Proceso De Alistamiento O Desinfección De Galpones

Bone morphogenetic proteins (BMPs) are expressed at a number of different tissues at many stages during embryogical development where they modulate a

variety of events (Hogan, 1996; Mehler, et a l, 1997). The BMP antagonist Chordin

is a well characterised modulator of BMP signalling (Sasai, et a l, 1994; Piccolo, et

a l , 1996), but recent advances have identified a number of molecules such as Xolloid, Cerberus and Tsg that impose a further level of control on BMP signalling

(Piccolo, et a l, 1997; Piccolo, et a l, 1999; Oelgeschlager, et a l, 2000; Chang, et a l,

2001). The identification of E l 3 and the data presented in this thesis demonstrate E13 is expressed at the correct time and location to interact with BMP molecules (Chapter 5) and indeed E13 has been shown to bind to BMP-4 and can modulate a downstream target of BMP signalling (Chapter 6).

(0 Does E l 3 associate with the extracellular matrix and localise BMP molecules? As discussed in Chapter 6, the proposed model for the role of E13 is to localise BMP molecules at sites where high levels of BMP signalling are required. To do this it has been reasoned that the E l 3 protein may interact with the extracellular matrix (ECM), preventing it from diffusing from its site of expression and acting as a molecular anchor of BMP-4 molecules (Chapter 6). Experiments in the laboratory are currently underway to determine if cE13 interacts with the ECM and if it can localise BMP molecules. To determine if E13 can bind to the ECM, a tagged recombinant cE13 protein is being expressed in a mammalian cell line. Chick E13 expressing cells will be separated from the ECM; the cells and ECM fractions will be assayed for the presence of cE13 protein by Western analysis (as previously

demonstrated by other ECM binding proteins such as the proto-oncogene int-1 and

the glycoprotein W n tll (Bradley and Brown, 1990; Christiansen, et a l, 1996)). To

determine if cE13 can localise BMP-4 molecules and restrict their domain of activity, an experiment is planned similar to one described by others utilising

injected Xenopus animal caps (Gurdon, et ah, 1994; Jones, et ah, 1996). Injected

ectodermal explants expressing either BMP-4 or BMP-4 and cE13 will be juxtaposed with un-injected ectoderm explants and incubated for approximately 4 hours before being fixed and analysed. The range of BMP-4 activity with and without cE13 will be analysed by determining the induction of downstream components of the BMP

signalling cascade (Xhox3) (Hemmati-Brivanlou and Thomsen, 1995) in the adjacent

non-injected tissue. If cE13 localises BMP-4 then the domain of Xhox3 expression

will be less in the BMP-4 and cE13 injected caps than in BMP-4 injected caps.

{ii) Is E l 3 protein cleaved in vivo?

The expression of recombinant cE13 protein in Drosophila Schneider 2 insect

cells identified a full-length and cleaved form of the chick E13 protein. This

observation requires further investigation to determine if this processing occurs in

vivo. To address this issue two peptide antibodies have been designed; one against the amino portion and the other against the carboxyl portion of the cE13 protein, either side of the predicted cleavage site. These peptides are being utilised to raise two antisera that will be used to detect the cE13 protein in a number of different experiments. These will include Western analysis of whole embryo extracts to

determine if cE13 is cleaved in vivo, and in situ immunochemistry experiments to

determine the distribution of cE13 protein in vivo.

If the cE13 protein is cleaved in vivo then the two forms of the cE13 protein

may have different activities within the developing embryo. If the full-length cE13 protein can localise BMP-4 via binding of the VWFD domain to extracellular matrix, cleavage of the protein may release BMP-4/cE13 complexes. To investigate this possibility experiments will use truncated forms of cE13 in different assays. These

assays include overexpression of truncated cE13 mRNAs in developing Xenopus

embryos and in animal caps expressing BMP-4, to determine if different portions of the cE13 protein have different effects on BMP signalling. Other experiments may include the production of truncated tagged cE13 proteins for use in binding assays to

determine what portion(s) of the cE13 protein is required to interact with BMP molecules.

(Hi) Functions of cE13 in vivo

Analysis of embryos overexpressing cE13 in the dorsal neural tube has focused on identifying changes in neural crest cell migration using migratory neural crest cell markers. Chick E l 3 has been shown to modulate downstream targets of BMP-4, and therefore it will be interesting to investigate if the levels of expression of other components of the BMP signalling pathway are affected when cE13 is

overexpressed in vivo. BMP-4 induces apoptotic elimination of neural crest cells in

r3 and r5 (Graham, et al., 1993; Graham, et at., 1994), therefore it would be

interesting to investigate if there is a change in the level of cell death when cE13 is overexpressed by using either acridine orange, nile blue or the TUNEL assay (Grasl-

Kraupp, et a l, 1995) to detect cells undergoing apoptosis. Another more quantative

assay to determine if the overexpression of cE13 effects neural crest cell development would be to electroporate cE13 into the developing chick neural tube, followed by neural tube explant cultures to determine if there are changes in the timing of neural crest cell migration or in the number of migratory neural crest cells.

A more informative approach to elucidate the function of cE13 may be loss of function experiments. One technique that may enable loss of function or transcript knock-down experiments are morpholino antisense oligomers, as previously described (Summerton and Weller, 1997; Nasevicius and Ekker, 2000; Tucker, 2001;

Kos, et at., 2001). As the sequence surrounding the initiation codon of both the chick

and zebrafish E l 3 has been identified anti sense morpholinos can be designed against these sequences. The production of E l 3 peptide antibodies will be a useful tool to determine the efficacy of the antisense morpholinos as the levels of E l 3 protein can be detected.

Another avenue of investigation that has been initiated in the laboratory is to generate a null mutation of the E13 gene in the mouse. As described in Chapter 4, a partial mouse E l 3 EST has been identified and this sequence will be used to identify genomic clones that are required for the targeted disruption of the mE13 gene. This knock-out will potentially provide a very useful tool in elucidating the function of E13.

(/v) Does E l 3 affect the specification of dorsal neuronal cell types in the neural tube? One aspect of BMP signalling that has not been investigated during this project is the role of BMP signalling in the establishment of dorsal neuronal cell types in the neural epithelium. The specification of neuronal cell types in caudal regions of the neural tube is dependent on the cells position within the dorso ventral axis (review: Briscoe and Eric son, 2001). Recent evidence suggests that two opposing signalling mechanisms are responsible for the specification of the neuronal cell type. Sonic hedgehog (Shh) is expressed ventrally with a graded signalling activity from high ventral to low dorsal, inducing ventral neuronal cell types (Marti,

et a l, 1995; Hammerschmidt, et a l, 1997; Briscoe and Eric son, 1999). Opposing this ventral signalling mechanism are the dorsal BMPs that are expressed in the surface

ectoderm and dorsal neural tube (review see: Mehler, et a l, 1997). Although the

dorsal to ventral distribution of BMP proteins have not been investigated in the neural tube, BMPs are proposed to diffuse away from the dorsal midline establishing a graded signal from high dorsal to low ventral and have been shown to induce

dorsal and intermediate neuronal cell types (Nguyen, et a l, 2000). The expression

pattern of cE13 in the dorsal neural tube is transient coinciding with the onset of neural crest cell migration and during this period BMPs have a number of roles

during emigration of these cells (Chapter 1: Graham, et a l, 1994; Sela-Donenfeld

and Kalcheim, 1999). If cE13 acts as a molecular anchor for BMP molecules then perhaps cE13 localises BMP family members expressed by pre-migratory neural crest cells, thus preventing ventral diffusion of these BMPs that could affect dorsal ventral patterning of neuronal cell types. Therefore, ectopic expression of cE13 in the neural tube is predicted to affect the formation of the different neuronal cell types along the dorso-ventral axis. Further to this, a collaboration with a colleague in the department (J. Briscoe) has been initiated to determine if the overexpression of cE13 affects the specification of neuronal cell types along the dorsal to ventral axis in the developing chick embryo.

The identification of E l 3 and the experiments that have been presented in this thesis represent a significant first step in elucidating the modulating function of cE13 on BMP signalling. Clearly, further investigation is required to fully understand the role of E13 during embryonic development and its relationship with BMPs.

APPENDIX A

GENERAL SOLUTIONS:

DepcPBS 0.001 % (v/v) Depc and IX PBS in DDW and autoclaved.

LB (Broth) 1 % (w/v) bacto-tryptone, 0.5 % (w/v) yeast extract, 0.5 %

(w/v) NaCl pH 7.4.

LB-agar L-Broth supplemented with 1.5 % (w/v) bacto-agar.

PBS Prepared by adding phosphate buffered saline tablets (Oxoid

BRI4a) to DDW and autoclaving.

PBTw 0.1 % (v/v) Tween20 in IX PBS DDW

PBTx 0.1 % (v/v) TritonXlOO in IX DepcPBS.

RT-PCR-loading dye 80 % (v/v) Form am ide, 1 mM EDTA, 0.1 % (w/v) bromophenol blue, 0.1 % (w/v) xylene cyanal

Xgal stain solution 5 mM K3pe(CN)6, 5 mM K4pe(CN)6.(3H20, 2 mM MgClj,

0.01 % (w/v) sodium deoxycholate, 0.02 % (w/v) NP40, 1

mg/ml Xgal in DepcPBS.

ELECTROPHORESIS BUFFERS:

TBE 0.089 M Tris Borate, 0.002 M EDTA pH 8.0.

TAE 0.04 M Tris Acetate, 0.02 M EDTA pH 8.0.

lOX Load Buffer 2.5 % (w/v) Ficoll 400, 0.042 % (w/v) xylene cyanol, 10 %

PROTEIN BIOCHEMICAL REAGENTS: Blocking Solution Coomassie stain Gel destain PLC Buffer SDS running buffer SDS sample buffer Transfer Buffer

5 % (w/v) Skimmed milk powder (Marvel), 0.2 % (v/v)

Tween20 in PBS.

0.25 % (w/v) Coomassie brilliant blue, 50 % (v/v) methanol,

10 % (v/v) glacial acetic acid.

10 % (v/v) methanol, 7 % (v/v) glacial acetic acid.

50 mM Hepes (pH7.5), 150 mM NaCl, 1.5 mM MgClj, 1.5

mM CaCl2, 0.1 % (w/v) CHAPS, 0.1 % (w/v) Octylglucoside,

1 % (v/v) TritonXlOO, 10 % (v/v) Glycerol, 1 mM EGTA, 10

mM NaPi, 100 mM NaF, Ix Protease Inhibitors, 0.5 % (w/v) BSA in DDW.

0.075 M Tris base, 0.192 M glycine, 0.1 % (w/v) SDS, pH 8.3.

80 mM Tris-H C l, 10 % (v/v) glycerol, 50 mM 2 p-

mercaptoethanol, 0.01 % (w/v) bromophenol blue, pH 6.8.

25 mM Tris-base, 0.1 M glycine, 20 % (w/v) methanol, 0.05 % (v/v) SDS, pH 7.4.

XENOPUS SOLUTIONS:

lOX NAM 110 mM NaCl, 2M KCl, 1 mM Ca(N03)z, 1 mM MgSO^, 0.1

mM EDTA.

10 % NAM (500 ml) 5 ml lOX NAM, 10 ml 0.1 M sodium phosphate (pH7.4), 2.5

ml 10 mg/ml gentamycin.

75 % NAM (500 ml) 37.5 ml lOXNAM, 10 ml 0.1 M sodium phosphate (pH7.4), 5

ml 0.1 M NaHCOg, 2.5 ml 10 mg/ml gentamycin.

2 % cysteine hydrochloride pH7.9 - 8.1 (200 ml)

4.4 g L-cysteine hydrochloride monohydrate, 1.33 - 1.36 g

NaOH, H2O to 200 ml.

lOX MEM salts 1 M MOPS, 20 mM EDTA, 10 mM MgSO^.