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Glossary Inner Root Sheath

layer of cells supporting and shaping the growing hair shaft

The Inner Root Sheath (IRS) is a layer of cells that surrounds and supports the growing hair shaft within the hair follicle. It plays a crucial role in shaping the hair and guiding it as it emerges from the scalp. The IRS is composed of three distinct layers: Henle's layer, Huxley's layer, and the cuticle of the inner root sheath, each contributing to the structural integrity and function of the hair follicle.

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Premature Desquamation of the Inner Root Sheath in Noninflamed Hair Follicles as a Specific Marker for Central Centrifugal Cicatricial Alopecia

research Premature Desquamation of the Inner Root Sheath in Noninflamed Hair Follicles as a Specific Marker for Central Centrifugal Cicatricial Alopecia

6 citations , December 2018 in “The American Journal of Dermatopathology”

This study found that the presence of premature desquamation of the inner root sheath in noninflamed hair follicles is a relatively specific marker for diagnosing central centrifugal cicatricial alopecia.

research Four murine monoclonal antibodies specific for the inner root sheath in the human hair follicle

1 citations , January 1989

This study produced and characterized four new monoclonal antibodies that specifically recognize differentiation antigens in human hair follicle and epidermal structures.

research 889 Trpv3 gain-of-function mutation impairs differentiation of hair follicle inner root sheath

April 2019 in “The journal of investigative dermatology/Journal of investigative dermatology”

In this study, the researchers introduced a mutation in mice to mimic Olmsted syndrome and found that the mutation caused hair loss due to impaired keratinocyte differentiation and depletion of hair follicle stem cells.

research Vesicle Formation and Follicular Root Sheath Separation in Mice Homozygous for Deleterious Alleles at the Balding (bal) Locus

38 citations , September 1997 in “The journal of investigative dermatology/Journal of investigative dermatology”

This study identified histologic lesions and a defect in adhesion molecules causing hair loss in mice with the bal mutation, linked to a mutation in the desmoglein 3 gene.

research Keratin K6irs is specific to the inner root sheath of hair follicles in mice and humans

38 citations , October 2001 in “British Journal of Dermatology”

This study identified a new keratin, K6irs, as a potential histological marker for the inner root sheath of hair follicles in mice and humans, and as a candidate gene for hereditary hair defects.

The Early Region of Trichodysplasia Spinulosa Polyomavirus Drives Proliferation, Altered Differentiation, and Ectopic Expression of Hair Follicle Differentiation Markers in Interfollicular Tail Epidermis

research LB1019 The early region of trichodysplasia spinulosa polyomavirus drives proliferation, altered differentiation, and ectopic expression of hair follicle differentiation markers in interfollicular tail epidermis

July 2022 in “The journal of investigative dermatology/Journal of investigative dermatology”

In this study, researchers found that TSPyV T antigens can disrupt normal cell differentiation and proliferation in hair follicles and interfollicular epidermis, possibly contributing to trichodysplasia spinulosa pathology.

research Cytokeratins as Markers of Follicular Differentiation

121 citations , December 2001 in “American Journal of Dermatopathology”

This study found that trichoblastomas and nodular basal cell carcinomas have similar cytokeratin expression patterns, indicating differentiation towards the outer root sheath epithelium.

LGR5 Is a Conserved Marker of Hair Follicle Stem Cells in Multiple Species and Is Present Early and Throughout Follicle Morphogenesis

research LGR5 is a conserved marker of hair follicle stem cells in multiple species and is present early and throughout follicle morphogenesis

8 citations , June 2022 in “Scientific Reports”

Using a transgenic pig model, this study demonstrated that LGR5 is a marker of hair follicle stem cells across different species, with important similarities and differences in gene expression and developmental processes.

research The cDNA-deduced amino acid sequence for trichohyalin, a differentiation marker in the hair follicle, contains a 23 amino acid repeat.

39 citations , February 1990 in “The journal of cell biology/The Journal of cell biology”

This study identified trichohyalin as an early differentiation marker in hair follicles, with potential structural roles related to alpha-helical formations, based on the partial characterization of its cDNA in sheep.

research K6irs1, K6irs2, K6irs3, and K6irs4 Represent the Inner-Root-Sheath-Specific Type II Epithelial Keratins of the Human Hair Follicle1

130 citations , April 2003 in “Journal of Investigative Dermatology”

This study reports the cloning and expression details of two new human type II keratins, K6irs3 and K6irs4, in the hair follicle's inner root sheath, suggesting a distinct functional role related to hair structure.

research Heparanase 1: a key participant of inner root sheath differentiation program and hair follicle homeostasis

22 citations , June 2008 in “Experimental Dermatology”

This study found that heparanase is primarily located in the inner root sheath of human hair follicles during the anagen phase, and inhibiting it in cultured hair follicles induces a catagen-like process.

research Progenitor cells expressing nestin, a neural crest stem cell marker, differentiate into outer root sheath keratinocytes

12 citations , July 2019 in “Veterinary Dermatology”

The study suggests that nestin-expressing progenitor cells can differentiate into outer root sheath keratinocytes in hair follicles, indicating distinct progenitors for different hair follicle and epidermal components.

research Self-assembled complete hair follicle organoids by coculture of neonatal mouse epidermal cells and dermal cells in Matrigel

4 citations , July 2022 in “Annals of translational medicine”

This study successfully developed 3D hair follicle organoids from neonatal mouse epidermal and dermal cells, showing structural and molecular resemblance to native anagen hair follicles.

Stress-Sensing in the Human Greying Hair Follicle: Ataxia Telangiectasia Mutated (ATM) Depletion in Hair Bulb Melanocytes in Canities-Prone Scalp

research Stress-sensing in the human greying hair follicle: Ataxia Telangiectasia Mutated (ATM) depletion in hair bulb melanocytes in canities-prone scalp

14 citations , October 2020 in “Scientific reports”

This study found that ATM protein plays a crucial role in protecting human hair follicle melanocytes from oxidative stress, which is linked to the greying of hair.

research Stem cell markers (cytokeratin 15, CD34 and nestin) in primary scarring and nonscarring alopecia

54 citations , January 2009 in “British Journal of Dermatology”

This study found that in scarring alopecia, stem cells are differentially localized, suggesting that both inner and outer root sheath stem cells, rather than just follicular bulge stem cells, are involved.

research Global gene expression and comparison between multiple populations in the mouse epidermis

11 citations , June 2016 in “Stem Cell Research”

This study found that a multicolor panel of four surface markers can identify new stem cell populations in mouse hair follicles, providing insights into stem cell diversity and gene expression discrepancies during tissue culture.

Involucrin, But Not Filaggrin and Kdap mRNA, Expression Is Downregulated in 3-D Cultures of Intact Rat Hair Bulbs After Calcium Stimulation

research Involucrin, but not filaggrin and Kdap mRNA, expression is downregulated in 3-D cultures of intact rat hair bulbs after calcium stimulation

3 citations , July 2011 in “Folia Histochemica et Cytobiologica”

This study concluded that the inner root sheath inhibits the expression of certain differentiation markers in hair bulbs, with calcium-induced changes paralleling those seen in hair follicle mid-segments.

research Activation of the OVOL1-OVOL2 axis in the hair bulb and in pilomatricoma and pilomatrix carcinoma

September 2016 in “Journal of dermatological science”

The researchers reported that the OVOL1-OVOL2 axis may play a role in hair follicle differentiation and tumorigenesis, and OVOL1 and OVOL2 are potential diagnostic markers for pilomatricoma and pilomatrix carcinoma.

research Hopx expression defines a subset of multipotent hair follicle stem cells and a progenitor population primed to give rise to K6+ niche cells

74 citations , March 2013 in “Development”

This study found that Hopx labels a long-lived progenitor population in hair follicles, which contributes to hair follicle stem cell homeostasis and has an alternative origin from previously thought progenitors.

research Transforming growth factor-alpha immunoreactivity during induced hair follicle growth cycles in sheep and ferrets.

6 citations , April 1996 in “Journal of histochemistry and cytochemistry/The journal of histochemistry and cytochemistry”

This study suggests that TGF-alpha may function in an autocrine or juxtacrine manner rather than promoting cell proliferation during hair growth cycles in ferrets and sheep.

research 011 Central Centrifugal Cicatricial Alopecia (CCCA) Under the Scope: Histological Similarities between CCCA and Lichen Planopilaris

September 2017 in “The journal of investigative dermatology. Symposium proceedings/The Journal of investigative dermatology symposium proceedings”

This case report suggests that in African-American patients, the histology of Central Centrifugal Cicatricial Alopecia may resemble lichen planopilaris, indicating a potential diagnostic challenge.

research Keratin Expression Provides Novel Insight into the Morphogenesis and Function of the Companion Layer in Hair Follicles

38 citations , December 2006 in “Journal of Investigative Dermatology”

Keratin patterns in hair follicles help understand hair growth and potential hair and nail disorders.

Acidic and Basic Hair/Nail (Hard) Keratins: Their Colocalization in Upper Cortical and Cuticle Cells of the Human Hair Follicle and Their Relationship to Soft Keratins

research Acidic and basic hair/nail ("hard") keratins: their colocalization in upper cortical and cuticle cells of the human hair follicle and their relationship to "soft" keratins.

356 citations , December 1986 in “The journal of cell biology/The Journal of cell biology”

This study found that specific human hair keratins are differentially expressed in the hair follicle, suggesting a shared pathway of epithelial differentiation between hair cortex and nail plate cells.

CD10 and CD34 in Fetal and Adult Human Hair Follicles: Dynamic Changes in Their Immunohistochemical Expression During Embryogenesis and Hair Cycling

research CD10 and CD34 in fetal and adult human hair follicles: dynamic changes in their immunohistochemical expression during embryogenesis and hair cycling

25 citations , July 2008 in “British Journal of Dermatology”

This study observed dynamic changes in CD10 and CD34 expression in fetal and adult human hair follicles during embryogenesis and hair cycling.

research Hair follicle regeneration from human pluripotent stem cells

January 2017 in “Journal of clinical & experimental dermatology research”

This study found that human embryonic and induced pluripotent stem cells differentiated into specific bulge stem cells and successfully formed new hair follicles when transplanted with mouse dermal cells in immunodeficient mice.

research ILK modulates epithelial polarity and matrix formation in hair follicles

22 citations , December 2013 in “Molecular biology of the cell”

This study found that ILK deficiency disrupts hair follicle development by impairing cell polarity and laminin-511 assembly, but these defects can be partially reversed with exogenous laminin-511.

Nestin as a Marker of Unipotent Epithelial Progenitor Cells Differentiating into Outer Root Sheath Keratinocytes in Embryonic and Adult Hair Follicles

research Nestin as a marker of unipotent epithelial progenitor cells differentiate into outer root sheath keratinocytes in embryonic and adult hair follicles

June 2022 in “Research Square (Research Square)”

This study revealed that nestin-expressing progenitor cells capable of becoming ORS keratinocytes are present during both hair follicle development and in adult hair follicles.

Nestin as a Marker of Unipotent Epithelial Progenitor Cell Differentiation into Outer Root Sheath Keratinocytes in Embryonic and Adult Hair Follicles

research Nestin as a marker of unipotent epithelial progenitor cell differentiation into outer root sheath keratinocytes in embryonic and adult hair follicles

May 2022 in “Research Square (Research Square)”

This study found that nestin-expressing unipotent progenitor cells capable of differentiating into outer root sheath keratinocytes are present during hair follicle development and in adult hair follicles.

Fine Structure and Immunocytochemistry of Monotreme Hairs, with Emphasis on the Inner Root Sheath and Trichohyalin-Based Cornification During Hair Evolution

research Fine structure and immunocytochemistry of monotreme hairs, with emphasis on the inner root sheath and trichohyalin‐based cornification during hair evolution

15 citations , July 2004 in “Journal of morphology”

This study analyzes the fine structure and protein distribution in monotreme hairs, finding similarities with other mammals and detailing unique immunocytochemical features in their inner root sheaths.

Ultrastructural Immunolocalization of Involucrin in the Medulla and Inner Root Sheath of Human Hair

research Ultrastructural immunolocalization of involucrin in the medulla and inner root sheath of the human hair

7 citations , December 2011 in “Annals of anatomy”

This study found that involucrin likely plays a key role in forming the cornified material of the medulla and inner root sheath of human hair, contributing to its mechanical strength.