Impact of Undergraduate Research Training Programs: An Illustrative Example of Finding a Comparison Group and Evaluating Academic and Graduate School Outcomes

In this study, researchers at a large, urban, comprehensive minority-serving institution used propensity score matching to identify a unique comparison group to study academic and graduate school outcomes in students served by the National Institutes of Health-funded Building Infrastructure Leading to Diversity (BUILD) Initiative. Acknowledging that students' self-selection biases may confound findings, the use of propensity methods to match students served with those who were not (but were otherwise eligible) provides a valuable tool for evaluators and practitioners to combat this challenge and better evaluate their effectiveness and impact on students' success. This study's findings indicate that BUILD participants had higher academic and graduate school success with regard to cumulative GPA, units attempted and completed, graduation status, and application and admission to graduate programs.

Evaluation of a bioengineered construct for tissue engineering applications

Effective biomaterial options for tissue repair and regeneration are limited. Current biologic meshes are derived from different tissue sources and are generally sold as decellularized tissues. This work evaluated two collagen based bioengineered constructs and a commercial product in a model of abdominal full thickness defect repair. To prepare the bioengineered construct, collagen type 1 from porcine skin was isolated using an acid solubilization method. After purification, the collagen was formed into collagen sheets that were physically bonded to form a mechanically robust construct that was subsequently laser micropatterned with pores as a means to promote tissue integration (collagen only construct). A second engineered construct consisted of the aforementioned collagen construct embedded in an RGD-functionalized alginate gel that serves as a bioactive interface (collagen-alginate construct). The commercial product is a biologic mesh derived from bovine pericardium (Veritas^® ). We observed enhanced vascularization in the midportion of the engineered collagen-alginate construct 2 weeks after implantation. Overall, the performance of the bioengineered constructs was similar to that of the commercial product with comparable integration strength at 8 weeks. Bioengineered constructs derived from monomeric collagen demonstrate promise for a variety of load bearing applications in tissue engineering. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 2345-2354, 2018.

An immobilized liquid interface prevents device associated bacterial infection in vivo

Virtually all biomaterials are susceptible to biofilm formation and, as a consequence, device-associated infection. The concept of an immobilized liquid surface, termed slippery liquid-infused porous surfaces (SLIPS), represents a new framework for creating a stable, dynamic, omniphobic surface that displays ultralow adhesion and limits bacterial biofilm formation. A widely used biomaterial in clinical care, expanded polytetrafluoroethylene (ePTFE), infused with various perfluorocarbon liquids generated SLIPS surfaces that exhibited a 99% reduction in S. aureus adhesion with preservation of macrophage viability, phagocytosis, and bactericidal function. Notably, SLIPS modification of ePTFE prevents device infection after S. aureus challenge in vivo, while eliciting a significantly attenuated innate immune response. SLIPS-modified implants also decrease macrophage inflammatory cytokine expression in vitro, which likely contributed to the presence of a thinner fibrous capsule in the absence of bacterial challenge. SLIPS is an easily implementable technology that provides a promising approach to substantially reduce the risk of device infection and associated patient morbidity, as well as health care costs.

Engineered composite fascia for stem cell therapy in tissue repair applications

A critical challenge in tissue regeneration is to develop constructs that effectively integrate with the host tissue. Here, we describe a composite, laser micromachined, collagen-alginate construct containing human mesenchymal stem cells (hMSCs) for tissue repair applications. Collagen type I was fashioned into laminated collagen sheets to form a mechanically robust fascia that was subsequently laser micropatterned with pores of defined dimension and spatial distribution as a means to modulate mechanical behavior and promote tissue integration. Significantly, laser micromachined patterned constructs displayed both substantially greater compliance and suture retention strength than non-patterned constructs. hMSCs were loaded in an RGD-functionalized alginate gel modified to degrade in vivo. Over a 7 day observation period in vitro, high cell viability was observed with constant levels of VEGF, PDGF-β and MCP-1 protein expression. In a full thickness abdominal wall defect model, the composite construct prevented hernia recurrence in Wistar rats over an 8-week period with de novo tissue and vascular network formation and the absence of adhesions to underlying abdominal viscera. As compared to acellular constructs, constructs containing hMSCs displayed greater integration strength (cell seeded: 0.92 ± 0.19 N/mm vs. acellular: 0.59 ± 0.25 N/mm, p=0.01), increased vascularization (cell seeded: 2.7-2.1/hpf vs. acellular: 1.7-2.1/hpf, p<0.03), and increased infiltration of macrophages (cell seeded: 2021-3630 μm(2)/hpf vs. acellular: 1570-2530 μm(2)/hpf, p<0.05). A decrease in the ratio of M1 macrophages to total macrophages was also observed in hMSC-populated samples. Laser micromachined collagen-alginate composites containing hMSCs can be used to bridge soft tissue defects with the capacity for enhanced tissue repair and integration.

STATEMENT OF SIGNIFICANCE

Effective restoration of large soft tissue defects caused by trauma or treatment complications represents a critical challenge in the clinic. In this study, a novel composite construct was engineered and evaluated for stem cell delivery and tissue repair. Laser micromachining was used to fabricate patterned, microporous constructs designed with pores of defined size and distribution as a means to tune mechanical responses, accommodate and protect incorporated cells, and enhance tissue integration. The construct was embedded within an engineered alginate gel containing hMSCs. Upon repair of a full thickness abdominal wall defect in a rat model, the composite construct modulated host innate immunity towards a reparative phenotypic response, promoted neovascularization and associated matrix production, and increased the strength of tissue integration.

Localized delivery of mechano-growth factor E-domain peptide via polymeric microstructures improves cardiac function following myocardial infarction

The Insulin like growth factor-I isoform mechano-growth factor (MGF), is expressed in the heart following myocardial infarction and encodes a unique E-domain region. To examine E-domain function, we delivered a synthetic peptide corresponding to the unique E-domain region of the human MGF (IGF-1Ec) via peptide eluting polymeric microstructures to the heart. The microstructures were made of poly (ethylene glycol) dimethacrylate hydrogel and bioengineered to be the same size as an adult cardiac myocyte (100 × 15 × 15 μm) and with a stiffness of 20 kPa. Peptide eluting microrods and empty microrods were delivered via intramuscular injection following coronary artery ligation in mice. To examine the physiologic consequences, we assessed the impact of peptide delivery on cardiac function and cardiovascular hemodynamics using pressure-volume loops and gene expression by quantitative RT-PCR. A significant decline in both systolic and diastolic function accompanied by pathologic hypertrophy occurred by 2 weeks which decompensated further by 10 weeks post-infarct in the untreated groups. Delivery of the E-domain peptide eluting microrods decreased mortality, ameliorated the decline in hemodynamics, and delayed decompensation. This was associated with the inhibition of pathologic hypertrophy despite increasing vascular impedance. Delivery of the empty microrods had limited effects on hemodynamics and while pathologic hypertrophy persisted there was a decrease in ventricular stiffness. Our data show that cardiac restricted administration of the MGF E-domain peptide using polymeric microstructures may be used to prevent adverse remodeling of the heart and improve function following myocardial infarction.

Sustained delivery of MGF peptide from microrods attracts stem cells and reduces apoptosis of myocytes

Local release of drugs may have many advantages for tissue repair but also presents major challenges. Bioengineering approaches allow microstructures to be fabricated that contain bioactive peptides for sustained local delivery. Heart tissue damage is associated with local increases in mechano growth factor (MGF), a member of the IGF-1 family. The E domain of MGF peptide is anti-apoptotic and a stem cell homing factor. The objectives of this study were to fabricate a microrod delivery device of poly (ethylene glycol) dimethacrylate (PEGDMA) hydrogel loaded with MGF peptide and to determine the elution profile and bioactivity of MGF. The injectable microrods are 30 kPa stiffness and 15 μm widths by 100 μm lengths, chosen to match heart stiffness and myocyte size. Successful encapsulation of native MGF peptide within microrods was achieved with delivery of MGF for 2 weeks, as measured by HPLC. Migration of human mesenchymal stem cells (hMSCs) increased with MGF microrod treatment (1.72 ± 0.23, p < 0.05). Inhibition of the apoptotic pathway in neonatal rat ventricular myocytes was induced by 8 h of hypoxia (1 % O2). Protection from apoptosis by MGF microrod treatment was shown by the TUNEL assay and increased Bcl-2 expression (2 ± 0.19, p < 0.05). Microrods without MGF regulated the cytoskeleton, adhesion, and proliferation of hMSCs, and MGF had no effect on these properties. Therefore, the combination microdevice provided both the mechanical cues and 2-week MGF bioactivity to reduce apoptosis and recruit stem cells, suggesting potential use of MGF microrods for cardiac regeneration therapy in vivo.

Discrete microstructural cues for the attenuation of fibrosis following myocardial infarction

Chronic fibrosis caused by acute myocardial infarction (MI) leads to increased morbidity and mortality due to cardiac dysfunction. We have developed a therapeutic materials strategy that aims to mitigate myocardial fibrosis by utilizing injectable polymeric microstructures to mechanically alter the microenvironment. Polymeric microstructures were fabricated using photolithographic techniques and studied in a three-dimensional culture model of the fibrotic environment and by direct injection into the infarct zone of adult rats. Here, we show dose-dependent down-regulation of expression of genes associated with the mechanical fibrotic response in the presence of microstructures. Injection of this microstructured material into the infarct zone decreased levels of collagen and TGF-β, increased elastin deposition and vascularization in the infarcted region, and improved functional outcomes after six weeks. Our results demonstrate the efficacy of these discrete anti-fibrotic microstructures and suggest a potential therapeutic materials approach for combatting pathologic fibrosis.

Integrin α3 blockade enhances microtopographical down-regulation of α-smooth muscle actin: role of microtopography in ECM regulation

Development of functional engineered matrices for regenerative therapies can benefit from an understanding of how physical cues at the microscale affect cell behavior. In this work, we use microfabricated systems to study how stiffness and microscale topographical cues in the form of "micropegs" affect extracellular matrix synthesis. Previous work from our lab has shown that microtopographical cues in 2D and 3D systems decrease cellular proliferation and regulate matrix synthesis. In this work, the combined role of stiffness and topography on ECM synthesis is investigated in a 2D micropeg system. These studies show that fibroblasts cultured on polydimethylsiloxane (PDMS) substrates with micropegs have reduced expression of collagen type I (Col I) and collagen type VI (Col VI) compared to fibroblasts cultured on flat substrates. In addition, cells on micropegged substrates exhibit down-regulation of other important regulators of ECM synthesis such as α-smooth muscle actin (α-SMA), and integrin α3 (Int α3). Interestingly, this effect is dependent on the contractility and adhesion of the cells. When cultured in the presence of RhoA kinase (ROCK) and myosin light chain kinase (MLCK) inhibitors, no significant differences in the expression of collagen, α-SMA, Int α3, and TGFB1 are observed. Additionally, disruptions in cell adhesion prevent microtopographical regulation of ECM synthesis. When using an antibody to block the extracellular domain of Int α3, no differences in the expression of collagen are observed and blocking Int α3 results in enhanced down-regulation of α-SMA on the stiffer micropegged substrates. These findings demonstrate that regulation of extracellular matrix production by cells on a synthetic substrate can be guided via physical cues at the microscale, and add to the body of knowledge on the role of integrin-mediated mechanotransduction.

Microtopographical cues in 3D attenuate fibrotic phenotype and extracellular matrix deposition: implications for tissue regeneration

Recent studies have highlighted the role of external biophysical cues on cell morphology and function. In particular, substrate geometry and rigidity in two dimensions has been shown to impact cell growth, death, differentiation, and motility. Knowledge of how these physical cues affect cell function in three dimensions is critical for successful development of novel regenerative therapies. In this work, the effect of discrete micromechanical cues in three-dimensional (3D) system on cell proliferation, gene expression, and extracellular matrix synthesis was investigated. Poly(ethylene glycol) dimethacrylate hydrogel microrods were fabricated using photolithography and suspended in gel to create a 3D culture with microscale cues of defined mechanical properties in the physiological range (2-50 kPa). These microrods significantly affected fibroblast proliferation, matrix production, and gene expression. Cultures with stiff microrods reduced fibroblast proliferation and downregulated expression of key extracellular matrix proteins involved in scar tissue formation. In addition, the contractility marker alpha smooth muscle actin and adhesion molecule integrin alpha3 were also significantly downregulated. Cultures with soft microrods had no significant difference on fibroblast proliferation and expression of Cyclin D1, alpha smooth muscle actin, and integrin alpha3 compared to cultures with no microrods. Here, we present a new platform of potentially injectable microrods with tunable elasticity; in addition, we show that cell proliferation and gene expression are influenced by discrete physical cues in 3D.

Spectroscopic characterization of N-doped single-walled carbon nanotube strands: an X-ray photoelectron spectroscopy and Raman study

We have studied in detail the carbon and nitrogen bonding environments in nitrogen-doped single-walled carbon nanotubes (SWCNTs). The samples consisting of long strands of N-doped SWCNTs were synthesized using an aerosol assisted chemical vapor deposition method involving benzylamine-ethanol-ferrocene solutions. The studied samples were produced using different benzylamine concentrations in the solutions, and exhibited a maximum concentration of ca. 0.3%at of N, determined by X-ray photoelectron spectroscopy (XPS). In general, we observed that the ratio between substitutional nitrogen and the pyridine-like bonded nitrogen varied upon the precursor composition. Moreover, we have observed that the sp2-like substitutional configuration of the C-N bond does not exceed the 50% of the total N atomic incorporation. In addition, we have characterized all these samples using Raman spectroscopy and electron microscopy.

Three-dimensional culture with stiff microstructures increases proliferation and slows osteogenic differentiation of human mesenchymal stem cells

A small quantity of stiff microstructures in a 3D matrix regulates human mesenchymal stem cells to increase proliferation and slow differentiation after 10 days in culture. Cell morphology, clustering and gene expression are significantly different although the stiff microstructures are only 0.07% of the total gel volume.

Real-time monitoring of Streptococcus mutans biofilm formation using a quartz crystal microbalance

The ability of Streptococcus mutans, a well-known etiological agent in dental caries, to attach and form a biofilm is an important key to its virulence. The effects of various environmental factors (i.e. sucrose concentration, flow rate and temperature as well as genetic manipulations) on the capability of S. mutans (UA 140) to attach, form and detach were monitored in situ using quartz crystal microbalance. The biofilm growth rate was much slower than that of planktonic growth. Greater availability of sucrose contributed to biofilms with less lag time, lower doubling times and earlier detachment. Flow rate experiments showed that as the shear stress was reduced, the maximum mass accumulated also decreased. However, the detachment process was independent of shear force, perhaps indicative of quorum sensing. Increasing the incubation temperature from 37 to 40 degrees C extended the lag period and inhibited the ability of the biofilm to attach readily. Absence of either the ciaH, luxS, gtfB or gtfC genes also greatly affected the ability of the S. mutans to adhere to a surface in comparison to the wild type. Quartz crystal microbalance results indicate that the gtfC gene possibly has a greater contribution to biofilm attachment than the gtfB gene, that the presence of the luxS gene is critical for attachment and that the ciaH gene primarily affects the initial reversible attachment of the biofilm.

Infection of epithelial cells by pathogenic neisseriae reduces the levels of multiple lysosomal constituents

Members of our group reported recently that neisseria infection of human epithelial cells results in accelerated degradation of the major lysosomal integral membrane protein LAMP1 and that this is due to hydrolysis of this glycoprotein at its immunoglobulin A1 (IgA1)-like hinge by the neisseria type 2 IgA1 protease (L. Lin et al., Mol. Microbiol. 24:1083-1094, 1997). We also reported that the IgA1 protease plays a major role in the ability of the pathogenic neisseriae to survive within epithelial cells and hypothesized that this is due to alteration of lysosomes as a result of protease-mediated LAMP1 degradation. In this study, we tested the hypothesis that neisseria infection leads to multiple changes in lysosomes. Here, we report that neisseria infection also reduces the levels of three other lysosomal markers: LAMP2, lysosomal acid phosphatase (LAP), and CD63. In contrast, neither the epidermal growth factor receptor level nor the beta-tubulin level is affected. A detailed examination of LAMP2 indicated that the reduced LAMP2 levels are not the result of an altered biosynthetic rate or of cleavage by the IgA1 protease. Nevertheless, the protease plays a role in reducing LAMP2 and LAP activity levels, as these are partially restored in cells infected with an iga mutant. We conclude that neisseria infection results in multiple changes to the lysosomes of infected epithelial cells and that these changes are likely an indirect result of IgA1 protease-mediated cleavage of LAMP1.

The Neisseria type 2 IgA1 protease cleaves LAMP1 and promotes survival of bacteria within epithelial cells

Infection of human epithelial cells by Neisseria meningitidis (MC) and Neisseria gonorrhoeae (GC) increases the rate of degradation of LAMP1, a major integral membrane glycoprotein of late endosomes and lysosomes. Several lines of evidence indicate that the neisserial IgA1 protease is directly responsible for this LAMP1 degradation. LAMP1 contains an IgA1-like hinge region with potential cleavage sites for the neisserial type 1 and type 2 IgA1 proteases. Neisserial type 2 IgA1 protease cleaves purified LAMP1 in vitro. Unlike its wild-type isogenic parent, an iga mutant of N. gonorrhoeae cannot affect LAMP1 turnover and its growth in epithelial cells is dramatically reduced. Thus, IgA1 protease cleavage of LAMP1 promotes intracellular survival of pathogenic Neisseria spp.

Increase in mRNA of multiple Eh pgp genes encoding P-glycoprotein homologues in emetine-resistant Entamoeba histolytica parasites

With the goal of understanding possible mechanisms of drug resistance by the protozoan parasite Entamoeba histolytica (Eh), two novel Eh P-glycoprotein (Pgp) genes (Eh pgp5 and Eh pgp6) were sequenced, and the expression of four Eh pgp genes determined in wild-type (wt) clone A and emetine-resistant (EmR) clone C2 amebae. The Eh pgp5 gene encodes a 1301-amino acid (aa) protein that is similar to those of Eh pgp1 (64% aa identity), Eh pgp2 (61%), Eh pgp6 (39%) and Homo sapiens MDR (multidrug-resistance-encoding)(Hs MDR1; 38%) genes. The 1282-aa Eh pgp6 open reading frame (ORF), which is 19-28 aa shorter than those encoded by other Eh pgp, is also similar to those of Eh pgp1 (46% aa identity), Eh pgp2 (38%), and Hs MDR1 (39%). Both Eh pgp5 and Eh pgp6 ORF predict two ATP-binding cassettes and twelve hydrophobic alpha-helices, which form the putative transmembrane channel. EmR clone C2 amebae, growing at all concentrations of drug, show increased amounts of Eh pgp1 and Eh pgp6 mRNA when compared to wt clone A amebae. In contrast, only clone C2 amebae selected for growth at the highest concentrations of emetine (100-200 micrograms/ml) show increased Eh pgp5 mRNA, while mRNA of both clone C2 and clone A Eh amebae fail to bind an Eh pgp2-specific probe. It appears then that multiple Pgp may contribute to amebic Em resistance in vitro.

Expression of sequences related to c-myc in Entamoeba

The evolutionarily conserved proto-oncogene c-myc is involved in both proliferation and differentiation processes of higher eukaryotic cells. We report here the identification and characterization of sequences homologous to c-myc in different Entamoeba species using a fragment of the mammalian c-myc gene as a probe. This probe hybridized with fragments of 3.5 and 3.4 kilobases (kb) in E. histolytica HindIII of EcoRI digested DNA. In E. invadens it recognized fragments of 3.1 and 2.8 kb, and in Laredo strain (reported as E. moshkovskii by Clark and Diamond in 1991) the probe hybridized with fragments of 17 kb. The c-myc probe identified transcripts of 3.3 and 1.5 kb in E. histolytica, transcripts of 1.8 and 1.3 kb in Laredo strain, and transcripts of 3.7, 1.8, 1.5 and 1.1 kb in E. invadens. Antibodies against a highly conserved region of the c-myc protein recognized in E. histolytica polypeptides of 35, 40, and 60 kDa. The expression of the 60 kDa polypeptide was temperature-inducible in Laredo strain. In E. invadens a 110 kDa strong band was detected by the antibodies. Surprisingly, E. invadens myc-like sequences and proteins showed greater homology to mammalian c-myc gene and proteins. Expression of proteins antigenically related to c-myc varied according to the cell cycle phase of E. histolytica. These proteins peaked during D, G1, and S phases and declined during G2.

Primary sequences of two P-glycoprotein genes of Entamoeba histolytica

Two P-glycoprotein genes (EhPgp1 and EhPgp2) from the protozoan parasite Entamoeba histolytica were sequenced from a genomic library made with the DNA of an emetine-resistant ameba mutant, which overexpresses mRNAs homologous to segments of the human mdr1 (P-glycoprotein) gene. The open reading frames for EhPgp1 and EhPgp2 were 1302 and 1310 amino acids long, respectively, and showed a 67% positional identity with each other and 41% and 40% positional identities, respectively, with human mdr1 gene. Within each ameba P-glycoprotein were the ATP-binding sites found twice in eukaryotic P-glycoproteins and once in prokaryotic transport proteins. Hydropathy plots of the ameba P-glycoproteins were nearly superimposable on that of the human mdr 1, showing 2 homologous halves, each containing an ATP-binding site and 6 hydrophobic transmembrane domains that form the putative channel. A phylogenetic tree showed that the Entamoeba P-glycoproteins are more related to the human and mouse P-glycoproteins than to the Plasmodium and Leishmania P-glycoproteins. Also identified in the E. histolytica genomic library were 2 P-glycoprotein pseudogenes, each with a frame shift and stop codons in identical places within the amino ATP-binding site. In conclusion, the 2 E. histolytica P-glycoproteins encoded by the EhPgp1 and EhPgp2 genes are similar in structure to the mammalian P-glycoproteins and so may be involved in energy-dependent drug efflux by this human parasite.

P-glycoprotein genes of Entamoeba histolytica

Six different P-glycoprotein gene segments were identified from an emetine-resistant E. histolytica mutant, which overexpresses mRNAs homologous to segments of the human mdr1 (P-glycoprotein) gene. The open reading frames of two completely sequenced genes EhPgp1 and EhPgp2 were 1,302 and 1,310 amino acids long, respectively, and showed a 67% positional identity with each other and 41 and 40% positional identities, respectively, with human mdr1 gene. Within each ameba P-glycoprotein were the ATP-binding sites found twice in eukaryotic P-glycoproteins and once in prokaryotic transport proteins. A phylogenetic tree showed that Entamoeba P-glycoproteins are more related to the human and mouse P-glycoproteins than to the Plasmodium and Leishmania P-glycoproteins. In addition, there were two P-glycoprotein pseudogenes, each with a frame shift and stop codons in identical places within the amino ATP-binding site.

Entamoeba histolytica: physiology of multidrug resistance

Cross-resistance to unrelated drugs has been previously observed in multidrug-resistant carcinoma cells and the goal of this work was to determine whether a similar mechanism existed in Entamoeba histolytica. An emetine and a colchicine-resistant clone, C2(90) (IC50 = 62 microM, and 1.5 mM, respectively), and the parental clone, A (IC50 = 5 microM and 1 mM, respectively), were analyzed for resistance to other drugs and for the effect of verapamil. Both clones, C2(90) and A, exhibited similar resistance to both daunomycin (IC50 = 50 microM) and actinomycin D (IC50 = 13 nM). In the presence of verapamil, the IC50 for emetine was reduced to 0.5 microM, while the IC50 for colchicine was reduced to 0.3 mM. These results demonstrate that verapamil reverses both emetine and colchicine resistance in the mutant C2(90). In uptake experiments with [3H]emetine, drug accumulation was lower in resistant trophozoites. However, in the presence of verapamil, drug accumulation was increased in clone C2(90) to a level close to that of the parental strain, clone A. These results are consistent with observations made using malaria and multidrug-resistant tumor cells and suggest that a P-glycoprotein-like molecule may play a role in drug resistance in E. histolytica.

Emetine-resistant mutants of Entamoeba histolytica overexpress mRNAs for multidrug resistance

We report here the identification of multiple 344-bp segments of amoeba DNA similar to the human multidrug resistance (mdr) gene using primers to conserved regions of the P-glycoprotein and the polymerase chain reaction (PCR). The amino acid sequences of amoeba mdr-like PCR products were 46-97% identical to each other, 46-51% identical to human mdr1 sequences, and 30-35% identical with Plasmodium falciparum mdr-like sequences. On Northern blots, the mdr-like PCR products identified amoeba mRNAs 4.5-5 kb long, similar to the 5-kb mRNAs reported for the mammalian mdr gene. These mdr-like mRNAs were increased at least 7 times in emetine-resistant mutant clone C2 amoebae vs. wild-type clone A parasites. Furthermore, the expression of the mdr-like mRNAs was increased 3-4 times when clone C2 mutants were grown under drug pressure vs. the same parasites grown without emetine. In contrast, the number of genomic copies of the mdr-like DNA segments was not increased in the mutant clone C2 vs. the wild-type clone A amoebae, and no rearrangements of the mdr-like DNA segments by the mutant were identified on Southern blots. In conclusion, there appears to be a family of mdr-like genes in Entamoeba histolytica, which may be involved in drug resistance by the parasite because they are overexpressed in drug-resistant mutants.