Structural Requirements for Activity of Mind bomb1 in Notch Signaling.

Mind bomb 1 (MIB1) is a RING E3 ligase that ubiquitinates Notch ligands, a necessary step for induction of Notch signaling. The structural basis for binding of the JAG1 ligand by the N-terminal region of MIB1 is known, yet how the ankyrin (ANK) and RING domains of MIB1 cooperate to catalyze ubiquitin transfer from E2~Ub to Notch ligands remains unclear. Here, we show that the third RING domain and adjacent coiled coil region of MIB1 (ccRING3) drives MIB1 dimerization and that ubiquitin transfer activity of MIB1 relies solely on RING3. We report x-ray crystal structures of a UbcH5B-ccRING3 complex as a fusion protein and of the ANK region. Directly tethering the N-terminal region to ccRING3 forms a minimal MIB1 protein, which is sufficient to induce a Notch response in receiver cells. Together, these studies define the functional elements of an E3 ligase needed for ligands to induce a Notch signaling response.

Notch signaling in development and homeostasis.

Notch signaling is a highly conserved signaling pathway that coordinates cellular differentiation during the development and homeostasis in numerous organs and tissues across metazoans. Activation of Notch signaling relies on direct contact between neighboring cells and mechanical pulling of the Notch receptors by the Notch ligands. Notch signaling is commonly used in developmental processes to coordinate the differentiation into distinct cell fates of neighboring cells. In this Development at a Glance article, we describe the current understanding of the Notch pathway activation and the different regulatory levels that control the pathway. We then describe several developmental processes where Notch is crucial for coordinating differentiation. These examples include processes that are largely based on lateral inhibition mechanisms giving rise to alternating patterns (e.g. SOP selection, hair cell in the inner ear and neural stem cell maintenance), as well as processes where Notch activity is oscillatory (e.g. somitogenesis and neurogenesis in mammals).

A Nesprin-4/kinesin-1 cargo model for nuclear positioning in cochlear outer hair cells.

Nuclear positioning is important for the functionality of many cell types and is mediated by interactions of cytoskeletal elements and nucleoskeleton proteins. Nesprin proteins, part of the linker of nucleoskeleton and cytoskeleton (LINC) complex, have been shown to participate in nuclear positioning in multiple cell types. Outer hair cells (OHCs) in the inner ear are specialized sensory epithelial cells that utilize somatic electromotility to amplify auditory signals in the cochlea. Recently, Nesprin-4 (encoded by Syne4) was shown to play a crucial role in nuclear positioning in OHCs. Syne4 deficiency in humans and mice leads to mislocalization of the OHC nuclei and cell death resulting in deafness. However, it is unknown how Nesprin-4 mediates the position of the nucleus, and which other molecular components are involved in this process. Here, we show that the interaction of Nesprin-4 and the microtubule motor kinesin-1 is mediated by a conserved 4 amino-acid motif. Using in vivo AAV gene delivery, we show that this interaction is critical for nuclear positioning and hearing in mice. Nuclear mislocalization and cell death of OHCs coincide with the onset of hearing and electromotility and are solely restricted to outer, but not inner, hair cells. Likewise, the C. elegans functional homolog of Nesprin-4, UNC-83, uses a similar motif to mediate interactions between migrating nuclei and kinesin-1. Overall, our results suggest that OHCs require unique cellular machinery for proper nuclear positioning at the onset of electromotility. This machinery relies on the interaction between Nesprin-4 and kinesin-1 motors supporting a microtubule cargo model for nuclear positioning.

Has Psychoanalysis Reached Its Limits in the Question of the Trans Child and Adolescent?

New medical advances and options for transitioning along with an array of gender representations have provided gender diverse children and adolescents liberating possibilities. The transitioning youth's demands for recognition and/or support for initiation of medical intervention pushes against the analyst's theories of gender and challenges conservative understanding of sexual identity, moving it closer to the multidetermined nature of dreamwork. In this article, the author traces recurrent metaphors in discussions about gender transitioning with a focus on selected articles recently published in the International Journal of Psychoanalysis, particularly an essay authored by David Bell (2020) entitled "First Do No Harm." The author focuses on three images-contagion, the naturality of gender, and amputation-to ask, what do these apparently disparate signifiers reveal about the anxieties in the field?

Adolescent Ruthlessness and the Transitioning Of The Analyst's Mind.

Features of ruthlessness may come into play in the encounter between adolescents who come into the therapeutic space with clear and precise demands to be supported through their gender transition. Winnicott's concept of ruthlessness, extended from the infant-mother matrix to the emotional situation of the clinic, allows a consideration of the conditions under which the analyst can think about adolescent demands. These conditions involve the desire of both patient and analyst for certitude and the analyst's urgency to respond, as well as the adolescent's contradictory desires to both destroy and create gender. The work of Sally Swartz, who brought to Winnicott's conception a notion of ruthlessness in protest, helps us consider the qualities of ruthlessness in constituting gender. A snippet of work with a nonbinary patient shows how questions of gender cannot be understood apart from the intersubjective transferential field. Tying ruthlessness to the enigma of desire illuminates the emotional situation of the clinical encounter between the nonbinary or trans patient and the analyst, a situation that is also libidinal. An analytic move from the question of gender identity to the realm of an emotional situation allows the analyst to meet adolescent ruthlessness. This meeting is an ethical attempt to understand the other, but also reveals one's resistance to giving up something in order to understand.

Transgender Children: From Controversy to Dialogue.

In March 2021, Hannah Wallerstein and Jordan Osserman facilitated a live dialogue over Zoom on the subject of transgender young people, with four psychoanalytic clinicians and thinkers. The conversation draws on short essays submitted in this section of The Psychoanalytic Study of the Child as a springboard for discussion. It has been transcribed and edited for length and clarity, and is reproduced here. Questions explored include the differences surrounding gender identity in childhood versus adulthood, the use of medical interventions for children experiencing gender dysphoria, the tension between psychoanalytic neutrality and affirmation, and the ethical stakes of working in this field.

From Continuity to Contiguity: A Response to the Fraught Temporality of Gender.

This paper examines current psychoanalytic engagements with the use of hormone blockers in transsexual children and the underlying premises concerning our understanding of the child's process of coming into his or her gendered self. Rather than taking sides in the debate, I explore how the "hormones question" becomes entangled in a series of misreadings and displacements through which the child's request could potentially be missed. In examining psychoanalytic conceptualizations of the trans child's agency, autonomy, and future and the relation between the natal body and gender, I ask, how is psychoanalytic discourse implicated in the very dilemmas it attempts to elucidate? Specifically, the essay examines critically the psychoanalytic use of continuity, authenticity, and alignment as implicit ideals, interrogates the focus on mourning as therapeutic horizon, and proposes that we conceive of gender as a good-enough placeholder with the potential to carry us from the ideal of continuity to an ethos of contiguity.