Apaf1 apoptotic function critically limits Sonic hedgehog signaling during craniofacial development

Abstract

Apaf1 is an evolutionarily conserved component of the apoptosome. In mammals, the apoptosome assembles when cytochrome c is released from mitochondria, binding Apaf1 in an ATP-dependent manner and activating caspase 9 to execute apoptosis. Here we identify and characterize a novel mouse mutant, yautja, and find it results from a leucine-to-proline substitution in the winged-helix domain of Apaf1. We show that this allele of Apaf1 is unique, as the yautja mutant Apaf1 protein is stable, yet does not possess apoptotic function in cell culture or in vivo assays. Mutant embryos die perinatally with defects in craniofacial and nervous system development, as well as reduced levels of apoptosis. We further investigated the defects in craniofacial development in the yautja mutation and found altered Sonic hedgehog (Shh) signaling between the prechordal plate and the frontonasal ectoderm, leading to increased mesenchymal proliferation in the face and delayed or absent ossification of the skull base. Taken together, our data highlight the time-sensitive link between Shh signaling and the regulation of apoptosis function in craniofacial development to sculpt the face. We propose that decreased apoptosis in the developing nervous system allows Shhproducing cells to persist and direct a lateral outgrowth of the upper jaw, resulting in the craniofacial defects we see. Finally, the novel yautja Apaf1 allele offers the first in vivo understanding of a stable Apaf1 protein that lacks a function, which should make a useful tool with which to explore the regulation of programmed cell death in mammals.

Face morphogenesis is promoted by Pbx-dependent EMT via regulation of Snail1 during frontonasal prominence fusion

“…However, we reported that not all epithelial cells undergo apoptosis at the fusion site (Ferretti et al, 2011). Moreover, mice mutant for CPP32 (CASP3) (Kuida et al, 1996) fail to execute apoptosis but do not exhibit CL or CPO, and mice mutant for Apaf, a proapoptotic factor, display orofacial clefting on a C3H/HeJ strain (Long et al, 2013) but not on a C57BL/6 background (Jin and Ding, 2006). These findings suggest that, in addition to apoptosis, other cellular behaviors mediate prominence fusion at the λ.…”

Apaf1 in embryonic development - shaping life by death, and more

“…2) (Long et al, 2013). Yautja is a novel loss-of-function allele of Apaf1 harboring a Leu375Pro point mutation which produces Apaf1 at normal levels during embryonic development, although it represents a functionally-null protein (Long et al, 2013).…”

“…2) (Long et al, 2013). Yautja is a novel loss-of-function allele of Apaf1 harboring a Leu375Pro point mutation which produces Apaf1 at normal levels during embryonic development, although it represents a functionally-null protein (Long et al, 2013). In particular, Long and colleagues found significant morphological alterations in the yautja mutant due to a defective craniofacial development, including cleft maxilla and widened frontonasal prominence (FNP).…”

RNA-seq analysis identifies cytoskeletal structural genes and pathways for meat quality in beef

“…The most important DE genes associated with meat quality in the present analysis are described below.The APAF1 gene was identified as DE in the WBSF and tenderness analyses, and identified as downregulated in tender meat; this protein is a central component of the apoptosome, a mitochondrial caspase activation pathway which mediates apoptosis. After activation of this pathway, the mitochondria release Cytochrome C which in turn binds to APAF1 and promote apoptosis by activating Caspase 9[43,44]. [44] characterized an APAF1 mutant mouse line which does not promote apoptosis.…”

“…After activation of this pathway, the mitochondria release Cytochrome C which in turn binds to APAF1 and promote apoptosis by activating Caspase 9[43,44]. [44] characterized an APAF1 mutant mouse line which does not promote apoptosis. These mouse embryos presented decreased apoptosis, nervous system development defects and craniofacial deficiencies associated with higher mesenchymal proliferation and delayed ossification resulting in perinatal death.…”