Cuestionario:

MOPS (pH8) Formaldehyde Glycerol Bromophenol blue H2O AMOUNT 0.75mL 0.15mL of a 1 OX stock solution 0.24mL of 37% stock solution O.lmL o f autoclaved stock solution 0.08mL o f a 10%w/v stock solution O.lmL

5pL o f total RNA (10-30pg) was mixed with 25pL o f RNA electrophoresis buffer (5 volumes). The sample was incubate at 70^C for 15 minutes, chilled on ice for 1 minute and centrifuged for 30 seconds at 14,000 rpm to collect the sample. IpL o f a ImgmL'* ethidium bromide stock solution was added to the sample, which was loaded onto a formaldehyde/ agarose gel (see Section 2.12.15). The samples were separated by electrophoresis at 5 to lOV for 18 hours.

Chapter 2. Methods and Materials

Section 2.12.13 Preparation o f 1 OX DNA electrophoresis buffer.

COM POSITION AMOUNT

Xylene cyanole 0.04g

Glycerol 5mL

Bromophenol blue 0.04g

H2O up to lOmL

0.04g o f bromophenol blue (BDH, Cat No-44305), and 0.4g o f xylene cyanole (Sigma, Cat No- X4126) was dissolved in 5mL of sterile H2O. 5mL o f 50% glycerol was added to the mixture and the volume made up to lOmL with sterile H2O to give a final concentration o f 0.4% bromophenol blue, 0.4% xylene cyanole, and 50% glycerol. The lOX DNA

electrophoresis buffer was stored in lOOpL aliquots at -20°C.

Chapter 2. Methods and M ateriab

Section 2,13 Statistical analysis.

All values are reported as mean +SEM. Statistical significance for two unpaired groups was assessed by the Student’s t test (P<0.05). ANOVA was used to assess variance between multiple groups.

Chapter 3. Results

C hapter 3. R esults.

Section 3,1 Relative expression o f SCL and LYL-1 mRNA in mouse tissues.

Semi-quantitative RT-PCR was used to determine the relative expression o f SCL mRNA between samples o f cDNA derived from the brain, thymus, liver, 14.5dpc fetal liver, spleen and adult bone marrow o f LYL-C'^^, LYL-C% and LYL-L " mice (for details see Chapter 2 Methods and Materials section 2.7).

Figures 12 show the p-actin, SCL and LYL-1 signals for brain, liver, thymus, 14.5dpc fetal liver, bone marrow and spleen o f LYL-C'^^, LYL-C% and LYL-L'^* mice. Disruption o f the LYL-1 locus was confirmed by the absence o f LYL-1 mRNA in LYL-1 mice, and the presence of lacZ transcript in RT-PCR experiment specific for the E coli derived lacZ (data not shown). The intensity o f the signals from the P-actin RT-PCR reactions were directly related to the amount o f cDNA used in each reaction. Therefore, the relative amount o f cDNA in each LYL^'^^, LYL^^", and LYL-L^ P-actin RT-PCR could be estimated. For

example, the amount o f 14.5dpc fetal liver cDNA used in SCL and LYL-1 specific RT-PCR reactions was highest in LYL^^', followed by LYL-1 and LYL^^ (Figure 12). Therefore, the SCL and LYL-1 signals from the LYL-1' ", and LYL^^^ 14.5dpc fetal liver could be corrected for the difference in the amount o f cDNA relative to the LYL^^' p-actin signal. Using this analysis, level o f LYL-1 mRNA expression was found to be highest in the bone marrow and

14.5dpc fetal liver (Figure 12). LYL-1 mRNA expression was 16-fold lower in the spleen and thymus, and at least 32-fold lower in the brain. The liver had an almost undetectable level o f LYL-1 mRNA. These results confirm the presence o f LYL-1 mRNA at highest levels in haematopoietic organs. However, LYL-1 mRNA may also expressed in cells present in non- haematopoietic organs, such as brain, in the adult mouse.

Chapter 3, Results

F igure 12. Semi-quantitative RT-PCR for SCL mRNA isolated from brain, thymus, liver, 14.5dpc fetal liver, spleen and bone marrow of LYL-1^ \ LYL-1^ ' and LYL-L ' mice. 5pi (1:1) o f each cDNA, and 5pl o f 5%, 2.5%, 1.25%, and 0.625% o f the total cDNA (see Section 2.7) were amplified in LYL-1 (top panel), SCL (middle panel), and p-actin (bottom panel) specific PCR reactions. Reactions with water replacing cDNA, and with water replacing the reverse transcriptase were performed as negative controls. Targeting o f the LYL-1 locus was confirmed by the absence o f LYT-1 mRNA in each tissue examined. There was no significant difference in the relative expression of SCL mRNA between LYL-1" ' (left), LYL-1 (middle), and LYL-1^'^^ (right) brain, thymus, liver, 14.5dpc fetal liver, and bone marrow. The spleen o f LYL-1 " mice expressed more SCL mRNA than LYL-1 and LYL-1 littermate controls.

Chapter 2. Results $ + /-

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Chapter 3. Results

SCL mRNA expression mirrors that o f LYL-1 with highest levels in the 14.5dpc fetal liver and bone marrow (Figure 12). Correction o f the SCL mRNA signals for differences in cDNA input showed that these organs expressed approximately 8-fold more SCL mRNA than the spleen. The brain expressed 16-fold less SCL mRNA, and the liver expressed at least 32-fold less SCL mRNA than 14.5dpc fetal liver. The thymus expressed the lowest level o f SCL mRNA (Figure 12). These data show that SCL mRNA expression is highest in

haematopoietic organs such as bone marrow, fetal liver and spleen, but was also expressed at a somewhat lower level in the brain and liver. The rank order o f expression of LYL-1 mRNA was 14.5dpc fetal liver/ bone marrow, thymus/ spleen, brain and liver; and for SCL the order o f expression was 14.5dpc fetal liver/ bone marrow, spleen, brain, liver and thymus. As predicted, the level of LYL-1 mRNA in cDNA samples derived from LYL-1^ ' tissues was approximately half the level in corresponding LYL-1 tissues (data not shown).

Section 3.2 SCL mRNA expression is increased in the spleen o f LYL-T^' mice.

The semi-quantitative RT-PCR assay employed in this study was able to identify changes of no less than 4-fold in the level o f SCL mRNA expression in heterogeneous cell populations from the different tissues analysed (for details see Chapter 2 Methods and Materials section 2.1). With this degree of sensitivity, there was no difference in the level o f SCL mRNA expression in the 14.5dpc fetal liver, brain, thymus and liver ofLYL-1^^, LYL-1^% and LYL-1 ^ mice (Figure 12). There was no difference in level o f SCL mRNA expression in LYL-L " bone marrow or fetal liver compared to controls, although a marginal increase in the bone marrow may have been at the very limit o f the assay and therefore could not be

determined accurately. However, the level o f SCL mRNA in the LYL-1'^' spleen was

markedly increased compared to controls (Figure 12). Results from five independent sets o f data are represented in Figure 13. The LYL-1 " spleen expressed 22.2 +2.9-fold more SCL

Chapter 3. Results

Figure 13. Enhanced expression o f SCL mRNA in LYL-1 ' spleen. (A). SCL signals

corrected for differences in the amount o f cDNA in each reaction showed LYL-1'^' spleen to contain more SCL mRNA than controls. (B). The P-actin signals from the semi-quantitative RT-PCR reactions were used to standardize the SCL signals from LYL-1^% LYL-1^'^' and LYL-1' ' spleen. LYL-L'^' spleen expressed 22.2 + 2.9-fold more SCL mRNA than LYL-1^^^ littermates (n=4) (P<0.05), and 5.8 + 2.2-fold more than LYL-T^"^' littermates (n=4) (P<0.05). The level o f SCL mRNA in LYL-1^^' mice (n=6) was not statistically different to SCL

mRNA in the LYL-1^^^ spleen (n=6) (P<0.05) but was significantly lower than SCL mRNA expression in the LYL-1 spleen.

Chapters. Results 70000 60000 5* 50000 ë g 40000 i 30000 c g 20000 +/+ spleen +/- spleen V- spleen 2 4 8 D ilution (xfbid) 16

Chapter 3, Results

mRNA than the spleen o f LYL-1 mice. Although there was a tendency towards increased SCL mRNA expression in the LYL-1^ ' spleen compared to LYL-1^^"^ spleen, this increase was not significant (Figure 13). The increase in SCL mRNA expression in the LYL-1 spleen was not gender specific, and was not affected by age, since it was observed in the spleen from male and female mice, and in mice o f eight weeks up to nine months o f age (data not shown).

These data showed that in the absence of a functional LYL-1 protein, there is a dramatic, and specific increase in the level of SCL mRNA in the spleen.

The increase in SCL mRNA in the spleen of LYL-1'^' mice could be due to an increase in the number of cells expressing SCL mRNA, or to an increase in the level of SCL mRNA

expression in individual cells. The semi-quantitative RT-PCR data did not elucidate the contribution of these (or other) causes for the increase in SCL mRNA. In order to determine the expression o f SCL mRNA at the cellular level, in situ RT-PCR specific for SCL mRNA was performed in 5pm paraformaldehyde-fixed paraffin sections o f spleen from LYL-1^^^ and LYL-T'^' mice.

Section 3.3 The spleen o f L YL-T^' mice comprised more cells expressing SCL

mRNA than the spleen o f LYL-1^^ mice.

Figures 5, and 14 show the result o f in situ RT-PCR specific for SCL mRNA in the spleen of LYL-1^^^ and LYL-l’^' mice (see Chapter 2 Methods and Materials section 2.5). Cells

positive for SCL mRNA (SCL mRNA^'^ were located in the red pulp o f the spleen o f both LYL-1^^^ (Figures 5A-C, G) and LYL-1"^" mice (Figures 5D-F, H). The specificity o f the signals was confirmed by negative control experiments performed in the absence o f reverse

Chapter 3. Results

F igure 14. Many o f the SCL mRNA"^® cells are arranged into clusters in the LYL-1^^^ (A-D) and LYL-1'^' (E-H) spleen. LYL-l ' spleen contained more clusters that were larger (G, H) than those found in LYL-1^^^ spleen (C, D). The level SCL mRNA expression in some cells in the LYL-1 ' spleen (E, F, and G) was higher than in the majority of cells in LYL-l^'^^ spleen (A, B, and C). All images were taken at 60x magnification.

Chapter.^. Results

LYL-1 -/- spleen comprise more cells that

express SCL mRNA than LVL-1+/+ spleen.

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Chapter 3. Results

transcriptase (Figure 51) or in the absence o f SCL specific primers (Figure 5 J). SCL

cells were found in the splenic parenchyme (Figures 5B, C, and G; 5E, F, H) and the subcapsular region (Figures 5 A; 5D, and F). LYL-L'^' spleen contained more SCL mRNA'^® cells (Figure 5D-E, H) than LYL-1+/+ spleen (Figure 5A-C, 0). Many o f the SCL mRNA^^® cells were arranged in clusters in the spleen ofLYL-1^^^ (Figures 14A-D), and LYL-l ’^' (Figures 14E-H) mice. Most clusters in the LYL-L^' spleen were composed o f more SCL mRNA"^® cells (Figure 14E, G, H) than in LYL-l^'^^ spleen (Figures 14A-C). It was apparent that some o f the cells in the LYL-L'^' spleen stained stronger (Figures 14G) than many of the SCL mRNA"^® cells in the LYL-1^^^ controls (Figure 14C). Although the number o f SCL m R N A ^ cells in the LYL-1^^^ and LYL-1 ^ spleen were not quantified accurately, the spleen o f LYL-1^' mice comprised approximately 5 to 10 times more SCL m R N A ^ cells than the LYL-1 spleen.

These data showed that the increase in SCL mRNA in the LYL-r"^' spleen determined by semi-quantitative RT-PCR was primarily due to an increase in the number o f cells expressing SCL mRNA. It also suggested that in the absence of a functional LYL-1 protein, the number o f cells expressing SCL mRNA was increased in the spleen.

The spleen can serve as a site for erythroid expansion when bone marrow erythropoiesis is stressed (Broudy et al., 1996) and serves as a station for the scavenging o f aged erythrocytes by macrophages (a process known as erythrophagocytosis) (Caceci,

http://www.cvm.tamu.edu/). Development of the most primitive HSCs and progenitors in the spleen is documented in many studies (Broudy, et al., 1996; Hendrikx, et al., 1996; Hunt, 1998) and the spleen is the major site o f regenerative re-population o f haematopoietic progenitors in mice (Saitoh, et al., 1999). Furthermore, Epo induced splenic erythropoiesis

Chapter 3. Results

can be optimized by manipulation o f the spleen microenvironment (Nijhof, et al., 1993). Since SCL is expressed in day 12 spleen colony forming units (CFU-S), in almost all erythroid colony forming cells (CFCs) (Elefanty, et al., 1998), and is up-regulated upon erythroid differentiation (Elefanty, et al., 1998; Apian, et al., 1992) and growth (Green, et al., 1991), it was likely that many o f the cells expressing SCL mRNA in the spleen o f LYL-1 ' mice were erythroid. To examine this proposition, sections o f spleen were subjected to specific histological and immunohistochemical analyses to establish the presence, and distribution of erythroid cells.

Section 3,4 The spleen o f L mice comprised more erythroid cells than the

spleen o f LYL-J^''^ mice.

The May-Grunwald and Giemsa stain was used to identify haematopoietic cells in sections o f spleen from LYL-1^^^ and LYL-1 ' mice (see Chapter 2 Methods and Materials section

2.1.11). This stain allowed the different types of blood cell to be distinguished

morphologically. Several different haematopoietic cell types were identified in the spleen o f LYL-1^^^ and LYL-T'^* mice including granulocytes (Gra), macrophages (Mac), erythrocytes (Ery) and erythroblasts (ProEry, Poly, Baso) (Figure 15). Spleens of both LYL-1^^^ (Figure 15 A, B) and L Y L -1(F igure 15C, D) LYL-1 mice contained clusters o f erythroblasts. However, the clusters in the LYL-1'^' spleen (Figure 15C, D) were more frequent and

comprised many more cells than in LYL-L^'^^ spleen (Figure 15A, B). The clusters in LYL-1^' spleen were larger because they composed more proerythroblasts, polychromatic and

basophilic erythroblasts (Figure 15C, D). It was apparent that the red pulp ofLYL-1^^ spleen (Figure 15 A, B) contained more erythrocytes than the LYL-T^' spleen (Figure 14C, D). These results supported the proposition that the clusters o f SCL mRNA^^® cells, identified in the LYL-T'^' spleen by SCL-specific in situ RT-PCR, were erythroid.

Chapter 3. Results

Figure 15. May-Grunwald and Giemsa stain o f haematopoietic cells in mercuric-fixed paraffin sections o f LYL-1 (A, B) and LYL-1' ' (C, D) spleen (see Section 2.1.8). Several different haematopoietic cells can be identified including erythroblasts (Poly- polychromatic; Baso- basophilic; ProEry- proerythroblasts); erythrocytes (Ery), macrophages (Mac),

granulocytes (Gra), and megakaryocytes (Mega) in spleen sections. Erythroid clusters were larger and more frequent in the LYL-1 ' spleen (C, D) compared to LYL-1^^^ erythroid clusters (A, B). Erythrocytes (stained pink) were less frequent in the LYL-l ' spleen sections (D) compared to LYL-l^"^^ controls (B). All images were taken at 20x magnification.

Chapter 3. Results

In document Narrativas de infancia de Niñas y Niños del Barrio Nacederos de Pereira: constructores de vínculos familiares (página 71-75)