-uns des plus grands sont métacentriques. Le chiffre semble représenter le plus grand nombre de chromosomes trouvé dans une espèce de Vertébré. On a comparé les chromosomes de P.marinus avec ceux des autres espèces de lamproies.

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Holder of a Science Research Council Fellowship.     

Dimorphic sperms ofRhinopoma kinneari (Chiroptera)

Résumé Les spermatozoïdes deRhinopoma kinneari sont dimorphes et diffèrent les uns des autres dans leur forme et leur longeur totale, mais la longueur de leur tête reste constante. Ils peuvent être du type X et Y comme ceux des autres mammifères.     

Effect of adaptation level on maintained firing and sensitivity in receptive field center of X and Y cells

Maintained firing rates of X cells and Y cells were compared at 6 adaptation levels (AL) between -2.71 log cd/m2 and 2.28 log cd/m2 (10 mm2 pupil size). X cell maintained firing was higher at all ALs and was statistically different at medium and high ones. Changes in AL had nearly identical effects upon X and Y cell suprathreshold sensitivity to a flashing spot in the center of their receptive fields; the Weber function had a slope of 0.744 for Y cells and 0.743 for X cells. These values are not statistically different.     

Sex determining mechanismXY 1Y2 inArtibeus lituratus lituratus (Chiroptera-phyllostomidae)

Resumen En el murciélagoArtibeus lituratus lituratus el nÚmero de cromosomas es de 2n=30 en la hembra y de 2n=31 en el macho. El mecanismo de determination del sexo esXX/XY ₁Y₂. La translocación de un autosoma alX resultó en la diferenciación del neo-Y. Son descritos los aspectos del comportamiento del trivalente sexual durante la meiosis. Estos son comparados a los que presenta la especieNoctilio leporinus (2n=34) cuyo mecanismo esXX/X Y.

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This work was supported by Public Health Service Research Grant No. GM-14577-03 from the National Institute of General Medical Sciences and by the Fundo de Pesquisas do Instituto Butantan. R. F. B. holds a FAPESP training fellowship.     

A review of the properties of sustained and transient retinal ganglion cells

Résumé De récentes recherches sur les cellules ganglionnaires du chat ont montré deux types d'unités se distinguant par leur réponse à l'éclairement. Le type X répond d'une façon soutenue, le type Y d'une façon transitoire. Ces unités sont décrites et mises en correlation avec leurs particularités anatomiques et les propriétés fonctionnelles qu'on leur attribue. Les implications de cette classification à l'égard de l'arrangement spatial et temporelle des champs récepteurs sont discutés.     

Chromosomes of the lancelet,Branchiostoma floridae (order amphioxi)

Résumé Une étude des chromosomes deBranchiostoma floridae Hubbs, une espèce de lancelet de l'Atlantique occidentale, révéla la présence d'haplocaryons et diplocaryons au nombre de 19 et de 38 respectivement. Ces chromosomes furent comparés à ceux de 2 espèces de lancelets du Vieux Monde,Branchiostoma lanceolatum etB. belcheri. On résume les études concernant les chromosomes des Urochordata et des Agnatha et on émet des hypothèses sur las relations possibles entre les Protochordata et Agnatha.

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This research was supported by Samford University Research Fund, Grant No. 24, to Howell.