A novel categorization of the muscular branches of the tibial nerve within the popliteal fossa.

BACKGROUND: The muscular branches of the tibial nerve within the popliteal fossa innervate the gastrocnemius, soleus, plantaris, and popliteus muscles. Various branching patterns have been described in textbooks; however, the underlying fundamental rules explaining the patterns remain unclear. Understanding the fundamental rule explaining the branching pattern of the innervating nerves is essential for understanding the ontogeny of skeletal muscles. Therefore, this study aimed at establishing a theory to explain the branching pattern of the muscular branches of the tibial nerve within the popliteal fossa. METHODS: The branching patterns of the muscular branches of the tibial nerve within the popliteal fossa were examined macroscopically in 62 lower limbs derived from 31 adult cadavers (22 males and 9 females, aged 49-95 years). RESULTS: The branch to the medial head of the gastrocnemius muscle invariably arose from the posteromedial side of the tibial nerve. The branches to the soleus muscle and lateral head of the gastrocnemius muscle had a common trunk in all the lower limbs and invariably arose from the posterolateral side. The branches to the plantaris and popliteus muscles arose anteriorly from the tibial nerve in this order (plantaris branch first, followed by the popliteus branch). These branches invariably arose more distally than the branch to both the heads of the gastrocnemius and soleus muscles. CONCLUSIONS: Based on these fundamental branching patterns, we suggest a novel branching categorization. The branches could be categorized into a posterior group and an anterior group, which has independent branches to the plantaris and popliteus muscles. This fundamental branching pattern and novel categorization contribute to the understanding of the ontogeny of the skeletal muscles around the flexor compartment of the leg.

A bilateral third head of the gastrocnemius which is morphologically similar to the plantaris.

PURPOSE: An extra muscle was observed on both sides of the popliteal fossa in the cadaver of a 78-year-old Japanese male during dissection. The aim of this case report was to identify whether this variant is a double plantaris or a third head of the gastrocnemius according to its morphological characteristics and innervation. METHODS: The muscles were displayed by careful dissection and delineation of surrounding structures. The size of each of the muscle bellies and tendons of those extra muscles were measured manually by the vernier caliper. RESULTS: The origin of each extra muscle was lateral to the tibial nerve and superior to the plantaris, and each extra muscle which transitioned to a descending tendon parallel to the plantaris had a cone-shaped belly. However, the tendon of the extra muscles was fused into the investing fascia of the gastrocnemius with a tendon length of 4.5 cm on the left and 4.6 cm on the right. The extra muscles were innervated by the branch of the tibial nerve to the medial head of the gastrocnemius on both sides. CONCLUSION: Although they had an origin and shape similar to that of the plantaris, we identified the extra muscles in this case as a third head of the gastrocnemius, because of innervation to the plantaris arises directly from the tibial nerve. This case highlighted that the innervation is essential to understanding the myogenesis of extra muscles, especially in cases which are difficult to categorize based on the morphological features of the muscle.

SCYL1 arginine methylation by PRMT1 is essential for neurite outgrowth via Golgi morphogenesis.

Arginine methylation is a common posttranslational modification that modulates protein function. SCY1-like pseudokinase 1 (SCYL1) is crucial for neuronal functions and interacts with γ2-COP to form coat protein complex I (COPI) vesicles that regulate Golgi morphology. However, the molecular mechanism by which SCYL1 is regulated remains unclear. Here, we report that the γ2-COP-binding site of SCYL1 is arginine-methylated by protein arginine methyltransferase 1 (PRMT1) and that SCYL1 arginine methylation is important for the interaction of SCYL1 with γ2-COP. PRMT1 was colocalized with SCYL1 in the Golgi fraction. Inhibition of PRMT1 suppressed axon outgrowth and dendrite complexity via abnormal Golgi morphology. Knockdown of SCYL1 by small interfering RNA (siRNA) inhibited axon outgrowth, and the inhibitory effect was rescued by siRNA-resistant SCYL1, but not SCYL1 mutant, in which the arginine methylation site was replaced. Thus, PRMT1 regulates Golgi morphogenesis via SCYL1 arginine methylation. We propose that SCYL1 arginine methylation by PRMT1 contributes to axon and dendrite morphogenesis in neurons.

Temporal expression profiling of DAMPs-related genes revealed the biphasic post-ischemic inflammation in the experimental stroke model.

The neuroinflammation in the ischemic brain could occur as sterile inflammation in response to damage-associated molecular patterns (DAMPs). However, its long-term dynamic transcriptional changes remain poorly understood. It is also unknown whether this neuroinflammation contributes to the recovery or just deteriorates the outcome. The purpose of this study is to characterize the temporal transcriptional changes in the post-stroke brain focusing on DAMPs-related genes by RNA-sequencing during the period of 28 days. We conducted the RNA-sequencing on day 1, 3, 7, 14, 28 post-stroke in the mouse photothrombosis model. The gross morphological observation showed the ischemic lesion on the ipsilateral cortex turned into a scar with the clearance of cellular debris by day 28. The transcriptome analyses indicated that post-stroke period of 28 days was classified into four categories (I Baseline, II Acute, III Sub-acute-#1, IV Sub-acute-#2 phase). During this period, the well-known genes for DAMPs, receptors, downstream cascades, pro-inflammatory cytokines, and phagocytosis were transcriptionally increased. The gene ontology (GO) analysis of biological process indicated that differentially expressed genes (DEGs) are genetically programmed to achieve immune and inflammatory pathways. Interestingly, we found the biphasic induction of various genes, including DAMPs and pro-inflammatory factors, peaking at acute and sub-acute phases. At the sub-acute phase, we also observed the induction of genes for phagocytosis as well as regulatory and growth factors. Further, we found the activation of CREB (cAMP-response element binding protein), one of the key players for neuronal plasticity, in peri-ischemic neurons by immunohistochemistry at this phase. Taken together, these findings raise the possibility the recurrent inflammation occurs at the sub-acute phase in the post-stroke brain, which could be involved in the debris clearance as well as neural reorganization.

PRMT3 is essential for dendritic spine maturation in rat hippocampal neurons.

Protein arginine N-methyltransferase 3 (PRMT3) is a cytoplasmic enzyme that utilizes S-adenosyl-L-methionine (AdoMet) to methylate specific proteins, most of which contain GAR (glycine-arginine rich) motifs. PRMT3 has been shown to play a role in the proper maturation of the 80S ribosome by binding to and catalyzing the methylation of rpS2, a component of the 40S ribosomal subunit. However, the other roles of PRMT3 are fairly unclear, particularly in the brain, which is abundant in methylated proteins. In this study, we perturbed PRMT3 expression in cultured rat hippocampal neurons by transiently introducing siRNA oligonucleotides that were designed to hybridize with PRMT3 mRNA and then we examined the morphological and functional effects of neuronal PRMT3 depletion. PRMT3-defective neurons showed deformed spines without any change in spine number; less BDNF-induced protein translation of alphaCaMKII; and diminished rpS2 protein stability. Furthermore, overexpression of a methylation-resistant rpS2, whose methylated arginine residues were deleted, produced phenotypes that were similar to those associated with PRMT3 downregulation. These findings demonstrated that PRMT3 possibly plays a pivotal role in neuronal translation by interaction with rpS2 and that it contributes to activity-dependent changes in the dendritic spines.

PRMT1 and Btg2 regulates neurite outgrowth of Neuro2a cells.

Neurite outgrowth is one of the crucial events in the formation of neural circuits. The majority of studies on neurite outgrowth have focused on signal transduction processes based on phosphorylation and acetylation; a few studies have suggested the involvement of other molecular mechanisms. Recent progress in understanding the nature of protein arginine N-methyltransferases (PRMTs) raises the possibility of the involvement of protein methylation accompanied by cell shape changes during neuronal differentiation. Here, we show that PRMT1 play a pivotal role in the neurite outgrowth of Neuro2a cells. Our results revealed that PRMT1 depletion specifically affected neurite outgrowth but not the physiological processes involved in cell growth and differentiation. Furthermore, we demonstrated that Btg2, one of the PRMT1 binding partner, depletion down-regulated arginine methylation in the nucleus and inhibited neurite outgrowth. These results indicate that protein arginine methylation by PRMT1 in the nucleus is an important step in neuritogenesis.

Mouse Prickle1 and Prickle2 are expressed in postmitotic neurons and promote neurite outgrowth.

The Drosophila planar cell polarity (PCP) gene prickle has been previously indicated as one of the regulators of gastrulation in the early embryonic stage. However, the functional role of prickle in the brain in particular is not known. We first indicated that mouse Prickle1 and Prickle2 are continually expressed in the brain throughout the embryonic stages and are observed to be specifically expressed in the postmitotic neurons. Furthermore, Prickle1 or Prickle2 depletion effectively decreases the neurite outgrowth levels of mouse neuroblastoma Neuro2a cells. These results indicate that mouse Prickle1 and Prickle2 possibly regulate positive neurite formation during brain development.

Specific regional distribution of protein arginine methyltransferase 8 (PRMT8) in the mouse brain.

The regional distribution of PRMT8 transcript was examined in mouse brain using in situ hybridization (ISH) histochemistry. The PRMT8 cRNA probe was specifically hybridized with CNS and the signals were observed only in the neurons. The distribution of the neurons expressing PRMT8 mRNA was not even throughout the brain. All of the regions related to general somatosensory system expressed PRMT8 mRNA strongly. Most of the relay nuclei intervening the special somatosensory system, such as the auditory, visual, and vestibular systems, were packed with PRMT8 mRNA expressing neurons. Forebrain limbic areas and thalamic nuclei relevant to limbic areas were also strongly labeled with the probe. Some areas related to the motor system, such as the caudate putamen, Purkinje cells, inferior olivary nucleus and cerebellar nuclei expressed PRMT8 mRNA strongly. These findings suggest that PRMT8 is chiefly involved in the somatosensory and limbic systems, and a part of motor system.

CARM1 regulates proliferation of PC12 cells by methylating HuD.

HuD is an RNA-binding protein that has been shown to induce neuronal differentiation by stabilizing labile mRNAs carrying AU-rich instability elements. Here, we show a novel mechanism of arginine methylation of HuD by coactivator-associated arginine methyltransferase 1 (CARM1) that affected mRNA turnover of p21cip1/waf1 mRNA in PC12 cells. CARM1 specifically methylated HuD in vitro and in vivo and colocalized with HuD in the cytoplasm. Inhibition of HuD methylation by CARM1 knockdown elongated the p21cip1/waf1 mRNA half-life and resulted in a slow growth rate and robust neuritogenesis in response to nerve growth factor (NGF). Methylation-resistant HuD bound more p21cip1/waf1 mRNA than did the wild type, and its overexpression upregulated p21cip1/waf1 protein expression. These results suggested that CARM1-methylated HuD maintains PC12 cells in the proliferative state by committing p21cip1/waf1 mRNA to its decay system. Since the methylated population of HuD was reduced in NGF-treated PC12 cells, downregulation of HuD methylation is a possible pathway through which NGF induces differentiation of PC12 cells.

Local protein synthesis by BDNF is potentiated in hippocampal neurons exposed to ephrins.

Local protein synthesis in neuronal dendrites is one of the mechanisms that may mediate a rapid and synapse-specific mobilization of proteins from the resident mRNAs. A great deal of effort has been made in analyzing the dynamic state of protein synthesis in the living cells chiefly by quantifying protein level. However, the protein level cannot mirror the spatiotemporal alteration of translation because it can be affected, not only by protein synthesis, but also by other factors, like degradation. Therefore, it is problematic to visualize the dynamic state of translation by the present methods. To solve the problem, we applied fluorescence resonance energy transfer (FRET) technique to in situ detection of the assembly and disassembly cycle among a pair of translation initiation factors [eukaryotic initiation factors (eIFs)], thereby showing that BDNF and ephrin could potentiate local protein synthesis in the dendrites of hippocampal neurons.