The embryonic trunk neural crest microenvironment regulates the plasticity and invasion of human neuroblastoma via TrkB signaling.

Mistakes in trunk neural crest (NC) cell migration may lead to birth defects of the sympathetic nervous system (SNS) and neuroblastoma (NB) cancer. Receptor tyrosine kinase B (TrkB) and its ligand BDNF critically regulate NC cell migration during normal SNS development and elevated expression of TrkB is correlated with high-risk NB patients. However, in the absence of a model with in vivo interrogation of human NB cell and gene expression dynamics, the mechanistic role of TrkB in NB disease progression remains unclear. Here, we study the functional relationship between TrkB, cell invasion and plasticity of human NB cells by taking advantage of our validated in vivo chick embryo transplant model. We find that LAN5 (high TrkB) and SHSY5Y (moderate TrkB) human NB cells aggressively invade host embryos and populate typical NC targets, however loss of TrkB function significantly reduces cell invasion. In contrast, NB1643 (low TrkB) cells remain near the transplant site, but over-expression of TrkB leads to significant cell invasion. Invasive NB cells show enhanced expression of genes indicative of the most invasive host NC cells. In contrast, transplanted human NB cells down-regulate known NB tumor initiating and stem cell markers. Human NB cells that remain within the dorsal neural tube transplant also show enhanced expression of cell differentiation genes, resulting in an improved disease outcome as predicted by a computational algorithm. These in vivo data support TrkB as an important biomarker and target to control NB aggressiveness and identify the chick embryonic trunk neural crest microenvironment as a source of signals to drive NB to a less aggressive state, likely acting at the dorsal neural tube.

The Frequency and Outcomes of Nerve Palsies in Operatively Treated Supracondylar Humerus Fractures.

BACKGROUND: A high index of suspicion for nerve palsy is essential in the setting of a displaced supracondylar humerus fracture (SCHF) with careful attention to the examination. We hypothesize that nerve injuries are more prevalent in higher energy type III and flexion SCHFs compared with type II fractures. METHODS: A retrospective review was performed of 1085 operatively treated SCHFs in pediatric patients, aged 0 to 14 years, between January 1, 2015 and December 31, 2018. There were 979 patients eligible for analysis. Exclusion criteria included follow-up <3 weeks, polytrauma, pathologic fracture, and prior fracture of the ipsilateral elbow. RESULTS: The overall rate of nerve injury was 10.6% (104/979). A significant difference in the rate of nerve palsy was identified between fracture types: 0.9% type II, 19.3% type III, and 10.7% flexion type SCHFs ( P <0.001). Median nerve palsy was the most common (n=65). An increased rate of ulnar nerve palsy was observed in flexion type SCHFs. The rate of nerve palsy was higher in the medial pin group (14.9%, P =0.035) but no significant association with iatrogenic ulnar nerve palsy was present. In type III and flexion SCHFs, operative time >60 minutes ( P =0.023) and the need for open reduction ( P =0.012) were significantly associated with postoperative nerve palsy. Referral to therapy was required in 30.8% of patients with a nerve palsy compared with 7.9% of patients without ( P <0.001). CONCLUSION: Longer operative times, need for open reduction, and significantly higher rates of nerve palsy among type III and flexion SCHFs are best explained by the unstable nature of the fracture and greater degree of soft tissue trauma. Given prolonged duration of follow-up and more frequent need for therapy demonstrated in patients with a nerve palsy, these data can be used to improve counseling for families and patients after displaced SCHF. LEVEL OF EVIDENCE: Level III-retrospective comparative study.

Visual and circadian regulation of Drosophila BDBT and BDBT effects on DBT and PER localization.

BRIDE OF DOUBLETIME (BDBT) interacts with the circadian kinase DOUBLETIME (DBT) and accumulates in eye foci during the dark of a light:dark cycle. BDBT foci are shown here to be broadly expressed in constant dark and low in constant light. Analysis of circadian photoreceptor cry and visual photoreceptor ninaE mutants showed that disappearance of eye BDBT foci requires both the CRYPTOCHROME and the RHODOPSIN-1 pathways. The arr1 and arr2 mutants, which affect rhodopsin quenching, eliminated BDBT foci under dark conditions. arr1 and arr2 mutants also caused increased nuclear PER protein. The changes in BDBT foci do not result from altered BDBT levels in the eye but from changes in its immunodetection. Knockdown of BDBT specifically in the eye produced constitutively nuclear PER and constitutively cytosolic DBT. The results show that BDBT is necessary for co-transport of DBT and PER into the nucleus and suggest that this process is regulated by a light-dependent mechanism.