Unser Haushund: Eine Spitzmaus im Wolfspelz? - Wolf-Ekkehard ...

76mice, white spotting is often associated with other congenital abnormalitiesincluding anaemia, megacolon and craniofacial malformation, indicating theimportance of the neural crest in multiple developmental areas and/or a commonset of signalling pathways used by multiple different cell lineages (Baxter et al.,2004). In contrast, white spotting in dogs is occasionally associated with hearingproblems, but not with more severe problems (Strain, 2004) [beim Dalmatiner bis zu 30%,Bull Terrier weiß und Jack Russel Terrier [letzterer polygen]: beide 19,1%, Catahoula Leopard Dog bis 68,8% (zumMerle-Gen siehe Fußnote)] 120 ” – ein Unterschied, den die Autoren auf die künstliche Selektionbeim Hund zurückführen (ein tauber Wolf dürfte so seine Probleme in der freienNatur haben). Der Pigmentverlust selbst ist jedoch bei den rezessiven Allelen desSpotting locus 121 (und den Allelen weiterer Loci) bereits eine Funktions-Einschränkung/Störung der normalen Pigmentproduktion ("Alleles resulting ina more completely pigmented body surface are dominant to those with lesspigmentation (Little, 1957)" – Kaelin und Barsh 2012, p. 62 [Solid (S), Irishspotting (s i ), Piebald spotting (s p ), Extreme white spotting (s w )]). Und einige s w /s wTiere sind vollständig oder fast vollständig weiß, ein Phänomen, das zum nächstenUnterthema überleitet.Zu den Haarformen des Haushunds siehe unten.9.7 Weißes Fell und unterschiedliche FellfarbenWeißes Fell: Zahlreiche Autoren sprechen auch hier von "angeborenenStörungen", "Defekt-Mutationen", "Fehlentwicklungen" in häufig rezessivenErbgängen. Zur Dokumentation hier einige Beispiele von Fachautoren sowie ausder vom Publikum häufig zu Rate gezogenen Wikipedia.Erwähnen wir zunächst kurz den Albinismus (kommt auch beim Hund vor, aberselten, z. B. beim Pekingesen: Folge von TYR Verlustmutation ("assumed to be dueto a TYR loss-of-function allele (c) (Whitney, 1979)" – Kaelin und Barsh 2012,p. 65). In der Wikipedia lesen wir zum Albinismus völlig zutreffend u. a.:Albinismus (von lateinisch albus ‚weiß'[1]) ist eine Sammelbezeichnung für angeborene Störungen inder Biosynthese der Melanine (das sind Pigmente oder Farbstoffe) und der daraus resultierenden helleren120 http://www.leveste.de/dalmaweb/platten.htm: dort auch Tabelle Taubheit bei Hunderassen. Originalartikel unter http://www.lsu.edu/deafness/VetClinNA.htm. undhttp://www.ncbi.nlm.nih.gov/pubmed/10390790 (G.M. Strain 1999): "Congenital deafness in dogs and cats is primarily of the hereditary sensorineural formassociated with white pigmentation genes, although acquired forms of deafness are possible. Highest prevalence is seen in white cats, especially those with blueeyes, and the Dalmatian, with many other dog breeds affected to some extent. This deafness results from degeneration of the cochlear blood supply at age 3-4 weeks,presumably resulting from suppression of melanocytes by the white (cat) or merle or piebald (dog) genes.” Zum Dalmatiner siehe weiter B. M. Cattenach (1999):The Dalmatian dilemma: http://www.steynmere.com/DALM_DEAFNESS.html ("Breed specific deafness attributable to s and M alleles": American Dalmatians,White Bull Terrier und weitere Rassen: Genotype s w s w ). Siehe auch http://www.americanboxerclub.org/white-deafness.html. Ausführlich weiter George M. Strain(2011): Deafness in Cats and Dogs. CABI; Wallingford, UK (150 pp.). Zum Catahoula Leopard Dog: "Although many breeders believe double merle to be the causeof the deafness problem, I believe the problem to be piebold. My belief is based on production of four litters from to sets of double merle parents. Of the four littersproduced, only one puppy, which was dominantly white, was deaf. If double merle breeding in the Catahoula were as disastrous as that of the Australian Shepherd,ther should have been four litters of totally deaf puppies” – 2011, p. 37 of The Complete Lousiana Catahoula Leopard Dog by Don Abney. AuthorHouse,Bloomington, IN, USA (174 pp.).121 Vgl. dazu die detaillierten Ausführungen von Kaelin und Barsh 2012, pp. 62/63: "Microphthalmia-associated transcription factor (MITF) was identified as thegene responsible for white spotting in dogs […]. MITF is a helix-loop-helix transciption factor involved in the development of several cell types, including mastcells, osteoclasts, the retinal pigment epitelium and melanocytes. In melanocytes and the retinal pigment epithelium, MITF activates the expression of manymelanogenic enzymes and proteins, and has been referred to as a 'master regulator' of pigmentation (Goding, 2000; Levy et al., 2006; Arnheiter, 2010). In laboratorymice, alleles that disrupt the MITF protein usually affect both melanocytes and the retinal pigment epithelium; the latter cell type is important for proper eyedevelopment, which is why many mouse alleles cause microphthalmia in addition to white spotting. Because MITF is expressed in many different cell types, itmakes use of several alternative promoters and transcription initiation sites (Bismuth et al. 2005; Bharti et al., 2008). Work from Karlsson et al. (2007) demonstratedthat genetic markers near the melanocyte-specific MITF-M promoter demonstrate the strongest association with spotting. Sequencing a 102 kb candidateregion from S and sw chromosomes did not uncover coding differences between the alleles (further implying a MITF-M regulatory mutation), but revealed 46 distinctmolecular alterations, including a short interspersed nuclear element (SINE) insertion ~ 3 kb upstream of the MITF-M promotor in sw but not in S chromosomes, and apolymorphic homopolymer tract ~100 bp upstream of the MITF-M promotor that is longer in sw than in S-bearing chromosomes.” Dem Irish spotting Allel (s i ) fehltjedoch die SINE insertion, "[H]owever, all three alleles (s i , s p , s w ) carry a homopolymer tract that is longer than the version found in solid (S/S) dogs."Siehe weiter Schmutz et al. (2009): MITF and white spotting in dogs: A population study: http://jhered.oxfordjournals.org/content/100/suppl_1/S66.full