Chromatin changes in SMARCAL1 deficiency: A hypothesis for the gene expression alterations of Schimke immuno-osseous dysplasia

Figures & data

Table 1. Suppressors and enhancers of the ectopic wing vein phenotype induced by the overexpression of Drosophila Marcal1 and human SMARCAL1.

Gene	Allele^1	Effect on Drosophila Marcal1 overexpression phenotype	Effect on human SMARCAL1 overexpression phenotype
Trithorax group
ash1	B1	S	S
ash2	1	0	0
	EY03971	0	0
brm	2	S	S
	d00415	S	S
Iswi	1	S	S
	2	S	S
kis	1	E	E
	k13416	0	0
	EY12846	S	S
mor	1	E	E
osa	00090	S	S
	308	S	S
	EY09619	E	E
Snr1	01319	S	S
trx	1	0	0
	E2	0	0
z	1	S	S
	a	S	S
	a694	S	S
Polycomb group
Asx	1	S	S
	XF23	S	S
	EY07384	E	E
crm	7	E	E
	EY05302	E	E
E(Pc)	1	S	S
	EP608	0	0
E(z)	32	S	S
	61	S	S
esc	21	0	0
	KG07458	0	E
Pc	1	E	E
	3	E	E
	6	E	E
Pcl	11	S	S
	EY08457	E	E
pho	1	0	0
	b	0	0
ph-d	401	E	E
	BG02139	E	E
	VA174	E	E
ph-p	15	S	0
	410	S	S
	lac	0	0
Psc	1	S	S
	h27	S	S
	k07834	S	S
psq	D91	0	0
	E39	S	S
	F112	S	S
Sce	1	E	E
Scm	D1	0	0
Su(z)2	1	S	E
	1.a1	0	0
	1.b7	0	0
	k06344	0	0

¹ All alleles were analyzed in heterozygosity.

Abbreviations: 0, neither a suppressor nor an enhancer; E, enhancer; S, suppressor.

Figure 1. The heterozygous and homozygous mutation of Marcal1 genetically interact with trithorax group (trxG) and Polycomb group (PcG) members and suppress the ectopic expression of Ultrabithorax induced by PcG loss-of-function mutations. (A) Homozygous mutation of Marcal1 enhances the small and rough eye phenotype induced by the eye-specific expression of the dominant negative allele brm^K804R. (B) Heterozygous mutation of Marcal1 suppresses the ectopic wing veins (arrows) induced by the Pc¹ allele in heterozygosity. The boxed regions in the overview image correspond to the higher magnification images on the right. (C) The male-specific sex combs are a dense row of bristles on the prothoracic legs and allow for successful mating. Loss-of-function PcG mutant alleles ph-p⁴¹⁰ in hemizygosity and Pc¹, Psc¹, and Scm^D1 in heterozygosity cause a homeotic transformation of the mesothoracic legs (T2), and often the metathoracic legs (T3), to the prothoracic legs (T1). Extra sex combs that are characteristic of the prothoracic legs are therefore observed on the mesothoracic and metathoracic legs due to loss of silencing of homeotic genes by the PcG proteins. Heterozygous mutation of Marcal1 suppresses and homozygous mutation of Marcal1 further suppresses the extra sex comb phenotype of the mesothoracic legs of these PcG mutant alleles. Data are presented as bar graphs of the percentage of mesothoracic legs with 1-3 sex comb bristles (light gray), 4-6 sex comb bristles (medium gray), or ≥7 sex comb bristles (dark gray). Diamonds denote genotypes that were not assessed due to their lethality. Statistical significance of the data was assessed using the Student's t-test. n.s., not significant; *** p < 0.001. (D) Homozygous mutation of Marcal1 suppresses the partial homeotic transformation of the wing to haltere induced by the heterozygous mutation of ph-p⁴¹⁰ and Pc¹. (E) Immunostaining of wing imaginal discs for Ultrabithorax from ph-p^410/+; Pc^1/+ (left panel) and ph-p^410/+; Marcal1^del/del; Pc^1/+ (right panel) larvae. Homozygous mutation of Marcal1 suppresses the ectopic expression of Ultrabithorax (α-Ubx) induced by the heterozygous mutation of ph-p⁴¹⁰ and Pc¹. Scale bars: 100 μm. (F) Immunostaining of PBX-PRE_D-IDE-Ubx-lacZ wing imaginal discs for β-galactosidase (α-β-gal) in the background of ph-p^410/+; Pc^1/+ (left panel) and ph-p^410/+; Marcal1^del/del; Pc^1/+ (right panel) larvae. Homozygous mutation of Marcal1 suppresses PBX-PRE_D-IDE-Ubx-lacZ reporter gene expression induced by the heterozygous mutation of ph-p⁴¹⁰ and Pc¹. Scale bars: 100 μm. (G) Photograph of an agarose gel stained with ethidium bromide (EtBr) following electrophoretic separation of nucleosome-protected DNA samples from Marcal1^1+/+ and Marcal1^del/del adult flies after SphI restriction digestion and partial digestion with micrococcal nuclease (MNase) (left panel). For Southern blot analysis of the Ultrabithorax (Ubx) promoter (right panel), Ubx promoter-specific DNA was detected using a probe against the transcription start site of Ubx (lower panel). Note that Marcal1^del/del decreases MNase sensitivity of the Ubx promoter. Abbreviations: bp, base pairs; DAPI, 4′, 6-diamidino-2-phenylindole; EtBr, ethidium bromide; ey>brm^K804R, eyeless-GAL4, UAS-brm^K804R; MNase, micrococcal nuclease; MW, molecular weight; Pc, Polycomb; PcG, polycomb group; ph-p, polyhomeotic proximal; Psc, posterior sex combs; Scm, Sex comb on midleg; trxG, trithorax group; Ubx, Ultrabithorax.