Developmental expression of chicken FOXN1 and putative target genes during feather development

Abstract

FOXN1 is a member of the forkhead box family of transcription factors. FOXN1 is crucial for hair outgrowth and thymus differentiation in mammals. Unlike the thymus, which is found in all amniotes, hair is an epidermal appendage that arose after the last shared common ancestor between mammals and birds, and hair and feathers differ markedly in their differentiation and gene expression. Here, we show that FOXN1 is expressed in embryonic chicken feathers, nails and thymus, demonstrating an evolutionary conservation that goes beyond obvious homology. At embryonic day (ED) 12, FOXN1 is expressed in some feather buds and at ED13 expression extends along the length of the feather filament. At ED14 FOXN1 mRNA is restricted to the proximal feather filament and is not detectable in distal feather shafts. At the base of the feather, FOXN1 is expressed in the epithelium of the feather sheath and distal barb and marginal plate, whereas in the midsection FOXN1 transcripts are mainly detected in the barb plates of the feather filament. FOXN1 is also expressed in claws; however, no expression was detected in skin or scales. Despite expression of FOXN1 in developing feathers, examination of chick homologs of five putative mammalian FOXN1 target genes shows that, while these genes are expressed in feathers, there is little similarity to the FOXN1 expression pattern, suggesting that some gene regulatory networks may have diverged during evolution of epidermal appendages. KEY WORDS: chick, forkhead, WHN, HFH11, thymus, nudeeThe forkhead family transcription factor FOXN1 (formerly called Winged helix transcription factor nude, Whn (Meier et al., 1999) and HNF-3/forkhead homolog 11, Hfh11 (Segre et al., 1995) is essential for hair and thymus development in mammals. Hair production is complex and cyclic, involving many transcription factors and their targets (Lee and Tumbar, 2009;Lin et al., 2009). In the murine hair follicle FOXN1 exhibits a dynamic expression pattern that is dependent on the stage of the hair cycle. FOXN1 appears to be strongly expressed in the anagen or growth phase and its expression decreases by the telogen or quiescent phase. In the mature hair follicle FOXN1 is expressed in the hair shaft and the inner root sheath (Lee at al., 1999). In the hair shaft, FOXN1 is expressed in the cortex, which is consistent with absence of the cortex in Nude (FOXN1 nu / nu ) mice. Nude mice develop normal hair follicles and produce hair shafts, but the cortex fails to form most keratins so the hair does not extend. The absence of visible Int.

Notch and Hedgehog in the thymus/parathyroid common primordium: Crosstalk in organ formation

“…Although hair is an epidermal appendage that arose after the last shared common ancestor between mammals and birds, embryonic chicken feathers and nails also express Foxn1, demonstrating the conservation of these developmental processes during evolution (Darnell et al, 2014). In addition, nude mice (Foxn1 -/-) have two major defects, abnormal hair growth and defective development of the thymic epithelium (Nehls et al, 1996;Blackburn et al, 1996;Bleul et al, 2006), suggesting a common Notch-Foxn1 pathway in both developmental processes.…”

Expression of Fox genes in the cephalochordate Branchiostoma lanceolatum

“…Moreover, in mammals, FoxN1 is essential for hair formation whereas it is also expressed in chick during feather development (Darnell et al, 2014). Although mammal and fish FoxN1s are able to activate the expression of hair keratin genes, FoxN1/4 from amphioxus is not because its N-terminal region of the forkhead domain is different compared with vertebrates (Schlake et al, 2000).…”

Estudo da expressão temporal e espacial de FoxN1 em modelos biológicos, durante o desenvolvimento embrionário e em jovens adultos

“…Também está expresso na região supra-matricial do bulbo capilar, local onde acontecem os primeiros estágios de diferenciação terminal (Baxter e Brissette, 2002) e que dará origem aos fios de cabelo e a bainha interna da raiz (Prowse et al, 1999). No ciclo de formação do folículo capilar, Foxn1 parece estar fortemente expresso na fase de crescimento e sua expressão diminui na fase quiescente desse ciclo (Darnell et al, 2014).…”

“…A árvore filogenética construída por meio do software CLUSTALW também corrobora com essa afirmação, pois apresenta FoxN1 (Albuquerque et al, 2002;Bleul et al, 2006;Cheng et al, 2009;Dooley et al, 2005), inclusive Darnell et al, 2014. Não foi detectado, em nosso estudo expressão no cérebro do jovem adulto (Fig.…”

“…28) corroborando vários estudos (Albuquerque et al, 2002;Bleul et al, 2006;Cheng et al, 2009;Dooley et al, 2005), inclusive Darnell et al, 2014. Não foi detectado em nosso estudo expressão no cérebro do jovem adulto nem pela análise molecular de qPCR em G. gallus nem por análise macroscópica dos cérebros de M. musculus (Fig.…”