LNX1 and LNX2 in the central nervous system: linking behavioural, cellular and molecular perspectives

Ligand of Numb protein-X (LNX) proteins are a conserved family of E3 ubiquitin ligases with emerging roles in neuronal development and function. In the central nervous system, LNX1p70/p62 isoforms and LNX2 show dynamic expression during development, with nearly undetectable protein abundance in the adult brain, making them notoriously difficult to study. Despite their low abundance, both proteins interact with multiple synaptic components, suggesting potential roles in shaping neuronal circuits. This dissertation investigates the behavioural, cellular and molecular consequences of Lnx1p70/p62 and/or Lnx2 deletion in mice, as explored across the following chapters. Chapter 2 revealed, through an extensive behavioural analysis, that loss of both proteins contributed to decreased anxiety-related behaviour, with LNX2 having a stronger influence on impulsivity and risk-taking phenotypes. These changes are consistent with altered stress-axis regulation. In contrast, Lnx1p70/p62 deletion is involved in altered pup ultrasonic vocalisation following maternal separation and reduced body weight. To further examine the potential role of Lnx1p70/p62 in growth and early development, Chapter 3 revealed a disruption of pruning and maturation of hippocampal CA3-mossy fiber synapses in Lnx1p70 deficient mice, associated with defects in social memory establishment. Furthermore, Lnx1p70/p62 deficient mice showed a decrease in circulating IGF-1 and leptin levels, possibly explaining the reduction in body weight. Novel LNX1p70 interactions with growth-related proteins, such as GHRHR, GIPR, TRIP6 and IGF1R were also characterised. In parallel, a possible role of LNX2 in stress response was examined in Chapter 4. In cultured cortical neurons, LNX2, but not LNX1p70, was transcriptionally induced following neuronal activation, suggesting a distinct, activity-dependent function. Proteomic analyses further revealed that Lnx2 deletion resulted in region-specific alterations in cerebellar and olfactory bulb protein networks. Finally, Chapter 5 described a complementary project that identified and characterised a functional nuclear localisation signal (NLS) within both LNX1 p80 and p70 isoforms, which is absent in LNX2. This finding partially explains why LNX1 localises to the nucleus upon transfection, whereas LNX2 remains largely cytoplasmic. Bioinformatic analysis further revealed that LNX1 NLS interacts with importin alpha family members, supporting its role in regulating LNX1 nuclear translocation. Altogether, these findings revealed distinct, non-overlapping neuronal functions of LNX1p70/p62 and LNX2, linking them to behavioural phenotypes relevant to anxiety and neurodevelopmental disorders and highlighting their potential roles in neuronal activity, growth regulation, synaptic maturation and compartment-specific signalling organisation.

Grantor dc:publisher

University College Cork

Year dc:date.issued

2025

Author dc:creator

• Cioccarelli, Laura

Advisor dc:contributor.advisor

• Young, Paul

• Ligand of Numb protein-X (LNX)
• E3 ubiquitin ligase
• Anxiety
• Synaptic maturation
• Growth
• Ultrasonic vocalisation
• Nuclear localisation
• Impulsivity and risk taking
• Social memory
• Subcellular localisation
• Stress-induced gene expression

Statement dc:rights

• © 2025, Laura Cioccarelli.

Licence dc:rights.uri

• https://creativecommons.org/licenses/by-nc/4.0/

Language dc:language.iso

en

Handle dc:identifier.uri

https://hdl.handle.net/10468/18940

OAI identifier oai:identifier

oai:cora.ucc.ie:10468/18940