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their genomes (Ojkic and Nagy, 2000; Grgić et al., 2011; Marek is propagated in goose embryo hepatocytes (Kaján et al., 2012).
et al., 2013, 2014a,b, 2016; Slaine et al., 2016). HEV/MSDV can be propagated in turkey leucocytes (van den
Other capsid proteins include proteins IX (found in mas- Hurk, 1990).
tadenovirus only), IIIa, IVa2, VI and VIII. The capsid proteins Avian adenoviruses can also be propagated in continuous cell
surround the core, which is formed by interactions between the lines from various origins. For example, most FAdVs replicate
viral DNA genome and terminal protein and proteins V (absent well in chicken hepatoma cell lines such as CH-SAH and LMH
in avian adenoviruses), VII, X (also known as μ) and viral pro- (Alexander et al., 1998; Michou et al., 1999) and to a lesser extent
tease (Fig. 10.1A). Polypeptides VII (800 copies/virion) directly in quail fibroblasts (Mansoor et al., 2011). HEV/MSDV can be
interacts with the viral DNA to form nucleosome-like beaded successfully propagated in Marek’s disease-induced lympho-
units. In addition to polypeptides VII, interactions of the viral blastoid cell lines such as MDTC-RP16 and MDTC, which are
DNA with proteins V and X help condense the genome to fit used for vaccine preparation (Nazerian and Fadly, 1982). Cairina
within the capsid (Berk, 2013; Mangel and San Martín, 2014). retina (CR) and CR.pIX continuous cell lines that originate from
Alternative mechanisms by which the avian adenovirus genome embryonal primary retina cells of a domesticated Muscovy duck
interacts with core proteins for condensation are likely to occur can be used for the propagation of many avian viruses including
to compensate the lack of protein V. Physical binding between EDSV (Jordan et al., 2016).
the viral core and capsid seems to be mediated by polypeptides
VI and VIII. The N-and C-termini of each penton base monomer
and protein IIIa, respectively, also interact with the viral core Viral replication
(Berk, 2013). The replication cycle can be divided into 6 stages: attachment,
The characteristics of the genomes are described in a later sec- penetration, uncoating, biosynthesis, assembly and release.
tion under ‘Genome structure and organization’.
Attachment
Propagation Adenovirus attachment is mediated by interactions between the
Aviadenoviruses are generally propagated in embryonated eggs fibre knob and cell surface receptors of susceptible cells. Coxsacki-
or cell cultures obtained from chickens, turkeys, geese, ducks, evirus and adenovirus receptor (CAR) is the best characterized
quail, pigeons and other avian species. However, propagation of for virus entry for both mastadenoviruses and aviadenoviruses
some viruses in cell culture has been unsuccessful, such as raptor (Tan et al., 2001; Harrach et al., 2011). FAdV-1 fibre 1 mediates
adenovirus (Kovács and Benko, 2011). FAdVs infect chickens cell attachment to CAR receptor in both avian and mammalian
and other avian species such as turkeys, geese and ducks. How- cells. Fibre 2 mediates attachment to an unknown receptor(s)
ever, some viruses infecting the latter avian species do not grow in avian cells (Tan et al., 2001). The penton also participates in
or grow poorly in cell cultures of chicken origin (McFerran and secondary interactions that are essential for cell entry. Such inter-
Smyth, 2000). actions involve the recognition of cellular integrins by the RGD
FAdVs can be propagated in embryonated chicken eggs using peptide of the penton.
three routes of inoculation: yolk and chorioallantoic sacs and In addition to CAR, other cell surface receptors, mostly
allantoic cavity. Inoculations in the yolk and chorioallantoic characterized in mammalian cells, include heparan sulfate gly-
sacs are made in 5-to-7-day-old and 10-to-12-day-old embryos, cosaminoglycans, CD46 (species Human adenovirus), CD80,
respectively (Cowen, 1988). Eleven-day-old chicken embryos CD86, sialic acid (some members of species Human adenovirus
are used for inoculations in the allantoic cavity (Mendelson et C), integrins αMβ2 and αLβ2, α2 domain of the class I major
al., 1995). Pathogenicity of FAdVs in chicken embryos depends histocompatibility complex (MHC-I), vascular cell adhesion
on serotype, strain and routes of inoculation. Embryo mortality molecule 1 (VCAM-1) and dipalmitoyl phosphatidylcholine
and lesions are more severe when viruses are inoculated in the (DPPC) (Arnberg, 2012). A putative 200 K cell surface protein
yolk sac (Cowen, 1988). DAdV-1 (EDSV/MSDV) can be also expressed in the gizzard has been suggested to be the receptor
propagated in nine- to 11-day-old duck embryos by inoculation for FAdV-1 (JM 1/1 strain) (Taharaguchi et al., 2007), but it still
in the allantoic cavity (Senne, 1998). Propagation of TAdV-3 remains undetermined if one or both fibres mediate the attach-
(HEV/MSDV) in turkey embryos, on the other hand, has been ment to that receptor (Tan et al., 2001).
unsuccessful (Guy, 1998).
Primary cells for propagation of FAdVs include chicken Penetration and uncoating
embryo kidney (CEK) and liver (CELi) cells (Yates et al., 1970; Mechanisms of virus entry have been described in mostly human
Alexander et al., 1998). CELi cells have been also used for the adenoviruses. Upon binding to cell surface receptor and second-
propagation of other avian viruses including EDSV (Kang et al., ary interactions with integrins, activation of PI3 kinase, p130 CAS
2017) and pigeon adenovirus 1 (PiAdV-1) (Marek et al., 2014a). and Rho family GTPases take place to stimulate virus entry
EDSV is successfully propagated at high titres in primary cells through actin polymerization within the cytoskeleton (Arnberg,
of duck embryo origin such as kidney, liver or fibroblasts. EDSV 2012). Endocytosis of the virion takes place via clathrin-coated
grows poorly in CEK, chick embryo fibroblast and turkey cells, pits. Clathrin-independent mechanisms of endocytosis and
while virus replicates at high titres in goose cells (McFerran and macropinocytosis have been described for some members of
Smyth, 2000). Goose adenovirus type 4 (GoAdV-4, strain P29) Human adenovirus B species (Kälin et al., 2010). Uncoating of the