The small EF-hand protein CALML4 functions as a critical myosin light chain within the intermicrovillar adhesion complex

Inhibition of Prolactin Affects Epididymal Morphology by Decreasing the Secretion of Estradiol in Cashmere Bucks

Yanshan Cashmere bucks are seasonal breeding animals and an important national genetic resource. This study aimed to investigate the involvement of prolactin (PRL) in the epididymal function of bucks. Twenty eleven-month-old Cashmere bucks were randomly divided into a control (CON) group and a bromocriptine (BCR, a prolactin inhibitor, 0.06 mg/kg body weight (BW)) treatment group. The experiment was conducted from September to October 2020 in Qinhuangdao City, China, and lasted for 30 days. Blood was collected on the last day before the BCR treatment (day 0) and on the 15th and 30th days after the BCR treatment (days 15 and 30). On the 30th day, all bucks were transported to the local slaughterhouse, where epididymal samples were collected immediately after slaughter. The left epididymis was preserved in 4% paraformaldehyde for histological observation, and the right epididymis was immediately preserved in liquid nitrogen for RNA sequencing (RNA-seq). The results show that the PRL inhibitor reduced the serum PRL and estradiol (E2) concentrations (p < 0.05) and tended to decrease luteinizing hormone (LH) concentrations (p = 0.052) by the 30th day, but no differences (p > 0.05) occurred by either day 0 or 15. There were no differences (p > 0.05) observed in the follicle-stimulating hormone (FSH), testosterone (T), and dihydrotestosterone (DHT) concentrations between the two groups. The PRL receptor (PRLR) protein was mainly located in the cytoplasm and intercellular substance of the epididymal epithelial cells. The PRL inhibitor decreased (p < 0.05) the expression of the PRLR protein in the epididymis. In the BCR group, the height of the epididymal epithelium in the caput and cauda increased, as did the diameter of the epididymal duct in the caput (p < 0.05). However, the diameter of the cauda epididymal duct decreased (p < 0.05). Thereafter, a total of 358 differentially expressed genes (DEGs) were identified in the epididymal tissues, among which 191 were upregulated and 167 were downregulated. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes analyses revealed that ESR2, MAPK10, JUN, ACTL7A, and CALML4 were mainly enriched in the estrogen signaling pathway, steroid binding, calcium ion binding, the GnRH signaling pathway, the cAMP signaling pathway, and the chemical carcinogenesis-reactive oxygen species pathway, which are related to epididymal function. In conclusion, the inhibition of PRL may affect the structure of the epididymis by reducing the expression of the PRLR protein and the secretion of E2. ESR2, MAPK10, JUN, ACTL7A, and CALML4 could be the key genes of PRL in its regulation of epididymal reproductive function.

Investigating the impact of pigmentation variation of breast muscle on growth traits, melanin deposition, and gene expression in Xuefeng black-bone chickens

The blackness traits, considered an important economic factor in the black-bone chicken industry, still exhibits a common phenomenon of significant difference in blackness of breast muscle. To improve this phenomenon, this study compared growth traits, blackness traits, and transcriptome of breast muscles between the High Blackness Group (H group) and Low Blackness Group (L group) in the Xuefeng black-bone chickens. The results are as follows: 1) There was no significant difference in growth traits between the H group and the L group (P > 0.05). 2) The skin/breast muscle L values in the H group were significantly lower than those in the L group, while the breast muscle melanin content exhibited the opposite trend (P < 0.05). 3) A significant negative correlation was observed between breast muscle melanin content and skin/breast muscle L value (P < 0.05), and skin L value exhibiting a significant positive correlation with breast muscle L value (P < 0.05). 4) The breast muscle transcriptome comparison between the H group and L group revealed 831 and 405 DEGs in female and male chickens, respectively. This included 37 shared DEGs significantly enriched in melanosome, pigment granule, and the melanogenesis pathway. Seven candidate genes (DCT, PMEL, MLANA, TYRP1, OCA2, EDNRB2, and CALML4) may play a crucial role in the melanin production of breast muscle in Xuefeng black-bone chicken. The findings could accelerate the breeding process for achieving desired levels of breast muscle blackness and contribute to the exploration of the mechanisms underlying melanin production in black-bone chickens.

Epigenetic Modifications of White Blood Cell DNA Caused by Transient Fetal Infection with Bovine Viral Diarrhea Virus

Bovine viral diarrhea virus (BVDV) infections cause USD 1.5-2 billion in losses annually. Maternal BVDV after 150 days of gestation causes transient fetal infection (TI) in which the fetal immune response clears the virus. The impact of fetal TI BVDV infections on postnatal growth and white blood cell (WBC) methylome as an index of epigenetic modifications was examined by inoculating pregnant heifers with noncytopathic type 2 BVDV or media (sham-inoculated controls) on Day 175 of gestation to generate TI (n = 11) and control heifer calves (n = 12). Fetal infection in TI calves was confirmed by virus-neutralizing antibody titers at birth and control calves were seronegative. Both control and TI calves were negative for BVDV RNA in WBCs by RT-PCR. The mean weight of the TI calves was less than that of the controls (p < 0.05). DNA methyl seq analysis of WBC DNA demonstrated 2349 differentially methylated cytosines (p ≤ 0.05) including 1277 hypomethylated cytosines, 1072 hypermethylated cytosines, 84 differentially methylated regions based on CpGs in promoters, and 89 DMRs in islands of TI WBC DNA compared to controls. Fetal BVDV infection during late gestation resulted in epigenomic modifications predicted to affect fetal development and immune pathways, suggesting potential consequences for postnatal growth and health of TI cattle.

Loss of intermicrovillar adhesion impairs basolateral junctional complexes in transporting epithelia

Transporting epithelial cells in the gut and kidney rely on protocadherin-based apical adhesion complexes to organize microvilli that extend into the luminal space. In these systems, CDHR2 and CDHR5 localize to the distal ends of microvilli, where they form an intermicrovillar adhesion complex (IMAC) that links the tips of these structures, promotes the formation of a well-ordered array of protrusions, and in turn maximizes apical membrane surface area. Recently, we discovered that IMACs can also form between microvilli that extend from neighboring cells, across cell-cell junctions. As an additional point of physical contact between cells, transjunctional IMACs are well positioned to impact the integrity of canonical tight and adherens junctions that form more basolaterally. Here, we sought to test this idea using cell culture and mouse models that lacked CDHR2 expression and were unable to form IMACs. CDHR2 knockout perturbed cell and junction morphology, led to loss of key components from tight and adherens junctions, and impaired barrier function and wound healing. These results indicate that, in addition to organizing apical microvilli, IMACs provide a layer of cell-cell contact that functions in parallel with canonical tight and adherens junctions to support the physiological functions of transporting epithelia.

The microvillar protocadherin CDHR5 associates with EBP50 to promote brush border assembly

Transporting epithelial cells of the gut and kidney interact with their luminal environment through a densely packed collection of apical microvilli known as a brush border (BB). Proper brush border assembly depends on the intermicrovillar adhesion complex (IMAC), a protocadherin-based adhesion complex found at the distal tips of microvilli that mediates adhesion between neighboring protrusions to promote their organized packing. Loss of the IMAC adhesion molecule Cadherin-related family member 5 (CDHR5) results in significant brush border defects, though the functional properties of this protocadherin have not been thoroughly explored. Here, we show that the cytoplasmic tail of CDHR5 contributes to its correct apical targeting and functional properties in an isoform-specific manner. Library screening identified the Ezrin-associated scaffolds EBP50 and E3KARP as cytoplasmic binding partners for CDHR5. Consistent with this, loss of EBP50 disrupted proper brush border assembly with cells exhibiting markedly reduced apical IMAC levels. Together, our results shed light on the apical targeting determinants of CDHR5 and further define the interactome of the IMAC involved in brush border assembly.

Adhesion-based capture stabilizes nascent microvilli at epithelial cell junctions

To maximize solute transport, epithelial cells build an apical "brush border," where thousands of microvilli are linked to their neighbors by protocadherin-containing intermicrovillar adhesion complexes (IMACs). Previous studies established that the IMAC is needed to build a mature brush border, but how this complex contributes to the accumulation of new microvilli during differentiation remains unclear. We found that early in differentiation, mouse, human, and porcine epithelial cells exhibit a marginal accumulation of microvilli, which span junctions and interact with protrusions on neighboring cells using IMAC protocadherins. These transjunctional IMACs are highly stable and reinforced by tension across junctions. Finally, long-term live imaging showed that the accumulation of microvilli at cell margins consistently leads to accumulation in medial regions. Thus, nascent microvilli are stabilized by a marginal capture mechanism that depends on the formation of transjunctional IMACs. These results may offer insights into how apical specializations are assembled in diverse epithelial systems.

Defects in microvillus crosslinking sensitize to colitis and inflammatory bowel disease

Intestinal epithelial cells are covered by the brush border, which consists of densely packed microvilli. The Intermicrovillar Adhesion Complex (IMAC) links the microvilli and is required for proper brush border organization. Whether microvillus crosslinking is involved in the intestinal barrier function or colitis is currently unknown. We investigate the role of microvillus crosslinking in colitis in mice with deletion of the IMAC component CDHR5. Electron microscopy shows pronounced brush border defects in CDHR5-deficient mice. The defects result in severe mucosal damage after exposure to the colitis-inducing agent DSS. DSS increases the permeability of the mucus layer and brings bacteria in direct contact with the disorganized brush border of CDHR5-deficient mice. This correlates with bacterial invasion into the epithelial cell layer which precedes epithelial apoptosis and inflammation. Single-cell RNA sequencing data of patients with ulcerative colitis reveals downregulation of CDHR5 in enterocytes of diseased areas. Our results provide experimental evidence that a combination of microvillus crosslinking defects with increased permeability of the mucus layer sensitizes to inflammatory bowel disease.

Molecular regulatory mechanism of human myosin-7a

Myosin-7a is an actin-based motor protein essential for vision and hearing. Mutations of myosin-7a cause type 1 Usher syndrome, the most common and severe form of deafblindness in humans. The molecular mechanisms that govern its mechanochemistry remain poorly understood, primarily because of the difficulty of purifying stable intact protein. Here, we recombinantly produce the complete human myosin-7a holoenzyme in insect cells and characterize its biochemical and motile properties. Unlike the Drosophila ortholog that primarily associates with calmodulin (CaM), we found that human myosin-7a utilizes a unique combination of light chains including regulatory light chain, CaM, and CaM-like protein 4. Our results further reveal that CaM-like protein 4 does not function as a Ca2+ sensor but plays a crucial role in maintaining the lever arm's structural-functional integrity. Using our recombinant protein system, we purified two myosin-7a splicing isoforms that have been shown to be differentially expressed along the cochlear tonotopic axis. We show that they possess distinct mechanoenzymatic properties despite differing by only 11 amino acids at their N termini. Using single-molecule in vitro motility assays, we demonstrate that human myosin-7a exists as an autoinhibited monomer and can move processively along actin when artificially dimerized or bound to cargo adaptor proteins. These results suggest that myosin-7a can serve multiple roles in sensory systems such as acting as a transporter or an anchor/force sensor. Furthermore, our research highlights that human myosin-7a has evolved unique regulatory elements that enable precise tuning of its mechanical properties suitable for mammalian auditory functions.

Heart rate monitoring to detect acute pain in non-verbal patients: a study protocol for a randomized controlled clinical trial

BACKGROUND

Autism entails reduced communicative abilities. Approximately 30% of individuals with autism have intellectual disability (ID). Some people with autism and ID are virtually non-communicative and unable to notify their caregivers when they are in pain. In a pilot study, we showed that heart rate (HR) monitoring may identify painful situations in this patient group, as HR increases in acutely painful situations.

OBJECTIVES

This study aims to generate knowledge to reduce the number of painful episodes in non-communicative patients' everyday lives. We will 1) assess the effectiveness of HR as a tool for identifying potentially painful care procedures, 2) test the effect of HR-informed changes in potentially painful care procedures on biomarkers of pain, and 3) assess how six weeks of communication through HR affects the quality of communication between patient and caregiver.

METHODS

We will recruit 38 non-communicative patients with autism and ID residing in care homes.

ASSESSMENTS

HR is measured continuously to identify acutely painful situations. HR variability and pain-related cytokines (MCP-1, IL-1RA, IL-8, TGFβ1, and IL-17) are collected as measures of long-term pain. Caregivers will be asked to what degree they observe pain in their patients and how well they believe they understand their patient's expressions of emotion and pain. Pre-intervention: HR is measured 8 h/day over 2 weeks to identify potentially painful situations across four settings: physiotherapy, cast use, lifting, and personal hygiene.

INTERVENTION

Changes in procedures for identified painful situations are in the form of changes in 1) physiotherapy techniques, 2) preparations for putting on casts, 3) lifting techniques or 4) personal hygiene procedures.

DESIGN

Nineteen patients will start intervention in week 3 while 19 patients will continue data collection for another 2 weeks before procedure changes are introduced. This is done to distinguish between specific effects of changes in procedures and non-specific effects, such as caregivers increased attention.

DISCUSSION

This study will advance the field of wearable physiological sensor use in patient care.

TRIAL REGISTRATION

Registered prospectively at ClinicalTrials.gov (NCT05738278).

Biomimetic Remodeling of Microglial Riboflavin Metabolism Ameliorates Cognitive Impairment by Modulating Neuroinflammation

Neuroinflammation, for which microglia are the predominant contributors, is a significant risk factor for cognitive dysfunction. Riboflavin (also known as vitamin B2) ameliorates cognitive impairment via anti-oxidative stress and anti-inflammation properties; however, the underlying mechanisms linking riboflavin metabolism and microglial function in cognitive impairment remain unclear. Here, it is demonstrated that riboflavin kinase (RFK), a critical enzyme in riboflavin metabolism, is specifically expressed in microglia. An intermediate product of riboflavin, flavin mononucleotide (FMN), inhibited RFK expression via regulation of lysine-specific methyltransferase 2B (KMT2B). FMN supplementation attenuated the pro-inflammatory TNFR1/NF-κB signaling pathway, and this effect is abolished by KMT2B overexpression. To improve the limited anti-inflammatory efficiency of free FMN, a biomimetic microglial nanoparticle strategy (designated as MNPs@FMN) is established, which penetrated the blood brain barrier with enhanced microglial-targeted delivery efficiency. Notably, MNPs@FMN ameliorated cognitive impairment and dysfunctional synaptic plasticity in a lipopolysaccharide-induced inflammatory mouse model and in a 5xFAD mouse model of Alzheimer's disease. Taken together, biomimetic microglial delivery of FMN may serve as a potential therapeutic approach for inflammation-dependent cognitive decline.

Adhesion-based capture stabilizes nascent microvilli at epithelial cell junctions

Differentiated transporting epithelial cells present an extensive apical array of microvilli - a "brush border" - where neighboring microvilli are linked together by intermicrovillar adhesion complexes (IMACs) composed of protocadherins CDHR2 and CDHR5. Although loss-of-function studies provide strong evidence that IMAC function is needed to build a mature brush border, how the IMAC contributes to the stabilization and accumulation of nascent microvilli remains unclear. We found that, early in differentiation, the apical surface exhibits a marginal accumulation of microvilli, characterized by higher packing density relative to medial regions of the surface. While medial microvilli are highly dynamic and sample multiple orientations over time, marginal protrusions exhibit constrained motion and maintain a vertical orientation. Unexpectedly, we found that marginal microvilli span the junctional space and contact protrusions on neighboring cells, mediated by complexes of CDHR2/CDHR5. FRAP analysis indicated that these transjunctional IMACs are highly stable relative to adhesion complexes between medial microvilli, which explains the restricted motion of protrusions in the marginal zone. Finally, long-term live imaging revealed that the accumulation of microvilli at cell margins consistently leads to accumulation in medial regions of the cell. Collectively, our findings suggest that nascent microvilli are stabilized by a capture mechanism that is localized to cell margins and enabled by the transjunctional formation of IMACs. These results inform our understanding of how apical specializations are assembled in diverse epithelial systems.

The morphological and functional diversity of apical microvilli

Sensory neurons use specialized apical processes to perceive external stimuli and monitor internal body conditions. The apical apparatus can include cilia, microvilli, or both, and is adapted for the functions of the particular cell type. Photoreceptors detect light through a large, modified cilium (outer segment), that is supported by a surrounding ring of microvilli-like calyceal processes (CPs). Although first reported 150 years ago, CPs remain poorly understood. As a basis for future study, we therefore conducted a review of existing literature about sensory cell microvilli, which can act either as the primary sensory detector or as support for a cilia-based detector. While all microvilli are finger-like cellular protrusions with an actin core, the processes vary across cell types in size, number, arrangement, dynamics, and function. We summarize the current state of knowledge about CPs and the characteristics of the microvilli found on inner ear hair cells (stereocilia) and cerebral spinal fluid-contacting neurons, with comparisons to the brush border of the intestinal and renal epithelia. The structure, stability, and dynamics of the actin core are regulated by a complement of actin-binding proteins, which includes both common components and unique features when compared across cell types. Further, microvilli are often supported by lateral links, a glycocalyx, and a defined extracellular matrix, each adapted to the function and environment of the cell. Our comparison of microvillar features will inform further research into how CPs support photoreceptor function, and also provide a general basis for investigations into the structure and functions of apical microvilli found on sensory neurons.

Myosin motors in sensory hair bundle assembly

Mechanosensory hair bundles are assembled from actin-based stereocilia that project from the apical surface of hair cells in the inner ear. Stereocilia architecture is critical for the transduction of sound and accelerations, and structural defects in these mechano-sensors are a clinical cause of hearing and balance disorders in humans. Unconventional myosin motors are central to the assembly and shaping of stereocilia architecture. A sub-group of myosin motors with MyTH4-FERM domains (MYO7A, MYO15A) are particularly important in these processes, and hypothesized to act as transporters delivering structural and actin-regulatory cargos, in addition to generating force and tension. In this review, we summarize existing evidence for how MYO7A and MYO15A operate and how their dysfunction leads to stereocilia pathology. We further highlight emerging properties of the MyTH4/FERM myosin family and speculate how these new functions might contribute towards the acquisition and maintenance of mechano-sensitivity.

Myosin 5b is required for proper localization of the intermicrovillar adhesion complex in the intestinal brush border

Intestinal enterocytes have an elaborate apical membrane of actin-rich protrusions known as microvilli. The organization of microvilli is orchestrated by the intermicrovillar adhesion complex (IMAC), which connects the distal tips of adjacent microvilli. The IMAC is composed of CDHR2 and CDHR5 as well as the scaffolding proteins USH1C, ANKS4B, and Myosin 7b (MYO7B). To create an IMAC, cells must transport the proteins to the apical membrane. Myosin 5b (MYO5B) is a molecular motor that traffics ion transporters to the apical membrane of enterocytes, and we hypothesized that MYO5B may also be responsible for the localization of IMAC proteins. To address this question, we used two different mouse models: 1) neonatal germline MYO5B knockout (MYO5B KO) mice and 2) adult intestinal-specific tamoxifen-inducible VillinCreERT2;MYO5Bflox/flox mice. In control mice, immunostaining revealed that CDHR2, CDHR5, USH1C, and MYO7B were highly enriched at the tips of the microvilli. In contrast, neonatal germline and adult MYO5B-deficient mice showed loss of apical CDHR2, CDHR5, and MYO7B in the brush border and accumulation in a subapical compartment. Colocalization analysis revealed decreased Mander's coefficients in adult inducible MYO5B-deficient mice compared with control mice for CDHR2, CDHR5, USH1C, and MYO7B. Scanning electron microscopy images further demonstrated aberrant microvilli packing in adult inducible MYO5B-deficient mouse small intestine. These data indicate that MYO5B is responsible for the delivery of IMAC components to the apical membrane.NEW & NOTEWORTHY The intestinal epithelium absorbs nutrients and water through an elaborate apical membrane of highly organized microvilli. Microvilli organization is regulated by the intermicrovillar adhesion complexes, which create links between neighboring microvilli and control microvilli packing and density. In this study, we report a new trafficking partner of the IMAC, Myosin 5b. Loss of Myosin 5b results in a disorganized brush border and failure of IMAC proteins to reach the distal tips of microvilli.

Myosins and membrane trafficking in intestinal brush border assembly

Myosins are a class of motors that participate in a wide variety of cellular functions including organelle transport, cell adhesion, endocytosis and exocytosis, movement of RNA, and cell motility. Among the emerging roles for myosins is regulation of the assembly, morphology, and function of actin protrusions such as microvilli. The intestine harbors an elaborate apical membrane composed of highly organized microvilli. Microvilli assembly and function are intricately tied to several myosins including Myosin 1a, non-muscle Myosin 2c, Myosin 5b, Myosin 6, and Myosin 7b. Here, we review the research progress made in our understanding of myosin mediated apical assembly.

Bioinformatic Characterization of Whole Blood Neutrophils in Pelvic Inflammatory Disease: A Potential Prognostic Indicator for Transumbilical Single-Port Laparoscopic Pelvic Abscess Surgery

The purpose of this research is to determine the prognosis of patients treated with transumbilical single-port laparoscopic surgery for acute pelvic inflammatory illness. Postoperative data on 129 patients treated with laparoscopic surgery for acute pelvic inflammatory illness were obtained retrospectively. It was observed that the shorter the time required for postoperative leukocyte recovery to normal, the shorter the time required for postoperative pain and diet recovery, as well as hospital stay, in such individuals. CIBERSORT was used to examine patient data from GEO. The most significant difference between the normal and pelvic inflammatory groups was in neutrophil content. Association study found a substantial positive correlation between the quantity of neutrophils infiltrating the immune system and the abundance of monocyte M0 infiltrating the immune system. Neutrophil immune infiltration was strongly inversely linked with plasma cells, activated CD8+ Tm cells, and active CD4+ Tm cells. Four mRNAs linked with pelvic inflammatory illness were revealed to be strongly associated with neutrophil immune infiltration, notably CALML4, COQ10B, DCPS, and PPP2R1A. The ROC revealed that CALML4 (area under the curve (AUC): 0.769, 95% confidence interval (CI): 0.638-0.881), COQ10B (AUC: 0.742, 95% CI: 0.587-0.881), PPP2R1A (AUC: 0.733 95% CI: 0.593-0.857), and DCPS (AUC: 0.745, 95% CI: 0.571-0.900) were potential markers for predicting pelvic inflammatory disease. CALML4, COQ10B, PPP2R1A, and DCPS may be critical determinants determining the amount of preoperative neutrophil infiltration and the time required for leukocyte recovery after single-port laparoscopy in acute pelvic inflammatory illness.

Comparative analysis of the MyTH4-FERM myosins reveals insights into the determinants of actin track selection in polarized epithelia

MyTH4-FERM (MF) myosins evolved to play a role in the creation and function of a variety of actin-based membrane protrusions that extend from cells. Here we performed an analysis of the MF myosins, Myo7A, Myo7B, and Myo10, to gain insight into how they select for their preferred actin networks. Using enterocytes that create spatially separated actin tracks in the form of apical microvilli and basal filopodia, we show that actin track selection is principally guided by the mode of oligomerization of the myosin along with the identity of the motor domain, with little influence from the specific composition of the lever arm. Chimeric variants of Myo7A and Myo7B fused to a leucine zipper parallel dimerization sequence in place of their native tails both selected apical microvilli as their tracks, while a truncated Myo10 used its native antiparallel coiled-coil to traffic to the tips of filopodia. Swapping lever arms between the Class 7 and 10 myosins did not change actin track preference. Surprisingly, fusing the motor-neck region of Myo10 to a leucine zipper or oligomerization sequences derived from the Myo7A and Myo7B cargo proteins USH1G and ANKS4B, respectively, re-encoded the actin track usage of Myo10 to apical microvilli with significant efficiency.

The many roles of myosins in filopodia, microvilli and stereocilia

Filopodia, microvilli and stereocilia represent an important group of plasma membrane protrusions. These specialized projections are supported by parallel bundles of actin filaments and have critical roles in sensing the external environment, increasing cell surface area, and acting as mechanosensors. While actin-associated proteins are essential for actin-filament elongation and bundling in these protrusions, myosin motors have a surprising role in the formation and extension of filopodia and stereocilia and in the organization of microvilli. Actin regulators and specific myosins collaborate in controlling the length of these structures. Myosins can transport cargoes along the length of these protrusions, and, in the case of stereocilia and microvilli, interactions with adaptors and cargoes can also serve to anchor adhesion receptors to the actin-rich core via functionally conserved motor-adaptor complexes. This review highlights recent progress in understanding the diverse roles myosins play in filopodia, microvilli and stereocilia.

A new light chain for myosin-7

Recent research has revealed that an adhesion complex based on cadherins and the motor protein myosin-7b (MYO7B) links the tips of intestinal microvilli. Choi et al. now report that a largely uncharacterized protein known as calmodulin-like protein 4 (CALML4) is a component of this adhesion complex and functions as a light chain for myosin-7b. Because the intermicrovillar adhesion complex is homologous to the myosin-7a (MYO7A)-based Usher syndrome complex and Choi et al. also report that CALML4 can bind to myosin-7a, this work also has important implications for research on myosin-7a and hereditary deaf-blindness.

A heterologous in-cell assay for investigating intermicrovillar adhesion complex interactions reveals a novel protrusion length-matching mechanism

Solute transporting epithelial cells build arrays of microvilli on their apical surface to increase membrane scaffolding capacity and enhance function potential. In epithelial tissues such as the kidney and gut, microvilli are length-matched and assembled into tightly packed "brush borders," which are organized by ∼50-nm thread-like links that form between the distal tips of adjacent protrusions. Composed of protocadherins CDHR2 and CDHR5, adhesion links are stabilized at the tips by a cytoplasmic tripartite module containing the scaffolds USH1C and ANKS4B and the actin-based motor MYO7B. Because several questions about the formation and function of this "intermicrovillar adhesion complex" remain open, we devised a system that allows one to study individual binary interactions between specific complex components and MYO7B. Our approach employs a chimeric myosin consisting of the MYO10 motor domain fused to the MYO7B cargo-binding tail domain. When expressed in HeLa cells, which do not normally produce adhesion complex proteins, this chimera trafficked to the tips of filopodia and was also able to transport individual complex components to these sites. Unexpectedly, the MYO10-MYO7B chimera was able to deliver CDHR2 and CDHR5 to distal tips in the absence of USH1C or ANKS4B. Cells engineered to localize high levels of CDHR2 at filopodial tips acquired interfilopodial adhesion and exhibited a striking dynamic length-matching activity that aligned distal tips over time. These findings deepen our understanding of mechanisms that promote the distal tip accumulation of intermicrovillar adhesion complex components and also offer insight on how epithelial cells minimize microvillar length variability.

A cryptic sequence targets the adhesion complex scaffold ANKS4B to apical microvilli to promote enterocyte brush border assembly

Nutrient-transporting enterocytes interact with their luminal environment using a densely packed collection of apical microvilli known as the brush border. Assembly of the brush border is controlled by the intermicrovillar adhesion complex (IMAC), a protocadherin-based complex found at the tips of brush border microvilli that mediates adhesion between neighboring protrusions. ANKS4B is known to be an essential scaffold within the IMAC, although its functional properties have not been thoroughly characterized. We report here that ANKS4B is directed to the brush border using a noncanonical apical targeting sequence that maps to a previously unannotated region of the scaffold. When expressed on its own, this sequence targeted to microvilli in the absence of any direct interaction with the other IMAC components. Sequence analysis revealed a coiled-coil motif and a putative membrane-binding basic-hydrophobic repeat sequence within this targeting region, both of which were required for the scaffold to target and mediate brush border assembly. Size-exclusion chromatography of the isolated targeting sequence coupled with in vitro brush border binding assays suggests that it functions as an oligomer. We further show that the corresponding sequence found in the closest homolog of ANKS4B, the scaffold USH1G that operates in sensory epithelia as part of the Usher complex, lacks the inherent ability to target to microvilli. This study further defines the underlying mechanism of how ANKS4B targets to the apical domain of enterocytes to drive brush border assembly and identifies a point of functional divergence between the ankyrin repeat-based scaffolds found in the IMAC and Usher complex.