Paul Rack - Academia.edu (original) (raw)

Papers by Paul Rack

Mammalian spermiogenesis is a remarkable cellular transformation, during which round spermatids e... more Mammalian spermiogenesis is a remarkable cellular transformation, during which round spermatids elongate into chromatin-condensed spermatozoa. The signaling pathways that coordinate this process are poorly understood, and here we demonstrate that homeodomain-interacting protein kinase 4 (HIPK4) is required for sperm head shaping and male fertility in mice. HIPK4 is expressed in round and early elongating spermatids. Hipk4 knockout males are sterile, exhibiting phenotypes consistent with oligoasthenoteratozoospermia. Mutant sperm have reduced oocyte binding and are incompetent for in vitro fertilization, but can produce viable offspring via intracytoplasmic sperm injection. Ultrastructural analyses of HIPK4-null male germ cells reveal defects in the filamentous actin (F-actin)-scaffolded acroplaxome during spermatid elongation and abnormal head morphologies in mature spermatozoa. We further observe that HIPK4 overexpression induces branched F-actin structures in cultured fibroblasts,...

As cancer treatments have shifted toward targeted therapies, the role of developmental signaling ... more As cancer treatments have shifted toward targeted therapies, the role of developmental signaling pathways in tumorigenesis has garnered special attention. For example, the Hedgehog (Hh) pathway is required for cerebellar development, and its constitutive activation can lead to pediatric medulloblastomas. Hh signaling is normally initiated by the binding of Hh ligands (Shh, Ihh, and Dhh) to the 12TM Patched1 (Ptch1) receptor resulting in accumulation and activation of the G protein-coupled receptor-like protein Smoothened (Smo) within the primary cilium. How Smo regulates Gli transcription factor function remains unclear, but this process involves the scaffolding protein Suppressor of Fused (Sufu), which can directly inhibit the Gli proteins and facilitate their proteolytic processing into N-terminal repressors. Smo is perhaps the most “druggable” target within the Hh pathway, and Smo inhibitors have demonstrated efficacy in murine tumor models and human clinical trials. However, cer...

Nature Medicine, 2014

The application of primary organoid cultures containing epithelial and mesenchymal elements to ca... more The application of primary organoid cultures containing epithelial and mesenchymal elements to cancer modeling holds promise for combining the accurate multilineage differentiation and physiology of in vivo systems with the facile in vitro manipulation of transformed cell lines. Here, a single air-liquid interface culture method was used without modification to engineer oncogenic mutations into primary epithelial/mesenchymal organoids from mouse colon, stomach and pancreas. Pancreatic and gastric organoids exhibited dysplasia upon Kras G12D expression and/or p53 loss, and readily generated adenocarcinoma upon in vivo transplantation. In contrast, primary colon organoids required combinatorial Apc, p53, Kras G12D

Proceedings of the National Academy of Sciences, 2014

Hedgehog (Hh) pathway activation and Gli-dependent transcription play critical roles in embryonic... more Hedgehog (Hh) pathway activation and Gli-dependent transcription play critical roles in embryonic patterning, tissue homeostasis, and tumorigenesis. By conducting a genome-scale cDNA overexpression screen, we have identified the Rho GAP family member Arhgap36 as a positive regulator of the Hh pathway in vitro and in vivo. Arhgap36 acts in a Smoothened (Smo)-independent manner to inhibit Gli repressor formation and to promote the activation of full-length Gli proteins. Arhgap36 concurrently induces the accumulation of Gli proteins in the primary cilium, and its ability to induce Gli-dependent transcription requires kinesin family member 3a and intraflagellar transport protein 88, proteins that are essential for ciliogenesis. Arhgap36 also functionally and biochemically interacts with Suppressor of Fused. Transcriptional profiling further reveals that Arhgap36 is overexpressed in murine medulloblastomas that acquire resistance to chemical Smo inhibitors and that ARHGAP36 isoforms capable of Gli activation are upregulated in a subset of human medulloblastomas. Our findings reveal a new mechanism of Gli transcription factor activation and implicate ARHGAP36 dysregulation in the onset and/or progression of GLI-dependent cancers.

PLoS ONE, 2014

The Hedgehog (Hh) pathway is essential for embryonic development and tissue regeneration, and its... more The Hedgehog (Hh) pathway is essential for embryonic development and tissue regeneration, and its dysregulation can lead to birth defects and tumorigenesis. Understanding how this signaling mechanism contributes to these processes would benefit from an ability to visualize Hedgehog pathway activity in live organisms, in real time, and with single-cell resolution. We report here the generation of transgenic zebrafish lines that express nuclear-localized mCherry fluorescent protein in a Gli transcription factor-dependent manner. As demonstrated by chemical and genetic perturbations, these lines faithfully report Hedgehog pathway state in individual cells and with high detection sensitivity. They will be valuable tools for studying dynamic Gli-dependent processes in vertebrates and for identifying new chemical and genetic regulators of the Hh pathway.

Proceedings of the National Academy of Sciences, 2009

Inappropriate activation of the Hedgehog (Hh) signaling pathway has been implicated in a diverse ... more Inappropriate activation of the Hedgehog (Hh) signaling pathway has been implicated in a diverse spectrum of cancers, and its pharmacological blockade has emerged as an anti-tumor strategy. While nearly all known Hh pathway antagonists target the transmembrane protein Smoothened (Smo), small molecules that suppress downstream effectors could more comprehensively remediate Hh pathway-dependent tumors. We report here four Hh pathway antagonists that are epistatic to the nucleocytoplasmic regulator Suppressor of Fused [Su(fu)], including two that can inhibit Hh target gene expression induced by overexpression of the Gli transcription factors. Each inhibitor has a unique mechanism of action, and their phenotypes reveal that Gli processing, Gli activation, and primary cilia formation are pharmacologically targetable. We further establish the ability of certain compounds to block the proliferation of cerebellar granule neuron precursors expressing an oncogenic form of Smo, and we demonstrate that Hh pathway inhibitors can have tissue-specific activities. These antagonists therefore constitute a valuable set of chemical tools for interrogating downstream Hh signaling mechanisms and for developing chemotherapies against Hh pathway-related cancers.

Brain Research, 1998

. Ž . Application of N-methyl-D-aspartate NMDA to the supraoptic nucleus of the hypothalamus SON ... more . Ž . Application of N-methyl-D-aspartate NMDA to the supraoptic nucleus of the hypothalamus SON generates clustered firing that may be important in hormone release. However, synaptically evoked EPSPs recorded from SON neurons exhibit varying contributions from NMDA receptors. We used the high resolution of single-channel recording to examine the receptor and ion channel properties of NMDA receptors expressed by SON neurons in 'punch' culture. Biocytin introduced into individual neurons during patch clamp Ž . Ž . recording revealed large 32.1 " 3.3 mm , oblong somas and bipolar extensions typical of magnocellular neuroendocrine cells MNCs .