Studies in nuclear cytology

My work falls broadly into three groups of subjects:1. Studies on the determination of secondary sex characters in invertebrates : papers 2, 3 and 4.These papers describe research on one of the first problems which engaged my attention : the causal determination of the differentiation of secondary sex characters in invertebrates. While I was a student at Naples in 1938/9 I was impressed by the problem of parasitic castration and sex reversal in crustacea. The problem has great physiological and genetic interest it has also great complexity. This became apparent to me when I found that the effects of epicarid isopods on their prawn hosts is quite unlike the action of similar isopods on Upogebia, this latter animal showing all the familiar features of sex reversal when parasitised. The castration of unparasitised prawns by means of X -rays gave evidence that the cyclically developed female secondary sex characters are dependent on the presence of a maturing ovary for their differentiation : the same situation was found, thong of published, for the adult female characters of the crab Pachygrapsus, though this animal undergoes sex reversal, male to female, on being parasitised. It was hoped that castration of males might be accomplished by means of X -rays since this would supply crucial evidence for the resolution of the whole problem. However, too high a level of irradiation. is necessary for castration of male crabs, which die before completing a further moult. Surgical castration likewise proved impracticable and the problem was left in this state.2. Studies in chromosome cytology : papers 5,6,70,9,10, 11,14,(16,17),19,20 and 21.My interest in chromosome cytology, originally aroused by Dr J.R.Baker and Dr E.B.Ford,F.R.S., at Oxford 2. and further stimulated by contact with Dr C.D.Darlington, P.R.S., then of Merton,London, led me to study a number of problems in this field. It is with these problems that the main bulk of my papers are concerned.Paper 6 demonstrated that a mmltiple chromosome mechanism determines sex in the earwig. The situation is complicated by the fact that males may have two alternative chromosome constitutions and that the Y chromosome in this species is dicentric :the mechanism is considered to be related to the abnormal sex ratios in earwigs which are found in the wild.Paper 8 describes the behaviour of a supernumerary autosome at meiosis in the grasshopper Mecostethus. Paper 9 describes how a fertile plant hybrid has arisen by the hybridisation of two autopolyploid species : this mechanism is an alternative means of arriving at an alloployploid constitution.Paper 10 describes the discovery of low temperature sensitive heterochromatic segments of the chromosomes of newts both at mitosis and meiosis and leads to the inference that desoxyribose nucleic acid ix plays an important role in chromosome spiralisation.Paper 11 describes _the upsets to the spindle mechanism at mitosis which can arise as a result of exposure of newt cells to low temperature or to the action of colchicine.Paper 14 demonstrates that the centromere is not necessarily a barrier to chiasma interferenee at meiosis, as was previously held to be the case. This was first shown for the mosquito Culex and has subsequently proved true for many other animal.Paper 19 shows how chiasma interference across the centromere is suppressed waen multivalent chromosome associations are formed at meiosis.Papers 20 and 21 describe the reduction in chiasma frequency and the localisation of chiasmata in hybrids between geographical races of newts. Evidence is also given of the origin of a chromosomal translocation which distinguishes the chromosome complement of one race from the other two and which can act as a barrier to genetic leakage between these races.Papers 16 and 17, which do not rightly fall under the heading of chromosome cytology, are nevertheless_ related to this theme since they are concerned with the possibility of .a connection between heterorshromatic chromosome segments, ribose nucleic acid synthesis and growth rate determination.3. Experimental work with giant nuclei : papers (12, 13), 15, 18, 22, 23.Partly as a result of a controversy over the distribution of nucleic acid in the cell (papers 12 and 13) and more generally because, having worked for some years in the field of descriptive cytology and cytogenetics, 1 was impressed with the need for an experimental attack on the many outstanding and general problems concerning the cell nucleus, i turned my attention three years ago to the exploitation of giant nuclei.A great deal of this work is not yet ready for publication : it is the general line of research in which I an most actively engaged at the present time. Since, however, a number of observations have already been made, these are summarised in a final manuscript entitled " Experimental studies on amphibian oocyte nuclei ". This should be read as an introduction to my published papers in this field.LIST OF PUBLICATIONS:1. 1938. "GUI size in millipedes ". NATURE, 141, 247 || 2. 1939. "The absence of a sex -hormone controlling regeneration of the hectocotylus in Octopus vulgaris Lam. ". Pubbl.Staz.zool.Napoli, 18, 15 || 3. 1940. "The effects of castration by parasites and .K-rayti on the secohdary sex chcracters of prawns ". J. exp. Biol., 17, 168. || 4. 1940. (with F.G.i.Knowles) "A change in the chromatophore pattern of crustacea at sexual maturity ". J. exp. Biol., 17, 262. || 5. 1940. "The chromosomes of the cymothoid isopod Anilocra" Çuart.J.micr.Sci., 82, 327. || 6. 1941. "The sexTdetermining mechanism of the earwig, Forficula.auricularia ". J.Genet. 41, 349. || 7. 1941. "Determination of sex in Scalpellum ". -NATURE, 148, 258 . || 8. 1941. "A trisomic grasshopper ". J.Hered. 32, 296. || 9. 1941. "The cytology of Gaulthettya wisleyensis (Marchant Rehder: a new mode of species formation." An.n.Bot.Lond.,N.S.5, 579 || 10. 1942. "Heterochromatin in Triton ". Proc.roy.Soc. B. 130, 324. || 11. 1943. (with H.N.Barber) "The effects of cold and colchicine on mitosis in the newt ". Proc. roy. Soc. B. 131, 258. || 12. 1943. "Distribution of nucleic acid in the cell" NATURE, 152, 503 || 13. 1944. (with 11.:.Barber) "Distribution of nucleic acid in the cell ". HATURE, 153, 109. 2. || 14. l947.(with G. _'ontalenti) "Chiasma interference in Mosquitoes". J. Genet., 48,119. || 15. 1948. "Alcune proprietà fisiche della membrana nucleare ". Ricercha Scientifica, 18, 1. || 16. 1948. "Ribose nucleic acid in the Drosophila egg ". NATURE, 161, 440. || 17. 1949. "Cleavage rate, oxygen consumption and ribose nucleic acid content of sea urchin eggs ". Biochem.et Biophys..cta, 3, 92. || 18. 1949 (with J.T.Randall,- . .S., and S.G.Tomlin) "An electron microscope study of the nuclear membrane" NATURE, 163, 280. || 19. 1949. "Chiasma interference in diploid, tetraploid and interchange spermatocytes of the earwig ". J. Genet. 49, 209. || 20. 1950 (with H.Spurway) "Hybrids between some members of the Rassenkreis Triturus cristatus ". EXPERIENTIA, in press. || 21. 1950 (wroth H.Spurway) "A study of meiosis in interracial hybrids of the newt Triturus cristatus ". J. Genet. in press. || 22. 1950 (with GiL.Brown and G.Leaf) "The chemical nature of nuclear sap ". NATURE, in press. || 23. 1950 (with S.G.Tornlin) "Experimental studies on amphibian oocyte nuclei.l. Invettigation of the structure of the nuclear membrane by means of the electron microscope". Proc.roy.Soc.B, in pres

Boundary susceptibility in the spin-1/2 chain: Curie like behavior without magnetic impurities

We investigate the low-temperature thermodynamics of the spin-1/2 Heisenberg chain with open ends. On the basis of boundary conformal field theory arguments and numerical density matrix renormalization group calculations, it is established that in the isotropic case the impurity susceptibility exhibits a Curie-like divergent behavior as the temperature decreases, even in the absence of magnetic impurities. A similar singular temperature dependence is also found in the boundary contributions of the specific heat coefficient. In the anisotropic case, for $1/2<\Delta<1$, these boundary quantities still show singular temperature dependence obeying a power law with an anomalous dimension. Experimental consequences will be discussed.Comment: 5 pages, 1 figure, final versio

Low-Lying Dirac Eigenmodes, Topological Charge Fluctuations and the Instanton Liquid Model

The local structure of low-lying eigenmodes of the overlap Dirac operator is studied. It is found that these modes cannot be described as linear combinations of 't Hooft "would-be" zeromodes associated with instanton excitations that underly the Instanton Liquid Model. This implies that the instanton liquid scenario for spontaneous chiral symmetry breaking in QCD is not accurate. More generally, our data suggests that the vacuum fluctuations of topological charge are not effectively dominated by localized lumps of unit charge with which the topological "would-be" zeromodes could be associated.Comment: Presented by I. Horvath at the NATO Advanced Research Workshop "Confinement, Topology, and other Non-Perturbative Aspects of QCD", January 21-27, 2002, Stara Lesna, Slovakia. 12 pages, 6 figures, uses crckapb.st

Corrections to D-brane Action and Generalized Boundary State

In this paper, we generalize a boundary state to the one incorporating non-constant gauge field strength as an external background coupled to the boundary of a string worldsheet in bosonic string theory. This newly defined boundary state satisfies generalized nonlinear boundary conditions with non-constant gauge field strength, and is BRST invariant. The divergence immanent in this boundary state coincide with the one calculated in a string sigma model. We extract the relevant massless part of this generalized boundary state, and give a part of the D-brane action with the non-constant gauge field strength, that is, derivative corrections to the D-brane action.Comment: 21 pages, LaTeX, 2 eps figures, a reference added, typos correcte

A simple derivation of the Overlap Dirac Operator

We derive the vector-like four dimensional overlap Dirac operator starting from a five dimensional Dirac action in the presence of a delta-function space-time defect. The effective operator is obtained by first integrating out all the fermionic modes in the fixed gauge background, and then identifying the contribution from the localized modes as the determinant of an operator in one dimension less. We define physically relevant degrees of freedom on the defect by introducing an auxiliary defect-bound fermion field and integrating out the original five dimensional bulk field.Comment: 9 pages, LaTe

Dynamics of the DBI Spike Soliton

We compare oscillations of a fundamental string ending on a D3-brane in two different settings: (1) a test-string radially threading the horizon of an extremal black D3-brane and (2) the spike soliton of the DBI effective action for a D3-brane. Previous work has shown that overall transverse modes of the test-string appear as l=0 modes of the transverse scalar fields of the DBI system. We identify DBI world-volume degrees of freedom that have dynamics matching those of the test-string relative transverse modes. We show that there is a map, resembling T-duality, between relative and overall transverse modes for the test-string that interchanges Neumann and Dirichlet boundary conditions and implies equality of the absorption coefficients for both modes. We give general solutions to the overall and relative transverse parts of the DBI coupled gauge and scalar system and calculate absorption coefficients for the higher angular momentum modes in the low frequency limit. We find that there is a nonzero amplitude for l>0 modes to travel out to infinity along the spike, demonstrating that the spike remains effectively 3+1-dimensional.Comment: 15 pages, 1 figur

Fermionic Zero Modes on Domain Walls

We study fermionic zero modes in the domain wall background. The fermions have Dirac and left- and right-handed Majorana mass terms. The source of the Dirac mass term is the coupling to a scalar field $\Phi$. The source of the Majorana mass terms could also be the coupling to a scalar field $\Phi$ or a vacuum expectation value of some other field acquired in a phase transition well above the phase transition of the field $\Phi$. We derive the fermionic equations of motion and find the necessary and sufficient conditions for a zero mode to exist. We also find the solutions numerically. In the absence of the Majorana mass terms, the equations are solvable analytically. In the case of massless fermions a zero energy solution exists and we show that although this mode is not discretely normalizable it is Dirac delta function normalizable and should be viewed as part of a continuum spectrum rather than as an isolated zero mode.Comment: 6 pages, 3 figures, matches version published in PR

SO(10) Cosmic Strings and Baryon Number Violation

SO(10) cosmic strings formed during the phase transition Spin(10) $\rightarrow$ SU(5) $\times{\cal Z}_2$ are studied. Two types of strings --- one effectively Abelian and one non-Abelian --- are constructed and the string solutions are calculated numerically. The non-Abelian string can catalyze baryon number violation via the ``twisting'' of the scalar field which causes mixing of leptons and quarks in the fermion multiplet. The non-Abelian string is also found to have the lower energy possibly for the entire range of the parameters in the theory. Scattering of fermions in the fields of the strings is analyzed, and the baryon number violation cross section is calculated. The role of the self-adjoint parameters is discussed and the values are computed.Comment: LaTex (RevTex), 36 pages, 6 figures (available upon request), MIT-CTP#215