kitb, a second zebrafish ortholog of mouse Kit

Abstract

The large numbers of duplicated pairs of genes in zebrafish compared to their mammalian counterparts has lead to the notion that expression of zebrafish co-orthologous pairs in some cases can together describe the expression of their mammalian counterpart. Here, we explore this notion by identification and analysis of a second zebrafish ortholog of the mammalian Kit receptor tyrosine kinase (kitb). We show that in embryos, kitb is expressed in a non-overlapping pattern to that of kita, in the anterior ventral mesoderm, Rohon-beardRohon-Beard neurons, the otic vesicle, and trigeminal ganglia. The expression pattern of kita and kitb in zebrafish together approximates that of Kit in mouse, with the exception that neither zebrafish kit gene is expressed in primordial germ cells, a site of kit expression in the mouse embryo. In addition, zebrafish kita is expressed in a site of zebrafish primitive hematopoiesis but not required for blood development, and we fail to detect kitb expression in sites of zebrafish hematopoiesis. Thus, the expression and function of zebrafish kit genes cannot be described as a simple partition of the expression and function of mouse Kit. We discuss the possibility that these unaccounted for expression domains and functions are derived from more ancestral gene duplications and partitioning instead of the relatively recent teleost teleost-specific duplication.

Kit‐like immunoreactivity in the zebrafish gastrointestinal tract reveals putative ICC

“…Expression of kita and kitb was not detected previously in zebrafish larvae at 4 dpf using in situ hybridization techniques (Parichy et al, 1999;Mellgren and Johnson, 2005). Our data confirm this result.…”

“…This raises the possibility for a different physiological function for mammalian Kit and zebrafish kita. The recent discovery of a second Kit orthologue in the zebrafish, kitb, provides the possibility that kitb may be sufficient to support partial or complete ICC development and survival in the zebrafish GI tract (Mellgren and Johnson, 2005). Survival of homozygous kita null mutants suggests that kitb at least partially supports ICC development.…”

“…Two orthologs of the mammalian cKit receptor tyrosine kinase have been identified in the zebrafish, kita and kitb (Parichy et al, 1999;Mellgren and Johnson, 2005). The zebrafish Sparse mutant is characterized by a deficit in stripe melanocytes resulting from a null allele of kita (Parichy et al, 1999).…”

Evolution of danio pigment pattern development

“…Intriguingly, null alleles of mouse Kit and Ednrb completely lack melanocytes and have pleiotropic effects on other cell types (Besmer et al, 1993;Shin et al, 1999;Pla and Larue, 2003;Wehrle-Haller, 2003), whereas in D. rerio only embryonic and early appearing metamorphic melanophores require kit, only late appearing metamorphic melanophores require ednrb1, and even null alleles of these genes lack gross pleiotropic defects in other traits. These observations identify fertile ground for investigating how gene functions and pleiotropy itself evolve, particularly as simple gene duplication and partitioning of ancestral functions (Force et al, 1999) seem unlikely to explain genetic requirements for these particular loci (Mellgren and Johnson, 2004;Mellgren and Johnson, 2005). Double mutant analyses have revealed additional genes required by the kit-independent late metamorphic melanophores in D. rerio.…”

The presence and role of interstitial cells of Cajal in the proximal intestine of shorthorn sculpin (Myoxocephalus scorpius)

“…ICC were originally described over a century ago, as small fusiform or stellate cells with prominent varicose processes that formed networks in gastrointestinal tissues (Cajal, 1911). Antibodies against Kit have been used extensively to label ICC throughout the gastrointestinal tract in a wide range of vertebrates (Christensen, 1992), but success in labelling of ICC using Kit antibodies in teleosts has been variable (Ball et al, 2012;Mellgren and Johnson, 2005;Parichy et al, 1999;Rich et al, 2007;Wallace et al, 2005). Recently, anoctamin 1 (Ano1), a Ca 2+ -activated Cl − channel found to be expressed exclusively in ICC has been used as a more specific marker for ICC (Espinosa et al, 2008;Gomez-Pinilla et al, 2009;Hwang et al, 2009).…”