Science - USA (2020-09-25)

By examining the tissue-specific expression
of differentially regulated genes on an adult
schistosome single-cell expression atlas using
cells from schistosome somatic tissues ( 17 ), we
found that roughly 40% (51 of 129) of the
most–down-regulated genes aftertaoand
stk25RNAi were specific markers of parasite
muscle cells (fig. S10, A to C, and table S9).
Indeed, nearly half of all mRNAs specifically
enriched in muscle cells (60 of 135) from this
single-cell atlas, including key muscle contrac-
tile proteins, were down-regulated after RNAi
oftaoandstk25(Fig.3F;fig.S10,BandD;and
table S10). These transcriptional effects ap-
peared to be largely specific to parasite mus-
cles (Fig. 3F, fig. S10B, and table S10).
In principle, loss of muscle-specific mRNAs
could be due to either loss of muscle cells or
down-regulation of muscle-specific mRNAs.
We therefore labeled F-actin in schistosome
muscle fibers with phalloidin and performed
in situ hybridization to detect muscle-specific
mRNAs. RNAi-treated parasites exhibited a
reduction in the expression of mRNAs encod-

ing the contractile proteins tropomyosin 1 and

myosin light chain by in situ hybridization

(Fig. 3G) but no qualitative defects in phal-

loidin staining of body wall muscles (fig. S11).

Thus, it appears that these kinases are re-

quired to maintain the transcription of many

muscle-specific mRNAs in intact muscle cells.

The heads oftaoandstk25RNAi parasites

retained their capacity for movement (movie

S4) and partially maintained the expression

of muscle-specific mRNAs (Fig. 3G). Thus,

there appears to be a relationship between

the maintenance of muscle-specific mRNA ex-

pression and locomotion.

Taken in their entirety, our data suggest

that STK25 and TAO kinases cooperate in the

schistosome to mediate signaling essential for

sustaining the transcription of muscle-specific

mRNAs. As a consequence, loss of either

SmSTK25 or SmTAO activity results in muscu-

lar function defects compromising parasite sur-

vival in vivo. As whole-body knockouts of mouse

STK25 are homozygous viable and display no

obvious deleterious phenotypes ( 18 ), SmSTK25

represents an attractive target for therapeu-

tic intervention. Similar cross-examination of

genes associated with other phenotypic classes

(e.g., tissue edema) may provide insights into

the specificity of the various phenotypes ob-

served in this work.

Technological advances have paved the way

for large-scale analyses of gene function in

protozoan parasites ( 19 – 21 ), but such analyses

have been lacking for helminth parasites. Our

systematic analysis of gene function in schisto-

somes allowed us to effectively prioritize tar-

gets and potential specific inhibitors with

activities on worms. Future efforts should

further explore the potency and selectivity of

not only the compounds our studies have un-

covered (Fig. 2, A and B, and table S6) but also

larger libraries of compounds with known mo-

lecular targets ( 22 ). However, to mitigate po-

tential issues with host toxicity, it is also worth

exploring whether parasite-selective inhibitors

of validated target proteins can be uncovered.

Not only does this study enhance our under-

standing of schistosome biology, but also it

1652 25 SEPTEMBER 2020•VOL 369 ISSUE 6511 sciencemag.org SCIENCE

cntl

(RNAi)

tao

(RNAi)

stk25

(RNAi)

AB

-4-3-2-1012345

-4

-3

-2

-1

0

1

2

3

4

5

C

stk25

tao

cntl

(RNA

i)

tao

(RNAi)

stk25

(RNAi)

EGF tpm1 myl2

Log 2 fold change

−

• 
  

SmSTK25

kdSmSTK25

SmTAO

kdSmTAO

p-SmSTK25

• 
  

• 
  

• 
  

• 
  

++

• 
  

• 
  

• 
  

• 
  

− +

−

−

−

−

−

−

−

−

−

−

−

−

−

−

−

−−

−

+ATPSmSTK25

• ATP

p-SmSTK25

SmSTK25

Log 2 fold change, stk25(RNAi)

Log

fold change, 2

tao

(RNAi)

0

20

40

60

80

100

0

20

40

60

80

100

cntl

(RNAi)

stk25

(RNAi)

tao

(RNAi)

cntl

(RNAi)

% parasites recovered

tropomyosin−2/Smp_031770

troponin I/Smp_018250

myosin light chain/Smp_340130

calponin−3/Smp_126480

paramyosin/Smp_021920

actin−2/Smp_307020

calpain/Smp_214190 (tegument)

novel/Smp_096790 (parenchyma)

cathepsin B/Smp_103610 (gut)

nanos−1/Smp_055740 (germline)

7B2/Smp_073270 (neurons)

stk25/Smp_096640

tao/Smp_068060

−2 −1 0 1 2

tao

(RNAi)

stk25

(RNAi)

Non-Muscle

Muscle

% parasites recovered

D

Fig. 3. The protein kinases SmSTK25 and SmTAO are essential to
maintain muscular function.(A)RNAiofstk25ortaocauses parasite
hypercontraction. (BandC) Percent recovery ofstk25(RNAi),tao(RNAi),
or control(RNAi) male parasites surgically transplanted into mice.n≥ 11
transplants for each group. ****P< 0.0001,ttest. Data are means ± 95%
CIs. (D) Western blot to detect phospho-T173 (p-SmSTK25) or total SmSTK25
after an in vitro kinase reaction with or without ATP. Data represent results

of two experiments. (E) Scatter plot showing the relationship between the

differentially expressed genes [P(adjusted) < 0.001; Benjamini-Hochberg–

corrected Wald test] afterstk25ortaoRNAi treatment (r= 0.9,P< 0.0001;

Pearson correlation). (F) Heat map showing expression of tissue-specific

transcripts after RNAi oftaoorstk25.(G) In situ hybridization for

tropomyosin 1(tpm1; Smp_340760) and a myosin light chain (myl2;

Smp_132670) after RNAi at day 13. Scale bars, 500mm (A) or 100mm (G).

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