An alternative model for the structural mechanics of hagfish slime threads.

Hagfish slime threads are an interesting intermediate filament (IF) system in that, in contrast to hair, they appear to be a series system of IFs, consisting of rods and terminal domains (TDs), without matrix. The protein composition also differs from hair. Published data show that the wet stress-strain curve consists of four regions: I, increasing low modulus; II, plateau; III increasing higher modulus; IV decreasing modulus to break. Beyond 34% extension, there is plastic deformation, which contrasts with the elastic deformation of most biological fibres. The paper considers two explanations, one published by Fudge et al. [D.S. Fudge, K.H. Gardner, V.T. Forsyth, C. Riekel, J.M. Gosline, Biophys. J. 85 (2003) 2015] and one new, of deformation in the four regions. The former regards the TDs as elastic, entropic coils, which extend in region I. The latter regards the TDs as having a plastic, energy-dependent extension in regions III and IV, which is comparable to the drawing of polyester fibres. A rough theoretical model of jumps over energy barriers gives a similar prediction. Twist is suggested as a mechanism for overall thread cohesion. Experimental and theoretical ways forward to a greater understanding of the structural mechanics of hagfish threads are suggested. The behaviour of the total thread/mucus/water system is discussed and some speculations on the defensive mechanisms that have evolved are presented.

A critical review of the structural mechanics of wool and hair fibres.

The potential of genetic engineering gives current importance to the need to clarify the relations between structure, properties and performance of wool. There are at present three different models to explain the tensile stress-strain properties of alpha-keratin fibres: a development by Wortmann and Zahn (W/Z) of Feughelman's series-zone model based on the structure of intermediate filaments and a gel-->sol matrix; a new model by Feughelman (F94) based on a matrix of protein globules surrounded by water; and Chapman's model based on the composite mechanics of microfibrils, characterised by critical and equilibrium stresses for the alpha<-->beta transition, in an elastomeric matrix. This paper examines the arguments related to these theories, with additional attention to the Chapman/Hearle (C/H) treatment. The main area of uncertainty, on which more information is much needed, concerns the chemical and physical structure and properties of the matrix, which is composed of keratin-associated proteins. The conclusion is that the C/H model, which is based on reasonable values of input parameters and gives good agreement with a wide range of experimental results, is most likely to be valid, though it needs some additional refinement and incorporation in a total model, which includes larger-scale structural features.

A survey of contact with offspring and assistance with child care among parents with psychotic disorders.

To help improve services for parents with psychotic disorders, patients with such disorders in three treatment agencies in Queensland, Australia, were surveyed about whether they were parents, how much contact they had with their offspring, and who provided assistance with child care. Of the 342 individuals with psychotic disorders who participated in the study, 124 were parents. Forty-eight parents in the study had children under age 16, and 20 of these parents (42 percent) had their children living with them. Most parents relied on relatives or friends for assistance with child care. Barriers to child care services identified by parents were inability to pay, lack of local services, and fear of losing custody of children.

The fertility and fecundity of patients with psychoses.

OBJECTIVE: Previous research has suggested that patients with schizophrenia have fewer offspring compared to the general population. Reduced fertility in a disorder with a strong genetic component and an apparently stable incidence has implications for models of genetic transmission. There is also a need to obtain contemporary estimates of the prevalence of parenthood among subjects with psychotic disorders in order to inform service planning. The aim of this study was to determine the fertility and fecundity of a representative sample of individuals with psychoses who were in contact with mental health services, and to explore the interactions between age at first diagnosis and fertility. METHOD: All clients of two community mental health clinics and an extended-care psychiatric hospital were surveyed. Data on diagnosis, age at first diagnosis, and the number and age of offspring were collected. Based on interviews with the proband and chart review, a genogram of the probands' family was drawn that identified sex, age, affected status and the number of offspring for each patient and their siblings. RESULTS: In total, 36% of all patients were parents. Most women with psychoses (59%) were mothers. Patients with psychoses had fewer offspring compared to their unaffected same-sex siblings. This was especially the case for men with non-affective psychoses. Higher levels of fertility were associated with a later age at first diagnosis. CONCLUSION: The consistent finding of reduced 'reproductive fitness' in those with non-affective psychoses needs to be incorporated in the genetic epidemiology of these disorders. Despite this reduction in fertility and fecundity, many patients with psychoses are parents. Services need to remain mindful of the special needs of these patients.