High impact information on Espn

• Espin level was also positively correlated with stereocilium length in hair cells [1].
• The espin actin-bundling proteins, which are the target of the jerker deafness mutation, caused a dramatic, concentration-dependent lengthening of LLC-PK1-CL4 cell microvilli and their parallel actin bundles [1].
• This additional actin-binding site bound to F-actin with a K(d) of approximately 1 microM, decorated actin stress fiber-like structures in transfected cells, and was mapped to a peptide between the two proline-rich peptides in the N terminus of espin [2].
• Espin was detected at approximately 4-5 x 10(6) copies per ectoplasmic specialization, or approximately 1 espin per 20 actin monomers and accumulated there coincident with the formation of parallel actin bundles during spermiogenesis [2].
• This activity was observed for wild-type espins targeted to the centrosome in transfected neuronal cells and for jerker espins targeted to the nucleolus in a wide variety of transfected cells as a result of the frameshifted peptide introduced into the espin C-terminus by the jerker deafness mutation [3].

Biological context of Espn

• We present a detailed high-resolution genetic and physical map of markers located at distal chromosome 4 and demonstrate concordance of Espn with jerker [4].
• A frame-shift mutation in the actin bundling gene Espin (Espn) leads to hair bundle defects by disrupting the actin filament assembly in stereocilia [4].
• Differential expression of espin isoforms during epithelial morphogenesis, stereociliogenesis and postnatal maturation in the developing inner ear [5].
• Late in embryonic development, espin was also present in a tail-like process that emanated from the hair cell base [5].

Anatomical context of Espn

• The 837-amino-acid "espin" of Sertoli cell-spermatid junctions (ectoplasmic specializations) and the 253-amino-acid "small espin" of brush border microvilli are splice isoforms that share a C-terminal 116-amino-acid actin-bundling module but contain different N termini [2].
• A recessive mutation in the espin gene (Espn) has been detected in the jerker mouse and causes deafness, vestibular dysfunction, and hair cell degeneration [6].
• Here, we demonstrate that the different espin isoforms are expressed in complex spatiotemporal patterns during inner ear development [5].
• Espin also accumulated in the epithelium of branchial clefts and pharyngeal pouches and during branching morphogenesis in other embryonic epithelial tissues, suggesting general roles for espins in epithelial morphogenesis [5].
• Increases in the levels of espin 1 and espin 4 isoforms correlated with stereocilium elongation and maturation in the vestibular system and cochlea, respectively [5].

Associations of Espn with chemical compounds

• Certain espin isoforms can also bind phosphatidylinositol 4,5-bisphosphate, profilins or SH3 proteins [7].

Other interactions of Espn

• Finally, we found Sertoli-spermatid junctions in nectin-2LacZ/LacZ mice to be virtually devoid of the actin-bundling protein espin, suggesting that ectoplasmic specializations fail to form in the absence of nectin-2 [8].
• Moreover, the ovaries express mRNA for the testis-specific Sertoli cell transcription factor Sox 9 and espin protein, which is specific for inter-Sertoli cell junctions [9].

Analytical, diagnostic and therapeutic context of Espn

• On the basis of results obtained using an antigen-retrieval method in conjunction with double immunofluorescence for espin and sensory taste cell-specific markers, we propose that espins are expressed predominantly in the sensory cells of taste buds [10].
• We compared seminiferous epithelial cytology in adult hpg, immature and adult wild-type mice using unbiased optical disector-based stereology, immunolocalization of Sertoli cell microtubules (MT), espin (a component of the blood-testis barrier), markers of Sertoli cell maturity (p27(kip1) and WT-1), and electron microscopy [11].

References