The cell biology of the retinal pigment epithelium

In the paper

“Expression of “RPE signature” genes is important (Strunnikova et al., 2010); however, more importantly, the resulting proteins must be localized properly; e.g. the Na+/K+-ATPase should be in the apical membrane (not basal as is the case in RPE-J cells).”

What the sources say

• Supported

  The Discussion describes the highly expressed genes as a functional signature of RPE and suggests that a core set is minimally required for the RPE phenotype. The Strunnikova et al. citation is attached to the importance of expressing those genes, not to the subsequent statement about protein localization. (LLM, conf=0.92)

  cites Strunnikova et al., 2010 source

In the paper

“before the identification of a genomic deletion in these animals that resulted in a truncated MERTK protein and lack of MERTK signaling (D’Cruz et al., 2000; Nandrot et al., 2000).”

What the sources say

• Not checked yetcites D’Cruz et al., 2000
• Partly supported

  The Introduction and the section on rat c-mer cDNA report a deletion in affected RCS rats that produces a shortened transcript encoding a 20-amino-acid peptide. In the section on evidence for c-mer as the causal gene, the authors say the peptide is *presumably* devoid of signaling capability; they do not establish the claim’s unqualified lack of MERTK signaling. The reported deletion was identified in cDNA, rather than directly demonstrated in genomic DNA in these passages. (LLM, conf=0.84)

  cites Nandrot et al., 2000 sourceExperimental — accuracy not yet measured

In the paper

“Rubicon-deficient macrophages undergo normal levels of phagocytic uptake yet fail to recruit LC3B-II to phagosomes (Kim et al., 2013; Martinez et al., 2015; Wong et al., 2018).”

What the sources say

• Partly supported

  The Results section reports that silencing Atg5 or Beclin1 in retinal pigment epithelial cells prevented LC3 association with engulfed photoreceptor outer segments while having little effect on their uptake. The paper also describes LC3-associated phagocytosis in macrophages, but our copy does not report phagocytic uptake or LC3B-II recruitment in Rubicon-deficient macrophages (searched: Rubicon and Rubicon-deficient macrophages). (LLM, conf=0.78)

  cites Kim et al., 2013 sourceExperimental — accuracy not yet measured
• Supported

  In Results (‘Rubicon is required for LAP’; page unavailable), the paper reports equivalent phagocytosis in wild-type and Rubicon-deficient macrophages, but no LC3 translocation to LAPosomes in the deficient cells. It also reports compromised LC3-II recruitment there; a later Results section identifies LC3B on LAPosomes. (LLM, conf=0.91)

  cites Martinez et al., 2015 source
• Partly supported

  In “Rubicon in LC3-associated phagocytosis” (page unavailable), the review says Rubicon-deficient cells phagocytose normally but fail to recruit LC3-II to cargo-containing phagosomes. It does not specify macrophages or the LC3B isoform, so those details are not established by this copy. (LLM, conf=0.83)

  cites Wong et al., 2018 sourceExperimental — accuracy not yet measured

In the paper

“However, prolonged stress downregulates autophagy, which could send the cell into a spiral of increased debris, mitochondrial injury, and eventual metabolic reprogramming (Leidal et al., 2018; Levine and Kroemer, 2019).”

What the sources say

• Not checked yetcites Leidal et al., 2018 source
• Partly supported

  In “Autophagy in Genomic Stability and Tumor Suppression” (page unavailable), the review says impaired autophagy allows an autophagy substrate to accumulate and describes autophagy’s removal of dysfunctional mitochondria. It does not say that prolonged stress downregulates autophagy or that the resulting damage eventually causes metabolic reprogramming; its discussion of metabolic reprogramming concerns autophagy sustaining that process in pancreatic cancer cells. (LLM, conf=0.85)

  cites Levine and Kroemer, 2019 sourceExperimental — accuracy not yet measured

In the paper

“Although not explicitly reported in the literature, we have observed high passage-number cultures of RPE cells from human ESCs and iPSCs undergoing dedifferentiation.”

In the paper

“Nevertheless, the ARPE-19 cells remain a widely used cell line, with ~170 papers published annually that mention “ARPE-19” or “ARPE19” in the title or abstract (based on a current PubMed search), and, presumably, many others that still report experiments on the ARPE-19 cells, but may not mention the cell line by name in the abstract.”

In the paper

“These cultures can survive up to 10 days and are amenable to experimental manipulations including transfection, transduction, and live-cell imaging (Gibbs et al., 2003).”

What the sources say

• Not checked yetcites Gibbs et al., 2003

In the paper

“Nevertheless, a very high TER may be a characteristic of fetal RPE, and thus a potential drawback for modeling adult RPE.”

In the paper

“Primary porcine RPE cultures, grown on Transwell filters, exhibit correct localization of tight junction markers, such as ZO-1, and have a TER of ~400 Ω cm2, as early as 2 weeks in culture (Toops et al., 2014).”

What the sources say

• Not checked yetcites Toops et al., 2014 source

In the paper

“Moreover, an advantage of porcine eyes is that humans and pigs share similarities with regards to their immune systems, which is an advantage for studying diseases with a strong immune component like age-related macular degeneration (AMD) (Mair et al., 2014).”

What the sources say

• Not checked yetcites Mair et al., 2014 source

In the paper

“A freshly-prepared RPE/choroid/sclera flatmount represents a close in situ approximation to in vivo RPE.”

In the paper

“First, certain genes associated with human disease, such as the three different human-specific isoforms of apolipoprotein E, are not expressed in mice, pigs, or cattle, making it necessary to genetically modify these cells or to perform certain studies in human tissues.”

In the paper

“An important characteristic of primary RPE, iPS-RPE, and ES-RPE cells is that they can form well-differentiated, RPE-like cultures, demonstrating a polarized epithelial organization (Fig. 2), close approximation of native RPE gene and protein expression, and the ability to perform RPE functions, such as the ingestion and degradation of OSs over a time-course that is comparable to that in vivo (Mam”

What the sources say

• Not checked yetcites Maminishkis et al., 2006 source
• Not checked yetcites Strunnikova et al., 2010 source
• Not checked yetcites Blenkinsop et al., 2013 source

In the paper

“Apical localization of Na+/K+-ATPase is likely to be important for spatial buffering of ions in the subretinal space and for depolarizing the photoreceptor plasma membrane during phototransduction.”

In the paper

“ESCs and iPSCs can spontaneously differentiate along the neural lineage, and then to RPE cells, which are readily identified by virtue of pigmentation and cobblestone appearance (Kawasaki et al., 2002; Buchholz et al., 2009) (Fig. 4).”

What the sources say

• Not checked yetcites Kawasaki et al., 2002 source
• Not checked yetcites Buchholz et al., 2009 source

In the paper

“As discussed below, crosstalk between lysosomal clearance of OSs, autophagic machinery and the endosomal network, as well as oxidative metabolism, is essential for maintaining RPE health and function.”

In the paper

“A limitation of these flatmounts is that they maintain many of their characteristics in culture medium for only a matter of hours, so that many manipulations are not practicable.”

In the paper

“With the addition of pyruvate in high-glucose DMEM, it was shown that ARPE-19 cells recapitulated key features of RPE cells including RPE-specific differentiation markers, polygonal morphology, polar expression of proteins, extensive microvilli, the ability to phagocytose, and secretion of VEGF (Ahmado et al., 2011).”

What the sources say

• Not checked yetcites Ahmado et al., 2011 source

In the paper

“However, these cell lines have genetic abnormalities, with triploidy in the D407 line (Davis et al., 1995), and an abnormal karyotype (most notably, a loss of one copy of chromosome 15, and an unbalanced translocation between the chromosome 15q and 19q) in the ARPE-19 line (Fasler-Kan et al., 2018; Hazim et al., 2019).”

What the sources say

• Not checked yetcites Davis et al., 1995
• Not checked yetcites Fasler-Kan et al., 2018 source
• Not checked yetcites Hazim et al., 2019 source

In the paper

“Most animals (including mouse, rat, cat, hamster, Xenopus laevis, goldfish, rabbit, and chick) appear to be entrained to a circadian rhythm, which is cued by the light/dark cycle and persists even when the animal is maintained in absolute darkness (LaVail, 1976; Besharse et al., 1977; Grace et al., 1996), but not in absolute light (Teirstein et al., 1980).”

What the sources say

• Not checked yetcites LaVail, 1976 source
• Not checked yetcites Besharse et al., 1977 source
• Not checked yetcites Grace et al., 1996 source

In the paper

“General disadvantages of stem cell-derived cultures, like those of primary cultures, include inefficient transfection (although not viral transduction), as well as the limited number of times they can be passaged before failing to re-differentiate fully into RPE cells (Adijanto and Philp, 2014).”

What the sources say

• Not checked yetcites Adijanto and Philp, 2014

In the paper

“However, they do not develop polarity and a “cobblestone” organization that is typical of well-differentiated RPE monolayers.”

In the paper

“The model of choice is dictated by the scientific question; to begin with, the cells should be RPE-like with respect to characteristics that are central to the mechanisms to be studied (Pfeffer and Philp, 2014).”

What the sources say

• Not checked yetcites Pfeffer and Philp, 2014

In the paper

“The overall process of phagocytosis involves a series of stages. A prerequisite binding between the OS plasma membrane and the apical membrane of the RPE is followed by the formation of a phagocytic cup around the distal OS. The distal tip of the OS is then ingested and transported into the cell. The phagosome is degraded following interactions with endolysosomes, a process that appears to involve”

In the paper

“Across species, rod OS phagosomes are most abundant just after light onset, whereas cone OS phagosomes, depending on the species, appear at the same time as rod OS phagosomes, or demonstrate a peak of phagocytosis just after lights-off, as in lizard, chicken, goldfish, and ground squirrels (Young, 1977, 1978; Ruggiero and Finnemann, 2014).”

What the sources say

• Not checked yetcites Young, 1977 source
• Not checked yetcites Young, 1978
• Not checked yetcites Ruggiero and Finnemann, 2014

In the paper

“Immortalized or transformed RPE cell lines, of course, differ in one major respect from RPE in vivo; that is, they must proliferate.”

In the paper

“These protocols required 3–4 months for RPE differentiation, whereas, a more recent protocol was able to achieve a similar level of differentiation within 4 weeks through the addition of nicotinamide instead of pyruvate (Hazim et al., 2019) (Fig. 5).”

What the sources say

• Not checked yetcites Hazim et al., 2019 source

In the paper

“In other animals, like the frog, Rana pipiens, there is a strong dependency on external light stimuli to initiate OS phagocytosis; complete darkness prevents phagocytosis (Basinger et al., 1976).”

What the sources say

• Not checked yetcites Basinger et al., 1976 source

In the paper

“They have been reported to express some RPE-associated proteins (e.g. cellular retinaldehyde-binding protein [CRALBP]) and become pigmented in the absence of serum after 4 or 8 weeks in culture (Rambhatla et al., 2002).”

What the sources say

• Not checked yetcites Rambhatla et al., 2002

In the paper

“A few studies found that disruption of this region did not abrogate the daily schedule of the number of OS phagosomes and concluded that cues for OS phagocytosis were intrinsic to the eye (Currie et al., 1978; Hollyfield and Basinger, 1978; LaVail and Ward, 1978; Tamai et al., 1978; Besharse and Dunis, 1983; Terman et al., 1993).”

What the sources say

• Not checked yetcites Currie et al., 1978 source
• Not checked yetcites Hollyfield and Basinger, 1978
• Not checked yetcites LaVail and Ward, 1978

In the paper

“Polarity and differentiation are not only influenced by the source of the cells (transformed, primary, stem cell-derived), but also by plating density (Adijanto and Philp, 2014; Toops et al., 2014), and the substrate on which the cells are grown (Opas, 1989).”

What the sources say

• Not checked yetcites Adijanto and Philp, 2014
• Not checked yetcites Toops et al., 2014 source
• Not checked yetcites Opas, 1989 source

In the paper

“However, in his original paper, LaVail showed that blockage of the rat pineal gland with reserpine prevented the sudden increase in phagosome number that occurs after light onset (LaVail, 1976), suggesting some extraocular influence on circadian OS phagocytosis.”

What the sources say

• Not checked yetcites LaVail, 1976 source

In the paper

“The second method of ARPE-19 cell differentiation is the growth of cells on extracellular matrix-rich membranes such as porcine lens capsule (Turowski et al., 2004). Such cells have been reported to have improved phagocytosis and TER values reaching 200 Ω cm2.”

What the sources say

• Not checked yetcites Turowski et al., 2004 source

In the paper

“However, a significant problem is that many published studies have used poor culture conditions, so that the cell cultures bear little resemblance to an epithelium, let alone the retinal pigment epithelium.”

In the paper

“An apical membrane, containing receptors such as Mer tyrosine kinase (MERTK) and αvβ5 integrin, an actin-rich apical domain, and a cell body, with an epithelial microtubule organization and organelle distribution, are all polarity characteristics of a differentiated RPE cell”

In the paper

“Studies utilizing RPE-J cells routinely require pulses that are several hours long, with one study noting that the binding phase requires 2 h and subsequent ingestion another 2–3 h (Finnemann et al., 1997).”

What the sources say

• Not checked yetcites Finnemann et al., 1997

In the paper

“In a netcasting spider, which detects its prey by visual cues in dense rainforest at night, nearly all the phototransductive membrane is shed following dawn, and the rhabdomeres are then, essentially, entirely resynthesized at dusk (Blest, 1978).”

What the sources say

• Not checked yetcites Blest, 1978

In the paper

“Early evidence suggested that different classes of phospholipids may be effective ligands for RPE phagocytic receptors (Effron et al., 1981).”

What the sources say

• Not checked yetcites Effron et al., 1981

In the paper

“External PS on OSs is bound by milk fat globule E8 (MFGE8) which, in turn, serves as the ligand for αvβ5 integrin, residing in the apical RPE (Finnemann et al., 1997).”

What the sources say

• Not checked yetcites Finnemann et al., 1997

In the paper

“However, human, rat, and mouse RPE cells in culture can phagocytose OS membrane isolated from retinas of mice, rats, cows or pigs, with no obvious differences among species, suggesting mechanistic robustness across species (Mazzoni et al., 2014)”

What the sources say

• Not checked yetcites Mazzoni et al., 2014 source

In the paper

“MFGE8 protein levels in the retina are highest around light onset and decrease thereafter, thus coinciding with the phagocytic burst (Ruggiero and Finnemann, 2014).”

What the sources say

• Not checked yetcites Ruggiero and Finnemann, 2014

In the paper

“Primary rat RPE cultures exhibited a specificity for phagocytosis of isolated rat OSs; compared with red blood cells, levels of OS binding and OS ingestion were 250 and 970 times, respectively, greater (Mayerson and Hall, 1986).”

What the sources say

• Not checked yetcites Mayerson and Hall, 1986

In the paper

“phosphatidylserine (PS) has been widely studied as a phagocytic ligand; it is the classic ‘eat-me’ signal displayed by apoptotic cells and it is recognized by surface receptors on various phagocytic cells (Segawa and Nagata, 2015).”

What the sources say

• Not checked yetcites Segawa and Nagata, 2015

In the paper

“- OS phagocytosis involves mechanisms that are specific for OSs.”

In the paper

“although, with highly differentiated cultures, there appears to be a latency period prior to binding, likely due to the extensive microvilli impeding the association of suspended OSs with RPE membrane receptors.”

In the paper

“Analysis of two locust species that migrate at night found that the rhabdomeral cross-sectional area was 5-fold greater at night than during the day (Williams, 1982a, b), providing a concomitant increase in photoreceptor sensitivity at the expense of spatial resolution (Williams, 1983).”

What the sources say

• Not checked yetcites Williams, 1982a
• Not checked yetcites Williams, 1982b
• Not checked yetcites Williams, 1983 source

In the paper

“In the central human retina, there are 33 photoreceptors associated with each RPE cell (Osterberg, 1935), and, in the center of a mouse retina, there are more than 200 photoreceptors for every RPE cell (Volland et al., 2015); the ratio decreases to ~12 in the periphery of the human retina and 100–120 in the periphery of a mouse retina (Volland et al., 2015).”

What the sources say

• Not checked yetcites Volland et al., 2015 source

In the paper

“Most of the phototransductive membrane of nocturnal arthropods therefore lasts half a day, a considerably shorter time than the 10–50 days for the disk membranes of vertebrates (Young, 1967; Young and Bok, 1969).”

What the sources say

• Not checked yetcites Young, 1967 source
• Not checked yetcites Young and Bok, 1969

In the paper

“In arthropods, phototransductive membrane is microvillar and forms rhabdomeres, which are comparable to the outer segments of vertebrate photoreceptors; the closely packed microvillar membrane provides an alternative way to form a structure that contains a high concentration of opsin and other phototransductive proteins.”

In the paper

“While each OS phagosome contains densely packed membranes, it represents only 10% of the OS in mammals, such as mouse and rat, and ~2% in the frog, Rana (Young, 1967; Young and Bok, 1969).”

What the sources say

• Not checked yetcites Young, 1967 source
• Not checked yetcites Young and Bok, 1969

In the paper

“Arthropod photoreceptors typically degrade their own shed phototransductive membrane.”

In the paper

“The timing of ingestion can be controlled by lowering the temperature at which cells are fed OSs to 17–20 °C (Hall and Abrams, 1987). This cooler temperature permits binding but blocks ingestion.”

What the sources say

• Not checked yetcites Hall and Abrams, 1987

In the paper

“Adult rat RPE expresses two different αv integrins, αvβ3 and αvβ5 (Finnemann and Rodriguez-Boulan, 1999), although only αvβ5 facilitates OS binding and localizes to the apical surface (Finnemann et al., 1997).”

What the sources say

• Not checked yetcites Finnemann and Rodriguez-Boulan, 1999
• Not checked yetcites Finnemann et al., 1997

In the paper

“One such flippase, ATP8A2, has been localized to OS disk membranes and shown to translocate PS and, to a much lesser extent, phosphatidylethanolamine, implicating the enzyme in maintaining PS asymmetry in the OS (Coleman et al., 2009).”

What the sources say

• Not checked yetcites Coleman et al., 2009 source

In the paper

“The vast majority of phototransductive membrane is turned over each day in nocturnal arthropods.”

In the paper

“- MERTK is required for ingestion and is activated through αvβ5 integrin engagement and binding to Gas6/Protein S ligands.”

In the paper

“- TYRO3 and CD36 may be additional pathways mediating OS ingestion.”

In the paper

“- Release of a packet of disk membranes from the OS tip requires the RPE.”

In the paper

“OS phagocytosis is similarly arrhythmic, but not blocked in Mfge8−/− mice (Nandrot et al., 2007).”

What the sources say

• Not checked yetcites Nandrot et al., 2007 source

In the paper

“The lipid receptor, CD36, is not required for OS binding but is involved in phagosome engulfment, possibly as a signaling molecule (Finnemann and Silverstein, 2001), as antibodies against CD36 inhibited OS membrane ingestion by RPE cells (Ryeom et al., 1996).”

What the sources say

• Not checked yetcites Finnemann and Silverstein, 2001
• Not checked yetcites Ryeom et al., 1996 source

In the paper

“- Actin rearrangement is required for formation of the phagocytic cup and phagosome ingestion.”

In the paper

“Although CD36 functions in OS membrane uptake during normal conditions (Ryeom et al., 1996), it also recognizes oxidized phospholipids, such as oxidized PS and oxidized phosphatidylcholine, and may be functionally advantageous under oxidative stress (e.g., from intense light exposure) as an aid for the MERTK pathway (Greenberg et al., 2006; Sun et al., 2006).”

What the sources say

• Not checked yetcites Ryeom et al., 1996 source
• Not checked yetcites Greenberg et al., 2006 source
• Not checked yetcites Sun et al., 2006 source

In the paper

“The interaction between αvβ5 and OS binding is specific as antibodies against the integrin block OS binding, but not the binding or uptake of latex beads (Finnemann et al., 1997).”

What the sources say

• Not checked yetcites Finnemann et al., 1997

In the paper

“In general, MERTK plays a key role in a variety of phagocytic events, such as microglial phagocytosis to mediate synaptic pruning (Chung et al., 2013), macrophage phagocytosis to remove apoptotic immune cells (Scott et al., 2001), and phagocytosis of apoptotic germ cells and the residual body from maturing sperm by Sertoli cells in the testes (Breucker et al., 1985).”

What the sources say

• Not checked yetcites Chung et al., 2013 source
• Not checked yetcites Scott et al., 2001 source
• Not checked yetcites Breucker et al., 1985 source

In the paper

“Due to defective phagocytosis, and thus a blockage of OS disk membrane turnover, the structure of OSs in RCS rats begins to deteriorate, leading to a complete loss of OSs within 3 months of age.”

In the paper

“In the absence of the β5 subunit, the daily rhythm of phagocytosis is lost and while OS ingestion is impaired, it is not absent (Nandrot et al., 2004), suggesting the existence of potential β5 compensatory mechanisms.”

What the sources say

• Not checked yetcites Nandrot et al., 2004 source

In the paper

“For example, inositol triphosphate (IP3) was identified as a secondary messenger downstream of MERTK, as RCS rats do no exhibit the characteristic increase in IP3 levels upon OS phagocytic challenge (Heth et al., 1995).”

What the sources say

• Not checked yetcites Heth et al., 1995

In the paper

“Furthermore, TYRO3 exhibited gene dosage-dependent suppressive effects on the degree of retinal degeneration observed in Mertk−/− animals, but did not prevent it entirely, suggesting that MERTK is still indispensable.”

In the paper

“FAK operates downstream of αvβ5 integrin and shows a diurnal pattern of phosphorylation similar to that of MERTK, peaking after light onset and diminishing as phagosome degradation proceeds (Nandrot et al., 2004).”

What the sources say

• Not checked yetcites Nandrot et al., 2004 source

In the paper

“The strength of adhesion peaked 3.5 h after light onset, i.e., past the phagocytic peak (Nandrot et al., 2006).”

What the sources say

• Not checked yetcites Nandrot et al., 2006 source

In the paper

“Engagement of the αvβ5 integrin initiates a signaling cascade that triggers OS ingestion, predominantly mediated by MERTK (Gal et al., 2000), a member of the Tyro-Axl-Mer (TAM) ingestion receptor family, that is present in the RPE apical membrane (Prasad et al., 2006).”

What the sources say

• Not checked yetcites Gal et al., 2000 source
• Not checked yetcites Prasad et al., 2006 source

In the paper

“Given the importance of MERTK to phagocytosis, mutations in the human MERTK gene can lead to retinitis pigmentosa, rod-cone dystrophies, and cone-rod dystrophies (Nandrot, 2014).”

What the sources say

• Not checked yetcites Nandrot, 2014

In the paper

“Although the extent of its requirement may differ among different tissues, it nevertheless plays a central role, directly or indirectly affecting the regulation of a wide variety of genes including those involved in cytoskeletal rearrangement and phagosome maturation (Shelby et al., 2013; Penberthy et al., 2017).”

What the sources say

• Not checked yetcites Shelby et al., 2013 source
• Not checked yetcites Penberthy et al., 2017 source

In the paper

“β5−/− mice do not undergo retinal degeneration, but do demonstrate vision loss, as measured by electroretinograms (ERGs), from 6 months of age. They also accumulate fluorescent lipofuscin deposits, an inherent feature of the aging retina.”

In the paper

“the presence of the MERTK ingestion receptor (discussed in the section 3.5.1) limits OS binding via αvβ5 integrin, such that transient reduction of MERTK expression or use of cells lacking MERTK results in excessive OS binding (Nandrot et al., 2012).”

What the sources say

• Not checked yetcites Nandrot et al., 2012 source

In the paper

“As noted in section 3.5, however, OS ingestion does occur in these mice, suggesting that the basal level of phosphorylated MERTK that persists is sufficient to mediate phagocytosis.”

In the paper

“While deletion of either ligand alone does not affect retinal function in mice (Hall et al., 2005; Burstyn-Cohen et al., 2012), mice lacking both Gas6 and Protein S do develop moderate to severe retinal degeneration, demonstrating that at least one ligand is required for MERTK activation (Burstyn-Cohen et al., 2012).”

What the sources say

• Not checked yetcites Hall et al., 2005 source
• Not checked yetcites Burstyn-Cohen et al., 2012 source

In the paper

“Some mutant retinas also showed structures resembling drusen, and neovascularization of the RPE and photoreceptor layers (Jiang et al., 2015).”

What the sources say

• Not checked yetcites Jiang et al., 2015 source

In the paper

“It appears, then, that OS phagosomes are highly motile, undergoing rapid bidirectional movements, while maintaining an overall bias towards the basal domain of the RPE.”

In the paper

“Upon OS feeding of cultured RPE, there is a brief burst of RAC1 activity together with colocalization of RAC1 with OS phagosomes.”

In the paper

“- OS phagosomes mature by migrating from the apical to basal side of the RPE, while undergoing gradual acidification and degradation by hydrolases.”

In the paper

“PI3K is required for OS engulfment, possibly due to a role in promoting phagocytic cup formation, while AKT is not required for ingestion, and appears to restrict the size of the phagocytic cups and myosin-2 recruitment to the cup (Bulloj et al., 2013).”

What the sources say

• Not checked yetcites Bulloj et al., 2013 source

In the paper

“Consistent with its function, ANXA2 localizes to the phagocytic cup and the early phagosome but dissociates from fully ingested phagosomes (in vivo and in vitro) (Law et al., 2009), mirroring the association kinetics of actin.”

What the sources say

• Not checked yetcites Law et al., 2009 source

In the paper

“MERTK activation is neither required for nor affected by RAC1 activation and subsequent actin remodeling (Mao and Finnemann, 2012), consistent with the observation that actin is recruited to bound OS in RPE cells of the RCS rat (Chaitin and Hall, 1983b).”

What the sources say

• Not checked yetcites Mao and Finnemann, 2012
• Not checked yetcites Chaitin and Hall, 1983b

In the paper

“RAC1 inhibition prevents actin recruitment to the bound OS particle and therefore, prevents ingestion.”

In the paper

“But, this, too, appears to be an event that could be regulated by the RPE, given that the frequency of stained OS tips was affected by the light exposure that the intact animal received prior to retinal dissection (while the OSs were still associated with the RPE) (Matsumoto and Besharse, 1985).”

What the sources say

• Not checked yetcites Matsumoto and Besharse, 1985

In the paper

“Annexin A2 (ANXA2) is a membrane-associated protein that regulates actin dynamics and binds signaling intermediates such as Ca2+, cholesterol-rich membranes, and phosphoinositides, serving as a direct or indirect linker between the phagosome membrane and actin cytoskeleton (Turowski et al., 2004; Law et al., 2009).”

What the sources say

• Not checked yetcites Turowski et al., 2004 source
• Not checked yetcites Law et al., 2009 source

In the paper

“This activity is dependent upon αvβ5 integrin engagement by MFGE8 and is essential for phagosome ingestion (Mao and Finnemann, 2012).”

What the sources say

• Not checked yetcites Mao and Finnemann, 2012

In the paper

“An earlier report showed that freshly isolated frog retinas incubated in the low molecular weight dye, Lucifer Yellow, incorporated the dye into the distal tips of the OSs, suggesting that the opening of some distal disks to the extracellular space is an early step that leads to phagocytosis of the OS tip (Matsumoto and Besharse, 1985).”

What the sources say

• Not checked yetcites Matsumoto and Besharse, 1985

In the paper

“Demonstrated association with subunits of both kinesin-1 (Jiang et al., 2015) and cytoplasmic dynein-1 (Esteve-Rudd et al., 2018), which are plus- and minus-end directed microtubule motors, respectively, is consistent with bidirectional motility along microtubules.”

What the sources say

• Not checked yetcites Jiang et al., 2015 source
• Not checked yetcites Esteve-Rudd et al., 2018 source

In the paper

“- Phagosome acidification mediated by v-ATPase is required for protease activation.”

In the paper

“it has been shown that the detachment of retinas in frog eyecups in vitro prevents the release of the distal disks from the region of detachment, demonstrating that OS membrane shedding does not occur in the absence of the RPE (Williams and Fisher, 1987).”

What the sources say

• Not checked yetcites Williams and Fisher, 1987

In the paper

“The entry of phagosomes into the cell body region is retarded in Myo7a-null mice, as is the overall rate of OS phagosome degradation (Gibbs et al., 2003).”

What the sources say

• Not checked yetcites Gibbs et al., 2003

In the paper

“RAC1 is a small GTP-binding protein in the Rho family of GTPases that destabilizes F-actin and facilitates its branching for the formation of the dynamic phagocytic cup.”

In the paper

“- The RPE cytoskeleton and its motor proteins support rapid bidirectional motility of OS phagosomes, as well as basal migration, and are essential for normal phagosome degradation.”

In the paper

“The mobilization of myosin-2 to the phagocytic cup was severely diminished in RPE cells from RCS rats, suggesting that while αvβ5 integrin converges on actin rearrangement pathways, MERTK signaling independently converges on the myosin force generation required for particle engulfment following phagocytic cup formation.”

In the paper

“OS phagosomes in the RPE of Klc1−/− mice (which lack a light chain of kinesin-1) have impaired motility and are degraded more slowly.”

In the paper

“- The lysosomal aspartyl protease, cathepsin D, is essential for phagosome degradation, together with cysteine proteases such as cathepsin S.”

In the paper

“Older Klc1−/− mice develop AMD-like pathology, such as a slow loss of photoreceptor cells, complement hyperactivation, increased oxidative stress, and increased accumulation of neutral lipids such as lipoproteins and basal laminar deposits.”

In the paper

“Thus, the RPE cytoskeleton and its associated motors are not only key for the overall basal movement of OS phagosomes in the RPE, but also for the dynamic motility of phagosomes that appears to underlie their degradation.”