Abstract We engineered surfaces that permit the adhesion and directed growth of neuronal cell processes but that prevent the adhesion of astrocytes. This effect was achieved based on the spatial ...distribution of sub-micron-sized cell-repulsive poly(ethylene glycol) PEG hydrogels patterned on an otherwise cell-adhesive substrate. Patterns were identified that promoted cellular responses ranging from complete non-attachment, selective attachment, and directed growth at both cellular and subcellular length scales. At the highest patterning density where the individual hydrogels almost overlapped, there was no cellular adhesion. As the spacing between individual hydrogels was increased, patterns were identified where neurites could grow on the adhesive surface between hydrogels while astrocytes were unable to adhere. Patterns such as lines or arrays were identified that could direct the growth of these subcellular neuronal processes. At higher hydrogel spacings, both neurons and astrocytes adhered and grew in a manner approaching that of unpatterned control surfaces. Patterned lines could once again direct growth at cellular length scales. Significantly, we have demonstrated that the patterning of sub-micron/nano scale cell-repulsive features at microscale lengths on an otherwise cell-adhesive surface can differently control the adhesion and growth of cells and cell processes based on the difference in their characteristic sizes. This concept could potentially be applied to an implantable nerve-guidance device that would selectively enable regrowing axons to bridge a spinal-cord injury without interference from the glial scar.
•DARPA's programs foster multi-disciplinary collaborations.•DARPA's BCI programs span four major challenges: detect, emulate, restore, & improve.•Aims: restore function after injury; improve ...performance of healthy individuals.
The Defense Advanced Research Projects Agency (DARPA) has funded innovative scientific research and technology developments in the field of brain–computer interfaces (BCI) since the 1970s. This review highlights some of DARPA's major advances in the field of BCI, particularly those made in recent years. Two broad categories of DARPA programs are presented with respect to the ultimate goals of supporting the nation's warfighters: (1) BCI efforts aimed at restoring neural and/or behavioral function, and (2) BCI efforts aimed at improving human training and performance. The programs discussed are synergistic and complementary to one another, and, moreover, promote interdisciplinary collaborations among researchers, engineers, and clinicians. Finally, this review includes a summary of some of the remaining challenges for the field of BCI, as well as the goals of new DARPA efforts in this domain.
Chondroitin sulfate proteoglycans (CSPGs) are upregulated in the CNS after injury and participate in the inhibition of axon regeneration mainly through their glycosaminoglycan (GAG) side chains. In ...the present study, we have identified a new way to alleviate the inhibition of axonal regeneration by CSPG GAGs. We have successfully decreased the amount of CSPG GAG produced by astrocytes by targeting chondroitin polymerizing factor (ChPF), a key enzyme in the CSPG biosynthetic pathway. Using short interfering RNA (siRNA), we reduced ChPF mRNA levels by 70% in both the Neu7 astrocyte cell line and primary rat astrocytes. This reduction leads to a decrease in ChPF protein levels and a reduced amount of CSPG GAG chains in the conditioned media (CM) of these cells. Secretion of neurocan by primary astrocytes and NG2 core protein by Neu7 cells transfected with ChPF siRNA is not decreased, suggesting that inhibiting GAG chain synthesis does not affect core protein trafficking from these cells. CM from siRNA-treated Neu7 cells is a less repulsive substrate for axons than CM from control cells. In addition, axonal outgrowth from cerebellar granule neurons is increased on or in CM from ChPF siRNA-treated Neu7 cells. These data indicate that targeting the biosynthesis of CSPG GAG is a potentially new therapeutic avenue for decreasing CSPG GAG produced by astrocytes after CNS injury.
Saccharomyces cerevisiae cells reproduce by budding to yield a mother cell and a smaller daughter cell. Although both mother and daughter begin G1simultaneously, the mother cell progresses through ...G1more rapidly. Daughter cell G1delay has long been thought to be due to a requirement for attaining a certain critical cell size before passing the commitment point in the cell cycle known as START. We present an alternative model in which the daughter cell-specific Ace2 transcription factor delays G1in daughter cells. Deletion of ACE2 produces daughter cells that proceed through G1at the same rate as mother cells, whereas a mutant Ace2 protein that is not restricted to daughter cells delays G1equally in both mothers and daughters. The differential in G1length between mothers and daughters requires the Cln3 G1cyclin, and CLN3-GFP reporter expression is reduced in daughters in an ACE2-dependent manner. Specific daughter delay elements in the CLN3 promoter are required for normal daughter G1delay, and these elements bind to an unidentified 127-kDa protein. This DNA-binding activity is enhanced by deletion of ACE2. These results support a model in which daughter cell G1delay is determined not by cell size but by an intrinsic property of the daughter cell generated by asymmetric cell division.
Saccharomyces cerevisiae
cells reproduce by budding to yield a
mother cell and a smaller daughter cell. Although both mother and daughter
begin G
1
simultaneously, the mother cell progresses through
...G
1
more rapidly. Daughter cell G
1
delay has long been
thought to be due to a requirement for attaining a certain critical cell size
before passing the commitment point in the cell cycle known as START. We
present an alternative model in which the daughter cell-specific Ace2
transcription factor delays G
1
in daughter cells. Deletion of
ACE2
produces daughter cells that proceed through G
1
at
the same rate as mother cells, whereas a mutant Ace2 protein that is not
restricted to daughter cells delays G
1
equally in both mothers and
daughters. The differential in G
1
length between mothers and
daughters requires the Cln3 G
1
cyclin, and
CLN3
-GFP
reporter expression is reduced in daughters in an
ACE2
-dependent
manner. Specific daughter delay elements in the
CLN3
promoter are
required for normal daughter G
1
delay, and these elements bind to
an unidentified 127-kDa protein. This DNA-binding activity is enhanced by
deletion of
ACE2
. These results support a model in which daughter
cell G
1
delay is determined not by cell size but by an intrinsic
property of the daughter cell generated by asymmetric cell division.
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