Lymphatic vessels arise from specialized angioblasts within a venous niche.

How cells acquire their fate is a fundamental question in developmental and regenerative biology. Multipotent progenitors undergo cell-fate restriction in response to cues from the microenvironment, the nature of which is poorly understood. In the case of the lymphatic system, venous cells from the cardinal vein are thought to generate lymphatic vessels through trans-differentiation. Here we show that in zebrafish, lymphatic progenitors arise from a previously uncharacterized niche of specialized angioblasts within the cardinal vein, which also generates arterial and venous fates. We further identify Wnt5b as a novel lymphatic inductive signal and show that it also promotes the 'angioblast-to-lymphatic' transition in human embryonic stem cells, suggesting that this process is evolutionarily conserved. Our results uncover a novel mechanism of lymphatic specification, and provide the first characterization of the lymphatic inductive niche. More broadly, our findings highlight the cardinal vein as a heterogeneous structure, analogous to the haematopoietic niche in the aortic floor.

The capacity for romantic intimacy: exploring the contribution of best friend and marital and parental relationships.

This study examined, in a longitudinal design, the contributions of three different relationships, namely marital, parent-child and best friend, to the capacity for intimacy in romantic relationships of Israeli male adolescents, as well as the mediating role of socio-emotional capacities. Eighty-four 17-year-old adolescents and their parents filled out questionnaires concerning the quality of these relational contexts. Four years later the Intimacy Status Interview was administered to the adolescents at the conclusion of their mandatory military service to examine closeness, separateness, and commitment within their romantic relationships. Results showed that all relational contexts were related to capacity for intimacy (directly or indirectly), with higher relational qualities associated with better capability for intimacy. The marital relationship was associated with intimacy through its effect on the parent-child relationships. The effects of the parent-child relationships on the capacity for intimacy were mediated through the adolescents' socio-emotional capabilities. The contribution of the parent-adolescent relationships to the capacity for closeness and commitment was further mediated through relationships with the best friend, whereas the contribution to the capacity for separateness was not. A substantial number of our participants showed high capability for intimacy although in the military service context the circumstances for the development of intimacy were quite limited and non-optimal. Exploration of the separateness and closeness facets of intimacy in romantic relationships in the two sexes and in other contexts is recommended.

Mother's attachment concerns regarding spouse and infant's temperament as modulators of maternal separation anxiety.

The modulators of maternal separation anxiety were examined in a longitudinal study with 97 mothers of infants from 3 to 9 months of age. The objective of the study was to examine the joint contribution of the mother's attachment concerns as related to her husband together with the perception of the infant's temperament to her concerns over separation from her child. Maternal worries about separation from 3-month-old infants predicted maternal separation anxiety when infants were 9 months old. Mother's attachment to her husband and her perception of her child's temperament further predicted maternal separation anxiety at 9 months over and above the worries at 3 months. Mothers who feared dependent relationships with their husbands experienced high levels of maternal separation anxiety. This tendency was particularly marked when the infant was perceived as adaptable at 3 months. In addition, secure mothers, namely, mothers low in fear of abandonment and in fear of being dependent, increased their maternal separation anxiety as a function of their infant's perceived unadaptability.

Mothers of anxious/ambivalent infants: maternal characteristics and child-care context.

A general model of the determinants of parenting was employed to explore the antecedents of the ambivalent attachment pattern in Israel. Specifically, three classes of variables were identified: maternal, infant, and child-care context. Participants were 98 mothers and their infants. This research was part of a longitudinal study on sleep patterns. Mothers filled out questionnaires and were observed with their infants in the Ainsworth Strange Situation laboratory procedure. Mothers of ambivalent infants showed lower education level, higher separation anxiety, and higher parenting stress than mothers of secure infants. Infants' perceived difficult temperament did not discriminate between the two groups. Longer hours spent at work and placement in group day-care were both associated with ambivalent attachment. The findings are discussed in light of the importance of considering distal factors such as maternal attitudes and general caregiving strategy in clarifying the antecedents of attachment patterns.

Sleeping out of home in a Kibbutz communal arrangement: it makes a difference for infant-mother attachment.

Attachment classification distributions of infant-mother dyads living in 2 types of Israeli kibbutzim were compared. The subjects were 48 infants, 14-22 months old (M = 18.29 months); 13 boys and 10 girls were from 23 kibbutz infants' houses with communal sleeping arrangements, and 13 boys and 12 girls were from 25 kibbutz infants' houses with home-based sleeping arrangements. The 2 groups did not differ on infants' temperament and early life events, mother-infant play interaction, quality of infants' daytime environment, or any of several maternal variables. Among the home-based infants, 80% were securely attached to their mothers versus 48% of the infants in communal sleeping arrangements. No avoidant relationships were found. Including the disorganized-disoriented attachment classification (44% in the communal group, 32% in the home-based group) did not change the results. We argue that the communal sleeping arrangement presents a childrearing environment that deviates markedly from the environment of evolutionary adaptedness.

Motivational effects in the social comparison of opinions.

Four experiments were executed to test the effects of different epistemic motivations on subjects' tendency to compare with agreeing or disagreeing others. We found that under high (vs. low) fear of invalidity, subjects tend more to compare with disagreeing (vs. agreeing) others. By contrast, under high (vs. low) need for self-confirmation or a high (vs. low) need for cognitive structure, subjects tended more to compare with agreeing others. These results are discussed in reference to social comparison formulations (Festinger, 1954; Goethals & Darley, 1977) and the theory of lay epistemology (Kruglanski & Ajzen, 1983; Kruglanski & Freund, 1983).