Molecular genetics

The main interest of the laboratory is to understand how the "hub" protein Dynein light chain (DYNLL1) that regulates the functions of more than one-hundred other proteins contributes to normal development and the onset of disease, including cancer.

Research Overview

DYNLL1 was first identified as a light chain of the Dynein motor complexes that move cargos along the microtubule network towards the cell center. However, it has become clear that beyond Dyneins, DYNLL1 is also a subunit of more than 100 other oligomeric protein complexes with diverse biological functions. In these complexes, DYNLL1 generally seems to act as a sequence-specific chaperone that promotes the ordered dimerisation of its interaction partners. We discovered a transcription factor, ASCIZ, that plays a key role in the regulation of DYNLL1's wide-ranging functions. ASCIZ is essential for activation of DYNLL1 gene expression but also contains a dozen DYNLL1 binding sites throughout its transcription activation domain, which enable it to "count" and adjust DYNLL1 protein levels to cellular needs. We are studying how this evolutionary highly conserved ASCIZ-DYNLL1 axis regulates normal cellular processes and how it contributes to disease mechanisms using mouse in vivo models and a range of cell-based assay systems.

Research Themes

Roles of ASCIZ and DYNLL1 in B cell development and antibody production

We have shown that ASCIZ and DYNLL1 are required for normal B cell development in mice, and also for the optimisation of antibody genes during the immune response of mature B cells. A main target of the ASCIZ-DYNLL1 axis during development is the cell death protein BIM whose activity is dampened directly by DYNLL1 binding. In mature B cells, and to some extent also in developing B cells, DYNLL1 promotes the oligomerisation of the key DNA repair protein 53BP1 which regulates the efficiency of antibody gene diversification by the non-homologous end-joining pathway. We recently found that the ASCIZ-DYNLL1 axis also plays a key role in regulating the activation of mature B cells in a highly signal-specific manner, and we are currently determining the underlying cellular mechanisms and their impact on antibody-mediated immune responses in mice.

Differential roles of ASCIZ and DYNLL1 in cilia signaling and organ development

In line with its original identification as a light chain of various Dynein complexes, we found that loss of DYNLL1 destabilizes the Dynein-2 complex that is specifically involved in the retrograde transport of signaling components from a small antenna-like structure, the primary cilium, present on most non-haematopoietic cells. Consequently, targeted removal of the Dynll1 gene in the limbs of developing mice mimics the severe bone shortening characteristic of a life-threatening human disorder with inherited Dynein-2 subunit mutations, Short-rib thoracic dystrophy/Jeune syndrome. In contrast to mice that completely lack DYNLL1, ASCIZ-deleted mice – which still contain about 10% of normal DYNLL1 protein levels – have almost normal bones, indicating that even very low residual DYNLL1 levels are sufficient for largely normal Dynein-2 complex activity. Our bone-specific DYNLL1-deleted mice currently represent the only viable animal model for Jeune syndrome, and provide a valuable tool for the exploration of potential therapeutic approaches.

Roles of the ASCIZ-DYNLL1 axis in DNA damage responses and cancer

One of the best-known targets of DYNLL1 is 53BP1, which plays a key role in directing the repair of DNA double-strand breaks towards the mutagenic non-homologous end-joining pathway and in this way promotes the therapeutic response of BRCA1-mutated breast and ovarian cancers to PARP inhibitors. Consequently, ASCIZ and DYNLL1 have recently also been identified as mediators of PARP inhibitor sensitivity in several functional genetic screens, consistent with their supportive role in 53BP1-mediated antibody gene rearrangements in B cells (see our other Research Theme). We have previously shown that ASCIZ also has a separate role as a DNA damage response factor that depends on DYNLL1 but is independent of its function as a transcription factor. Ongoing work in the laboratory investigates how these two roles of ASCIZ cooperate in the onset of cancer development in mice, and in the response of established cancer cells to chemotherapeutics.

Student Projects

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Publication Highlights

  1. Mcnees CJ, Conlan LA, Tenis N & Heierhorst J (2005).  ASCIZ regulates lesion-specific RAD51 focus formation and apoptosis after methylating DNA damage.  EMBO J. 24, 2447-2457.
  2. Jurado S, Smyth I, Van Denderen B, Tenis N, Hammet A, Hewiitt K, Ng JL, Mcnees CJ, Kozlov SV, Oka H, Kobayashi M, Conlan LA, Cole TC, Yamamoto K, Taniguchi Y, Takeda S, Lavin MF & Heierhorst J (2010).  Dual functions of ASCIZ in the DNA base damage response and pulmonary organogenesis.  PLOS Genetics 6, e1001170. 
  3. Jurado S, Conlan LA, Baker EK, Ng JL, Tenis N, Hoch NC, Gleeson K, Smeets M, Izon D & Heierhorst J (2012). ATM substrate Chk2-interacting Zn2+-finger (ASCIZ) is a bi-functional transcriptional activator and feedback sensor of dynein light chain (DYNLL1) expression. J. Biol. Chem.  287, 3156-3164.
  4. Jurado S, Gleeson K, O'Donnell K, Izon DJ, Walkley CR, Strasser A, Tarlinton DM & Heierhorst J (2012).  The Zinc-finger protein ASCIZ regulates B cell development via DYNLL1 and Bim.  J. Exp. Med. 209, 1629-1639.
  5. Zaytseva O, Tenis N, Mitchell N, Kanno SI, Yasui A, Heierhorst J* & Quinn LM (2014).  The novel zinc finger protein dasciz regulates mitosis in Drosophila via an essential role in dynein light chain expression.  Genetics 196, 443-453. (*co-senior author)
  6. Wong DM, Li L, Jurado S, King A, Bamford R, Wall M, Walia MK, Kelly GL, Walkley KR, Tarlinton DM, Strasser A & Heierhorst J (2016).  The transcription factor ASCIZ and its target DYNLL1 are essential for the development and expansion of MYC-driven B cell lymphoma. Cell Reports 14, 1488-1499.
  7. Liu R, King A, Hoch NC, Chang C, Kelly GL, Deans AJ & Heierhorst J (2017). ASCIZ/ATMIN is dispensable for ATM signalling in response to replication stress. DNA Repair 57, 29-34.
  8. King A, Li L, Wong DM, Liu R, Bamford R, Strasser A, Tarlinton DM & Heierhorst J (2017). Dynein light chain regulates adaptive and innate B cell development by distinctive genetic mechanisms. PLOS Genetics 13, e1007010.
  9. Clark SA, Myers JB, King A, Fiala R, Novacek J, Pearce G, Heierhorst J, Reichow SL, Barbar E (2018). Multivalency regulates activity in an intrinsically disordered transcription factor. Elife 7, e36258.
  10. Becker JR, Cuella-Martin R, Barazas M, Liu R, Oliveira C, Oliver AW, Bilham K, Holt AB, Blackford AN, Heierhorst J, Jonkers J, Rottenberg S & Chapman JR (2018). The ASCIZ-DYNLL1 axis promotes 53BP1-dependent non-homologous end joining and PARP inhibitor sensitivity. Nature Commun. 9, 5406.