A Freeze-Fracture Study of the Cortex of Xenopus laevis Eggs

The organization of the cortex of Xenopus laevis eggs was investigated by freeze-fracture electron microscopy. The cortical endoplasmic reticulum (CER) formed a network surrounding and interconnecting the cortical granules. It formed junctions with the plasma membrane and was confluent with the ER in subcortical regions. Intramembranous particles (IMP₁) were only present in the P face of the CER, the E face being apparently devoid of pits and particles. Arrays of densely packed IMP₁, having a mean diameter of 17 nm, were restricted to the microvillar region of the plasma membrane. The cortical granule membrane also contained IMP₁ (mean diameter, 21 nm) that were sparsely and randomly distributed. Several types of cortical granule seemed to exist based on an analysis of the distribution of the different IMP sizes.     

Marital Relations in the Jos Plateau of Nigeria: Women's Weapons: The Politics of Domesticity among the Kofyar

Women in Kofyar society appear to have considerable independence and social power though their institutionalized roles in patrilineal kin groups and village politics are minimal, they own little property, they marry virilocally, and they play a subordinate part in religious observances. They do, however, make important economic decisions in allocating their own incomes and labor services. They also have the right to either terminate their marriages or to accept lovers in a socially recognized relationship. With a relatively unimportant sexual division of labor and limited marital and economic control, husbands are able to achieve little domestic authority over their wives. There are some indications that male distinctness and dominance are asserted chiefly, though not entirely successfully, in symbolic terms through sex-segregated rites and ritual injunctions. [West Africa, Kofyar, sex roles, marital stability, divorce]     

Formation of the Vertebrate Face Differentiation and Development

Any attempt at understanding the problem of differentiationwithin the face is one of understanding the processes whichmanipulate cranial neural crest into the myriad of tissue typesand forms this population of cells provides to the embryonicprimordia of the craniofacial region The differentiation offacial ectomesenchyme (neural crest-derived mesenchyme) is analyzedat 3 major developmental points 1). The early commitment ofneural crest prior to migration which will influence subsequentdifferentiation, 2). Induction and the inductive signal whichinitiates the differentiative cascade, and 3). The differentiativeevent itself, including factors which affect the processes ofdifferentiation and growth and our current (limited) state ofknowledge of the factors which control pattern formation duringthe differentiative process Experimental embryological evidenceand the analysis of in situ Hox gene expression is used to arguefor the early commitment of cranial neural crest with respectto antero-posterior position within the head The necessity ofepithelialmesenchymal interaction during induction and recentexperimental evidence which suggests that one or more of thebone morphogenetic proteins is the inductive signal is presentedOur current knowledge of the role(s) that growth factors, retinoicacid and Hox genes may be playing to modulate the differentiativeprocess, once activated by the inductive event, is discussedFinally, the limited knowledge which exists on pattern formationin the face is reviewed and some initial studies on regionalspecification of tissues within the facial primordia, beginningwith the chondrogenic potential of the avian mandible, is presentedas a method to initiate a search for the mechanism which controlspattern formation during facial differentiation.     

A REVIEW OF THE PROBLEMATIC OSTEOSTRACAN GENUS AUCHENASPIS AND ITS ROLE IN THYESTIDIAN EVOLUTION

Abstract:  The poorly understood osteostracan genus Auchenaspis , from the Upper Silurian of England, belongs to the thyestidians (Thyestiida), a controversial and important group that is key to the understanding of the evolution of the Osteostraci and paired pectoral fins. The two under-studied species of this genus are comprehensively reviewed using anatomical and novel statistical approaches. No reliable anatomical characters can be used to distinguish between the two species, yet discriminant analysis finds significant separation with respect to size. Potential causes of this conflict are discussed. The findings enable Auchenaspis to be considered in terms of wider thyestidian evolution and contradict previous interpretations of the genus as representing a paraphyletic taxon, whose morphology is intermediate between the general osteostracan condition and the highly derived tremataspids.     

Morphological Transformation of Rat Embryo Cells by the Combined Action of 3-Methylcholanthrene and Rauscher Leukaemia Virus

RAT embryo cells infected with either CF-1 or Rauscher C-type RNA murine leukaemia virus, when treated with diethylnitrosamine (DENA), undergo morphological transformation and become aneuploid¹. Untreated cells and cells treated with either virus or chemical alone do not transform. We describe here a similar effect of 3-methylcholanthrene (3 MC) on rat cells infected with Rauscher leukaemia virus.     

Translocation and Persistence of 1,2-14C-(2-Chloroethyl)-phosphonic Acid (Ethephon) in Thompson Seedless Grapes

Applications of 1,2^?14C-(2-chloroethyl)phosphonic acid (ethephon) were made to the surface of mature Vitis vinifera cv. Thompson Seedless berries. After 7 days, 62 % of the recovered radioactivity was still on the outside surface and was easily washed off. Within the berry, radioactivity was present only in the carbon-labeled ethephon fraction, as revealed by chromatographic analysis. Similar results were obtained when the compound was injected directly into the berries. Application of ethephon to the first leaf above the cluster, or to a berry pedicel or a peduncle, failed to result in measurable movement of the compound into the berries. Autoradiographic studies with young shoots indicated that ethephon translocated in the phloem in a source to sink relationship.