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Novel dendritic kinesin sorting identified by different process targeting of two related kinesins: KIF21A and KIF21B.

Marszalek JR, Weiner JA, Farlow SJ, Chun J, Goldstein LS - J. Cell Biol. (1999)

Bottom Line: KIF21A protein is localized throughout neurons, while KIF21B protein is highly enriched in dendrites.The plus end-directed motor activity of KIF21B and its enrichment in dendrites indicate that models suggesting that minus end-directed motor activity is sufficient for dendrite specific motor localization are inadequate.We suggest that a novel kinesin sorting mechanism is used by neurons to localize KIF21B protein to dendrites since its mRNA is restricted to the cell body.

View Article: PubMed Central - PubMed

Affiliation: Biomedical Sciences Graduate Program, Division of Cellular and Molecular Medicine, Department of Pharmacology, University of California San Diego, La Jolla, California 92093-0683, USA.

ABSTRACT
Neurons use kinesin and dynein microtubule-dependent motor proteins to transport essential cellular components along axonal and dendritic microtubules. In a search for new kinesin-like proteins, we identified two neuronally enriched mouse kinesins that provide insight into a unique intracellular kinesin targeting mechanism in neurons. KIF21A and KIF21B share colinear amino acid similarity to each other, but not to any previously identified kinesins outside of the motor domain. Each protein also contains a domain of seven WD-40 repeats, which may be involved in binding to cargoes. Despite the amino acid sequence similarity between KIF21A and KIF21B, these proteins localize differently to dendrites and axons. KIF21A protein is localized throughout neurons, while KIF21B protein is highly enriched in dendrites. The plus end-directed motor activity of KIF21B and its enrichment in dendrites indicate that models suggesting that minus end-directed motor activity is sufficient for dendrite specific motor localization are inadequate. We suggest that a novel kinesin sorting mechanism is used by neurons to localize KIF21B protein to dendrites since its mRNA is restricted to the cell body.

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KIF21A protein localizes to axons and dendrites while KIF21B protein is detected in dendrites but not axons. (A and B) Double staining of the spinal cord ventral horn for KIF21A and MAP2. Note the high degree of overlap of staining (arrowheads). (C and D)  Double staining of the spinal cord ventral horn for KIF21B and MAP2. Note that most MAP2 positive processes also stain for KIF21B.  (E and F) Ventral horn stained for KIF21A and pNF-H protein. (G) Merge of E and F. Note that many pNF-H positive axons are also  positive for KIF21A (yellow signal and arrows). (H and I) Ventral horn stained for KIF21B and pNF-H protein. (J) Merge of H and I.  Note that pNF-H positive processes do not stain for KIF21B (arrows). Bar, 100 μm.
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Figure 6: KIF21A protein localizes to axons and dendrites while KIF21B protein is detected in dendrites but not axons. (A and B) Double staining of the spinal cord ventral horn for KIF21A and MAP2. Note the high degree of overlap of staining (arrowheads). (C and D) Double staining of the spinal cord ventral horn for KIF21B and MAP2. Note that most MAP2 positive processes also stain for KIF21B. (E and F) Ventral horn stained for KIF21A and pNF-H protein. (G) Merge of E and F. Note that many pNF-H positive axons are also positive for KIF21A (yellow signal and arrows). (H and I) Ventral horn stained for KIF21B and pNF-H protein. (J) Merge of H and I. Note that pNF-H positive processes do not stain for KIF21B (arrows). Bar, 100 μm.

Mentions: To determine whether KIF21A or KIF21B protein is present in axons and/or dendrites, the spinal cord was double immunostained for each KIF21 protein and either phosphorylated neurofilament H (pNF-H), an axonal marker (Sternberger and Sternberger, 1983), or MAP2, a dendrite specific marker (Bernhardt and Matus, 1984). KIF21A protein colocalized with pNF-H and MAP2 positive processes, indicating KIF21A presence in dendrites (Fig. 6, A and B, arrowheads) and axons (Fig. 6, E–G, arrows). KIF21B protein only colocalized with MAP2 positive processes (Fig. 6, C and D, arrowheads), but not with most pNF-H positive processes (Fig. 6, H–J, arrows), indicating that KIF21B protein is primarily a somatodendritic protein that is highly enriched within dendrites. This localization pattern is consistent with the protein level observed by protein immunoblotting (i.e., absence from the sciatic nerve; Fig. 3 C), and the low levels of accumulation observed in a sciatic nerve ligation experiment (data not shown).


Novel dendritic kinesin sorting identified by different process targeting of two related kinesins: KIF21A and KIF21B.

Marszalek JR, Weiner JA, Farlow SJ, Chun J, Goldstein LS - J. Cell Biol. (1999)

KIF21A protein localizes to axons and dendrites while KIF21B protein is detected in dendrites but not axons. (A and B) Double staining of the spinal cord ventral horn for KIF21A and MAP2. Note the high degree of overlap of staining (arrowheads). (C and D)  Double staining of the spinal cord ventral horn for KIF21B and MAP2. Note that most MAP2 positive processes also stain for KIF21B.  (E and F) Ventral horn stained for KIF21A and pNF-H protein. (G) Merge of E and F. Note that many pNF-H positive axons are also  positive for KIF21A (yellow signal and arrows). (H and I) Ventral horn stained for KIF21B and pNF-H protein. (J) Merge of H and I.  Note that pNF-H positive processes do not stain for KIF21B (arrows). Bar, 100 μm.
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Figure 6: KIF21A protein localizes to axons and dendrites while KIF21B protein is detected in dendrites but not axons. (A and B) Double staining of the spinal cord ventral horn for KIF21A and MAP2. Note the high degree of overlap of staining (arrowheads). (C and D) Double staining of the spinal cord ventral horn for KIF21B and MAP2. Note that most MAP2 positive processes also stain for KIF21B. (E and F) Ventral horn stained for KIF21A and pNF-H protein. (G) Merge of E and F. Note that many pNF-H positive axons are also positive for KIF21A (yellow signal and arrows). (H and I) Ventral horn stained for KIF21B and pNF-H protein. (J) Merge of H and I. Note that pNF-H positive processes do not stain for KIF21B (arrows). Bar, 100 μm.
Mentions: To determine whether KIF21A or KIF21B protein is present in axons and/or dendrites, the spinal cord was double immunostained for each KIF21 protein and either phosphorylated neurofilament H (pNF-H), an axonal marker (Sternberger and Sternberger, 1983), or MAP2, a dendrite specific marker (Bernhardt and Matus, 1984). KIF21A protein colocalized with pNF-H and MAP2 positive processes, indicating KIF21A presence in dendrites (Fig. 6, A and B, arrowheads) and axons (Fig. 6, E–G, arrows). KIF21B protein only colocalized with MAP2 positive processes (Fig. 6, C and D, arrowheads), but not with most pNF-H positive processes (Fig. 6, H–J, arrows), indicating that KIF21B protein is primarily a somatodendritic protein that is highly enriched within dendrites. This localization pattern is consistent with the protein level observed by protein immunoblotting (i.e., absence from the sciatic nerve; Fig. 3 C), and the low levels of accumulation observed in a sciatic nerve ligation experiment (data not shown).

Bottom Line: KIF21A protein is localized throughout neurons, while KIF21B protein is highly enriched in dendrites.The plus end-directed motor activity of KIF21B and its enrichment in dendrites indicate that models suggesting that minus end-directed motor activity is sufficient for dendrite specific motor localization are inadequate.We suggest that a novel kinesin sorting mechanism is used by neurons to localize KIF21B protein to dendrites since its mRNA is restricted to the cell body.

View Article: PubMed Central - PubMed

Affiliation: Biomedical Sciences Graduate Program, Division of Cellular and Molecular Medicine, Department of Pharmacology, University of California San Diego, La Jolla, California 92093-0683, USA.

ABSTRACT
Neurons use kinesin and dynein microtubule-dependent motor proteins to transport essential cellular components along axonal and dendritic microtubules. In a search for new kinesin-like proteins, we identified two neuronally enriched mouse kinesins that provide insight into a unique intracellular kinesin targeting mechanism in neurons. KIF21A and KIF21B share colinear amino acid similarity to each other, but not to any previously identified kinesins outside of the motor domain. Each protein also contains a domain of seven WD-40 repeats, which may be involved in binding to cargoes. Despite the amino acid sequence similarity between KIF21A and KIF21B, these proteins localize differently to dendrites and axons. KIF21A protein is localized throughout neurons, while KIF21B protein is highly enriched in dendrites. The plus end-directed motor activity of KIF21B and its enrichment in dendrites indicate that models suggesting that minus end-directed motor activity is sufficient for dendrite specific motor localization are inadequate. We suggest that a novel kinesin sorting mechanism is used by neurons to localize KIF21B protein to dendrites since its mRNA is restricted to the cell body.

Show MeSH
Related in: MedlinePlus