Genetic control of multiple births in low ovulating mammalian species

In mammals, litter size is a highly variable trait. Some species such as humans or cattle are monotocous, with one or sometimes two newborns per birth, whereas others, the polytocous species such as mice or pigs, are highly prolific and often produce a dozen newborns at each farrowing. In monotocous species, however, two or three newborns per birth may sometime be unwanted. In more polytocous species such as sheep or pigs, litter size is studied in order to increase livestock prolificacy. By contrast, twinning rates in humans or cattle may increase birth difficulties and health problems in the newborns. In this context, the aim of our review was to provide a clearer understanding of the genetic and physiological factors that control multiple births in low-ovulating mammalian species, with particular focus on three species: sheep, cattle, and humans, where knowledge of the ovulation rate in one may enlighten findings in the others. This article therefore reviews the phenotypic and genetic variability observed with respect to ovulation and twinning rates. It then presents the QTL and major genes that have been identified in each species. Finally, we draw a picture of the diversity of the physiological mechanisms underlying multiple ovulation. Although several major genes have been discovered in sheep, QTL detection methods in humans or cattle have suggested that the determinism of litter size is complex and probably involves several genes in order to explain variations in the number of ovulations.

     

Resistance to freezing in liquid nitrogen of carnation (Dianthus caryophyllus L. var Eolo) apical and axillary shoot tips excised from different aged in vitro plantlets

The ability of shoot tips from carnation (Dianthus caryophyllus L., var. Eolo) cultured in vitro to develop resistance to freezing in liquid nitrogen depends on the physiological state of the cell material and the pretreatment conditions. Regrowth rates close to 100% have been obtained with apical shoot tips isolated from 2 month-old stems, precultured on medium supplemented with sucrose (0.75M) and treated with dimethylsulfoxide (5% or more). Resistance of axillary shoot tips decreased progressively as a funtion of their distance from the apical shoot tip. During the development of the stem from axillary buds (obtained by cutting), progressive increases in the regrowth rate of frozen apices were noted, from 30% before cutting (axillary buds) to 98% after 3 weeks of culture.Abbreviations DMSO dimethylsulfoxide - LN liquid nitrogen     

Fast visual categorization and speed of processing in migraine]

It has been suggested that the visual cortex of migraine sufferers is hypersensitive. To test this hypothesis, we compared the speed of visual processing in eight migraine patients (including three with aura) and nine controls performing two categorisation tasks of different complexity. In the complex task developed by Thorpe et al. (1996), subjects had to detect the presence of animals in briefly presented photographs (20 ms). The speed of visual processing was measured by the latency of the differential cerebral activity that appears around 150 ms between target and non-target trials. In the simple task, subjects performed a square/circle categorisation. All subjects were faster (445 ms/497 ms) with a higher rate of success (97%/91%) in the simple task. But in both tasks, the behavioural performance and the associated evoked potentials did not show any difference suggesting a cortical hypersensitivity in migraine sufferers.     

Postnatal Development and Possible Ligand Function of the CNS-Specific Membrane Glycoprotein CNSgp 130

CNSgp 130 is a CNS-specific membrane glycoprotein present in large amounts in the adult mammalian CNS. Using immunohistological techniques, we demonstrated that CNSgp130 is not detectable in the rat cerebellum at birth, and does not appear in the cerebellum until the tenth day of postnatal life. It is expressed first in the white matter of the cerebellar folia, and subsequently (by day 14) it is expressed also in the molecular layer. Expression in the granular layer is not seen until the 18th day of postnatal life, by which time the adult pattern of expression is established. CNSgp130 is also not detectable in the cerebrum at birth. However, it is expressed weakly but diffusely in the cerebrum by the fourth day of life. By the 10th day, there is strong expression in the cerebrum, in marked contrast to its virtual absence from the cerebellum at this stage. By quantitative absorption analysis, CNSgp 130 was undetectable on the day of birth, and increased steadily to 80% of adult values by the 22nd day of postnatal life. Binding studies with pure CNSgp130 demonstrated a Pronase-sensitive ligand in adult chicken brain. This ligand was absent from neonatal rat brain and non-CNS tissues.     

Nitrogen cycling in two riparian forest soils under different geomorphic conditions

At the floodplain scale, spatial pattern and successional development of riparian vegetation are under the control of geomorphic processes. The geomorphic and hydraulic characteristics of stream channels affect the sorting of organic material and inorganic sediment through erosion/sedimentation during floods. In turn, the proportion of fine sediments fractions differs by location within a given community of riparian forest succession. In this paper we tested the effect of geomorphic features of floodplains, through soil grain size sorting, on the nitrogen cycling in riparian forest soils. Two typical riparian forests formed by vertical accretion deposits from repeated addition of sediments from overbank flow have been chosen along the River Garonne, southwest France. These riparian forests had equivalent vegetation, flood frequency and duration, differing only in soil grain size composition: one riparian forest had sandy soils and the other had loamy soils. The evolution of the main soil physical and chemical parameters as well as denitrification (DNT), N uptake (N _U ) and mineralization (N _M ) rates were measured monthly over a period of 13 months in the two study sites. The loamy riparian forest presented a better physical retention of suspended matter during floods. Moreover,in situ denitrification rates (DNT) and N uptake by plants (N _U ) measured in the loamy riparian forest soils were significantly greater than in the sandy soils. Although DNT and N _U could be in competition for available nitrogen, the peak rates of these two processes did not occur at the same period of the year, N _U being more important during the dry season when DNT was minimum, while DNT rates were maximum following the spring floods. N retention by uptake (N _U ) and loss by DNT represented together the equivalent of 32% of total organic nitrogen deposited during floods on the sandy riparian forest soils and 70% on the loamy ones. These significant differences between the two sites show that, at the landscape level, one should not estimate the rates of N _U and DNT, in riparian forests soils only on the basis of vegetation, but should take also into account the geomorphic features of the floodplain.