Major Developmental Transitions Research Articles

Effect of incest on self and social functioning: a developmental psychopathology perspective.

The effects of child sexual abuse have become a leading concern of mental health service providers. Despite an explosion of studies, one major difficulty in this research is the lack of a developmentally sensitive model for conceptualizing short- and long-term effects and continuity and discontinuity of effects over time. This article proposes a model based in the perspective of developmental psychopathology. It is argued that incest has its unique negative effects in the domains of self and social functioning, specifically in jeopardizing self-definition and integration, self-regulatory processes, and a sense of security and trust in relationships. Studies with clinical samples indicate that diagnostic conditions associated uniquely with a history of incest reflect serious self- and social impairments. A review of the developmental literature on self and social development summarizes each major developmental transition from infancy to middle adulthood, and the implications for the negative effects of incest on development are discussed. Finally, implications for developmentally sensitive research are discussed.

The timing of compaction: control of a major developmental transition in mouse early embryogenesis

The effect of protein synthesis inhibitors on compaction of the 8-cell mouse embryo has been investigated. The effects observed depended upon the duration and time of drug application and on the features of compaction scored. Continuous application from the late 2-cell or early 4-cell stages allowed cell flattening and surface polarization to occur in most embryos and advanced development of these features in many of them. Cell coupling developed only when drug addition was delayed until the mid 4-cell stage, and cytoplasmic polarization developed only when drug addition was delayed until the late 4-cell stage. We suggest that control over the timing of compaction is achieved at a post-translational level via a global permissive change within the blastomeres of the embryo.

A major developmental transition in early Xenopus embryos: I. characterization and timing of cellular changes at the midblastula stage.

The Xenopus embryo undergoes 12 rapid synchronous cleavages followed by a period of slower asynchronous divisions more typical of somatic cells. This change in cell cleavage has been termed the midblastula transition (MBT). We show that at the MBT the blastomeres become motile and transcriptionally active for the first time. We have investigated the timing of the MBT and found that it does not depend on cell division, on time since fertilization or on a counting mechanism involving the sequential modification of DNA. Rather, the timing of the MBT depends on reaching a critical ratio of nucleus to cytoplasm. We view the MBT as a consequence of the titration of some substance, originally present in the egg, by the exponentially increasing nuclear material. When this substance is exhausted a new cell program is engaged, leading to the acquisition of several new cell properties.

A major developmental transition in early Xenopus embryos: II. Control of the onset of transcription.

We have shown in the accompanying paper that a developmental transition occurs at the midblastula stage (cleavage 12) in Xenopus embryos, and that this midblastula transition (MBT) is apparently initiated when the ratio of nucleus to cytoplasm reaches a critical value. One manifestation of this transition is the onset of transcription. We show here that a plasmid containing a cloned gene coding for a yeast leucine tRNA comes under developmental control when injected into cleaving eggs. In pre-MBT eggs this plasmid is transiently transcribed and then becomes inactive; however, it becomes transcriptionally active again at the MBT. This pre-MBT suppression of transcription can be reversed by addition of competing DNA. The amount of DNA needed to induce premature transcription is equal to the amount of nuclear DNA present after 12 cleavages (24 ng), suggesting that the MBT is triggered by the DNA through titration of suppressor components present in the egg.